question

krby avatar image

Leaving MultiPlus voltage sense connected when battery disconnect switch is OFF.

I'm building a portable-ish system with a MultiPlus 24/3000. The main switch on the MultiPlus will not be easily accessible. I'll have the positive line run from the battery thru a disconnect switch on its way to the MultiPlus. The negative directly from battery to MultiPlus. The disconnect switch will be in the OFF position for weeks at a time.

I'm going to hook up a separate smaller cable to the voltage sense terminals on the MultiPlus. I am planning on hooking the voltage sense cable directly to the battery terminals (not the disconnect switch) but I want to know if it is ok to leave the disconnect off while the voltage sense cable is connected.

Is there a problem with this? Is there a little current flowing on the voltage sense cable even with the disconnect switch OFF? If so, how much?




MultiPlus Quattro Inverter ChargerMultiplus-IIvoltage
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2 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @krby

I normally advice to not use any switches, as every time you connect with the switch, a big spark inside the switch damages it.

But if you really want to: make sure to indeed always leave the negative connected.

the inverter can be switched on/ off with an external switch, or with a 'remote control panel' (DMC)

https://www.victronenergy.com/panel-systems-remote-monitoring/digital-multi-control-panel-gx

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I'm aware of the pre-charge / spark problem, but was trying to simplify for this question. I'm actually going to use a multi position switch that always passes thru a position that pre-charges the inverter's capacitors thru an appropriately sized resistor.


But, I didn't know if I could leave the voltage sense wire connected while the disconnect was OFF, or what side effects this would have.

Ah glad to hear you've got that covered.

It shouldn't be a problem, side effects can be: when multi is powered from AC with battery disconnected: you can get a battery sense error when the voltage difference between the sense input and battery terminals is too big.

raymiller avatar image
raymiller answered ·

Avoid any high current switchers apart from say a fuse switch as they all have typically have a much higher resistance. I've been testing all cables and connections using a 10A constant current power supply and measuring the voltage drop (mV) across the various high current components. It is surprising what you find just using ohms law. That is where I found a 300A switch was unstable for isolating an inverter even though in theory it was should have worked, brand new, its resistance was different each time I tried with my test setup and was sensitive to high vibration.

Cheers

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