Replacing 12-volt batteries with 6-volt

[hedgehopper]

Have you replaced two 12-volt batteries in parallel with two 6-volt batteries in series to improve ampere hours? Were the results satisfactory? Please elaborate. Was the rewiring difficult?

[pianotuna]

ktmrfs,

no free lunch, and always trade offs. There is no ideal batter bank--but 1000 amp-hour Surette 2 volt cells in series would be a pretty nice bank.

LI won't be useful to me unless they do a chemistry that can be charged at low temperatures. It does exist--but not in large amp-hour capacities.

ktmrfs wrote:

pianotuna wrote:
It is not the capacity so much as the voltage drop. The more cells the lower the voltage drop.

and the thinner the plates and larger number of plates reduces voltage drop as well. But gives up cycle life and DOD capability. No free lunch.

[pianotuna]

Hi wa8yxm,

Not necessarily true. The paste is thicker therefore there is greater internal resistance and greater voltage drop.

Most jars are designed for 25 amps draw per cell. Anything over that and voltage drop increases.

Of course it is best to have all cells the same size, but there is no question that a 200 amp-hour bank of 12 volt format will exhibit far less voltage drop than a 200 amp-hour bank f 6 volt jars.

wa8yxm wrote:

The GC-2 Cells are bigger than say a Group 27.. So less drop.

[BFL13]

Nobody mentioned different charging difficulties between 12v M/RV "deep cycle" batts and 6v or 12v deep cycle batts.

It can matter if you don't have the right charging equipment or the time to get them up to "true full" for one or the other.

The M/RV ones need "low and slow" all the way to 16v to get to true full, while the deep cycle GC2s and 12v (like T-1275s) can get to true full with high amps much sooner at a "normal voltage" of 14.x

Not everybody 🙂 gets his batteries to true full anyway, so in that case it would not matter I suppose.

BTW I see some still believe AGMs charge "faster". Not true. At 55 amps they charge the same. The difference is that in some cases (not all) AGMs can accept more amps for the same size (in AH) batt at a voltage (in Bulk Stage) so with more amps, yes it will charge faster.

If you have a 55 amp converter it will not put out more amps just because you swap to AGMs. It will still do only the 55 amps.

[ktmrfs]

pianotuna wrote:
It is not the capacity so much as the voltage drop. The more cells the lower the voltage drop.

and the thinner the plates and larger number of plates reduces voltage drop as well. But gives up cycle life and DOD capability. No free lunch.

[wa8yxm]

pianotuna wrote:
It is not the capacity so much as the voltage drop. The more cells the lower the voltage drop.

First half true. Second half.... Well... NOt necessarily.

Not all cells are equal.. NOw the numbers I'm going to use are not accurate but they are "Example"

Assume you have a battery with a total cell surface area of 1 Square Foot.. draw 100 amps and there will be a specific voltage drop.

In theory you parallel with an identical battery the voltage drop gets cut in half.

But what happens if you build a battery with a plate surface of FOUR square feet.. Yup. 1/4 the voltage drop.

The GC-2 Cells are bigger than say a Group 27.. So less drop.

HOWEVER There is crop at the cable/battery connection. which is Why I get in there and clean 'em from time to time.

[3_tons]

pianotuna wrote:
It is not the capacity so much as the voltage drop. The more cells the lower the voltage drop.

Very true Don, thanks for the great point...

[pianotuna]

It is not the capacity so much as the voltage drop. The more cells the lower the voltage drop.

[ktmrfs]

3 tons wrote:

ktmrfs wrote:
6V advantage
1) can take 500+ charge discharge cycles to under 50% (more like 25%) SOC

Disadvantage:
do NOT work well with high current loads, like even 1000W inverter. First ALL the current is coming from each battery vs 1/2 the current from each battery in a similar parallel 12V, Next, they have much higher internal resistance than a 12V which means more voltage drop

6V vs 12V IMHO really depends on YOUR application. If you only occasionally dry camp, or often use high inverter loads, then 12V may be a better alternative.
.

Note that I have for a out 6 years routinely run my Coleman Mach 1 P.S. 11kbtu air conditioner for brief periods (up to an hour or more concurrent with 440w solar) from two 6v GC’s without a hitch (via ProSine 2.0 - 04 aught cables), with locked rotor starting amps at about 140amps - now running Costco GC’s...Cables do MATTER...

On 2 GC with short 4/0 welding cable I was able to run a 1KW load or so with my setup as well. However, usually only worked if the SOC of the batteries was in the 75% + or so or the inverter would kick out on startup. Now I have 4 GC and don't have a problem untill less than 50% SOC.

Now low voltage cutout likely varies by inverter so what works for one may not work for another. And the solar input helps as well. In any event the internal resistance of GC is higher than 12V and for the same AH you have 1/2 the load sharing with GC compared to 12v.

[marcsbigfoot20b]

2oldman wrote:

marcsbigfoot20b27 wrote:
Yup kinda and I hated it. Had one 12 volt from the factory. Added two 6 volt GC2 batteries to power my inverter. .

Maybe you should have removed the 12v.

2 -6v batteries are not enough for any big draw inverters. 4 minimum, 6 is better, but incredibly heavy.

At the time (years ago) I had added the two 6 volt stand alone portable sitting under the trailer hooked to the inverter, recharging with 100 watts portable solar.

Now it’s 3 AGM group 31 Dekka deep cycle in parallel powering everything Including inverter with 360 watts of mounted solar with MPPT.
With the solar I am recharged full every afternoon all 10 days in a row boondocking.

This year I finally junked the small microwave and got an inverter microwave. For you guys with two 6 volts it would work well cooking at 30-50% power or whatever you want and only drawing that much.......cooks more even and your inverter won’t complain.

[philh]

You must change out the convertor charger and get rid of the POS WFCO. I love my 2 6v batteries. Haven't run anything heavy, but they have performed well for me.

[wa8yxm]

SO that you know. with large inverters Xantrex suggests at leat one pair GC-2 per kilowatt of inverter.. Now when my GC-2s were new one pair would cook my lunch in the 1100 watt microwave with the 2KW inverter but they suggest one pair per KW.

And when you do the "how much power" math. for inverters assume 10 volts from the battery.. not dead on but by the time you factor in conversion loss (About 10 percent) and line loss.. Darn close.

[bpounds]

hedgehopper wrote:
Have you replaced two 12-volt batteries in parallel with two 6-volt batteries in series to improve ampere hours? Were the results satisfactory? Please elaborate. Was the rewiring difficult?

Just do it. You'll be happy you did.

[2oldman]

marcsbigfoot20b27 wrote:
Yup kinda and I hated it. Had one 12 volt from the factory. Added two 6 volt GC2 batteries to power my inverter. .

Maybe you should have removed the 12v.

2 -6v batteries are not enough for any big draw inverters. 4 minimum, 6 is better, but incredibly heavy.

[TomG2]

marcsbigfoot20b27 wrote:

Swapped the whole thing to 3 AGM 12 volt deep cycle batteries in parallel and couldn’t be happier. My solar charges them faster also.

That is a not often mentioned advantage of sticking with 12 volt batteries. One, two, three, four, or five all increase available power without having to buy in pairs.