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Disconnect for battery monitor

elewis33

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Feb 13, 2020
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I've built my own little solar generator/storage system using a small Lion Energy LiFePo4 25Ah battery.

https://diysolarforum.com/threads/diy-solar-power-pack.8847/

There's a battery monitor installed that seems to be discharging my battery (the battery holds a charge when disconnected but discharges when connected). I'm considering adding a disconnect switch to the monitor and wondering about where I should install such a switch?

If I put a basic single pole single throw switch inline on the negative battery connection side of the shunt will that provide the proper switching to keep my monitor working and still be able to disconnect from the battery when not in use?
 
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It appears you have a master on/off switch on the (+) side.

Is the battery monitor powered via a (+) lead from the battery?

If so, if you pass that lead so that it's through the master off switch, that should de-power the battery monitor when not in use.
 
I have a Victron monitor. The shunt itself doesn't use current. The electronics have a small feed from the positive. A small toggle switch would be more than enough to disconnect that 0.1 amp circuit. On my monitor the electronic feed negative is returned using the shunt's negative battery cable. There would be no current into the monitor if that cable is open. As you have only one negative cable connected to the battery, a switch or removal from battery, would end all phantom loads.
edit; I just read about the battery. LiFePo has a MBS that will continue to drain the battery. I think that is more likely to drain the battery than the monitor.
 
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I have a Victron monitor. The shunt itself doesn't use current. The electronics have a small feed from the positive. A small toggle switch would be more than enough to disconnect that 0.1 amp circuit. On my monitor the electronic feed negative is returned using the shunt's negative battery cable. There would be no current into the monitor if that cable is open. As you have only one negative cable connected to the battery, a switch or removal from battery, would end all phantom loads.
That's what I was thinking. Just wondered if if was using the correct logic and considering where and why I put in a disconnect switch.

edit; I just read about the battery. LiFePo has a MBS that will continue to drain the battery. I think that is more likely to drain the battery than the monitor.

You're right, the battery does have a built-in BMS, which I can't mess with, and the manufacturer acknowledges that there is a level of self discharge, but nothing that will fully drain the battery in 10-15 days like I'm seeing. I did a short test by pulling the battery from the solar generator and testing voltage then and then again 7 days later and the voltage was literally identical after that time.

Given that I'm starting to think that the discharge level I'm seeing has to do directly with the monitor or perhaps some of the connections that I made during assembly. I'm assuming poor quality connections can be a cause of power drains like this. Is that correct?
 
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