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  • 1 Post By noelex77
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Old 09-29-2011
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Charging Batteries at 15.5 volts

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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Old 09-30-2011
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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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Old 09-30-2011
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Quote:
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)?


Quote:
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?


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Old 09-30-2011
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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 (current up to 10% of capacity), Absorption (14.4V to 97% of capacity), Finishing (15.3V @ 3% or less of capacity) & Float.

2- The 15.3V they want to see as a finishing charge is 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.

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..

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. Most marine chargers are voltage regulated not current. 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% -80% SOC and ABSORPTION charging (@ 14.4V) to about 97% - 99%, depending upon your charger.

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" phases, or "absorption" & a current limited "finishing" charge, then I would urge you to reconsider the 15.5V recommendation from this rep. 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- If charging using what US calls "two stage charging" with "optional float", what most marine chargers do, then they want 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. If your charger is larger than 10% of C a reduction in absorption voltage may be warranted.

Deep cycle wet cells in marine applications are usually charged at 14.4V - 14.6V and do just fine. They'll do even better with occasional equalizing. I have set up some regulators, like Balmar's that do dual absorption stages, to push 14.8V then cut back to 14.4V but in each of these situations they batteries use considerably more water. The gassing voltage really begins at around 14.4V..



I will try and see if I can dig up the US Battery charging sheet for you as they sent it to me a while back. BTW US Battery makes EXCELLENT batteries that are right up there with Trojan in terms of quality.
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Last edited by Maine Sail; 09-30-2011 at 07:54 AM.
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Old 10-06-2011
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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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Old 10-06-2011
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Quote:
Originally Posted by YoMarco View Post
...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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