Erratic Charging Behavior After New Battery Installation

904man

I have recently completed the installation of new MK Deka Batteries (8L16's 370Ahr at C20 rating) for a friend in need. The battery bank is 24v with three strings of four batteries each for a total of approximately 1100Ahrs. I have completed similar installations with my own off-grid system without any problems.

However this install is proving to be a different animal. The installation was completed one week ago. The owner is diligent in monitoring her system and paying close attention to her AGS and the duration of run. She states that the batteries do not appear to be charging properly advising that leaving a light on for a short period will activate the AGS. Addtionally, with her previous, dying batteries, she could leave for the day, the PV would charge and the batteries were indicate a full. The MK's are not doing the same.

I will be going back to her home tomorrow to check for the obvious, current in the cables from the SW4024 inverter/charger during charge from PV and Gen and battery terminal connections. All parrallel, series and Main cables are 4/0 and new.

As of now, I have no information on the PV array but know that the gen is 9.5Kw after altitude correction.

Can any one offer any suggestions? If all of the aforementioned is found to be functional, is there any way to diagnos the SW4024?

bmet

Re: Erratic Charging Behavior After New Battery Installation

I would look at termination at the battery connections (weakest link). Are the connections accomplished commercially or home made?

Cariboocoot

Re: Erratic Charging Behavior After New Battery Installation

Welcome to the forum (at last!)

Without knowing how the charging parameters are set it is difficult to say. Do you know what the old battery bank was? Same capacity? Not all L16's are the same Amp hours.

Definitely take along the hydrometer and check all the SG's. Makes sure the gen runs long enough to fully charge the batteries before you leave; you need them starting out in tip-top condition.

1100 Amp hours is a lot of battery. The current requirements exceed what I think the SW4024 is capable of. Needless to say that from solar you're looking at:
110 Amps (two MPPT controllers) @ 24 Volts = roughly 3400 Watt array.

Also make sure you know what the load requirements are. That much battery could supply up to about 13kW hours, which is really large for off-grid. Is that much capacity needed? I have on more than one occasion found that reducing the battery capacity results in a better performing system: the charge power available is capable of handling the smaller capacity whereas the larger capacity is too much for it. Like trying to charge a car battery with a 100mA wall wart.

Blackcherry04

Re: Erratic Charging Behavior After New Battery Installation

I'd be suspicious that the charge controller was connected to the PV and then you hooked it back up to the batteries after they were replaced without disconnecting the PV. It should be hooked to the Batteries FIRST.

904man

Re: Erratic Charging Behavior After New Battery Installation

I last week I acquired the necessary battery paramenters for the system from an Engineer at Soligent in Sac, CA. I plan on confirming or changing the paratmenters accordingly.

The old battery bank consisted of (2) 1050Ahr fork lift batteries that lasted for just over ten years using all of the same equipment.

As for the PV Array, I do know that it only has one Out Back Flex Max 60 or 80 Charge Controller.

Lastly, all terminal connections for all cables were professionally made.

904man

Re: Erratic Charging Behavior After New Battery Installation

Thank you for the thought. Due to the installation being completed during peak sun hours, I confirmed that both the inverter, charger controller and DC disconnect were secured an off position.

Cariboocoot

Re: Erratic Charging Behavior After New Battery Installation

Two 1050 Amp hour forklift batteries could have (and likely were) run deficit charging for years before showing a problem. That's 2100 Amp hours @ 24 Volts, capable of up to 40 kW hours. Run a fraction of that daily, put it back but never completely recharge, and the batteries can just go down in capacity a significant amount over many years before any problem shows up.

You now have three parallel strings which should be connected to bus bars to work best. It may be possible that one or two strings are being left out, but probably not likely.

At this point I can only say that with an FM 80 maxed out with panels you'd have a 7% peak charge rate with 1100 Amp hours which still ought to work. With an FM60 it drops to 5% and problems would show up much faster. With only one controller supplying power I would have to say the system is not balanced with that much battery.

But we need more details.

904man

Re: Erratic Charging Behavior After New Battery Installation

I will provide additional information after complete the priliminary diagnosis. Thank you for the assistance.

Prior to departing the forum, can you make a recommendation on worth while temp comp hydrometer?

Cariboocoot

Re: Erratic Charging Behavior After New Battery Installation

I personally just use an inexpensive one from the auto parts store. But then I look at it in terms of relative, not absolute, readings.

Our host carries Brady hydrometers. Some have used other brands with success. Just stay away from the "floating ball" and "needle indicator" types as they seem to be quite inaccurate.