A little more on my low battery charging problem.

metalguy21

A couple weeks ago I posted a question on why my batteries (forklift) never seem to get a charge higher than an s.g. of 1.265.  We went through various suggestions but I didn't think to post the one idea I had that seemed most relevant.  The 3 stage charging always goes through to completion to float.  Is it possible the charging is simply going to float too soon - before the absorb charge has completed a full charge?

A few details:  I have the voltages set to EQ = 63v, Bulk and Absorb = 59, Float = 55.  These were determined in a very long thread last year and seem to be working.  The one variable I can set that I'm not so sure of is I can set the time in Absorb.  Currently I have it set to 180 minutes.  The manual says the charger will charge till the absorb current falls to 2% of battery capacity or whatever the time you set - whichever comes first.   I assume they mean at that 2% figure the battery should be fully charged - s.g. = 1.285.    

So ... is it possible that I have the time set to short and it's cutting things off before I get to the 2% figure and thus the batteries never get fully charged?  What seems to verify this as a possibility is that while I was getting that decent 1.625 charge earlier in the summer (still not a full charge though) I'm now only getting around a charge of 1.250 or less before it goes into float now that the monsoons are here and charge rates from my panels typically can run only half of capacity.  Does this suggest maybe I have my time setting too low?  Would it hurt anything to increase the absorb setting to say 240 minutes?  Or more.  It has a maximum setting of 480 minutes.  

Estragon

There are a couple of variables not accounted for here. The first is, how is the 2% threshold met. Is the system able to measure battery charging current alone, or could loads affect this measure? The second, and likely more important in context, is whether the 2% threshold is being met simply because pv can't supply more than that.

Another factor is depth of discharge. More deeply discharged batteries may need a longer absorb time.

If end amps is based on charging current only, extending the absorb time likely wouldn't hurt. If the absorb time is limited by solar availability, you may need to increase absorb voltage a bit to compensate. This only works to a point though. If monsoons mean there's not enough solar power to charge properly, you may need to do some bulk charging with a generator occasionally, and use available solar to finish charging completely.

mcgivor

The absorption time will largely depend on the amount of current available as well as the amount of time, hours of sunlight, this will differ depending on seasonal changes. Loads during charging also play into the equation, for example if there were a constant load greater than the 2% threshold transition to float would be controlled by the timer. Each system depends on variables unique to itself, getting settings correct is made difficult because it's a moving target, carefully monitoring is key throughout the first year, settings may well need adjustments, extending absorption time during winter to prevent pemature transition to float for example. My suggestion is to take the time to carefully monitor what is determining the float transition ( 2% or time) and make adjustments accordingly. If you suspect undercharging the importance of getting a full charge as soon as possible is of paramount importance even if it means using no loads for the time it may take because cronic undercharging is the most common reason of battery failure, the tell tale sign is a slow decline in SG readings.

metalguy21

"My suggestion is to take the time to carefully monitor what is determining the float transition ( 2% or time) and make adjustments accordingly. "

I'm not sure how to do this.  Monitor the s.g. during absorb to see what it says when it trips over to float?  I do have loads of around a consistent 650 watts at most all times.  So from what you guys say time would be the culprit?  Kick it up to maybe 240 and see how it goes.  Maybe kick the bulk/absorb voltages up to 60v?

I do need to get a handle on this as they were discharged down to 1.200 two days ago.  But that was after two very stormy cloudy days.

mcgivor

Watching the amperage near the time the absorption time is about to terminate, subtracting the load current present would result in the actual current going into the battery if it's near 2% then the time is close, if greater the absorb time probably needs extending. This is a time consuming process understandably but we'll worth checking, not just once but on a regular basis as seasons/weather changes, my checks are a daily glance to keep a finger on the pulse so to speak, a few days of overcast weather I increase the absorption time to 5 hours, then adjust back when sun returns, once you understand the way your system works it becomes easier to predict when adjustments are needed. 

mike95490

I'd go for the gold, and set absorb to 240min (4 hours) and see if that helps after 2 days.  Do you have any way to monitor time actually spent IN absorb, or just guessing by the desired time setting ?

metalguy21

Ok, that's all good input.  Let me mess with it for a couple days and I'll get back.

metalguy21

After a couple calls to tech support the problem was narrowed down to the battery capacity settings on the Inverter and charge controllers.  I had them set to the 1359AH in the battery specs.  But that meant the 2% figure for triggering float was 27amps.  Cutting out to float then always fell short of a full charge.  Setting this to force a set amount of time means you just lower the capacity to zero and that forces the charger to run the 5 hours I wanted.  The amps in absorb dropped over this time down to about 5 before it timed out. 

The suggestion by the tech was not to leave it that way as one does not always want that much charge.  They said to just set the capacity to slightly over my average draw (15 amps) so it would go on its own.  So instead of 1359 I use 750.  It runs MUCH longer in absorb this way (at least twice as long) and after 4 hours I'm up to 1.275.  It hasn't been that high in months.  I suspect if I run a couple equalizes I'll be close to 1.285.  

In any case I find that the batteries are definitely not a set it and forget it item in the system.  

MrM1

Just a passing thought to the statement "It hasn't been that hi in months". Is it possible then that u have only been charging to 90ish % SOC? Perhaps a good EQ would be in order as u closely monitor the SG.

jonr

I would take all charging parameters as "starting points" and then verify that you are getting to 100% SOC at least once per week.

I second MrM1 - if batteries have been undercharged for quite awhile, equalize them.

metalguy21

jonr/MrM1 - It's not only possible but certain I have not been getting a full charge.  I've never seen it above 1.265 in any cell.  i just checked and all are 1.275 - 1.280.  I assume that's pretty much 100% SOC.  That also reassures me there was no permanent damage done to the batteries from undercharging for so long.  Since I have not been able to get an EQ at full charge I'll do that tomorrow (getting too late today).  It only allows an hour at a time.  People tell me within reason you can do multiple hours of EQ.  Not really sure what the correct amount/answer is to this though.

mike95490

You do EQ charging (1hr, 2hr, 2hr ) until the batteries heat up and you stop, or the SG stops rising.  You can do it all in one batch, or a couple hours over a couple days.   The catch is - you have to complete Absorb, and then start EQ.  So maybe planning on some generator runtime, say early AM to do the bulk, let the solar do Absorb and EQ, and if you run out of sun, fire up the generator again and keep the EQ going.

metalguy21

Ya that is my understanding.  Today came off an almost zero charge day from monsoons yesterday but a 4 hour absorb brought it up from 1.200 this morning to 1.280 now with a 4 hour set absorb that it just went out of to float.  I figure starting tomorrow with less charge needed I'll likely get to full charge by around 2:00 so with the sun as high as it is I can get a couple EQs in before it gets too late.

Photowhit

Yeah, this time of year, I like to remind people to try to equalize when the batteries have been somewhat cool. Mine live outside and we've have a long hot summer. Hight time lows have just started dropping below 70 the last few days. I'll try to get in an equalizing charge tomorrow too!