advise for opto-coupler

[ltosolini]

I want to build an over-voltage-cut-off for my bulk charger for my 20S LiFePo4 pack.
I am thinking of using TLV431 voltage reference for every cell: the TLV will drive the optocoupler.
The first optocoupler to fire will switch a flip-flop which will disconnect the charger.

I need advise on optocoupler becuase I have never used one before; it should:
- contain multiple coupler units in the same package to reduce board size
- cheap because I need 20 of them

Thanks,
Luca.

 

[amberwolf]

You might look up Fechter and Goodrum's Zephyr BMS threads here on ES; sounds simliar to what you want to do. May help you design yours.

https://endless-sphere.com/forums/viewtopic.php?f=31&t=55125

https://endless-sphere.com/forums/viewtopic.php?f=14&t=26554

 

[Inwo]

I sent a link to a buddy, Steve, building similar.
He asks the same question.
Picked up some 12s dumb balance boards for prototyping. 12 / 431/ pots/ pnp one one board.

My suggestion is to make a mickey mouse or gate with the on board indicator leds.
Multiple leds and a single LDR. Need delay so cds should work.

Using some feedback to the 431 should add Schmitt trigger action.

More of a mechanical issue to get 20 leds in a small enough footprint for cds cell.

I have some finished using 12 bi-pin lamps for 2 amp shunts. If I enclose it in a dark box. An ldr will sense any light on.

 

[emiyata]

I am doing low voltage cell alarm at around 1.7vdc per cell. I use LTO cells that you can charge very quick. I will be charging around 18amps 48vdc. Worse case maybe 1.5 hr with a 25 a/hr pack. A well top balanced pack will not have a problem going over voltage on a cell on the tests I have done, but the low voltage cutoff is a different story. When I get near low voltage cutoff some cells drop faster than others . The idea is much the same but the opto's will have transistors on the output in parallel with a led and/or buzzer to alert me that I am running out of power. My LTO low voltage alarm project hasn't started at this point because the cells can be discharged below 1.5vdc (Low voltage cutoff) on a infrequent basis without damaging the battery.I think you will find the optos will be easy to design into your circuit. Good luck on your project!