# Can you overload a 12 volt battery?



## Bruce3966 (Feb 8, 2015)

I am getting ready to rewire my entire O'Day. PO had everything a big mess and stated the interior lights didn't work because of a lightening strike near his boat. I found that hard to believe so I ripped out all the wiring and found the wires for the cabin lights and hooked them straight to the battery and of course every light worked. I am replacing ALL wiring, fuse panels and lights (going to LED's) and adding several other electrical items. I understand DC and AC systems but my question is this, "Can a person overload a battery to the point of being a safety issue?" OR will it just make the battery last that much shorter? 

I know 50% of all boat fires are electrical related and most of those are due to wires chafing. I am installing two 6 gang fused panels. I am running all 12 gauge stranded wire because I have dozens of rolls of it already sitting in my pole barn. The items I will have running on the two 6 gang panels are listed below and the list names indicate each separate circuit. 

Cabin lights (5 LED lights)
Running Lights
Masthead light
Cockpit lights (2 LED's)
Head night light (1 LED)
Bilge Pump
Shore Radio
AM/FM radio
12 volt power socket (for charging phones)

I always have two deep cycle batteries and the boat does have shore power which I will have hooked up at my slip and be able to charge those batteries at any time. I am not worried about a dead battery...I am just worried about anything that could happen IF all circuits were powered on at the same time.....would it be just a quickly drained battery or is there more to this and possibly a fire issue (even using 12 gauge wire).


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## indicasteve (Sep 2, 2015)

I had to do almost the same thing this past spring. The previous owner rewired the boat. and he did a pretty good job for most of it, but I wanted to make changes.

This is how my boat is wired...

All devices negative (black) wires go straight to battery. So, 12 gauge is fine because each device has its own wire to the battery.

A heavy gauge red wire (welding cable) goes to 30 amp fuse then to a distribution block.

From there, 12 gauge red wires goes to a 10 amp fuse then to a switch then run out to the device/light to complete the circuit.

If you plan to install a power inverter, run it straight to battery, using appropriate fuse on red wire. I have a 400 watt and 200 watt inverter and neither work well when plugged into the lighter sockets installed in the boat.

You don't have to run the black wires all to the battery, you can make a distribution block somewhere, then run a piece of welding cable to it, if you have to, depending on the loads you expect.

On my switch panel I also installed a recessed LED volt / amp meter which is really handy. Get them on Amazon for a couple bucks.


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## Delirious (Dec 16, 2001)

Absolutely. But figure a size 24 can do 600 amps for starting and probably 25 amps on a longer draw for extended time. What you list is maybe 12 amps, tops, all running simultaneously. Put in a 10 amp fuse for the rest but run the bilge pump on its own 15 amp fuse. You can easily do five days on a charge provided you turn the lights off in the day and the pump only runs 10 minutes a day. THAT's the one on you list that sucks current.

LEDs and the phone charger are less than an amp an hour I'm guessing.


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## capta (Jun 27, 2011)

It sounds like neither of you guys is planning on using boat cable (tinned wire) and that will pretty much make your hard work a waste of time. Welding cable is NOT acceptable on boats these days, nor is untinned copper wire, stranded or otherwise. Ask anybody with a boat from the 80's who has ripped out apparently good welding cable, and replaced it with very expensive boat cable. A friend actually had a fire from a corroded spot in a welding cable start system. 
There are certain standards for wiring a boat that are not needed in other applications, and that is why we use different cabling and wire.


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## Bruce3966 (Feb 8, 2015)

Yup, studying this a tad more I have decided to spend another $200 and get marine wire to rewire the entire boat. Whats another couple hundred!


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## rnixon (May 7, 2013)

Bruce3966 said:


> I understand DC and AC systems but my question is this, "Can a person overload a battery to the point of being a safety issue?" OR will it just make the battery last that much shorter?


You won't overload the battery. Please ensure that you have the correct size wires, fused for, at most, their rated load. You also need to be careful to get the earthing right when on shore power - it can be lethal if not correct.


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## indicasteve (Sep 2, 2015)

Yeah, I agree with Capta. If you have the budget go with the tinned copper. It will be safer and last 10x longer than plain copper. I didn't have the budget this year, and neither did my boat's PO apparently.

I don't have anything that requires high loads so I'm not terribly worried about it, hopefully the fuse will catch any shorts. But there will be a day (sooner rather than later) when it will all have to be replaced. The sailing season is so short in Canada that the wires don't get a chance to get corroded anyway!

Just as Delirious suggested, my bilge pump also goes direct to battery, fused of course. It's connected with the original wires, so I would imagine it uses proper tinned wire. But it blew it's fuse recently, then stopped working altogether and needs replacing before I go out again.


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## Bruce3966 (Feb 8, 2015)

I will for sure order marine wire today. Looking at the O'Day original wiring diagram I see all circuits were run with 16/2 except for the wires from the battery to the fuse panel which they list as 12 gauge and the the cabin lights which were 14/2. I am assuming LED's take less amps, and the Whale Gusher bilge I am putting in pulls 2.4 and specs recommends a 5 amp fuse. 

O'Day's original fuse panel had a 15 amp fuse for cabin lights, a 10 amp fuse for running lights, a 5 amp fuse for masthead light and a 10 amp for accessory. I will try to figure out amperage for each circuit and go from there.


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## Don L (Aug 8, 2008)

I think 12 gauge from the battery to the panel is WAY too small! It would get to a 3% voltage drop with a 12 foot loop at just 10 amps. I would use at least a 6 and would fuse it at the battery. Instead of setting up for a large voltage drop and a fire do it right!


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## MarkSF (Feb 21, 2011)

When I rewired my batteries, I bought 00 gauge cables pre-made from Genuine Dealz. They use the right boat cable, and 4-jaw hydraulic crimper, and they pretty much just charge you for the materials. Quality is top-notch.


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## JimsCAL (May 23, 2007)

The LEDs will take a small fraction of the current the old incandescent bulbs did. In most cases if only LEDs are on a circuit, 12 gauge will be overkill. I am assuming you will run heavier wire to the fuse/breaker panels. And also assuming that your cables to the battery switch, starter and alternator are not part of this rewire. While you are at it, you might consider adding battery fuses since they were not required when your boat was built but now are. Blue Sea Systems has some that easily attach right to the battery.


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## Bruce3966 (Feb 8, 2015)

No starter etc on my boat--outboard motor. 

I will be using 6 gauge from battery to both fuse panels and have a 30 amp inline manual reset breaker between the battery and fuse panels and will be using a bus bar for the negative wires. I will size all feed lines accordingly and change the panel fuses to cover each separate circuits load. My biggest draw like others have stated is the bilge pump at 2.4 amps listed. I am also installing a volt and amp meter for the entire system for monitoring. My longest feed lines will be one to the bow nav lights and the other to the micro LED night light I am installing at the head location. Other than that most of my runs will be under 8 feet.


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## Bruce3966 (Feb 8, 2015)

rnixon said:


> You won't overload the battery. Please ensure that you have the correct size wires, fused for, at most, their rated load. You also need to be careful to get the earthing right when on shore power - it can be lethal if not correct.


Earthing right??? Is this meaning grounding? If so I have never heard it called Earthing. The PO installed the shore power and used the proper deck fitting and then just ran 10 gauge romex inside to a 30 amp CB disconnect and then installed two receptacles (1 at galley and 1 at the head sink).


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## travlin-easy (Dec 24, 2010)

Nothing on my boat draws more than 3 amps - 12 ga is fine.

Gary


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## capta (Jun 27, 2011)

travlineasy said:


> Nothing on my boat draws more than 3 amps - 12 ga is fine.
> 
> Gary


Your VHF draws less than 3 amps transmitting on hi power?


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## hellosailor (Apr 11, 2006)

"But figure a size 24 can do 600 amps for "
And somethihg in excess of 3000 amps in a crowbar short, which is why you attach a heavy battery primary fuse (i.e. 100-150A) directly at the battery positive post(s) and then connect everything else downstream of that fuse.
The purpose of that fuse is to prevent a catastrophic fire in the primary battery wiring in case you manage to short the battery cables themselves.

Unless you have a "crowbar" short like that (i.e. dropping a wrench across the battery terminals) you are unlikely the be able to do any damage to the battery, although charging mistakes and crowbar shorts can & do both cause battery explosions.


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## MarkSF (Feb 21, 2011)

I exploded a car battery with a crowbar (wrench) short, many years ago. Not something I'd like to repeat. It blew the entire top of the battery off, and showered me with electrolyte, including in my face and eyes. Fortunately, I was next to a sink at the time.


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## hellosailor (Apr 11, 2006)

Side terminal batteries, the kind you mainly used to see in cars? Were supposed to make that less likely, as there' nothing sticking out far enough to drop a crowbar on, once the cables are released.

So much for better mousetraps, huh?


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## casey1999 (Oct 18, 2010)

Little off topic but since we are talking batteries: Say you have a fully charged house battery that you have on a solar pv charging system. Now you have a second engine starting battery that is charged to 50%. What happens if I connect the engine battery to the fully charged house battery- will they equalize to 75% charge?


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## GeorgeB (Dec 30, 2004)

The house bank will discharge to the starting battery until both have equal voltages. Simple math: House is twice the size of start battery and is at 13.1 volts Starting battery is at 12.5 volts. The House would discharge to 12.9v from 13.1v and the start battery would charge to 12.9v

What you really want is an Echo charger so your solar charger can keep both banks charged without combining them. You will want all charging modes to first go to the house, then echo'd to the start.


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## Bruce3966 (Feb 8, 2015)

PO left a new one of these in the boat. Anybody use one and if so, thoughts?

Deltran Junior Battery Tender:


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## rnixon (May 7, 2013)

casey1999 said:


> Little off topic but since we are talking batteries: Say you have a fully charged house battery that you have on a solar pv charging system. Now you have a second engine starting battery that is charged to 50%. What happens if I connect the engine battery to the fully charged house battery- will they equalize to 75% charge?


I wouldn't do that - you'd get very high currents.


GeorgeB said:


> What you really want is an Echo charger so your solar charger can keep both banks charged without combining them. You will want all charging modes to first go to the house, then echo'd to the start.


I'd charge the starter battery first, then the house. If you can start your engine, then you have options, both for propulsion and for charging the house batteries.


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## GeorgeB (Dec 30, 2004)

Assuming that you are wired so the start battery is only connected to the starter and everything else is on the "house" side, it is more efficient to have the charging source directly wired to where there is more discharge. The drain on a start is very small when compared to the overnight discharge on a house bank. For example, my battery supplier recommended a motorcycle battery for starting my 30HP diesel engine. If you are echoing off a starting battery you will be using it more as a capacitor for charging the house bank.

Most boats are wired so the selector switch is set to "both" so both can get charged. So this current surge happens every time you get ready to start the engine. The battery cables should be of sufficient size to handle the loads.


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## casey1999 (Oct 18, 2010)

GeorgeB said:


> The house bank will discharge to the starting battery until both have equal voltages. Simple math: House is twice the size of start battery and is at 13.1 volts Starting battery is at 12.5 volts. The House would discharge to 12.9v from 13.1v and the start battery would charge to 12.9v
> 
> What you really want is an Echo charger so your solar charger can keep both banks charged without combining them. You will want all charging modes to first go to the house, then echo'd to the start.


Thanks Geroge. So if I want to do this manually (without Echo), can I just switch the batteries ("Both" on Battery switch) so they are connected to charge the engine start battery? I could connect them both at all times, however I am concerned about over charging the engine battery- The house battery is a West Marine 225 amp hour AGM and it charges at 18 volts in full sun (this may be high, but was like that 5 years ago when I bought the boat and has been charging that way for 8 years now). The engine battery is a west marine starting/deep cycle lead acid battery (I normally let the engine alternator charge this battery- it is only used for engine stating). I normally keep the house and start batteries isolated- sun charges house and engine alternator charges the engine start battery. Now that boat is on the hard, the engine start battery is not being charge, so trying to come up with a method (I could take it home and charge it with my home battery charger).


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## casey1999 (Oct 18, 2010)

Bruce3966 said:


> PO left a new one of these in the boat. Anybody use one and if so, thoughts?
> 
> Deltran Junior Battery Tender:


Looks like a 110 volt trickle charger- used to keep you battery topped up. Not needed if you use you engine frequently and run it long enough so it charges the battery. A small solar panel may be better than charging with dockside 110 volt- less chance of electrolisis problems and no need to plug to dockside and potential electrical/shock dangers.


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## GeorgeB (Dec 30, 2004)

Casey, At this point I (or better yet, Stu Jackson!) would need to see a schematic or wiring diagram for your boat. AGMs need to charge at higher voltages than the standard lead-acid. And charging the start battery at those higher volts could cook it. Is the solar voltage regulator set to AGM? How are you wired on the boat? Through an 1-both-2 switch? Or do you have a completely separate “engine on” switch? Most boats have the alternator wired to the common post on the battery switch so whatever battery is “on” gets the alternator charge. If your alternator is internally regulated then it is undercharging the AGM (will never get to full charge). But combining both banks through the switch and the solar is regulated at 18v, then you will cook-off the start battery. If you are going to do the discharge from one to another, you want to disconnect the solar charger first. With everything turned off on the boat, why is your starting battery discharging? It could be old and needing replacing which you would do with an AGM in order to keep your life simple.


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## Omatako (Sep 14, 2003)

casey1999 said:


> Thanks George. So if I want to do this manually (without Echo), can I just switch the batteries ("Both" on Battery switch) so they are connected to charge the engine start battery? I could connect them both at all times, however I am concerned about over charging the engine battery-


Unless you have a smart regulator (if your alternator has an internal regulator), the regulator will always sense the voltage of the stronger battery. So if your house bank is, say, at 13.5v and your start bank is at 12.3v, the internal regulator will back the charge rate off in reaction to the voltage of the house bank. So the house bank is protected and will not over-charge. But the start bank will also not charge - or charge real slow. Slowly but surely, your start bank state-of-charge will go south.

When I have a discrepancy in battery state-of-charge between house and start, I manage it simply by switching the master switch to the bank that needs the charge. That way, when the regulator looks for a voltage reading and gets 12.3v, it gets the charge rate up to do the business. My battery switch is a lot more reliable than any echo charger and it'll give the soft bank a decent charge, not 15A.

When I leave the boat, the master switch is on ALL - that way the passive systems (solar array and wind gen) charge both banks.

If you have a smart regulator the above is probably not valid, I don't have one of those.

And connecting a flat battery to a charged battery does cause current to flow from one to another and maybe over time the voltages will be equal but it's not quick. If it were, there would no market for jumper cables


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## casey1999 (Oct 18, 2010)

GeorgeB said:


> Casey, At this point I (or better yet, Stu Jackson!) would need to see a schematic or wiring diagram for your boat. AGMs need to charge at higher voltages than the standard lead-acid. And charging the start battery at those higher volts could cook it. Is the solar voltage regulator set to AGM? How are you wired on the boat? Through an 1-both-2 switch? Or do you have a completely separate "engine on" switch? Most boats have the alternator wired to the common post on the battery switch so whatever battery is "on" gets the alternator charge. If your alternator is internally regulated then it is undercharging the AGM (will never get to full charge). But combining both banks through the switch and the solar is regulated at 18v, then you will cook-off the start battery. If you are going to do the discharge from one to another, you want to disconnect the solar charger first. With everything turned off on the boat, why is your starting battery discharging? It could be old and needing replacing which you would do with an AGM in order to keep your life simple.


The way boat is wired: 80 watts of solar to a xantec (as I remember) solar charger (settings are for a AGM battery- I have seen as high as 18 volts as I remember) then from the xantec to the house battery. The house battery and start battery are connected on their neg terminals and a battery switch can connect the positive terminals. Normally I have the battery switch in the "off" position so the two batteries are not connected. The only time I connect the batteries is when the start battery is low on charge and it will not spin the diesel to start (I have since replaced the start battery). Since the start battery is normally only connected to the engine, the engine alternator only charges the start batt (if I do use the house battery to start engine, after starting I disconnect the house and only start battery gets charged by alternator) The start battery is a 7 months old, but since it has sat for 4 months it has come down on charge due to normal internal draining. So what I was thinking, if I am on the boat at night or cloudy day where say the charge voltage on the house is say below 15 volts, I would connect the start battery and get some charge on it. Saves me from moving a 50 lb battery.


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## Stu Jackson (Jul 28, 2001)

rnixon said:


> 1. I wouldn't do that - you'd get very high currents.
> 
> 2. I'd charge the starter battery first, then the house. If you can start your engine, then you have options, both for propulsion and for charging the house batteries.


1. Don't ever combine two banks especially if you know one is bad UNLESS you are charging; if one bank is bad, don't use it.

2. Wrong. Echo chargers MUST be connected to the house bank.

To the OP, your basic question indicates to me that you need to study more DC material. For example: Discussing wire sizing without distances and loads is meaningless.

Battery fusues are sized based on the wire. Poke around the Blue Sea website, they have a downloadable PDF of wire & fuse sizing.

Most all of this is well covered in almost all basic boat electrical system books, Charlie Wing's is very good. It answers all these questions, much of which is available on the internet as articles, too.

Good luck, study harder.  I did.

None of us was born an electrician.

George Bean is right.

You could start here:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

It also would ahve helped if this was originally posted in the electrical section, kinda that's why it is there.


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## hellosailor (Apr 11, 2006)

If you are seeing 18 volts from any "charger" to any battery, that's dangerously high voltage. 16V starts to blow lights and electronics, 17V blows them very quickly. 18V should never appear in the boat unless there's something very wrong or unconventional (and wrong).

Time to find a pencil with eraser, draw up a real schematic, and find out what each component exactly is, and is supposed to be doing.

Also, if you connect a 100% charged battery and a 50% charged battery? You won't end up with two 75% batteries, you will lose some amount of power (5-10% ?) in the circuit flowing between the two of them. Batteries typically lose 10% of the power applied to them when charging, your math may work out differently--but there's still a loss.


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## Ward H (Jun 23, 2012)

Bruce,
Check out this site Compass Marine How To Articles Photo Gallery by Compass Marine How To at pbase.com especially the article on battery fusing.

also, as another poster mentioned, the Genuinedealz web site is pretty good for marine electrical stuff.


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## travlin-easy (Dec 24, 2010)

capta said:


> Your VHF draws less than 3 amps transmitting on hi power?


2.08 amps @ 25-watts.


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## Omatako (Sep 14, 2003)

Just another thing if you're planning on rewiring the whole electrical setup and your stores are anything like ours here in NZ, it's really hard (and expensive) to get marine tinned wire in a range of different colors, someone a while ago (think it was Maine Sail, sorry to the correct person if it wasn't) had a great suggestion for wiring with one color of wire.

Get some clear heat-shrink, print all the names of the connections onto white paper, cut them out and shrink them to the ends of the wires. That way when you come to connecting stuff, the location/connection is easy to recognise. I've been using that since it was mentioned and it's a great solution.


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## Bruce3966 (Feb 8, 2015)

I just ordered 2 100 ft rolls of tinned marine wire (easy to get here), a battery switch, the fused battery terminal, a bus bar and a bunch of connectors with shrink wrap. I've drawn a wiring diagram and sized all wire according to amps and length. I love electrical work. 

I always use a label maker and label all my circuits as I go. 

Sent from my iPhone using Tapatalk


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## rnixon (May 7, 2013)

travlineasy said:


> 2.08 amps @ 25-watts.


I believe that 25W is the transmitted power. The radio is less than 100% efficient, so will consume more. For example, a Uniden Um380 consumes:


https://www.uniden.com/File%20Library/FooterNav/Product%20Information/Owners%20Manuals/UM380om.pdf said:


> 25 watts output: [email protected] DC


That's almost 83W!


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## travlin-easy (Dec 24, 2010)

I've monitored this many times, as well as all other systems on the boat. When my refrigerator/freezer is running,it draws 5.9 amps, and the battery bank voltage is 12.7 VDC. And yes, that is the output wattage of my radio when keyed, which is a rare occurrence. In the receive mode it's far less.

Gary


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## Bruce3966 (Feb 8, 2015)

I did read somewhere that on average a ship to shore radio will be at or near 6 amps keyed mic but only 1/2 amp when only incoming calls are received. 


Sent from my iPhone using Tapatalk


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## indicasteve (Sep 2, 2015)

Yeah, VHF uses between 4.5 -7 amps when transmitting and only 1/2 amp when receiving. 10 amp fuse should work on most radio circuits I would imagine.

A little off topic, but FM radio stations often boast 100,000 watts of transmission power and that makes me kind of curious as to what's going on because I'm not now sure if a tin foil hat is counterproductive or not.


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## casey1999 (Oct 18, 2010)

hellosailor said:


> If you are seeing 18 volts from any "charger" to any battery, that's dangerously high voltage. 16V starts to blow lights and electronics, 17V blows them very quickly. 18V should never appear in the boat unless there's something very wrong or unconventional (and wrong).
> 
> Time to find a pencil with eraser, draw up a real schematic, and find out what each component exactly is, and is supposed to be doing.
> 
> Also, if you connect a 100% charged battery and a 50% charged battery? You won't end up with two 75% batteries, you will lose some amount of power (5-10% ?) in the circuit flowing between the two of them. Batteries typically lose 10% of the power applied to them when charging, your math may work out differently--but there's still a loss.


The solar charge controller I have is the xantex c35, here is manual:

http://www.wsetech.com/pdfs/C_series_manual.pdf

This charger has been running and maintaining the AGM 225 Amp Hr battery for the past 8 years. I replace most wiring on the boat myself a few years back so I know the charge controller is wired correctly. I was thinking about replacing this C35 as I never liked the high voltages it seemed to charge the battery at, along with the fact the controller is not water proof and the settings are complicated for what I need.

Today re-reading the manual I see on page 26-26 if the charger is used on ni-cads or alkaline batteries, you cut out a resistor and it jumps the voltage up to 17 volts- I need to check this, maybe previous owner clipped the resistor and that could be the reason for my high charge voltages.


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## MarkSF (Feb 21, 2011)

indicasteve said:


> Yeah, VHF uses between 4.5 -7 amps when transmitting and only 1/2 amp when receiving. 10 amp fuse should work on most radio circuits I would imagine.
> 
> A little off topic, but FM radio stations often boast 100,000 watts of transmission power and that makes me kind of curious as to what's going on because I'm not now sure if a tin foil hat is counterproductive or not.


An interesting article on FM transmitter power :

https://en.wikipedia.org/wiki/Effective_radiated_power


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## hellosailor (Apr 11, 2006)

A PO could has misprogrammed it, accidentally or intentionally. Even the manual says the bulk charge voltage for lead batteries should not be exceeding 15V, so if you are seeing more, there's something wrong. And uless something is set wrong, you shouldn't be seeing 15V either, unless the battery maker specs it (unlikely) or someone was being creative about trying to overcome wiring losses.

Probably time to hit the big reset button, and then go over the installation and configuration from scratch. With a good, known accurate, voltmeter as well. A cheap one like Horror Freight can be off by almost half a volt right out of the box.


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## casey1999 (Oct 18, 2010)

hellosailor said:


> A PO could has misprogrammed it, accidentally or intentionally. Even the manual says the bulk charge voltage for lead batteries should not be exceeding 15V, so if you are seeing more, there's something wrong. And uless something is set wrong, you shouldn't be seeing 15V either, unless the battery maker specs it (unlikely) or someone was being creative about trying to overcome wiring losses.
> 
> Probably time to hit the big reset button, and then go over the installation and configuration from scratch. With a good, known accurate, voltmeter as well. A cheap one like Horror Freight can be off by almost half a volt right out of the box.


A few years ago when I rewired I checked the settings on the Xantec- they were as they should be. I did not however check to see if the resistor had been cut. As the manual indicates, cutting resistors changes all the potentiometer scales and puts out higher voltage. Also, the regulator/charger could be defective. I want to replace the unit in any case, so probably go that route. I also notice on my 91 Landcruiser the volt meter indicates the alternator is charging at 16 volts, even the OEM unit charged at that rate- also seems high, but she keeps running.


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## hellosailor (Apr 11, 2006)

16 v on the landcruiser means a bad regulator, or your voltmeter is badly out of calibration. Assuming a bad regulator, you will soon start an expensive course of replacing electronics and lamps in the landcruiser, unless you get on it quickly.
FWIW.


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## casey1999 (Oct 18, 2010)

hellosailor said:


> 16 v on the landcruiser means a bad regulator, or your voltmeter is badly out of calibration. Assuming a bad regulator, you will soon start an expensive course of replacing electronics and lamps in the landcruiser, unless you get on it quickly.
> FWIW.


I am going to throw a volt meter on the boat and car battery and see what I find- maybe the dash volt meter on the landcruiser is off calibration.


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## GeorgeB (Dec 30, 2004)

Guys, Casey has AGM (Glass Mat) batteries as a house bank and the "regular" deep cycle lead-acid battery for starting. Lead acids charge at 14.5V and AGMs due to their construction require 18.5V to charge. 18.5V is correct. If you tried to use 14.5V to charge an AGM, it would never get more than 2/3 charge. If you are seeing 18V on your VU meter, then the battery is either in a charging state or in an "excited" post-charge state. Disconnect the charger and wait an hour (or two) and your VU meter will read in the 13V range. That is why you never want to mix AGM with lead plate batteries.


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## overbored (Oct 8, 2010)

what am I missing here. 18.5 volts on an AGM? maybe a 18 volt power tool battery. Never seen a charger that high. AGM should be charged at 14.4 and float at 13.4 long term charge even the equalization charge is only 15.5


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## Ward H (Jun 23, 2012)

Bruce3966 said:


> I just ordered 2 100 ft rolls of tinned marine wire (easy to get here), a battery switch, the fused battery terminal, a bus bar and a bunch of connectors with shrink wrap. I've drawn a wiring diagram and sized all wire according to amps and length. I love electrical work.
> 
> I always use a label maker and label all my circuits as I go.
> 
> Sent from my iPhone using Tapatalk


Bruce, sounds like you have everything you need to do a good wiring job. May I suggest getting a good heat shrink gun for the terminals and heat shrink tubing. I used this one and it made shrinking things much easier. 
ECG HG-300D Mini Heat Gun - Power Heat Guns - [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/31GKM-4r%[email protected]@[email protected]@31GKM-4r%2B6L


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## casey1999 (Oct 18, 2010)

overbored said:


> what am I missing here. 18.5 volts on an AGM? maybe a 18 volt power tool battery. Never seen a charger that high. AGM should be charged at 14.4 and float at 13.4 long term charge even the equalization charge is only 15.5


GeorgeB, I think overbored is right, This is the manual I have for the charger wired between my pv and AGM battery. The manual gives good details on charging voltages for different battery types:
http://www.wsetech.com/pdfs/C_series_manual.pdf

Also in the manual:
Lead Acid Battery 12 Volt System:
Float 12.5 - 14.5 Vdc
Bulk 13.0 - 15.0 Vdc
EQ = +1 above Bulk

Also concerning EQ charge of batteries the manual states:

CAUTION: Damage to Loads
DC loads may need to be disconnected by turning off circuit
breakers or removing fuses before equalization to prevent damage
by the required higher voltages used in the equalization process.

And:
CAUTION: Damage to Batteries
Equalization should be done for standard electrolyte, vented
batteries only. Sealed, GEL cell, or NiCad batteries should not be
equalize-charged. Consult your battery supplier for details on
equalize-charging for the battery type in your system.


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## casey1999 (Oct 18, 2010)

hellosailor said:


> 16 v on the landcruiser means a bad regulator, or your voltmeter is badly out of calibration. Assuming a bad regulator, you will soon start an expensive course of replacing electronics and lamps in the landcruiser, unless you get on it quickly.
> FWIW.


Tested LC battery charger and it was 14.75 volt at fast idle, so looks like the meter is a little off. This week will take a look at the boat battery charger to see what is going on with it.


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## Delirious (Dec 16, 2001)

indicasteve said:


> Yeah, VHF uses between 4.5 -7 amps when transmitting and only 1/2 amp when receiving. 10 amp fuse should work on most radio circuits I would imagine.


You guys sure about that? A 25 watt transmitter (I think most boat radios are limited to that) at 12 volts is 2.08 amps.

I(a) = P(w)/V(v)

I guess there's probably internal loss that eays up some wattage(?).


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## overbored (Oct 8, 2010)

you can not use that formula on radio transmitter output.


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## rnixon (May 7, 2013)

Delirious said:


> You guys sure about that? A 25 watt transmitter (I think most boat radios are limited to that) at 12 volts is 2.08 amps.
> 
> I(a) = P(w)/V(v)
> 
> I guess there's probably internal loss that eays up some wattage(?).


Yes. If you look at my earlier post, a Uniden Um380 consumes ~83W to transmit 25W.


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## Maine Sail (Jan 6, 2003)

GeorgeB said:


> Guys, Casey has AGM (Glass Mat) batteries as a house bank and the "regular" deep cycle lead-acid battery for starting. Lead acids charge at 14.5V and AGMs due to their construction require 18.5V to charge. 18.5V is correct. If you tried to use 14.5V to charge an AGM, it would never get more than 2/3 charge. If you are seeing 18V on your VU meter, then the battery is either in a charging state or in an "excited" post-charge state. Disconnect the charger and wait an hour (or two) and your VU meter will read in the 13V range. That is why you never want to mix AGM with lead plate batteries.


Unfortunately there is nothing correct about this post. I don't know of any AGM charges at over 15.0V, unless you are equalizing a Lifeline AGM then it is a max of 15.5V.

AGM Absorption Voltages Max (All assume temp compensated charging)

Lifeline = 14.4V
Odyssey = 14.7V
Northstar = 14.7V
Firefly = 14.4V
Deka/East Penn = 14.6V
Optima = 14.7V (15.0V allowable in a few circumstances)
Full River = 14.7V
Trojan = 14.4V
Rolls = 14.7V


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## GeorgeB (Dec 30, 2004)

Mainesail, help me out. Why does my Truecharge 20 have separate settings for flooded, gel and AGM batteries if the charging is the same? Why does American Battery recommend against mixing the three types of batteries together? I might have missed the charging voltage for the AGM - but are you saying that I can mix them and ignore the settings on my charger?


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## Maine Sail (Jan 6, 2003)

GeorgeB said:


> Mainesail, help me out. Why does my Truecharge 20 have separate settings for flooded, gel and AGM batteries if the charging is the same?


Your Xantrex charger 150% lacks the proper settings for ALL batteries. Three settings is simply inadequate for today's extremely varied charging needs UNLESS one of those settings matches YOUR batteries. Ignore the _labels,_ AGM, GEL and Flooded and instead focus on the _actual voltages_ of those settings/labels then match them as CLOSELY as you can to your physical batteries. The labels AGM, GEL and FLOODED are only _voltage settings_. A truly _smart charger_ will have upwards of 10+ voltage profiles to choose from or a fully custom menu to perfectly match your banks recommended voltages...



GeorgeB said:


> Why does American Battery recommend against mixing the three types of batteries together? I might have missed the charging voltage for the AGM - but are you saying that I can mix them and ignore the settings on my charger?


I don't know who American Battery is nor what they meant by "mixing battery types". Did they mean for discharging or for charging? In one house bank or house & start?

Certainly you don't want a mixed contiguously wired (hard-wired) house bank of TPPL AGM's and flooded batteries together as the TPPL has a much lower internal resistance and will disproportionately do more of the inrush work. They also have considerably higher resting voltages, usually over 13V, thus will be dragged back down to the resting voltage of the flooded batteries, usually around 12.72V. So yes in one hard-wired bank you don't want to mix _types_ or _brands_.

When charging, so long as voltages are the same, or very similar, there are no issues with charging in parallel or via a combiner or Echo type charger. I have piles of banks out there with small AGM starting batteries charged with large flooded house banks. This is a non-issue when charging so long as the voltages match up or are very close......


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## hellosailor (Apr 11, 2006)

"AGMs due to their construction require 18.5V to charge."
George, you'd better run tell the folks at Deka about that. They seem to have a four volt disagreement with you.
As do JCI (Optima, flat or spiral) and some other companies that make & sell AGMs.
Most AGMs are designed to use the same charging systems as wet lead, nominally 14.4 if you ignore temperature and the slight variations in chemistry from one make to another. That's what the makers say, and I've had them last eight years that way, so my experience seems to confirm their opinion.

Delirious-
No radio transmitter is 100% efficient. 50% would be extremely good, 40% about all you will find. So if your 25 watt *output* radio is 40% efficient, it will take 62.5 watts of DC input power, on the power cord. At the 13.8 volts they are usually spec'd for, that's ~4.5 Amps. With a dying battery at 11.5 volts, it is closer to 5.5 A.
So in normal conditions, your "25 watt" radio would require a minimum of a 7.5 Amp fused power supply, and a 10A fuse wouldn't be totally unreasonable.


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## GeorgeB (Dec 30, 2004)

Mainesail, I know that you are not a fan of Xantrex, what charger would you recommend? I have a Link 1000, and wish to keep it unless there is a very compelling reason to go through the additional expense. If I have flooded cell batteries (pair of 4D house and an echo charged group 24 starting), isn't the flooded setting on the true charge "good enough"? I'm sorry, I thought that American Battery was nation-wide, they are the "go to" place around here for batteries. 

If I am understanding you, there is a difference between flooded, gel, and AGM battery types? And they should not be wired together and charged using a single charger setting? As in the OP's original question, his flooded and AGM Batteries shouldn't be wired together for the purpose of using his solar regulator's AGM setting? My True Charge manual intimated that the critical voltage was in the "float" mode that a too high voltage would cause excessive gassing. Is this true? and if so, is there a big difference between 1.7 and 1.V? That the OP is seeing 18v on his AGM batteries would indicate that they are being overly charged and most likely his solar regulator is broken? Upon re-reading my True Charge manual I see that the charger has over voltage protection if it exceeds 15.5V.

Thank you for your patience as I (just like a lot of your clients) have just enough electrical knowledge to be a little bit dangerous.


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## Maine Sail (Jan 6, 2003)

GeorgeB said:


> Mainesail, I know that you are not a fan of Xantrex, what charger would you recommend? I have a Link 1000, and wish to keep it unless there is a very compelling reason to go through the additional expense. If I have flooded cell batteries (pair of 4D house and an echo charged group 24 starting), isn't the flooded setting on the true charge "good enough"? I'm sorry, I thought that American Battery was nation-wide, they are the "go to" place around here for batteries.


Lets assume we want to charge an Odyssey TPPL AGM with a TrueCharge 20...

The optimal charging voltages for an Odyssey TPPL AGM, when used in a PSOC environment, are 14.7V absorption and a 13.6V Float.

Odyssey also wants a minimum charge rate of 40% of capacity and temp compensated charging but the TC-20 can't really do either of those, so we will focus only on voltage.

*Note:* I do not consider a dip switch for temp compensation a _safe alternative_ or healthy to a true _on-battery_ automatic temp compensation.

TC-20 Voltage Settings:

*FLOODED 14.4V & 13.5V
GEL 14.2V & 13.8V
AGM 14.3V & 13.4V*

The closest we can get to "optimal charging" for the Odyssey AGM with the TC 20 is absolutely not the AGM or GEL setting and it is actually the flooded setting. Still this charger, when used with Odyssey AGM batteries, or others that require more than 14.4V will lead to shorter cycle life.

In Odyssey/EnerSys testing the cycle life difference between charging at 14.2V and 14.7V is roughly 260 cycles at 80% DOD. This 260 cycle difference is for a battery rated at 400 cycles to 80% DOD in the lab. This is a MAJOR hit to the lifetime performance of the battery if your charger can't charge the batteries correctly. Selecting the AGM setting would result in just 14.3V yet setting it for Flooded would result in 14.4V, which is still low but far better than the AGM setting.

We could do the same with Trojan flooded batteries, which do extremely well, and are advised to be charged with 14.8V & 13.2V. Using the closest setting with the TC-20 we are still off by 0.4V in absorption and 0.3V in float.

This is why I say _"Ignore the labels AGM, GEL and FLOODED and instead focus on the voltages of each of those settings."_

A great charger for being able to properly align your charging voltages with your bank would be the ProMariner ProNautic P or the Sterling ProCharge Ultra. Both of these chargers have 11 pre-set charge voltage profiles plus a 12th fully user defined custom profile and a 13th equalization cycle... They also come standard with a temp sensor that automatically adjusts and temp compensates charging.. Beyond that we get into inverter/chargers and Magnum, Outback and Victron all allow excellent control over charging.

Most "smart chargers" _smart _only in the _marketing_..:wink



GeorgeB said:


> If I am understanding you, there is a difference between flooded, gel, and AGM battery types? And they should not be wired together and charged using a single charger setting?


Most "smart" chargers with simple AGM, GEL & FLOODED settings are not even going to be correct for the house bank in terms of float and absorption voltages. So even on the house bank most owners are doing themselves a disservice by simply selecting "FLOODED" for flooded batteries and thinking they are good to go. You may get lucky and it may be spot on but it always pays to look at the other voltage settings and "ignore the label"....

That said the issue is not in _charging_ but rather _discharging_.

Lets take a look at a Deka AGM starter and a Trojan flooded house bank. (had this exact scenario two weeks ago)

The Deka AGM wants 14.6v & 13.6V so the FLOODED setting is your closest match. Where this bank is not cycled, it is a starter only, 14.4V & 13.5V is pretty acceptable..

The Trojans want 14.8V and 13.2V so the FLOODED setting is your still your best match. These batteries are cycled deeply and the charger is really well under _optimal_ charge voltage for the extremely important absorption stage...

The TC-20 will do 14.4V and 13.5V when set to flooded. This is not optimal for either battery bank but the AGM will be closer and get charged closer to its _optimal_ than the Trojan bank will even when set to FLOODED. Both banks can be CHARGED in PARALLEL but just not DISCHARGED IN PARALLEL....

We also need to remember that battery chargers with two or three outputs are not three separate chargers (though a very, very select few are). This means all batteries connected to the charger see the same charge voltages and move from absorption to float together. The new Blue Sea charger pushes the start battery through an additional diode so it sees a sort of pre-float before true float.. The outputs of "multi-bank" charger simply have diodes or FET's to prevent them from being in "parallel" when discharging. An Echo Charger or combining relay achieves the same end result by turning off or isolating banks when in discharge mode.



GeorgeB said:


> As in the OP's original question, his flooded and AGM Batteries shouldn't be wired together for the purpose of using his solar regulator's AGM setting?


No not "permanently wired" in parallel. However he could use a charge management device such as an ACR/Combiner or an Echo type charger and feed solar direct to his house bank. Once the house bank voltage has risen enough to turn on the Echo or ACR/Combiner the start bank will also get charged. When the sun goes down the Echo or ACR will turn off and the banks are isolated. Using the BOTH switch is not ideal in this situation as the banks will remain in parallel, during discharge, when the sun goes down.



GeorgeB said:


> My True Charge manual intimated that the critical voltage was in the "float" mode that a too high voltage would cause excessive gassing. Is this true?


Gassing does not begin until the low 14's in healthy batteries. While float is important +/- .1V to .2V is less critical to overall cycle life than a proper absorption voltage. Heck temp compensation is even more important, especially in warm climates, yet less than 5% of the boats I set foot on have temp compensated charging. Temp compensation is a _requirement_ for EVERY AGM & GEL battery maker yet most boaters completely ignore this. Charge voltage needs to change with battery temperature!!

In a PSOC environment a slightly higher float can even be beneficial in reconverting lead sulfate but it is the absorption stage that really does the bulk of this work. I think Odyssey's data above makes that very clear. Many "smart" chargers, thanks to lawyers, also use really DUMB charging algorithms I call "egg timers". Some with as little as 1 or 2 hours at absorption voltage.... Dumb egg timer chargers do you and your batteries no good when they stiff you of a proper absorption charge cycle duration.



GeorgeB said:


> and if so, is there a big difference between 1.7 and 1.V? That the OP is seeing 18v on his AGM batteries would indicate that they are being overly charged and most likely his solar regulator is broken? Upon re-reading my True Charge manual I see that the charger has over voltage protection if it exceeds 15.5V.


I suspect that the volt meter used for the measurements is incorrect. With 18V + on an AGM the life is measured in weeks, not years. I had an AGM battery destroyed in 9 weeks, on a customers bass boat, using a small unregulated 17V (12V nominal) solar panel.. Actually I have had a number of batteries destroyed by small panels including golf cart batteries and AGM's..

An 8 year old AGM charged regularly anywhere near 18V is as much an impossibility as Hillary Clinton beating Lance Armstrong in a bike race. There is only so much electrolyte in an AGM mat and when it is gone, it is gone. The valves begin to open as low as 14.9 - 15V (even lower in high temps)....


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## Bruce3966 (Feb 8, 2015)

So was that a NO to my original question? 


Sent from my iPhone using Tapatalk


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