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Old 10-23-2013, 09:13 AM   #1
sjturbo
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Battery charging question

This is definitely a technical question to me. Having read the "12 volt side of life" and generally understanding it I have a question. I am running two 2 6V deep cycle batteries. When boondocking should I recharge them daily regardless of the voltage of the batteries, or should I wait until the batteries have reached 50% (12.06V)? Since the article states "You should recharge a deep cycle battery as soon as possible after each use" I am a bit confused. I thought that the batteries had a memory and it is better to recharge at a lower voltage? By the way I only have a eu3000 generator to run as the charger. Which brings up another question. I believe that using the generator to power the 5er will take longer to charge through the converter. Since the eu3000 has a battery charger connection (12V@12A) should I use that?
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Old 10-23-2013, 09:50 AM   #2
diugo
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Lead acid batteries do not exhibit memory effects. You should try to recharge them on a daily basis if possible.

To minimize generator running time, you might consider purchasing a separate automotive charger, which can easily produce 50-100 amperes to bulk charge the battery in no time at all. You should also invest in a small solar panel and charge controller to properly top off the battery each afternoon---a lengthy task very poorly suited to a noisy generator.
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Old 10-23-2013, 09:54 AM   #3
JRTJH
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You don't need to recharge every day, however regular charging before the batteries are discharged beyond the 50% charge is a good rule of thumb. The more often you charge them the less time needed for each charge cycle.

As for using your generator vs converter, the converter can charge at a rate of about 40 to 45 Amps (assuming you use 10-15 amps on lights, refrigerator operation, etc.) tapering down both in voltage and in amperage to maximize the charge on your batteries. The 12 Amp charger on your generator will not charge as fast and probably not as effectively as the converter, so you will probably be better off using the generator to power the RV, and letting the converter do the charging.

One thing you do NOT want to do is to connect the generator charger to the batteries and try to use the converter also. It won't damage anything, but the converter charging cycle is triggered and controlled by the battery output voltage. If you hook the generator charger to the batteries the converter will "sense" or "detect" the generator output (let's say 13.6 VDC) and will not provide the fast charging part of the cycle to the batteries (thinking they are already at 13.6 VDC so they must be charged more than they really are).

Today's converter charging circuits are a lot smarter and more efficient than they were several years ago. Depending on the state of discharge to your batteries, you should get an adequate charge in 2 or 3 hours using the converter and in 4 - 6 hours using the generator's charger.
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Old 10-23-2013, 10:40 AM   #4
sjturbo
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Thanks for the prompt responses!! I have a question for each of you. First what size solar panel and controller would be sufficient to "top off" the batteries and what low voltage would be considered for top off? Second question is what voltage should I start recharging to work with the 2 to 3 hr using the converter? Thanks again!!
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Old 10-23-2013, 10:54 AM   #5
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I would try to charge before you get to 12.4 (50%). If you can keep your batteries between 12.5 and 12.6 you should be OK. As for what size solar system, I'll leave that to someone more versed in solar panels. The best I can do is tell you about the panels that are on the lights around our garden, otherwise, I haven't gotten into solar yet.

Commonly accepted voltage/charge condition is:

12.6 full charge
12.4 50%
12.2 25%

Note: maybe it's a typo on your part but in your initial question, you say that you try to recharge when your battery voltage hits 50% ( 12.06 V) If you're letting them go that far, you're probalby closer to 10 or 15% charge condition.
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Old 10-23-2013, 11:42 AM   #6
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I recharge when my GC get to about 50% or lower state of charge or when I get home. Trojan GC are rated for something in excess of 750 charge/discharge cycles to 50% of capacity, well beyond what the vast majority of RV users will encounter in 10 years or so. Golf carts, another story. Using this after 10 years, my GC are still good. BTW the 750cycle life is when the battery has 50% of the initial capacity. And I usually have 30+ such cycles/year on my batteries. sometimes I'll even let them get down to about 30% SOC, even at that they are good for 500 cycles.

But make sure when you return they get FULLY charged and don't let water go below the plates. The two worst things you can do are not recharge within a week or so, and let water go below the plates.

As for solar, that's really an uknown unless you can give us more info
portable panels you can tilt or flat on the roof?
what latitude are you camping at
when in the year?? summer? spring? fall?
How many AH/day do you use??
do you want solar to fully charge the batteries every day or to just extend the time between generator runs?

All the above have an impact on how much solar you need.

As an example we mostly camp at 45 Latitude and up, spring summer and fall, but often partly cloudy. I have 4 GC batteries and LED lights. not anal about energy conservation but reasonable. run the fans during day when hot, furnace in the am when cold. DW occasionally uses the hairdryer on inverter and microwave on inverter. Sometimes TV at night. Lights on when we want them.

my portable 160W panels won't keep up with our useage. last trip out in Sept we were gone 8 days. Good solar about 6 hrs/day. At the end of 8 days the batteries were down to 50%SOC just using solar. But never had to run the generator. so basically I was "loosing" about 6% of capacity/day using solar. Based on how we were using stuff, w/o solar after around 4 days I would have had to turn on the generator.

Now w/o solar we probably would have been more anal and stretched out the batteries, but it sure is nice to not be completely anal about power useage.
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Old 10-23-2013, 02:10 PM   #7
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Trojan sez... 12.10V = 50%. 12.42V = 70%.

To properly top off batteries you need a panel capable of 2% of your battery's amp-hour rating. So if you have the typical 220Ah 6V batteries, that's 4.4A. Since most "12V" panels actually put out around 18V, we're talking about 80W or so. Today's $1/W panel prices are amazingly cheap---I paid 4X that for my 400W array of five 80W panels in '02. (I don't even own a generator.)

The charge controller ampere rating needs to exceed the max panel current. A low-cost PWM controller without a display is all you need. You might want to oversize the controller if you think you might add more panels later.

The correct top-off "setpoint" voltage is highly dependent on battery temperature. It usually ranges from 14.0V at 100°F to 15.0V at 40°F. So set it to 14.3V in April and 14.7V in October.

You want to run the generator until the correct setpoint voltage is reached. The charge controller will then hold the battery at that voltage the rest of the day. When charge current drops below 2% (4.4A), charging is done.
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