Opto Isolator for Two Signal BMS Assistant

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avontuur asked Sep 18, '19

Opto Isolator for Two Signal BMS Assistant

I want to use opto isolators between the load and charge outputs of my 123BMS using the two wire assistant for my Multiplus 3000.

I already see that the two Multiplus contact have 5v on them.

Can you tell me what is the cuurent to be switched through these contacts?

Then I can size an opto-isolator or use it to switch a transistor if more power is needed.

Or perhaps the current is so low that an opto isolator can be used directly - I have PC817 to use which can switch up to 50ma.

Thanks.

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Answer 1 · 2019-09-18T12:28:15Z

wkirby answered · Sep 18, 2019 at 12:28 PM

I have a very similar setup to what you propose, I am using 4N35.
4N35 is also 50mA.

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Answer 2 · 2019-09-18T14:00:29Z

kai answered · Sep 18, 2019 at 02:00 PM

I'm also using a similar arrangement, the current requirement through the interface is very low - on the order of 1mA according to following (the pullup is already there, internal to the multiplus)

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

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