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jordanb avatar image
jordanb asked

How do I connect a battery over/under-voltage signal to the CerboGX

I am installing a new LifePo4 battery bank (not Victron) on my boat. I have a Multiplus 120/3000 and a BMV700 and I am planning to install a CerboGX/GX50 at the same time as the new lithium batteries.

My question is about how to shut down the Multiplus via the CerboGX using a signal from the battery. The battery has a pair of signal wires available which, according to the documentation:

When voltage or temperature or current became abnormal, the resistance will be changed from infinite resistance (open circuit) to zero resistance (closed circuit).

So, I'm trying to understand how I could wire this to a relay (?) on the CerboGX so that when the battery signal wire closes the circuit, the CerboGX shuts down the Multiplus charger and/or inverter.

According to the battery manufacturer, the signal wires will close the circuit when either of voltage, temp or current goes out of spec (too high or low) and these set points are meant to be triggered before the BMS shuts down the battery, so that the signal can be used to shut down charge sources and loads before the BMS has to take action.

Presumably this signal will have 0vdc (infinite resistance) which means everything is ok, and will have battery voltage (12.xvdc) when the circuit is closed. Is this right?

Can this be done and if so, how? THANKS!

Multiplus-IIcerbo gx
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snoobler avatar image snoobler commented ·
What BMS?
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jordanb avatar image jordanb snoobler commented ·

The BMS is internal and not accessible. The battery has the external signal cables I described above. I am not sure it is necessary to say the brand on another brand's board. Also, I have not use the batteries in question and I don't want to appear to be endorsing them. There are several brands of LifePo batteries I have read about which have similar signal relay communication capabilities but do not have externally accessible BMSes and I have not yet decided which brand of battery to purchase.

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1 Answer
wkirby avatar image
wkirby answered ·

The type of BMS that you describe is known as a "two signal BMS".
The two signals, battery full and battery empty, connect to inputs on the MultiPlus. They do not connect to the CerboGX.
You configure the two signal BMS on the MultiPlus and connect the battery signals to the MultiPlus inputs.

This document should help you:
https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

Also, don't worry about mentioning other brands here. Especially batteries, there are hundereds of other brand batteries which are all permissable to use. Mentioning the brand can help to provide more informed answers with regards to configuring or interfacing.
Indeed, the two signal BMS support is intended primarily for other brand batteries.

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jordanb avatar image jordanb commented ·

Thanks for the info. I was hoping I could use the CerboGX just due to ease of access/installation for me (the Multiplus is hard to get access to in my case).

For the record, the batteries I am considering include Lithionics, BestGo, and Victron - cost as well as quality are huge factors. I saw a tear-down video with the BestGo and was very encouraged. The BestGo is the battery I was referring to, seems to be not a 2 signal as you describe: "The two signals, battery full and battery empty", but actually 6 signal because there are also (in addition to "battery full" - ie. voltage at high set point, and "battery empty" - ie. voltage at low set point) there are also signal wires for Temp too high and Temp too low, and also Current too high and Current too low. According to BestGo you can combine the voltage signal, temp signal and current signal wires together and thus you get 1 wire signals when any of the 6 conditions have been triggered, which sounds very flexible to me.

Anyway, thanks for clearing up the question about the Cerbo.

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