I'm trying to come up with some form of precise overvoltage protection between battery chargers and batteries between 12V and 48V batteries. I have 12 and 24 sorted using different methods: crowbar circuit, voltage monitoring relay, even Arduino and some voltage monitoring devices off of Adafruit.

However, 48V overvoltage protection is giving me a lot of grief. My crowbar circuit is way too imprecise and has too much tolerance... for VRLA batteries, the charging voltage is around 53.6V and I need the protection to trigger at 56.4V. Unfortunately, I cannot find a Zener diode with the required ratings, nor do voltage comparators like TL431 go up to that value. Industrial voltage monitoring relays are way too expensive. And I cannot find a solution using an Arduino because of the ratings. Keeping in mind, 48V battery charger supplies up to 250A (2500AH capacity batteries).

I'm having a bit of a mental block here. I am really hoping someone can point me to a standard configurable overvoltage protection device for the required rating.


  • \$\begingroup\$ My crowbar circuit is way too imprecise and has too much tolerance. Nevertheless, show us that circuit, perhaps it can be improved. I think you have a lot of X-Y problems, thinking that something has to be solved in a certain way but you cannot do that because you cannot find the components. I have no doubt there are other solutions to solve this. And I cannot find a solution using an Arduino because of the ratings. So you're saying, because of the 48 V and Arduino uses up to 9 V, you cannot use it? There are all kinds of circuit to make an Arduino work in a 48 V setup. \$\endgroup\$ – Bimpelrekkie Apr 15 at 14:01
  • \$\begingroup\$ @Bimpelrekkie Hi. Thanks for the reply. The two circuits I have so far are: systemvision.com/design/… and systemvision.com/design/crowbar-circuit-1 Regarding the Arduino, no I mean the sensors I know of on Arduino do not go up to 60V. \$\endgroup\$ – M.. Apr 15 at 14:49
  • \$\begingroup\$ You should include screendumps of those circuits in your question. Those are extremely simple circuits and will never be accurate. A more accurate crowbar is for example (top of the page): en.wikipedia.org/wiki/Crowbar_(circuit) . Note that that circuit will blow a fuse when there is overvoltage. Not sure if you were looking for that. I can only suggest to look at and try to understand similar circuits designed by others and use those as a basis. \$\endgroup\$ – Bimpelrekkie Apr 15 at 15:49
  • \$\begingroup\$ Hi @Bimpelrekkie Thanks again for replying. Yes indeed I looked at that circuit and for 12 and 24v batteries, that would be perfect. However, the LM431 is <36V and once again not good for the 48V batteries. I feel like involving a microprocessor, an arduino maybe, is the easiest way to go about it, just need to figure the best way. Perhaps having a current sensor on a 10k resistor across the battery charger that then shorts the battery charger like a crowbar using Thyristor or relay... \$\endgroup\$ – M.. Apr 16 at 7:29
  • \$\begingroup\$ However, the LM431 is <36V That can be solved with some additional circuitry like a zener diode and an NPN. It isn't trivial to design that though. But it can be done, I'd say it is impossible to without such protection circuitry. Explain why you need a microprocessor. I would use a comparator instead. Microcontrollers aren't "magical devices" that can solve anything. \$\endgroup\$ – Bimpelrekkie Apr 16 at 7:36

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