# Solar Panel / Overcharging ???



## Maine Sail (Jan 6, 2003)

Hi All,

Ok here's the question. I have a Siemans 75 watt panel mounted to my davits and I can't find any sort of solar charge controller that actually turns the panel off when the batteries reach 100%. I don't want to fry my batteries through over charging yet my charge controller continues to put out amps even when the batteries are at a 100% charge. So I know how to prevent discharging back through the panel at night and do have a charge controller but how do I stop it from charging when the batteries are full. I can't seem to find info on this anywhere on the net and I've been to the solar sites as well as the off the grid type sites..?? Six to seven hours a day of 1-4 amps is too much in my estimation if the batteries are already full.....


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## sailingdog (Mar 19, 2006)

Halekai-

It is very unlikely that your batteries will ever reach 100% under solar alone, and if they are wet-cell lead-acid batteries, they will begin to self-discharge almost immediately. Most good charge controllers will drop the voltage and amperage to a relatively safe "float" charge level.


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## kd3pc (Oct 19, 2006)

H

try Hamilton-Ferris, they have a nice charge controller that shuts off the current to the battery. It cycles with and audible click. Inexpensive in the grand scheme of things.

dave


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## camaraderie (May 22, 2002)

I'd be worried about frying my batts at 17V and 4.4 amps full output all day long. Get a regulator or an mppt controller!!


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## Maine Sail (Jan 6, 2003)

*Cam...*

What's an MPPT controller. I am charging at roughly 13.1 to 14.2 and anywhere between .5 amps and 4.5 amps depending on the sun. My Xantrex XBM tells me I'm at 100% yet the solar panel is still putting out. Will an MPPT stop the charging at a certain state of charge..??


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## Cruisingdad (Jul 21, 2006)

Halekai,

You would benefit from a MPPT controller. It stands for Max Power Point Tracking. It WILL increase the charging potential for your battery, 10-20% or so.

At that size solar panel, you should consider a Blue Sky... maybe a couple hundred bucks. You could probably even add a panel or two without too much fuss, if you have the money. Your setup is too small for an Outback.

Yes, it shuts off the charging and puts out the "extra power" as heat if there are no systems running. A good MPPT controller should be a must for every cruiser with solar today, in my opinion.

Here, talk to these guys. Ask for Ryan... Great people and very knowledgeable. http://store.solar-electric.com/index.html

- CD


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## bobmcgov (Jul 19, 2007)

Don't worry about it. Any reputable charge controller (like Trace/Xantrax, Outback, Blue Sky. Morningstar, etc) knows what it is about. One amp six hours a day is only six amp hours, not enuf to overpower most batteries. It IS enuf to compensate for self-discharge, small parasitic loads, and to undo damage by sulfation on the plates. A nominal twelve volt battery is really not 100% charged until about 14.4 V. Be especially aware of state-of-charge meters that rely on voltage readings instead of on amperage shunts.

Any PWM charger will taper and float without damage to your batteries -- IF you have it set for your type of battery. See if the manual mentions different bulk/absorb/float thresholds for flooded lead acid, sealed gel, AGM, and NiCads. For example, sealed gels should not be high-charged or equalized; NiCads require charging at higher voltages than other batteries. If you are really scared, flip the breaker to the PV. It can be dead-headed without harm.


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## Valiente (Jun 16, 2006)

Cruisingdad said:


> Yes, it shuts off the charging and puts out the "extra power" as heat if there are no systems running. A good MPPT controller should be a must for every cruiser with solar today, in my opinion.
> 
> Here, talk to these guys. Ask for Ryan... Great people and very knowledgeable. http://store.solar-electric.com/index.html


A question concerning the MPPT conversion of "excess" solar power to heat: Where does that heat go? Would it make sense to mount the MPPT to the outside of the boat, like in a vented box under the panels themselves? Assuming I have a big bank and an intermittant draw (like refrigeration), is this ever likely to be a problem (the solar can never quite top off the battery banks with a draw going on, and the MPPT never therefore goes into "heat to amps" mode).

Basically, I am trying to determine if the sensible thing would be to rig a load triggered by full batteries, like a fan that turned on at 13.5 V or something, because the idea of putting a box that can get hot from a couple of hundred watts running through it _inside _a boat seems a little counter-intuitive.


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## Cruisingdad (Jul 21, 2006)

Val,

Mine kicks on a fan internally. I did rig mine to be completely shut off easily with a switch. Doing so will put a small drain on the batteries, since the controller requires some power to run.

As far as the concern about it overheating the cabin, etc... I would not be too woried about it. Yes, until you are a LA/Cruiser, there is the real potential (like I have right now) that it will be severely underutilized. Turn it off if you are worried about it. However, once cruising, you will be always be taxing the system and the only heat you will be putting off is your frustration from the kids leaving all the lights on (in my experience).

I will see if I can get some pics for you soon so you can see how I set it up. I looked in my library and have no pics of the MX60. Sorry.

- CD


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## camaraderie (May 22, 2002)

Umm Bob...that is not correct..I think you meant to discuss bulk charging...a 12V battery fully charged at rest is 12.7 V or a few hundreths +/-. The BULK charging rate for a 12V battery is 14.4 volts tapering to a float charge of 13-13.5V and just and amp or less of current.

Link to charge state paper with chart: http://www.batteryfaq.org/
As you can see...12.65-12.8V is fully charged depending on battery type.


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## bobmcgov (Jul 19, 2007)

Cam: The phrase 'at rest' is the key here. Instantaneous voltage readings are poor indications of a battery's real state of charge. In order to get a battery sufficiently charged that, disconnected from all loads and inputs for twelve hours, it will read 12.6-12.8VDC (2.2 V per cell, per standard), you need to begin with an instantaneous voltage reading of about 14.4. This is the default Absorb setting on four different charge controllers I own or have owned. Bulk charging volts may be similar (with higher currents); or, with MPPT controllers, Bulk voltages should be lower -- usually battery voltage + 0.8V. Once the batteries are held at this 'full' Absorb state for an hour or two, most controllers allow them to cool down to about 13.6 to 13.8 V -- the Float voltage setting.

Agreed, if you disconnect topped batts and let them sit for half a day, they will read 12.6-12.8V max. But a good charge controller will always _try_ to hold the system voltage well over that. So if your instantaneous battery voltage reads 12.6 while your PV or wind are functioning, your batts ain't full yet.

BTW, if you employ batteries that require periodic equalization -- flooded cells in parallel strings, especially -- a typical EQ voltage is Absorb (14.4 or 28.8) *at full current.* So vent that H2 & check your water afterwards!


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## camaraderie (May 22, 2002)

Bob...we agree...just using different words to describe the same thing. BTW...Your house setup must be awesome. I wanna hear about that windgen on another thread (try Solar&Wind). Are you seeing anything developed for homes on the wind side that may pay off for marine use? 
*************
BTW there is no need to wait twelve hours for the "at rest" reading. 
Just run a 20 amp load for a few minutes after charging and that will wipe off the surface charge and give you a true at rest reading.


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