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muhucks avatar image
muhucks asked

Using the BMV-712 relay to start and stop an inverter.

Hi All,

I have installed a solar-powered bore pump at my house for watering the garden vegetables. The water table is 2 metres down so it's just a 640w Ozito surface pump.There are 3 solar panels on the roof with the DC running through an MPPT battery controller charging a 250 a/h AGM battery. Off the battery, I have an Edecoa 240v pure sine wave inverter ( https://www.ebay.com.au/itm/EDECOA-2000W-4000W-12V-240V-Power-Inverter-Camping-Boat-Caravan-cables-LCD-USB/361746792693?epid=20035053209&hash=item5439ca00f5:g:qigAAOSw-qlduldy ). The inverter has a low voltage cut off at 10.5 volts which is too low for the AGM battery so I have been trying to use the BMV-712 relay. The inverter has a remote switch with an SPDT toggle on/off button. After lots of trial and error, I connected the NO / Comm to a 1-second timer relay ( https://www.ebay.com.au/itm/New-Trigger-Cycle-Delay-Timer-Switch-Turn-On-Off-Relay-Module-LED-Display-DC-12V/164397473608?hash=item2646da5f48:g:MUgAAOSwnTZdf0eh ) and the NC / Comm to another timer. Both timer outputs are soldered to the SPDT switch in the remote ( I had to use a ferrite core to prevent stray inductions on the cable as the electronics in the switch are sensitive. The low voltage is set at 11.6 volts and the relay clear is set to 13 volts. I tested this using a lab power supply to avoid the hours to run the battery down and charge it again.

The question is has anybody needed to start / stop something that used a toggle switch and is there a better way of doing it from the BMV-712 relay? My concern is that if the relays get out of sequence the remote switch won't care about the battery voltage it will just switch on relay input.

bmv-712-setup-2.jpg

BMV Battery Monitor
bmv-712-setup-2.jpg (2.4 MiB)
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Alexandra avatar image Alexandra ♦ commented ·

@Muhucks

On the inverter is the on off just a switch? Where it is not current carrying?

On some inverters we use the bmv to trigger the inverter on and off based on SOC.

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muhucks avatar image muhucks Alexandra ♦ commented ·

@Alexandra

The inverter has an On / Off switch. The switch has to be in the off position for the remote switch to work.

What do you mean by "Where it is not current carrying?"

I tried using the SOC but the voltage varied in reference to the Low SOC. It was recommended to me to not go below 11.6 volts so using the "Low Voltage Relay" seemed more suitable.

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Alexandra avatar image Alexandra ♦ muhucks commented ·

You can use the no or nc on the back of the bmv monitor, rewire the switch if it is not carrying the current of the inverter to switch on and of based on soc. Not sure how you would use it as it looks as though your system already has yours wired up and in use.

img-20201104-172835.jpg

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1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Maybe it is easier to put a relay in the DC line to the inverter?
A cyrix-li-load for example.
https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-Li-ion-120-A-EN.pdf

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