cheap inverter that has low voltage cutoff but voltage is too low for my liking.

solarhungry · July 2017

The inverter I have has a low voltage cutoff of 11.5 I believe. I am saving up for a good inverter that hopefully I can set the low voltage. The issue I am having is I don't want to go below 75/80% drain and 11.5 volts is just too low it seems. Why do all the cheap inverter makers make the voltage shutoff that low? Am I not understanding ? I will have plenty of solar and a large battery bank. What I've seen is under a load the battery voltage will drop and once the load is off it will go up some. I never let my batteries from my other small play off grid system get that low which the inverter shuts down while I was home.
I went looking for a low voltage cut off that I can hook up to my inverter but the ones I saw didn't have the amps and thick wire gauge sizes.
This is a concern because I have a lot of money in my batteries as most of do. I work all day and can't be home to watch... if we have a bunch of clouds roll in and the inverter continues to drain the batteries until it's built in low voltage shuts off the inverter the batteries are putting into large stress and shorten the life or damage them. What I have read a battery of 11/11.5 is prettty much a dead bad battery. Thanks! Any suggestions till I get a real inverter.

littleharbor2 · July 2017

The low voltage cutoff is that low because when hit with a big load your batteries voltage will momentarily sag, then recover. If the cutoff were higher you would get nuisance tripping of the inverter. The cut off point isn't necessarily to protect the battery. If your batteries are at 11.5 volts they are completely discharged. I just noticed this graph is for AGM batteries but you get the point.

BB. · July 2017

Actually, 11.5 volts for LVD is quite high for an AC inverter. Most are in the 10 to 10.5 volt range.

11.5 volts is an "OK" LVD for battery banks under, relatively, heavy loads. 12.0 to 12.2 is really only for batteries not currently under load.

A few programmable inverters can do 12.0 volts for 1 hour, 11.5 volts for 5 minutes, and 10.5 volts for a few seconds.... But even though that would be a very nice setup, it is very rare (higher end products?).

Lead Acid battery voltage is only loosely based on State of Charge, current (charging/discharging), temperature, age of battery, type of LA battery all play into the voltage reading.

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

You can use a Battery Monitor Meter to estimate the state of charge of the battery bank. Tell your family to conserve if less than 75% SoC and poor weather forecast. At 50%, start the turn of loads or start the genset. If SoC continues to drop, cut all loads and give you a call.

Some BMMs do have alarm contacts (set alarm at 50% SoC, reset alarm at 80% SoC, or whatever makes sense to you).

https://www.victronenergy.com/battery-monitors/bmv-700

-Bill

solarhungry · July 2017

Thanks for the help, better understood now.

mike95490 · July 2017

not many 12V inverters have adjustable LVD. Sorry.

jonr · July 2017

Ideally, a LVD would not respond to short term loads. If you have only small loads, then indeed, a 11.5V LVD would be very bad for the battery.

My solution - use an arduino (ATtiny) programmed with an algorithm I like and wire a relay to the inverter on/off switch.

solarhungry · July 2017

@jonr
Thanks, For your solution I am going to look that up. I have never seen that but am curious now.

cheap inverter that has low voltage cutoff but voltage is too low for my liking.

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