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# Thread: Circuit to shut off inverter at low battery voltage set point = 50%

1. ## Circuit to shut off inverter at low battery voltage set point = 50%

Charge controlers have an adjustable high voltage set point, so the batteries are not over charged. If you place a relay circuit that disconnects the batteries from the inverter so the voltage does not fall below the 12.06 50% level it would reduce damage to the batteries. The problem is that the circuit will need to not enguage the inverter until the voltage is some what higher like 12.30 volts. If needed the relay could open the 115 volt side and the inverter would only draw a small amount of current, until you checked the battery voltage level.

Thanks for any help in this matter.
Dale La Roy Smith II
Cocoa, Florida

2. Some inverters have a "Low Battery Disconnect" in them, but they are set too low usually.
I think you could use a 12V relay, and a trim pot in series with it, to control the 115V output, adjust the trimpot so the relay just drops out at your desired voltage, and have a "override" push button switch to short out the trimpot, to reset the relay.
Has to be home brew, i've see nothing in stores.

3. ## Relay will bounce unless close voltage is set higher.

Here is what happens:
1. Voltage goes down to low set point = 12.06 ~ 50%
2. Relay opens, no load on batteries, now voltage goes above 12.06
3. Relay closes, which places load on batteries, now voltage goes below 12.06
4. Go back to step 2. repeat process ( relay now is in circular cycle )

Do you think the OUT BACK inverts have Low Battery Disconnect that is adjustable?

4. Here is the problem, State Of Charge Voltages is meaningless when the battery has a load on it or being charged. The only time SOC has any meaning is when the battery is disconnected from any load or charge currents and rested for several hours.

The only true measure of the state of charge is by using a temperature corrected hydrometer reading, then record the loaded voltages down as each data point is reached.

Secondly you are getting the bounce effect because you need 2 set points:

1. LVD or low voltage disconnect, say 11.9 volts
2. LVR or low voltage reconnect which has to be higher than LVD, like 12.3

If the two are equal or too close, you will just sit there and bounce.

5. ## Theory great actual circuit ?

Dear SunKing,

In theroy I understand but not sure how to connect circuit. Could you steer me in a direction to make a circuit that would do this?

Thanks.

6. My suggestion - use a manual reset, or a 4PDT 120VAC relay, and route the relay coil wire thru the NO cntact. Then you HAVE to manually reset it, the battery recovering won't trip it back on

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