Dual 6 volt GC2 batteries and charging characteristics

[busterbrown73]

We just returned home to Michigan from a 24 day trip around the southwest. This was the first big test of our new dual 6 volt battery bank (upgraded from a single group 24 12 volt).

As I have really no experience with charging behaviors of a serial 6 volt setup, I'm looking to see if I need to upgrade the OEM converter charger on my travel trailer. This is what I noticed during our trip.

1. Started with a fully charged 13.3 volt bank on the morning of our departure after plugged into shore power for 48 hours. The Duracell (215 amp hour) flooded batteries are brand new.

2. After using typical appliances through a dry camping night, (DC inverter for television/fan, furnace, led lights, LPG fridge, and water pump), the bank would drop to 12.4 to 12.6 volts. We would run our 3700 watt inverter generator for 5 to 6 hours during the next day to allow the converter to recharge the bank. I thought it was preforming as expected except that the converter would charge to about 12.8 to 12.9 volts. I never got back to 13.3 volts until we plugged into shore power at a full hookup campground.

3. On several legs of the journey, we would leave the dry camp location without running the generator in the morning and drive 4 or 5 hours to our next camp site. I checked the volts on arrival at the new site and my TV would barely provide a recharge (12.5 to maybe 12.6). The previous group 24 12 volt would be completely charged after just a couple of hours of running the truck. (Obviously, I have much more amp hours with the GC2s).

My concerns are:

1. Is my OEM converter the bottleneck in my coach's recharging capabilities?
2. For a dual 6-volt in-series battery bank (flooded), what should I expect as a full charge? I've read 13.3 volts as being 100% as a float charge but absorption voltage could be much higher.
3. Will a true 4 stage converter charger (bulk, absorption, float, equalize) help maximize battery usability and increase overall battery life?
4. If a new converter is needed, what size (amp) is preferred? Are converter/inverter types recommended as I see the price point goes much higher? Realistically, I would like to see a full charge after a couple hours of generator use.
5. Is a larger battery bank crippled by the inadequate charging abilities of the converter?

[busterbrown73]

wopachop wrote:
Maybe keep the stock converter and invest in a decent quality solar charger and panels instead?

You need something that can charge at 16.2 volts once a month and 14.8v with daily use. Good chance your stock converter is only doing 14.4v and never does an equalization charge at 16.2v.

Unfortunately, we camp much of our time in state parks throughout Michigan. The tree canopies are too abundant here as solar is usually a second thought. My trailer has a non-walkable roof so even a small solar setup on top would be difficult to maintain the panels.

[busterbrown73]

pauldub wrote:
Also, your TV alternator isn't the best charger for deep cycle batteries. Renogy makes a DC-DC charger if you really want to get the batteries properly charged while driving.

Does the DC to DC charger stay on the trailer or in the TV?

[busterbrown73]

mordecai81 wrote:
Voltage is a tricky indicator of charge level because the batts must rest for awhile after charging to read the true level via a voltmeter. After a few hrs rest 12.7 volts is a full battery.
A typical WFCO converter/charger will never get your batts up to full charge unless you are plugged into shore power for days and days. I get around that by using a stand alone 65 amp Boondocker charger run off my gen and hooked to the batts with jumper cables. 45 minutes in the morning and then solar the rest of the day works well to get the batts full.
Before adding solar, I would run the gen 3-ish hrs a day to get the batts to about 95% charge.
True deep-cycle batts like you have can take quite awhile in the absorption stage to to get to full. Very few stock converters are programmed to hold proper absorption voltage long enough to do the job.

Any contraindications to be plugged into an inverter generator at the same time using a stand-alone battery charger on the battery bank? This may be an affordable solution for the interim (until I upgrade to LiFePO4).

[busterbrown73]

3 tons wrote:
The capacity of your two GC 6v’s (connected in series to form one large battery) should be 215 amp/hrs because the amps are divided by two when the voltage is doubled...Versus the 85 or so amp/hrs of your previous group 24...And if you consider that your usable amp/hrs for most wet-cells is to about 50% of capacity (without causing long term damage), you gained about 65 amp/hrs additional capacity...

Per your example, it doesn’t sound like you’re using too much power, and consider that 12.6+ v is fully charged and 12.5v = 90%, 12.4v = 80% and 12.3v = 70% SOC (state of charge)...

Check to see what your charger is rated at...Mine is rated at 45 amps and does a ok job of charging my GC’s, but I also have a 100a pass-thru inverter/charger that (though a bit oversized) works better.

For instance (though not too scientific) this morning my two GC’s were down to about 71% SOC (per LinkLite meter and shunt) and when I kicked on the 100a charger, the amps started out at about 39a then began to slowly taper off (over a few minutes) to what was seemingly the apparant acceptance rate of the two batteries...

When I started out with the 45a factory converter-charger, the amps were only at about 14.5a which would mean I’d have to run the portable genny for quite some time...

Can you supply a link to which passthrough inverter charger you have? Thanks

[busterbrown73]

time2roll wrote:
In 3 hours your charging voltage should be 14.3+ volts. 13.3 is a trickle charge.

Consider this PD-60-14.8 converter made for GC batteries.

http://www.bestconverter.com/PD-9260C-148-60-Amp

I'm no where near 14.3 volts or 13.3. I may consider this progressive dynamics converter. Thanks.

[busterbrown73]

2oldman wrote:
What is the amp rating of your converter?

It's good to remember that 2-6v batteries are just one big 12v in two parts. It's that simple. Charging is the same, assuming your wiring is adequate and clean.

busterbrown73 wrote:
2.... (DC inverter for television/fan, furnace, led lights, LPG fridge, and water pump),

FYI.. the only thing on that list that runs on the inverter is the television.

3. Yes, a true 4 stage is better. 55 amps should be good.

If your 215amp-hour 'battery' has been drawn down to 50%, you need to replenish 107ah, which is at least 2 hours on a 55a charger. This also assumes you've used big enough wire from the converter to the batteries. Many of us use a tri-metric (I think) meter to measure amps in and out. A bit more accurate than voltage.

5. Yeah, too small of a charger takes forever.

All this said, it's common with us boondockers that we never get a 100% charge except on shore power. Reason is, flooded batteries take much longer than you think due to the absorption phase. I have Lithium batteries which don't have this problem.

I'm not sure the amp rating of my converter. Haven't looked. Will do this weekend. I own a typical 30 amp lightweight travel trailer from Keystone.

I would love to invest in lithium. Although, price is a barrier. Battle Born 100 amp hour batteries are $950 each. I may upgrade next year if an Alaska trip comes to fruition.

If my OEM converter is anything less than 40 amps, I will probably invest in a smart 3 or 4 phase converter.

[3_tons]

#1Flyboy wrote:
...Put some solar on the roof & you’re gonna be happy! Did I mention solar is quiet? And when you’re not using your camper the batteries will be full every day! No gas, no oil, no noise....

I agree completely, but even at 440w I was forced to run the genny today due to adverse weather and poor harvest...

[Ski_Pro_3]

If you are driving and your truck's charging system is connected through to the RV's batteries, they should fully recharge in a couple hours or so. If you are not driving, then a generator should recharge your batteries off the RV's charging system on AC just as quickly as it would plugged into any other AC source.
I can recommend you first get some decent gauges to read how your batteries are being used. A good volt meter and amp meter, preferably built in to the RV via a display panel would be best. I do that with volts but for amps I have a clamp-on amp meter. For example, I know my heater draws 4.7 amps to run the blower fan. When the air temps outside drop below freezing, it runs about 15 minutes on/15 minutes off all night long; call it 10 hours, so 5 hours @4.7amps equals 23.5Ah. All your other loads are inconsequential unless that AC inverter to run the TV is a real power hog. I bought a 12 volt powered LED TV and it uses 1.7amps at 12 volts. It's only a 17" screen, but still, not much power to watch a DVD movie. If I were to guess, I'd say you probably have a load over 24 hours in the range of 35Ah. Even if it was 50Ah, you should be able to go 2 full days before you really needed to charge that battery.
As someone already mentioned, you'd be a great candidate for solar. I have 250 watts of solar on the roof running through a Morningstar charge controller that displays volts as well as both charge and load amps. I know how much load I have at all times as well as how much my solar is charging my batteries. Rare is the day that my solar doesn't charge up my batteries to full by noon. I get a real 9amps of solar charging for at least 5 hours a day and a total for a full day that is sunny, about 70Ah. I've dry camped for many days in a row in the winter well below freezing and only once did I need to charge my batteries. A great thing abou solar is that your batteries are always kept charged when the RV is not in use and never needs to be plugged in when in storage.
I also see someone recommended you check the electrolyte levels on your batteries. I agree. Many times batteries leave the factory unable to meet their label specs. It's not the end-all to tell you capacity of the battery, but it will tell you if it's fully charged. Only a load test will give you capacity. If you want to run a load test, you should be able to using any of your on-board loads, measuring the amps draw against time and reading specific gravity on the battery's cells.

It's also important to check electrolyte levels fairly frequently on wet cell batteries. I have one of those set ups that replace the battery caps with a plumbed system that allows me to refill the batteries remotely. Use only distilled water. I'd say I go through a gallon of water a year, checking once a month.

[ktmrfs]

let me guess.

your converter is a WFCO. If so that is likely the problem. they seldom will charge at more than 13.2V.

Get a good 3 stage charger PD or Iota.

[_1Flyboy]

...Put some solar on the roof & you’re gonna be happy! Did I mention solar is quiet? And when you’re not using your camper the batteries will be full every day! No gas, no oil, no noise....

[MEXICOWANDERER]

This is the place for a hydrometer. Not guesswork

[wopachop]

Maybe keep the stock converter and invest in a decent quality solar charger and panels instead?

You need something that can charge at 16.2 volts once a month and 14.8v with daily use. Good chance your stock converter is only doing 14.4v and never does an equalization charge at 16.2v.

[pauldub]

Also, your TV alternator isn't the best charger for deep cycle batteries. Renogy makes a DC-DC charger if you really want to get the batteries properly charged while driving.

[mordecai81]

Voltage is a tricky indicator of charge level because the batts must rest for awhile after charging to read the true level via a voltmeter. After a few hrs rest 12.7 volts is a full battery.
A typical WFCO converter/charger will never get your batts up to full charge unless you are plugged into shore power for days and days. I get around that by using a stand alone 65 amp Boondocker charger run off my gen and hooked to the batts with jumper cables. 45 minutes in the morning and then solar the rest of the day works well to get the batts full.
Before adding solar, I would run the gen 3-ish hrs a day to get the batts to about 95% charge.
True deep-cycle batts like you have can take quite awhile in the absorption stage to to get to full. Very few stock converters are programmed to hold proper absorption voltage long enough to do the job.

[3_tons]

The capacity of your two GC 6v’s (connected in series to form one large battery) should be 215 amp/hrs because the amps are divided by two when the voltage is doubled...Versus the 85 or so amp/hrs of your previous group 24...And if you consider that your usable amp/hrs for most wet-cells is to about 50% of capacity (without causing long term damage), you gained about 65 amp/hrs additional capacity...

Per your example, it doesn’t sound like you’re using too much power, and consider that 12.6+ v is fully charged and 12.5v = 90%, 12.4v = 80% and 12.3v = 70% SOC (state of charge)...

Check to see what your charger is rated at...Mine is rated at 45 amps and does a ok job of charging my GC’s, but I also have a 100a pass-thru inverter/charger that (though a bit oversized) works better.

For instance (though not too scientific) this morning my two GC’s were down to about 71% SOC (per LinkLite meter and shunt) and when I kicked on the 100a charger, the amps started out at about 39a then began to slowly taper off (over a few minutes) to what was seemingly the apparant acceptance rate of the two batteries...

When I started out with the 45a factory converter-charger, the amps were only at about 14.5a which would mean I’d have to run the portable genny for quite some time...