# Charging Batteries at 15.5 volts



## YoMarco (Aug 6, 2011)

We have been having a "using too much electricity compared to making enough electricity" problem for awhile. We have 4 x 135 watt Kyocera solar panels and due to being stuck in the Bahamas when our batteries died, we had to buy 5 x 155 ah US Battery 12vxc. They are 12 volt deep cycle and all that was available within a reasonable time frame (NOT REASONABLE COST). Anyway, we seemed to always be using our generator to get even a reasonable charge, but our diesel costs were out of this world. Conserve as we tried, the only option looked like a wind generator. After talking to quite a few wind generator owners, I decided the cost vs. benefits for what might be the right one (D400) was just too much. We talked to the US Battery manufacturer's rep- Fred Waymire, in Georgia. He led us to believe that we are charging our batteries all wrong. According to Fred, this heavy duty deep cycle batteries need to be charged in either a true three stage (not including float) or as our Mastervolt 2500/100 Inverter/Charger can handle- two stage. He wants me to set the solar charger (Blue-Sky) and the Mastervolt (Generator power) at 15.2 - 15.5 volts until full and then float at 13.2. Then equalize at 15.5 for 2-3 hours once a month. Claims that not only does the US Battery prefers this, but that other deep cycle wet batteries, charge faster and last longer as well. 

All of my electronics can take between 16-33 volts with no damage (NEMA 2000 gear is the most sensitive); the Blue Sky engineer thinks it sounds right- but everyone else I have spoke with (MasterVolt's Rep I am sure had kittens when we have talked) hated the idea (By the way- I think the MasterVolt Rep had lots of good and valid bones to pick and seemed to be looking out for my best interest).

So quicker charges, better for the batteries life (per the battery manufacturer) and possibly no need for a wind generator. Again- heavy duty wet cell acid US Battery 155ah 12VXC's. Why not?

Marco


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## Noelex (Jan 23, 2008)

Its always worth listening to battery manufacturers, but the absorption voltage is a good deal higher and the float voltage lower than most people use. If they were my batteries I would set the limits to more usual values.
If you do follow the recommendation make sure you check the water often and have some temperature compensation of the charging voltage built in. Make sure the hydrogen cannot build up and be ignited. Wear some eye protection when checking water levels


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## chef2sail (Nov 27, 2007)

> We have been having a "using too much electricity compared to making enough electricity" problem for awhile.


What is your electerical diet in ah per day (usage)?



> We have 4 x 135 watt Kyocera solar panels and due to being stuck in the Bahamas when our batteries died, we had to buy 5 x 155 ah US Battery 12vxc


The Kyocera 135 makes 7.5 amps per hour max in optimal conditions. Bahamas has lots of sun, but mnaybe they are shaded partially so lets say each of the 4 panels produce 6 hours at 6 amps or 36 amps per panel times 4 panels. Thats 144 amps...which is quite substantial. What does your amp meter say is going into the batteries when they are charging? What is your power deficeit daily?

Dave


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## Maine Sail (Jan 6, 2003)

PLEASE be very careful with the advice you were given. He should have forwarded you their charging profile sheet.

Some things that were missing from his explanation:

*1-* They like to see a four stage algorithm like are used in big industrial or golf applications. The four stages are Bulk (CC/constant current) (current up to 10% of capacity), Absorption (CV/constant voltage) (14.4V to 97%+ of capacity), Finishing (CC/constant current) (15.3V @ 3% or less of capacity) & Float (CV/constant voltage).

*2-* The 15.3V they want to see as a finishing charge is constant current and current limited to 3% of the battery capacity and acts sort of like a mini-equalizing charge on each cycle. You WILL use a lot more water and in constant current the current can certainly push the voltage higher than 15.3V if you are not careful..

*3-* In marine applications we rarely have the time to wait for a charger that only pumps out 10% of the 20 hour capacity so the algorithm above likely changes. We also don't have chargers that know what the current is so it is tough to limit the current to 3% of C @ 15.3V.. We use CC/CV/CV chargers not CC/CV/CC/CV chargers.

*4- *In marine applications there are very few chargers that can do a current limited "finishing charge". Some may have the capability, but I don't know of one even deep into programming menus. Most marine chargers are voltage regulated not current regulated.. If you raise voltage, you also raise the current, unless you have a way to "limit it". Some limit current in _equalize mode_ but I can't think of a program on any of them that would allow you to include an equalizing voltage/current on each charge cycle.

*5-* Keep in mind that you will be cycling down to about 50% state of charge so BULK (below the chargers limiting voltage) will be from about 50% to 70%-85% SOC (depending upon charge rate) and ABSORPTION charging (CV) from that point on at 14.7V would ideally be held to about 97% - 99% SOC, depending upon your charger & how smart it really is.

*6-* If you set up a marine charger the way you were told you'd have a MUCH higher voltage, & potentially current, for a much longer time and could really do some damage to your batteries. Unless your charger can do two "absorption" stages, or "absorption" & a current limited "finishing" charge, then I would urge you to reconsider the 15.5V recommendation from Fred. It is also .2V higher than any voltage I remember US recommending except for perhaps an equalizing charge. The "finishing voltage" US recommends in their own lit is 15.3V or 2.55V per cell X 6 = 15.3V..

*7-* We charge using what US calls "_two stage charging_" with "_optional float_". This is what most marine chargers do. It is really just a CC (Bulk) to CV (Absorption) to CV (Float) charge profile. With this profile USB wants the absorption voltage at a max of 14.7V, then a float voltage, but remember this is all predicated on a charger rated at 10% of the 20 hour capacity. They recommend an equalizing voltage of 15.3V for this type of charging, but not every cycle.. If your charger is larger than 10% of C a reduction in absorption voltage may be warranted. All charging should be temp compensated.

Deep cycle wet cells in marine applications are usually charged at 14.6V - 14.8V, these voltages have continually crept upwards int he last ten years as battery makers finally began listening to what the folks in off grid/PSOC arena have been saying all along, and that is that 14.4V in a cycling application is simply too low. I have set up many regulators, such as Balmar's, that can do dual absorption stages, to push 14.8V then cut back to 14.6V - 14.7V but in each of these situations they batteries use considerably more water despite getting a helathier charge. Hydro caps are usually in order... The gassing voltage really begins at around 14.4V but the batteries really need more than 14.4V for optimal charging..

*EDIT: 9/12/16*

More information on this subject from 2015..

I have had long, long conversations with Fred W. USB's Senior VP of Engineering about this. The charge profile that original guidance was written around does not widely exist in the real world, CC/CV/*CC*/CV and not at all in the marine market, but it did in their labs and does in some very specific industrial settings.. After giving that guidance for a while they reverted to a much more _sane_ charge profile.

US Batteries current charging guidance is here: *US Battery Charge Recommendations*

For CC>CV charging (USB calls this "two stage) 14.7V - 15.0V for absorption. Fred W. strongly urged using the 14.7V end for marine applications, especially if all sources are not temp compensated and where we are using a higher charge rate than 10% of capacity. He still wants to see 13.0V - 13.2V for float. Equalization is 15.3V -15.6V if temp compensated. If not temp compensated Fred recommends a maximum voltage of 15.0V for EQ.

Please note that "_two stage with optional float_" is where you want to be. The USB three stage profile has a CC>CV>*CC*>CV profile not a CC>CV>CV profile like our marine charge sources use. We use CC>CV charging in the marine market... Also remember that guidance was written around a 3-4 hour period in absorption.

If you are charging using a higher current than .1C (10% of Ah capacity) then you will have longer absorption times and the voltage should be at the lower end of the 14.7V to 15.0V recomendation. At 10% of C in charge current you will be in bulk for the majority of the charge but as you bump up to .2C (20%) or .25C (25%) you extend the time you will be in absorption because you will attain absorption/limiting voltage sooner in the SOC curve....


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## YoMarco (Aug 6, 2011)

noelex77, chef2sail & especially Maine Sail- Thanks for your replies. I have been crazy busy getting ready to set sail for Colombia, and the time got away from me.

I have decided to dial back my charging methods to reflect yours and my still lingering charging concerns.

I have:

1) Installed a charging remote for the Blue Sky solar charger boost. I will charge at the higher rate of up to 15.5 (10% battery capacity) when the sun is available. Based on the limited time the sun is high enough this should be safe ). The remote allows me to override the averages involved in solar charging and allows for a shut-off when certain levels are hit.

2) Dropped my MasterVolt Mass Combi Inverter/Charger 12 volt 100 amp (via computer remote) back to 15.0 bulk, 15.0 absorption and 13.3 float (not that I will be running my generator that long (make water and extra power only at night after the solar is of no effect)

3) Installed a MasterVolt 40 amp (helps me close in on that 10% of 20 hour rating on my 155ah batteries. This I will leave at factory specs.

4) Installed a Pro-fill auto-leveling water system for the batteries. Makes it easy to stay on top of the watering.

5) Changed all my halogen lights with LED (nice selection at LEDLIGHT.com for boats- showed up when they said it would too). Fridge/Freezer are very efficient- so no change there and I put my sonar on separate breaker from the other electronics (helps hold down power usage during crossings and when the depth sounder alone will do).

I will try this for awhile and make changes as needed. 

By the way Mainsail's explanation and analogy, should be made a sticky, in my opinion.


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## junkrig (Jun 3, 2011)

YoMarco said:


> ...snipped out most of text...
> 
> By the way Mainsail's explanation and analogy, should be made a sticky, in my opinion.


+1 on this.


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## SVGG (Sep 12, 2016)

Thank you, Maine Sail. Excellent contribution. 
One additional question please. 
We have a Mastervolt Mass Combi 12/2500-100 and cannot figure out how to get it set to EQUALIZE. Can you offer help or a suggestion?
Thank you!


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## Maine Sail (Jan 6, 2003)

SVGG said:


> Thank you, Maine Sail. Excellent contribution.
> One additional question please.
> We have a Mastervolt Mass Combi 12/2500-100 and cannot figure out how to get it set to EQUALIZE. Can you offer help or a suggestion?
> Thank you!


This is a manual operation usually using the bottom row of dip switches. IIRC it is the last dip switch on the right but confirm this in your owner manual.. The batteries must be 100% charged and there can be no loads on while you are equalizing. It may not enter EQ if it senses too much load on its power supply. EQ is high voltage low current so the batts must be full first...


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