Low voltage issue?

Arkansasoffgrid · August 2015

Just moved into our off grid cabin last Friday. Have a question/issue with voltage. Charge controller display is showing batteries floating MPPT 89%, but only 46.9v.
Last night with batteries showing 80%, it went into fault mode because of low voltage. Have only lived here full-time for 7 days, so looking for suggestions concerning this low voltage when batteries show a large percent remaining.

Dave Angelini · August 2015

You need to list your settings that you have programmed. It is often a big mistake to depend on % state of charge. 49 volts is near as low as you should get overnight before sunrise if you are balanced. It does not look like you are what I would call balanced with golf car batteries running air conditioning, I assume.

westbranch · August 2015

Something is out of whack... what are your charge parameters?
Is that 89% and Float under load?
Did you do a commissioning charge before you turned on the inverter?
Have you used the Local APP to review all the settings.... ?

more later

hth

zoneblue · August 2015

You have to get clear about midnites charge stage terminology.

Float: means it has completed bulk and absorb stages today, and is holding float voltage,
Float mppt: means its acheived absorb termination today, hence is in float, but the mppt means that for whatever reason its no longer able to hold float voltage. The primary cause of that is when your loads exceed the ability of the controller to sustain, thus drwaing the bank down, and lowering the voltage (and possibly exacerbated by the sun disappearing).

So, first you have to ensure that absorb is working correctly, ie set to the right duration or end amps setting, ie that the battery is actually charged when absorb terminates. Thats the first thing, but it will pretty much take care of the rest. If you really do hammer in some major loads later in the day, then, you just have to keep an eye on things that you arent going into the night period at a lower SOC. Quite the opposite, do your heavy stuff early enough in the day , if the sun is shining. That allows some rebound by dark.

However its all about balance, you can only use what you can actually produce.

Arkansasoffgrid · August 2015

Settings are as follows, low battery cut out 44 VDC
Absorb time one hour
Charge rate 100%
Vac dropout 60 vac
The minisplit turns off around 5pm with batteries at 90% plus

Arkansasoffgrid · August 2015

I've been working/ running power tools from 9am till 4pm and batts stay at 100% even with minisplit running.
I've got 8 /420ah L16s ordered that will be here Monday, just trying to limp by till then.

inetdog · August 2015

Arkansasoffgrid wrote: »

Settings are as follows, low battery cut out 44 VDC
Absorb time one hour
Charge rate 100%
Vac dropout 60 vac
The minisplit turns off around 5pm with batteries at 90% plus

That is almost certainly too low a cutout voltage and definitely too short an absorb time.

westbranch · August 2015

That Absorb time is most likely at fault .....check what the manufacturer recommends.. should be in the > 2 and possibly up to 4 hrs or more depending on the make of battery. Absorb is a slow phase of the whole cycle

vtmaps · August 2015

inetdog wrote: »

That is almost certainly too low a cutout voltage and definitely too short an absorb time.

Totally agree. And don't believe those SOC numbers... they give you a false sense of security. Get an hydrometer if you want to know your SOC.

--vtMaps

Dave Angelini · August 2015

Actually the 44 volt low cut-off is about the only thing that is right here.
I do not know the make of your battery (you need to check this) but I would make sure you have at least a 3 hour absorb, close to 59v set-point and a float of around 53V. make sure for now that the end amps setting is as low as it can be set for now to insure you get a full charge. Measure specific gravity. Verify that your staying at the float set-point with your loads running.

I can tell you that the reason I use some form of tracking is because you will probably find your array can not maintain float at 5 pm with heat pumps running. Good thing it is a cabin and not a home.

zoneblue · August 2015

OK, yeah, the CC is terminating early, falsely setting SOC to 100%. Do as the others have said, you have flooded batteries, so use a good hydrometer to verify teh absorb termination time. If you can read SOC off the midnite, then you have the WbJr, so set the absorb time high, maybe 5 hours. Set EA to the battery manufacturers recomendation, 2% of capacity is a good place to start for FLA ie 200Ah bank= 4A end amps. That way the absorb time is a backstop to the EA function.

Best you get behind this asap, because the new bank will be no different. The bigger the battery the harder they fall. No battery tolerates incorrect charging.

Arkansasoffgrid · August 2015

Thanks, working on these issues.

Photowhit · August 2015

I would setup the Whiz Bang Jr if you don't have one get one, though if you're giving SOC while running heavy loads during the day, I suspect you have one.

You are seriously "Over paneled" for your current battery bank. I would set a charging limit, if boB has gotten this worked out to work with the Whiz Bang Jr, You have @4600 watt array capable of feeding roughly 71 amps (4590 watts X .75 NOCT value ÷ 48 ) at 48 volts into a battery bank of @220 amps at 48 volts. This would represent a charge rate around C/3 or 1/3rd of your battery bank capacity. Most batteries recommend a C/8 charge rate or about 1/8th of the battery bank capacity.

Even with L-16s you will be slightly over paneled, I think the 420 amp hour is a Discharge rate over 100 hours, I think capacity at C/20 (over 20 hours) is 370 amp hours....

Check your electrolyte levels regularly! adding Water Miser battery caps might help retain levels.

As others have stated, check battery SOC with a hydrometer until you find you have good settings with the battery capacity through the CC, then check now and then and monthly when doing maintenance/equalizing.

Low voltage issue?

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