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Cory Wikel avatar image

optocoupler/optoisolator to split allow to charge / discharge signals?

I've seen a few comments from users stating to use an optocoupler / optoisolater to split charge/discharge signalling from a 3rd party BMS to multiple downstream components... but maybe I'm dense and not seeing how that works. Can anyone take a moment and enlighten me?


Thanks!

BMS
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4 Answers
nebulight avatar image
nebulight answered ·

My BMS outputs 12v for separate high voltage disconnect and low voltage disconnect signals, so I invert the signal with an automotive relay. I then use this:


http://www.icstation.com/pc817-channel-optocoupler-isolation-opto-isolator-module-voltage-converter-module-p-11070.html

I take the high voltage signal to two of the in ports and the low voltage signal to two of the in ports so it gives me two optocoupler outputs for each condition. I have this enclosed in a plastic box so it's not exposed.

for HVD I have one going to the multiplus (to turn off the charger) and one going to a BP100 (that has my MPPT and DC-DC charger for alternator charging)

for LVD I have one going to the multiplus (to turn off the inverter) and one going to a BP65 to turn off my DC loads.

I also run the 12v signal for my HVD to my BMV712. I use that to control charging during low temperature. This is an older diagram before I got the 4 port board, but you can get the idea. The BPs just had the high signal from the BMS which still worked, but wanted to clean up the install with the 4 port board.


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wkirby avatar image
wkirby answered ·

The allow charge / allow discharge output terminal from a third party BMS should be able to drive a few tens of mA. You'd need to consult the datasheet for the BMS to be sure.

From this output you can connect the LED side of the opto coupler to this output. If you drive this LED with 10mA or so then you can have a few in parallel (depending upon the drive capabilities of the BMS output). Then use the transistor side of each separate opto coupler to signal the separate piece of equipment.

Remember that this method only works for equipment that can be signalled with "dry contacts". If the equipment that you want to signal needs a high or low Voltage to signal it then you'll have provide this Voltage from somewhere else. You'd likely need an isolated source if you have multiple different buts if equipment to signal.

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^this

Depending on the BMS output, you might also be able to put LEDs in series (if the output is at least a multiple of the LED's vdrop). Depending on your desired logic, it may or may not be helpful for a single optoisolator failure to knock out all the other downstream outputs.

mswoboda avatar image
mswoboda answered ·

Please, can somebody confirm?

Thank you!

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mswoboda avatar image
mswoboda answered ·

Hi,

I read this thread and I have a question to be sure that I got it right. I ordered the same board mentioned above.

I have a three phase system with 3xMultis2 5000. The battery is a 16cells LIPO4 280Ah with a Chargery BMS 16T. Its a 15,8kWP system with 3xMPPT 250/100 VE.Can and a Cerbo GX.

The BMS has 4 cables output:

+ and - for Charge Controller, HVD

+ and - for Discharge Controller, LVD

This output has 12V. Btw: What would happen if I connect this directly to the AUX input of the Multis II? Would it burn, or is it just not good?

Well, anyway thats the reason why I need the optocoupler...

So, e.g.:

I will connect the :

HVD + to "IN1" and the - to the G(1).

LVD + to "IN2" and the - to the G(2).

From the board I will connect:

"V1" to the + on the AUX 1 on the multi, and the "G(1)" to the - on the AUX 1

"V2" to the + on the AUX 2 on the multi, and the "G(2)" to the - on the AUX 2

The jumpers will stay on the board (what is it for?)

Then I have to configure (system configure) the multis (all three) to e.g. the AUX 1 and AUX2 in the right way (Bat. full: AUX1->open, bat. empty: AUX2->open). I know that I have to put the cables only to the Multi for L1.


Right?

Thanks,

Michael








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