DR2424 stuck in absorption charge, inverter or battery?

jperry

Hi,

I have a Trace, actually a Xantrex DR2424 inverter with twelve 6V cart batteries.
It as recently started to remain in the absorption charge mode, I have left it for about 12 hours but then turned the unit off fearing overcharging the batteries.
Can a bad battery cause the inverter to stay in absorption mode or should I be looking at the inverter?
I am going to try taking out two of the three battery legs, one at a time to see if this makes a difference but I thought I'd also throw the question out there to see if anyone else has had this issue.

cheers,
Jim

BB.

Certainly a shorted cell can cause all sorts of problems with charging/life of battery bank... But they tend to be a bit on the rare side. And if you have wildly out of balance cells, absorption can take a number of hours to complete.

For equalization--More or less, you are the only one that can tell when it is "complete".... So, what to look for. First, I would get a DC Current Clamp DMM (this one from Sears is good enough and cheap enough for our needs).

You want to check the voltage across each battery (or cell, if you can) and make sure that they are all at "reasonable" voltages. If you have one battery that is high or low voltage compared to the rest, you need to figure out why.

Also, use the DC current Clamp meter to measure the current into each battery string... If one battery bank is >2x the current as the rest (or 1/2 of the current or less), again, check for reasons why... Bad/corroded connections/bad cable/bad battery/etc.

And use a hydrometer to monitor the specific gravity... When charging, check the s.g. every 30-60 minutes... You are looking for the low cell(s) to continue to rise. When they stop rising, then the battery bank is fully equalized and these SG readings for each cell (temperature corrected) are your new 100% SOC SG readings. Once the SG stops rising, stop EQ. There is no reason to go any longer, and excessive EQ is hard on the batteries.

Note that equalization current is round 5% to 2.5% of the battery's AH capacity (100 AH battery, 2.5 to 5 amps current for equalization). Make sure that the plates are covered before equalizing (but not full--maybe 1/2 full maximum, gasses generated and electrolyte heating will cause full cells to push electrolyte out onto the top of the battery--Not good). After equalization is complete, then you can finish filling the cells.

Different manfuacturers have different eq requirements... Some suggest EQ is needed when SG readings vary by ~0.015 to 0.030 or more from low to high cells. Others suggest EQ ~once per month. AGM/GEL/Sealed Lead Acid Batteries are normally never equalized. AGMs may have "extended absorb charging for a few hours every 6 months as their "equalization" cycle).

Watch battery temperature--For EQ, it can be easy to overheat the battery bank--If it gets too hot (over ~110 to 120F), turn off the EQ until the batteries have cooled off. Heat is the enemy for Lead Acid batteries.

-Bill

706jim

I'm guessing that you have grid power and use the batteries as a backup only. Curious to see if disconnecting one or two of the strings solves your problem. I have a similar setup with three strings of GC's powering a similar DR1524.
Let us know here what you find out.

jperry

Yes, so I have a leased 6KW grid tied PV system and a separate 12 bank battery with DR2424 purely as a back up right now.
I will check the batteries out as I said before. Bill, thank you for your comment. I will buy a clamp meter if the battery leg experiment doesn't come up with anything useful.
btw, I'm a Fluke guy, I got my first and only Fluke meter at the age of 16, 31 years later it is still excellent and keeping up with the others on the market. But more $'s....
I'll post my results soon.

Jim

Vic

Hi Jim,

Looks like you have SIX parallel strings of batteries. You will probably want that Clamp DC Ammeter that BB Bill suggested, as string balance often changes over a period of time.

Also mentioned by Bill, DO measure the voltage of each battery. This may help you decide which batteries might need to be removed, and perhaps paired up with another laggard for some remedial charging, and so on.

Parallel strings can be managed, but it requires watching the current balance of each string, and the willingness to move batteries around, and perhaps charge them from an auxiliary charger.

Opinions, Vic

jperry

Hi and thanks for the input Vic.
So, it looks like you all are suggesting that it looks more likely that a bad battery is causing the inverter/charger to be stuck in absorption mode, rather than a problem with the DR2424 itself.
If so, removing the bad leg (once found) would remedy the problem until I can replace the bad battery, right?
I'll try to get to the test this weekend sometime and let you all know how it goes.
thanks
Jim

BB.

I am not sure... In theory absorb mode is typically hold a voltage (29 volts for 2-6 hours)--So the charge controller needs to reach the voltage set point, and a timer to hold it for X hours.

If the voltage never hits the programmed limit--That could be the batteries or it could be the DR inverter-charger. If the voltage is reached and held, then the timer (or whatever the DR uses for charge termination) is not right.

Are one or more of the batteries getting hot?

-Bill

jperry

OK, so here is the latest.
The system sat in absorb mode for 7 hrs today. The batteries started out fully charged, The voltage whilst in absorb mode was 29.0V for the entire 7hrs. Eventually I turned the system off. I briefly tried each leg separately but no change.
What used to happen is the system would sit in Float mode, waiting for a power cut. Then if the power just glitched for a second, the system would go into inverting mode for a minute, then switch to a very brief bulk and absorb mode and would be back into Float mode within about 20 seconds. It did this for a couple of years until the situation I now have happened.
I believe the inverter is at fault. No battery was hotter than any other and anyway, the system sat at 29.0V's the whole time.
So, if I am right, I don't believe this inverter uses a timer for the modes, it must use current and or voltage???
Any thoughts?
thanks
Jim

706jim

I think this model of inverter uses current and voltage rather than a timer. Batteries wont get hot, but just wont hold a charge. When the batteries are shot (see my signature) you will experience this sort of behaviour.

jperry

Hummm, I went from thinking batteries to thinking inverter and now I'm just not sure. I did open the battery breaker whilst in absorb mode and then close it again and the unit went to float mode and stayed in float mode.
Anyone know how to do a definitive test without buying a new set of batteries?