Battery charging problems

metalguy21 · June 2017

I have: 25 - 200W panels combined in 3 strings of 5 and 2 strings of 5 feeding two Xantrex XW - MPPT60 - 150 charge controllers. Inverter is Xantrex XW6048. This supplies 2 - 1380Ah GB forklift batteries - 48 volt (2x24v). Gen backup - 11,000 watt. All off grid in AZ max sun Country - 8 good hours at max every day at this time.

The background: The clown show that installed this got the array configuration wrong and by the time it was fixed the batteries were limping along at near total discharge. I knew once the generator backup came on I had a problem as it is set to come on at 43 volts.

The problem: The batteries drop to 47v overnight. The panels will bring the battery voltage up to float (53v) by about noon. But as soon as the sun sets thing start dropping quickly and I'm back to 48v by evening - 47 by morning. Here is the problem - no matter what the voltage says the batteries are clearly not taking a charge. s.g. is 1.15 and never rises. I do have power for the home at all times though (ave. - 1500w load)

The battery guy who is VERY knowledgeable says I went too long at this low voltage array setup before it got fixed for a new battery (six weeks old) and I'm not going to get them to charge till I get a good heavy equalization on them. OK but here's the rub, it takes till 2:00pm to get enough volt reading (56v for bulk/absorption setting) for it to trigger equalization and by then I'm headed towards the end of the days solar production so they never get a decent equalization which I believe to be about 4 hours. Somehow I must get out of this vicious circle and get a decent charge/equalization.

Possible solutions: 1. Set the absorb/bulk battery setting to something less than the 56 the tech says (say 52) so it triggers earlier and goes longer. 2. Run the generator to do the charge and equalization.

Some considerations and questions: re: #1, if I lower the bulk/absorption does the fact that the float voltage would then be lower than the bulk/absorb matter? re#2: the panel readout says the net to the batteries is around 120amps, is this too much to push to the batteries? There is a setting that says it won't push more than 60a so is this 120 that figure x 2? I'm sure there a many others but this is a start. Sorry for the book. I'm sure there is an answer - likely very simple that I'm just not seeing. Any thought would be appreciated.

Aguarancher · June 2017

Run the generator. First get the batteries fully charged and then run an EQ for as long as it takes. That's a lot of battery and will take some time. Keep an eye on the battery temps,

littleharbor2 · June 2017

+1 Aguarancher. Fire up that generator and give it all you can early in the morning so you can begin equalization as early as possible. You need your batteries to be fully charged before you start equalization.

Estragon · June 2017

+2 on the generator.

Also, the system should (by default) get the batteries up to temperature compensated absorb voltage daily and hold it there until current drops to minimal (typically ~1% of capacity, so around 15a, which will likely take a couple of hours after absorb voltage is reached), not just float voltage.

Just going to float voltage will take way too long to chargefully. Even in AZ you'll run out of sun.

If you have a system that sits with no loads for extended periods, you might want to just float daily and absorb periodically, but not when in daily use.

metalguy21 · June 2017

Agreed on the Gen. Kinda what i figured. Yes early morning is a must if for no other reason than it's getting to 115 every day. From what I can tell the system does indeed charge up to my set absorb voltage (56v). I'm not that clear on how or if I can set that but I'm going to call the techs tomorrow and ask. I note that the gen shows around a 120a net charge when it first starts charging. That produces quite the boiling gas discharge. It has a temperature sensing gizmo on it that supposedly will reduce charging if the temperature gets out of hand. The battery tech said the same thing, keep feeling it to make sure it's not getting too hot. Unfortunately I'm not sure what constitutes "hot".

bsolar · June 2017

you have ALOT of panel .. what i can tell you is that lowering your bulk/absorb and float alittle will barely affect the usable capacity and would simply be 'easier' on the entire bank .. if you hear bubbling and sizzling you are definitely getting enough to the batts to be called 'equalize' voltage , thats what equalization does is bubble the juice and stir it ... i cant discern your exact setup but the fact is if you are living on batts and you say an average 1500w load? at night? thats way to much to be sustainable .. you need to rethink your load on the batts, concentrate on your impressive output in daylight, get someone knowledgeable to make sure the batteries arnt being hit too hard in the morning by something being wired or set wrong ..

westbranch · June 2017

+3 on the generator,

Now how long is your ABSORB time set to?..... at this point you need at least 3 hours or more, and not enter FLOAT .... Have you checked all the cells ? are they all at 1.15 ? have you tested the Voltage of each cell?
I just did some quick numbers, 25 x 200w x .75 (overall efficiency) > ~ 3750W (actual) / 48v = ~ 78A max that your array will produce.....meanwhile your bank needs ~138 A for a 10% charge rate.... Presently you have about a 5% charge rate, it will work if the sun shines but only when everything is working to start... what is the makers recommendation on the maximum charge that should be applied? Forklift batteries usually get a hot charge due to their work cycle...
hth...

mcgivor · June 2017

Drawing a load while attempting a corrective EQ is not the best situation, especially the overnight load, if there is any way to eliminate these loads, it would be benificial, the process can take many hours not just 4, preferably continuously, which is difficult with solar, and more so when the battery is needed.

Estragon · June 2017

120a isn't surprising. Your bank may or may not take more, and that's likely a good load for the generator.

Keep an eye on water levels while charging. While gassing (which is not a bad thing) a little bit of water is lost. You want to add a bit of distilled water if the electrolyte level is getting close to the low (plate) level in the batteries while actively charging. Don't fill to maximum when the batteries are idle though, as charging could make them overflow.

To me, "hot" would be over 120-130f or so, but my banks usually sit at around 50-60f.

Your charge controller and inverter/charger should both have a "temperature gizmo", which should reduce voltage as the battery temperature rises. Each likely has it's own sensor, and with 115f ambient temps, that would be a detail worth knowing.

metalguy21 · June 2017

OK great info. Westbranh's calcs look dead on. Yes the cells are all at 1.15. The absorb time is set to 4 hours however the odd thing is that when it finally goes into absorb Eq it defaults back to an hour. That's a question for the xantrex techs. As per mcgivor, At full sun with 1500w load I have about 40a net to batteries. I have a small ac unit in the insulated room the batts sit in that I keep at 78 deg. Likely not going to do the job as an Eq source - so generator. I can get don to less than 1kw if I turn everything except refrigeration and the small ac off. Estragon - yes the gen set hums right along at 120a. I'll talk to the xantrex techs here in a while to see about the 60a limit setting that has been configured. The only concern I have is the "hot" thing but I assume at the temps we are talking this should be pretty obvious.

I just filled with water. Going to crank it up here in an hour or so (5:00am PST) I'll keep you people informed. I haven't mentioned but I do have grid available. The local utility won't allow hybrid systems so that's why mine is a complete off grid sys. Only the AC for the house and a spa heater run on grid. Maybe have grid sent up to the inverter for this situation?

mcgivor · June 2017

Having the grid adds a whole new dimension, my suggestion would be to remove the battery entirely and focus on the recovery process using grid power, generator power would be more costly especially in the EQ stage when current is low, getting the battery back would be my priority, but that's just an opinion

metalguy21 · June 2017

yes agreed but ... for now I'm kind of stuck with the generator as I would be to have the electricians come back and run a new line from the house over to the solar mechanical room 100' away. But yes, getting the battery back is top priority. The batter tech, who as I said is very knowledgeable assured me these batteries are not like a car battery where long periods of very low charge will kill them in a short time. He gave me a couple of anecdotes about extreme batter abuse in fork lift applications to bring that point home. That said, the sooner this is solved the better. The Genset and inverter just now charged up enough to go into EQ (took 2 hours) so we'll see how it goes. Unfortunately I have just been told I must stop after only an hour and a half because of other obligations. Again, we'll see if that makes a diff.

Anawa · June 2017

I may be off-base with this comment, but absorb at 56v seems low for a forklift battery. I have to set mine to the 60v range to get the SG to 1.285. I use 56v for my float.

mcgivor · June 2017

Anawa said:

I may be off-base with this comment, but absorb at 56v seems low for a forklift battery. I have to set mine to the 60v range to get the SG to 1.285. I use 56v for my float.

What voltage do you set for EQ? Around 64V ?

Anawa · June 2017

62.8v for the EQ that is maintained fairly steady. I make seasonal adjustments on the absorb voltage, 59.6 - 60.4.

mcgivor · June 2017

Was just curious as the OP's values did seem to be a little on the low side, i've no experience with forklift batteries but understand they are pretty rugged and can accept higher voltages for EQ, of course the manufacturers recommendations always prevail.

littleharbor2 · June 2017

With grid power available you could get a forklift battery charger which would have the correct parameters for properly charging your batteries. Not sure what the cost would be but thinking it would be worth it to have this option available.

Anawa · June 2017

I'm not sure the forklift manufacturers recommended charging rates are appropriate for batteries when they are used in off-grid PV applications. There's a lot of conversation and opinions about this on this forum, as well as, other forums.

My battery manufacturer (GB Industrial) specifies 1.238 per 24v battery or 57.12v for my 48v bank. I never got close to 1.285 at that rate. Grossly undercharged with a PV system. After much research, I started bumping up the rate to where I now range.

westbranch · June 2017

Metalguy21, If the Xantrex has a 1 hr EQ, set the Absorb to 5 hrs, IIRC the EQ in those is a fixed value ( = 1hr) and not adjustable

littleharbor2 · June 2017

Anawa said:

I'm not sure the forklift manufacturers recommended charging rates are appropriate for batteries when they are used in off-grid PV applications. There's a lot of conversation and opinions about this on this forum, as well as, other forums.

My battery manufacturer (GB Industrial) specifies 1.238 per 24v battery or 57.12v for my 48v bank. I never got close to 1.285 at that rate. Grossly undercharged with a PV system. After much research, I started bumping up the rate to where I now range.

Forklift batteries typically work 8 hours, daily and have 16 hours to charge and absorb. I'm not saying to use the charger on a daily basis as that would defeat the whole purpose of having an off grid setup. I'm thinking more for occasional corrective charging, especially considering the fact you are under paneled and have a very limited charging window with solar.

metalguy21 · June 2017

Anawa said:

I'm not sure the forklift manufacturers recommended charging rates are appropriate for batteries when they are used in off-grid PV applications. There's a lot of conversation and opinions about this on this forum, as well as, other forums.

My battery manufacturer (GB Industrial) specifies 1.238 per 24v battery or 57.12v for my 48v bank. I never got close to 1.285 at that rate. Grossly undercharged with a PV system. After much research, I started bumping up the rate to where I now range.

I have the same battery. The tech told me 1.16v per cell absorb for my 48v system - thus the 56v. Same for bulk setting. EQ at 1.31 = 63v. tried the whole cycle today and watching it the entire time the voltages responded pretty much exactly as they should have. I ran the genset for 3 hrs to get up to full charge, switched to solar for the EQ which it immediately went into. Did EQ 3 times. Batteries went to float when all was done. This scenario is just what it should look like and I should have been fully charged BUT the damn (sorry but this is REALLY getting annoying) s.g. never budged off 1.15. Your point certainly seems relevant. What did you finally end up at for bulk/absorb? What do you use for your EQ voltage?

Oops, edit: I see the values you posted now. I have 2 - 24v 12-25-15 Giant Batteries. What are you using?

littleharbor2 · June 2017

Have you tried a different Hydrometer?

westbranch · June 2017

Does your battery guy know you are solar charging and not on the Grid for this project? Grid charging is WAY different than Solar charging, mainly because the Grid can pound in the voltage and amps constantly, and Solar can not maintain the constant part of that statement nor the unlimited time that the grid can do...
+2 on Different Hydrometer

metalguy21 · June 2017

Yup bought a new hydrometer. Same reading from both. However, excellent suggestion. Been bit by that sort of thing more than once. And ya the tech knows I'm doing solar but he (from what I can tell it's just one guy there) looks to have given me and another poster a far different number for bulk/absorb voltage and the other one looks to be too low too.

mcgivor · June 2017

The SG of 1.15 is bothersome, see attached link, 9) at bottom of the page
http://gbbattery.com/FAQ.html

westbranch · June 2017

Mcgivor, agree with 1.115,,,, it is almost water, had mused that thought a couple of times, thinking about the use of different electrolytes, but none are this low...

metalguy21 · June 2017

Went over to the neighbors and got his new glass one with the floating bulb. With it I get right between 1.175 and 1.200. Hmmm. The other two are the O'reilly plastic ones with the little rotating pointer. Hmm.

Estragon · June 2017

Even 1.20 is pretty low for a useful battery. I'd keep at the EQing.

Do you rinse the hydrometer? Sometimes they stick.

mcgivor · June 2017

The apparent acceptance of charge, bulk, absorbtion and float being achieved, whilst the SG remains low, is an indication of lost capacity. Voltages can be misleading, a battery may have perfect voltage reading without load, but as soon as a load is introduced it cascades. Charging a 13 80Ah battery even with 120A for 3 hours would be nowhere near enough to recover a dead battery ,using the SG of 1.15 as an indicator, of this capacity. Given the history of under charging there is the possibility of chronic sulfation, not what anyone wants to hear so say, but realistically the symptoms do indicate this may well be the case.

Anawa · June 2017

Metal, do you have a clamp-on amp meter, or another means to measure the current going into the battery during a charge? You may want to increase the absorb voltage up to at least 58v and measure the current going to the battery. Hopefully you'll get at least 100 amps or so.

I went through similar frustration as you until I started raising the absorb voltage. Running the genny for hours and reading the same low SG is really a bummer. As littleharbor points out above, typical forklift batteries will charge for 12-16 hours. Being off-grid, we don't have that time luxury. Unfortunately, we (off-grid) have to raise the absorb voltage and the results may be that the overall life our battery is shortened. I don't know.

I opted to buy forklift batteries as my first set because I listened to the experts: until you learn how to maintain the most vulnerable element of an off-grid PV system, make the experience as inexpensive as possible (i.e. less painful).

BTW, part of my off-grid learning process was that I've increased my main system to 6.1kW.

metalguy21 · June 2017

mcgivor - yes that scenario had occurred to me but the batts are only about 6 weeks old. The battery tech insisted that over that short a time it would be almost impossible for me to have wrecked them. He had lots of stories of much worse abuse that their batteries survived. Anawa - ya that would be a good idea. I think I can be pretty certain I'm just not getting mush charging going on as everyone warns me to keep an eye on heat but they don't get even the slightest bit warm let alone hot. I got *another* hydrometer coming and I'm going to try my genset charge scenario I described above again in the morning at 58v bulk/absorb and see what happens. Seems to interest people so i'll keep you informed. Thanks to you all for your thoughts.

Battery charging problems

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