expected normal voltage drop from load?

[ewarnerusa]

Is there a rule of thumb or guidance for an expected voltage drop based on amp load on a pair of 6V GC batteries? I was tinkering in my trailer this weekend and ran a 750 watt AC electric heater off of my inverter. Batteries seemed fully charged prior to this based on voltage readings, but no SG reading taken. I had a much larger voltage drop than expected, it was pulled down to 10.5V and the inverter was giving an alarm. I assume due to low voltage. Although the whole time the heater was operating and I was getting hot air out of it. I let the heater run for only about 15-30 seconds. Ambient temp was around freezing (32F). I only did this experiment out of curiosity and not out of any need. Sometimes I'm just bored and want to tinker in the camper! Inverter wired with 0 gauge wiring, about 5' from batteries. Voltage came back up to about 12.5V after removing all loads.

I think I've done this same thing before and did not have such a large voltage drop. Due to the trailer being in the repair shop all summer and the batteries being in various states of disconnect/connected but no solar/solar on but parked inside, I think my batteries took a bit of a hammering. They were like 10.5V when I hooked up the trailer to bring home. I know that's totally dead for a 12V system, but they are deep cycle and this is the first time they were ever down that low. Batteries are 2 years old. I was going to wait until spring to replace them if needed, but I also thought they seemed to be behaving fine after several days of shore-power charging and then letting my solar take over. But it does seem like they are showing a larger voltage drop for small draws (like LED lights) than I remember before this summer.

[MEXICOWANDERER]

Helena Montana
December

CCA is about 40% of what it is in the summer. 360 CCA in the summer less than 200 in the winter

[BFL13]

ewarnerusa wrote:

BFL13 wrote:
...
Those poor batteries have been neglected for several months, and now they are going to be neglected some more, due to the situation. Perhaps it can't be helped, but IMO expect to be buying new batteries in the spring if you can't get them in and do some TLC on them (which might not work by now, but is worth a try for sure)...

I've always thought my solar did a nice job with my batteries. What additional neglect do you mean? I have put it through my charge controller's equalization cycle lately as well. 15.3 V for 2 hours.

At 32F, 15.2 is more like 14.7 at 80F, An E needs equivalent to 15.5 or so at 80F which would be 16.x in the cold. An E takes 8 to 10 hours, not 2 when the batts badly need an E, and for recovery efforts it could need to be repeated to get SG up where it belongs.

You don't know how much any of what you did do achieved without checking SGs to measure progress. It takes hours and hours and days and days to do a proper "recovery" with measurements of progress along the way.

Perhaps you actually did more than you indicated, but my impression (could be wrong) is the batts didn't get nearly enough TLC and now they are still in bad shape and under a snow bank getting worse. ?

So that's what I meant about likely needing new batts.

[ewarnerusa]

BFL13 wrote:
...
Those poor batteries have been neglected for several months, and now they are going to be neglected some more, due to the situation. Perhaps it can't be helped, but IMO expect to be buying new batteries in the spring if you can't get them in and do some TLC on them (which might not work by now, but is worth a try for sure)...

I've always thought my solar did a nice job with my batteries. What additional neglect do you mean? I have put it through my charge controller's equalization cycle lately as well. 15.3 V for 2 hours.

[RoyB]

Thanks Ed - I sort of remember some our conversations a year or so back getting all setup for OFF-ROAD camping... We was learning together back then haha...

We retired here in 2010 and never got off to a start doing any more OFF-ROAD camping since then. Too many bills and not enough planning haha...

This next season I expect to start getting some more OFF-ROAD camping starting up again. I got a new 4WD truck 6 months before retiring and it only has some 8K miles on it now - That shows how much it has been used haha... I did move my POPUP camper closer to the house and have been exercising my battery bank to support my Ham radio operations and run the house items when we have long power outages here in VA.

I'm anxious to get back into my OFF-ROAD outings...

Roy Ken

[ktmrfs]

BFL13 wrote:
There is more to battery usage than high current draws though. Golf cars that do that are in various iterations. 6-6s for 36v, 4-12s for 48v, 6-8s for 48v, and whatever.

I like 6s for easy recharge to true full after successive 50-90s. 12s are a bugger for that! 😞 I don't mind the extra voltage sag with high inverter draw, since I am set-up to deal with that. Solar doing daily 80-99s might be better with 12s, not sure. AGMs are known better for low voltage sag with high draws, but have their own "issues."

What you have to do, to get it right for your own camping situation, is read this forum for ten years, do a thorough analysis, and then flip a coin! 🙂

yup, you hit the big points on GC and the others. Important thing like you mention is there is no ONE right answer. Depends a lot on what you need.

Like you I have 4 GC, do lots of dry camping, like/need to draw them down well below 50% SOC, and want long cycle life. Usually am only drawing 5A or so, And work around the high current draw issues with careful planning and 4 cells.

[BFL13]

There is more to battery usage than high current draws though. Golf cars that do that are in various iterations. 6-6s for 36v, 4-12s for 48v, 6-8s for 48v, and whatever.

I like 6s for easy recharge to true full after successive 50-90s. 12s are a bugger for that! 😞 I don't mind the extra voltage sag with high inverter draw, since I am set-up to deal with that. Solar doing daily 80-99s might be better with 12s, not sure. AGMs are known better for low voltage sag with high draws, but have their own "issues."

What you have to do, to get it right for your own camping situation, is read this forum for ten years, do a thorough analysis, and then flip a coin! 🙂

[ktmrfs]

5' of #0 shouldn't give excessive drop for this current. Should be about 0.001 ohms (1 milliohm) resistance, x 75A is 0.075V drop little less than a tenth of a volt.

I still suspect that the biggest issue is the cold temps and something near 80% or less SOC. That combo with a pair of GC is marginal. I'd try a good charge and equalization cycle followed by measuring SG to see where you are.

Again, GC are not a good choice for continous high current draws. That's a job for good old 12V jars with very low internal resistance designed to handle very high currents.

[ewarnerusa]

RoyB,
It is about a 5' wire run with 0 gauge cables. I don't really ever draw that many amps during normal use, I was just out there tinkering because I haven't camped since summer '14 and I miss playing with this thing! I was exercising the inverter, let's say.

[ewarnerusa]

Agreed BFL13. The annoying thing is that I thought I had done a good job at preventing battery abuse by checking in on them periodically. And they still got abused, my first worry was when I checked on things to winterize in early October and noticed lots of corrosion on the battery terminals that had never been there before. Solar charging voltage looked fine, water levels down a bit but hardly low, but when I plugged my air compressor into the inverter the voltage dropped big time and it faulted out. I had to hook the inverter up to my truck battery to run the air compressor. That's when I first suspected I may have toasted batteries.

[RoyB]

Ed - Hope your battery cables are large enough to draw the high DC currents... I am getting away with just running a good solid 20-22 AMPS DC CURRENT from around 5 PM to 11-PM each evening on my off-road trips and my 12VDC batteries (255Ahs total) still holding up pretty good here...

Been doing this since around 2009 and I am just now starting to see my batteries performance just now starting to fall back on me.

I know next season is going to bad for my batteries for me as I didn't get to go out much the past two previous years like I usually do... I will need to replace them for sure...

Roy ken

[BFL13]

A pair of good 6s should do better than what was reported. It is true that 12s and AGMs do better for voltage sag under load than 6s do, but that is not the real issue here IMO.

Those poor batteries have been neglected for several months, and now they are going to be neglected some more, due to the situation. Perhaps it can't be helped, but IMO expect to be buying new batteries in the spring if you can't get them in and do some TLC on them (which might not work by now, but is worth a try for sure)

We hear about his all the time it seems. RVs going in the shop and coming out later with their batteries shot. It adds to the repair bill. I think I would try to take my batteries home and get them to use one of the shop's batteries while they have the rig, based on all the stories like this.

[ewarnerusa]

Thanks for the responses. I did suspect that the cold temps and higher resistance of 6V might be culprits for what I observed. The last time I did this experiment I do think I was still running 2x12V marine batteries. So that could explain me not remembering any low voltage issues.

I didn't take any SG readings prior to experiment due to darkness and laziness, nor afterwards. 12"+ new snow over night, I'm not going to unbury anything anytime soon to take readings!

[BFL13]

Seems like the inverter and wiring are ok but the batteries are at reduced capacity from the described situation they have been in.

First they need a real good charge to as near full as possible, then a good high voltage desulfation session to get them back as close as possible to proper SG.

Then see if they will "hold a charge" well enough for what you need them for, including with inverter loads.

[ktmrfs]

6v GC have higher signficantly internal resistance and hence voltage drop than do 12V starting or marine or for that matter deep cycle batteries. 750W load is around 60-70A, a pretty good load for a pair of GC.

Here is what I and some others have found with GC batteries. Once they get below about 80%SOC, a load in the 750-1000W range WILL very often trigger the low voltage alarm on a inverter and have a voltage in the 10.5ish range. The fact that it rose to 12.5 volts w/o a load is IMHO a good indicator that the batteries are probably around the 75-80% SOC and you just found the reason that those who draw 75+ Amps from a battery bank either go with mutiple 12V or a bank of 4 GC. It also doesn't help that you were around freezing. AH capacity of a battery decreases at low temps, and internal resistance rises. All going in the WRONG direction if your trying to get a big draw from GC batteries.

So.... before you get real worried, get the batteries FULLY charged with a good charger, measure the SG on each cell. Good chance what you will find is that you know the main drawback to GC batteries.

4 GC with 550AH capacity won't give the cranking amps that I get out of a puny 70AH 12V starting battery for my diesel.

[azrving]

Is the sg up?