Low Voltage Cut Off

Alaska Man

What is the recommened LVC for a 12V AGM?

I have mine set to 11.9V, but when the fridge kicks on and the bankis around 80% DOD, the surge has my Xentrex Beeping. It's not a big deal just, "Beep, Beep, Beep" and we all move on.

I went fishing this past weekend and it was the first time both the wife and I were away from the house for an extended period time since I installed the array this past spring. It was comforting to know if the sun didn't keep up that the inverter would cut out and not kill my bank.

Is 11.5v too low if it happens once or twice a year?

AuricTech

Re: Low Voltage Cut Off

First off, I hope you mean 80% state of charge (80% of capacity left), not 80% depth of discharge (80% of capacity used up). Second, 11.5V is essentially a dead battery (about 10% of capacity left), so I wouldn't want to go that far. You might be able to get away with setting the low-voltage cutoff at 11.8V (30% state of charge) without risking too much damage to your battery bank.

Blackcherry04

Re: Low Voltage Cut Off

There is a huge difference between Un loaded and Under load voltage on a 12 V system. Depending on your cables you will always see a .3 - .5 voltage sag no matter what the actual un-loaded voltage of the batteries are. You know your system better than anyone posting here. Check the voltage drop when the refrigerator comes on and check the drop if it's your biggest load. Personally I set up most 12 V systems at 11.4 v.

You can get into a cycle that is not good where the inverter drops and the will reengage over and over if you set it to high. As the load is dropped the batteries will recover rapidly.

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BB.

Re: Low Voltage Cut Off

I would also check the voltage at the battery terminals...

For a 12 volt system, if you have 0.5 volts or more of drop (during surge current)--Then the 11.5 volts at the inverter could easily be 12.0 volts at the battery bank.

Or, for short term heavy/surge loads (seconds to minutes), 11.5 volts at the inverter (or even the battery) would not be the "worst thing" in the world. Long term voltage below ~12 volts (minutes/hours) would be a better set point.

But--In the end, battery voltage is a very difficult gauge of battery state of charge (state of charge levels, discharge current, battery temperature, voltage drop, age of battery, etc.).

-Bill

Alaska Man

Re: Low Voltage Cut Off

Blackcherry04 wrote: »

There is a huge difference between Un loaded and Under load voltage on a 12 V system. Depending on your cables you will always see a .3 - .5 voltage sag no matter what the actual un-loaded voltage of the batteries are. You know your system better than anyone posting here. Check the voltage drop when the refrigerator comes on and check the drop if it's your biggest load. Personally I set up most 12 V systems at 11.4 v.

You can get into a cycle that is not good where the inverter drops and the will reengage over and over if you set it to high. As the load is dropped the batteries will recover rapidly.

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That happened to me once, I thought I was in disco, Lights on, Lights off, Lights on, Lights off rapidly..... almost had a seizure. ;-)

Alaska Man

Re: Low Voltage Cut Off

AuricTech wrote: »

First off, I hope you mean 80% state of charge (80% of capacity left), not 80% depth of discharge (80% of capacity used up). Second, 11.5V is essentially a dead battery (about 10% of capacity left), so I wouldn't want to go that far. You might be able to get away with setting the low-voltage cutoff at 11.8V (30% state of charge) without risking too much damage to your battery bank.

Yes, I always seem to get that backwards, 20% DOD

Alaska Man

Re: Low Voltage Cut Off

Thanks everyone, I think I will bump the set point down a bit and see if it stops the warning sounds.

I cut about 3' off the positive cable from the bank to the inverter, making it as short as I could hoping that would do it............. Nope

Cariboocoot

Re: Low Voltage Cut Off

If your 880 Amp hour battery bank is at 80% SOC you should not be seeing 11.9 Volts.
If that is at the inverter, the wires are too small and there's too much Voltage sag.
If that is at the battery, the batteries aren't at 80% SOC and/or their capacity is a lot less than 880 Amp hours.

Blackcherry04

Re: Low Voltage Cut Off

I can't speak to his batteries and setup, but I have 1300 amp hrs of 2 v Surrettes all cabled with 4/0 and when my refrigerator goes into defrost and is pulling 80 amps I get a .5 drop in the voltage that will dip and recover to about .3 or so. It's not unusual at all to see 11.7v @ 80% dod.

Alaska Man

Re: Low Voltage Cut Off

TriMetric is showing in the low 80s when it starts to beep at the fridge cycle. Usually the Xentrex, MN CLassic and the Xentrex Control Panel all read the same 12.2-12 .3 range. I watch it closer tonight and see if I can't read how much it sucks the bank down.

Thanks again.

AuricTech

Re: Low Voltage Cut Off

Blackcherry04 wrote: »

There is a huge difference between Un loaded and Under load voltage on a 12 V system.

Yeah, I dropped the ball on that one. Thanks for pointing out my error. :cool:

I still would be pretty conservative in setting the low-voltage cutoff, but not for the reason I originally posted.

Blackcherry04

Re: Low Voltage Cut Off

AuricTech wrote: »

Yeah, I dropped the ball on that one. Thanks for pointing out my error. :cool:

I still would be pretty conservative in setting the low-voltage cutoff, but not for the reason I originally posted.

Thats cool, Unless you have a 12v system it would seem like a lot of drop. One could say it's a reason to have a 24v or 48v they have a drop also, just not as large. A lot of it is just the nature of deep cycle batteries, their just slow to produce current, where as a starter battery will release current quickly. This is the reason most premium Inverters have settable delays on their LVD settings so the dip and recovery does not knock them out.