I have a 60V li-ion battery back with PCM board attached to it for protection. According to the PCM datasheet, under fault condition the PCM cuts off the load and thus isolates the battery bank. The battery bank has an array of solar panels connected to it through an mppt at all times. I wanted to isolate this source also from the battery pack during fault condition. Is there anyway other way I can achieve this except using a 60Vdc relay?

The datasheet of the PCM attached to battery


You can do this with a relay but its contacts have to be rated to carry the current that it may be switching. You haven't mentioned this but there are plenty of relays that can switch 10 amps at much higher voltages than 60 V dc.

What you may not have is a control voltage to activate the relay coil. Most typical relays will have variants that cover 5 volt and 12 volt coils so choose one that you prefer.

The fault condition you mention may provide a signal that can be used to activate the relay coil but again without more details of your setup it's impossible to say BUT there should be enough information here for you to make a start.

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  • \$\begingroup\$ The PCM I mentioned only shuts down the system or provides 60Vdc through the battery to the load. It's just a cut off mechanism so there is no control signal in that. The problem is, to use a 12Vdc relay(which is the highest voltage relay available to me) of my current requirement I will have to use a dc/dc converter of 60V to 12V. \$\endgroup\$ – Ayush Jun 6 '14 at 12:32
  • \$\begingroup\$ It depends on the power taken by the relay coil - if it is 200mW then losing 800mW in a dropper resistor may be an attractive solution due to its simplicity. For instance 200mW at 12 V implies a resistance of 720 ohms which, in turn implies a dropper resistor of 2880 ohms. \$\endgroup\$ – Andy aka Jun 6 '14 at 12:44
  • \$\begingroup\$ I am glad you mentioned this. It was also suggested to me by another source to add resistors, but what worried me was that as the power taken(due to current) change according to load, wont it change the drop across the resistors? \$\endgroup\$ – Ayush Jun 6 '14 at 12:48
  • \$\begingroup\$ I know it may look like a shot in the dark at the moment. I have added a rough schematic of my project with the question. Maybe that might help you decide. \$\endgroup\$ – Ayush Jun 6 '14 at 12:50
  • \$\begingroup\$ Instead of a dropper resistor you could use a constant current circuit that always tried to apply the right current to the coil to produce 12V across it. Add a 12V zener diode across the coil and it's a big improvement. Maybe you should also consider a P channel MOSFET for switching the battery? \$\endgroup\$ – Andy aka Jun 6 '14 at 12:57

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