Max Charging Current of typical GC2 battery

[brulaz]

Say the GC2 battery bank has been drawn down to 25-50%, what will be the max current they will initially accept?

For sure it's greater than the ~24A max my solar charger has reported as that was limited by the solar panel outputs.

[mike-s]

Chum lee wrote:
The standard book answer is: the amp-hr rating divided by 10. I know many people will argue with this.

So, if you have a pair of 232 Ah 6 volt deep cycle GC batteries in series that would be:

232 + 232 = 464 / 10 = 46 amps initial charge rate @ +- 14.8 volts or higher.

Nope. When combined in series, the voltage increases, but the capacity does not.

[brulaz]

mike-s wrote:
Note that manufacturers recommend limiting the charge current. Trojan says 3-5% of C20 (so about 11A for a 12V pair of GC2). US Battery says 10% of C20, Rolls and Crown say 10-20%.

Good point. Was wondering about temperature issues at the high charge rates mentioned above. But I won't be going anywhere near that.

In my case there are 4 GC2s in series, charging at 28-30V. Solar charging mostly from 690W on the roof. We often boondock.

But I also have a 120VAC-30VDC Meanwell PS which is only 500W, giving me ~16A max charging current. So far it has self-limited to ~16A without any problems when charging the depleted batteries on shorepower.

But wanted the truck's 220A alternator + two truck batteries to help charging the depleted trailer batts as well. And remembered that I still have the old 12VDC-120VAC 1000W PSW inverter. So am thinking to mount it in the Truck's cab or cap with 6awg to the truck batteries, and run an 120VAC extension cord to the Meanwell in the trailer. The max Meanwell load of ~500W might translate to 40A at the 14V alternator.

No need to purchase any new equipment, other than cables.

Also looked at a cheap 12VDC-30VDC step up converter on Ebay that said the load should always be less than the device's 400W rating ... not self-limiting? Anyway, avoided that.

[Chum_lee]

The standard book answer is: the amp-hr rating divided by 10. I know many people will argue with this.

So, if you have a pair of 232 Ah 6 volt deep cycle wet cell GC batteries in series that would be:

232 / 10 = 23.2 amps initial charge rate @ +- 14.8 volts or higher.

That said, they will accept much more than that if you have a charger that can do it. At higher charge rates the batteries will heat up and generate significant amounts of hydrogen and oxygen gas which is explosive. If you do not provide adequate ventilation to the battery compartment, eventually . . . . boom! Just like the picture Mexicowanderer posted the other day except you can expect sulferic acid to be splattered around the blast area too. If you are in a hurry to charge your batteries take adequate precautions unless you want mud (well in this case sulfuric acid) all over your face.

Corrected math. Thinking at the speed of light and writing at the speed of sound or less!

Chum lee

[mike-s]

Note that manufacturers recommend limiting the charge current. Trojan says 3-5% of C20 (so about 11A for a 12V pair of GC2). US Battery says 10% of C20, Rolls and Crown say 10-20%.

[MEXICOWANDERER]

At 68F it would not be unusual to have an instant 14.8 charge rate consume 108 amps with 6 cells and 216 amps with 12 cells of decent quality GC220 batteries.

Don't feel bad. It takes 670+ amps at 28 volts to get the attention of my 3,250 amp hour 24 volt bank. Stick & mud umbilical connection house.

It's all about slashing generator run time.

[ktmrfs]

I have stuffed 100-110A into a bank of two GC2 batteries on occasion when they were down around 50 percent. they will accept 100+A for around 30 minutes or more or so before the charge started to taper. That was charging from a PD55A and PD70A chargers in parallel.

I've done the same on a bank of four GC2 batteries. they will accept 100A for much longer as one would expect since each bank is getting around 50A in this configuration.

[MEXICOWANDERER]

Now,

Try parallel 2-banks 4 batteries with a typical onboard converter.

Start engine. Waste time.

An RV converter stops charging at about 90% state of charge. Keep it in mind.

Using a 1,500 lb oxen (your generator) to power a Little Red Wagon, toy converter. Waste of a good generator and noise pollution.

[SCVJeff]

brulaz wrote:
Say the GC2 battery bank has been drawn down to 25-50%, what will be the max current they will initially accept?

For sure it's greater than the ~24A max my solar charger has reported as that was limited by the solar panel outputs.

that also depends on the battery bank. Is this a pair of GC2's, or 4?

[brulaz]

red31 wrote:
If ya extrapolate both sides of BFL's ugly graph, I suggest 90-100A would get the battery to 14.4v in short order and then taper from there.
...

Thanks, that's a lot of amps!

[red31]

If ya extrapolate both sides of BFL's ugly graph, I suggest 90-100A would get the battery to 14.4v in short order and then taper from there. His graph is based on starting @ 50% with a charger that would max @ 14.4v, @70A, his 2GC held 70A for 30 minutes before hitting the charger set pt and tapering.