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?

[MEXICOWANDERER]

Good grade of AGM can withstand discharging to 30% soc but the maintenance for recharge must be as strictly rigid as a Trappist monastery.

This is where thick plates pay for their room and board.

[wa8yxm]

3 tons wrote:


Ok, lets cut through ‘my nonsense’ and do the math:

My two 6v Costco GC’s are rated at 210 amp/hrs per (other makes vary a bit)
Two times 210 = 420 - So you and I both agree Sir!!
BUT, once connected in series to arrive at 12v, the 420, is reduced by 1/2, so I’m now at 210 amp/hrs total...To arrive at 12v theres NO SUCH THING AS A FREE LUNCH ...

Now, to arrive at usable amp/hrs lets assume that for longivity’s sake the DOD should not go below about 50% - now were at about 105 usable amp/hrs...

But then again, this is just my opinion...

NO two 210 amp hour GC2' in serie is 210 amp hours. THE VOLTAGE DOUBLE the amp hours remain the same.

Two 130 (G-31) 12 volt batteries in PARALLEL the amp hours double (260) the voltage remains the same.

Battery 101

Now there is one other component where if you put 2 in series the value halves. but I won't even name it because you are already confused. I will only say the value that divides is NOT Voltage. NOR is it current.

[3_tons]

I agree that GC’s can be taken down to below a 50% depth, but voltage tapers off a bit as well...So I generally avoid doing so when supplying the air cond compressor motor...Lithiums tend to be far more forgiving in this regard...

[MEXICOWANDERER]

200 amp hours capacity seems to be a popular flooded battery number. If the batteries seem to discharge to 50% capacity in under a week, there is a very cheap and simple recharge formula that seems to work well enough to be considered...

An 800-watt Harbor Freight generator coupled to a 29-amp Megawatt makes an interesting "zot" charger that can recover adequate amperage to save the day for long weekend or weeklong camping trips.

Minimize unneeded battery loads in the rig.

Fill the generator and start it.

When the engine runs out of gas the 200 amp hour battery will have received enough to last until the next 12.00 start up.

Setting the Megawatt to 14.4 volts prevents accidental overcharge.

The 13.9 volts on a 200-amp hour system prevents sulfation.

Letting the gen run until it quits is a no-brainer.

This modus operendi will carry flooded batteries for 2-3 weeks before a thorough recharge is needed. The generator will run 4-6 hours on a tank full of 2-cycle fuel.

Best done in the afternoon when there are minima hotel loads.

Beats the hell out of running a big generator and whiffiepoo perverter. A small fraction of fuel would be used.

This is an affordable system. It would not even cost hundreds. It is simple, easy to use. and avoids wear and tear on expensive components.

[wopachop]

I saw a graph that was closer to 100 cycles before a golf cart battery reaches full capacity.

I have 2 brand new 6v still in the garage. I put a little 1amp light bulb on them and have been doing cycles.

In the same boat as the OP and looking for a better charger before i install them in my trailer.

[Latner]

Keep in mind that upgrading a wfco to something else is usually going to include upgrading the wiring between it and the batteries, unless you're lucky enough to have large wire from the factory. In my case I prefer to use a portable charger.

[landyacht318]

The WhiffCo strikes again.

How many batteries has this overemployed stock converter destroyed by refusing to seek and hold absorption voltage? Sure one might be able to maintain 13.2v powering 55 amps of DC loads when plugged into the grid or running a genset, but never ever expect that 55 amp potential be used to actually recharge the batteries in less than a week. And batteries already abused and sulfated from the Whiffcos chronic undercharging ploy, have Zero chance of ever reaching a true full charge at 13.2v, even if plugged in for months.

A 55 amp converter seeking 14.4v+ can do in an hour what would take the Whiffco a week. Running a generator to power a whiffco converter is throwing away gas money and time and annoying everybody within earshot of the generator.

The only good thing which ever came from a Whiffco, is when disassembled, they do have a nice big finned heatsink which can then be employed on capable electronics which deserve and are worthy of the extra heat dissipation. The included fan is a cheapo 80mm which is pretty high rpm and loud and powerful for an 80Mm fan. But it is sleeve bearing and prone to wearing out prematurely.

Any other converter is a serious upgrade which will pay for itself in the first set of battery's well extended lifespans, and the confidence that one has enough juice to run their loads overnight with healthy near fully charged batteries.

Anybody wishing to properly charge depleted batteries with a stock WhiffCo converter is throwing away time and money. Though those who are powerpole princesses will be 'just fine', until the Wfco fails prematurely, as they are known to do.

[3_tons]

2oldman wrote:

3 tons wrote:
My two 6v Costco GC’s are rated at 210 amp/hrs per (other makes vary a bit)
Two times 210 = 420 - So you and I both agree Sir!!
BUT, once connected in series to arrive at 12v, the 420, is reduced by 1/2, so I’m now at 210 amp/hrs total.

Which is easier to remember:

Series adds voltage, parallel adds amps..or

Add them all, if series divide amps by two.?

Exactly...I hope at this point that the OP hasn’t gotten too confused...; )

[2oldman]

3 tons wrote:
My two 6v Costco GC’s are rated at 210 amp/hrs per (other makes vary a bit)
Two times 210 = 420 - So you and I both agree Sir!!
BUT, once connected in series to arrive at 12v, the 420, is reduced by 1/2, so I’m now at 210 amp/hrs total.

Which is easier to remember:

Series adds voltage, parallel adds amps..or

Add them all, if series divide amps by two.?

[ktmrfs]

busterbrown73 wrote:

ktmrfs wrote:
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.

I'm leaning towards that now. Any specific model recommendations?

PD makes a drop in replacement for the guts of a WFCO. One version is 55A IIRC. that's the easiest to go with and will run off any generator 2000W or above. And it will get a bank of two GC charged to 90% or so from 50% in 2-3 hours or less.

[wanderingaimles]

Your comparasion of genny to shore power is going to have the problem of time.
Plugged into shore power, you are charging the entire time you are there, the batteries have time for the slow process of topping off the last 25% or so that they can take.
3-5 hours on a genny will not give that long sustained period.
Solar will give you a higher voltage for as long as you have good sun, it wont be 24 hours a day, but there is a good chance it will be 6-8 at the appropriate voltage to get the batteries topped off.
Also solar will charge while you are driving, something the genny or converter wont do with a tt unless your going to run your genny on a rack on the back of the trailer while travelling.

[wa8yxm]

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...

You just flunked composition. You are confused. NOTE you are not wrong. exactly. but confused.

You said the capacity of the two GC-2 in series is 215. Well I usually say 220 give or take (Mine are 230) but that is correct you then said "Because the amps are divided by two when the voltage doubles) and this is nonsense. THe AMP-HOURS of a matched pair of batteries in series are the same as the AMP-HOURS of the individual batteries they do not change. they do not divide. VOLTAGE doubles. That is all.

Now if you are talking about how much it takes to make say 20 watts. Then you got it right. but we are not talking watts (Which by the way the watt-capacity of a pair of matched batteries in series. like the voltage. doubles).

Someone up-thread said "Think of them as a big 12 volt battery" (to be specific a 4D is about right). I've been flamed for saying that but it is TRUE. two six volt in series are one big 12 volt electrically.

The only difference between his post and mine is I'd suggest a 60 amp converter.. Minor difference. Progressive Dynamics 9260 for a stand alone or 4660 if upgrading an integrated unit (Converter is part of breaker/fuse box/panel).

[3_tons]

busterbrown73 wrote:

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

I sent you a PM...

[time2roll]

Close to the trailer battery.

https://www.renogy.com/renogy-12v-dc-to-dc-on-board-battery-charger/

[busterbrown73]

ktmrfs wrote:
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.

I'm leaning towards that now. Any specific model recommendations?