I am overwhelmed with the variety of switching devices. MOSFETS/BJTS Relays(mechanical/solidstate),optoisolated solutions, etc..

I need to support 15V, 60A bursts, should be high efficiency, and switching time is not important since it wont be changing very often. Noise is also not a large issue. This will serve the function of a battery cut off in a circuit.

Based on these requirements, what would you guys recommend?

  • \$\begingroup\$ I removed the high-voltage tag since 15V did not seem very high to me. :) \$\endgroup\$
    – jpc
    May 14 '10 at 0:29
  • 2
    \$\begingroup\$ Everything below ~48V is considered low voltage. \$\endgroup\$ May 14 '10 at 15:08
  • \$\begingroup\$ yeah no worries I was initially going to make it much higher but changed my requirements \$\endgroup\$
    – stbtra
    May 15 '10 at 6:42
  • \$\begingroup\$ electronics.stackexchange.com/questions/15089/… \$\endgroup\$
    – endolith
    Jul 5 '11 at 15:35

Almost definitely a MOSFET. The only issue really is what voltage is available to drive it.

Let's say you have a 15V battery with a 5V on/off signal referenced to battery negative. If your load can float and can attach directly to the battery positive, then you can use an N-channel MOSFET: tie MOSFET source to battery negative, drain to the side of the load not connected to the battery, and the gate to the on/off signal through a small (50-200 ohm) resistor.

If the load needs to be grounded, you need to use a P-channel MOSFET with drain tied to the ungrounded end of the load, the source tied to battery positive, and the gate drive circuit may be a little more complicated (* = I might post details later).

A 15V battery is small enough that you can get away with a MOSFET rated for 25-40V range and there are super-low on-resistances that can handle 60A loads.

edit: you don't say what kind of packaging you are looking for. If you are planning on using a circuit board for other things, go with a MOSFET in an SO8, DPAK, or D2PAK package. SO8 sounds iffy for 60A loads unless it's for a really brief time, but it's probably the most cost-effective, though the worst for thermal dissipation. DPAK and D2PAK are beefier.

If you're not planning on using a circuit board, an automotive relay would probably be much easier to use.

  • \$\begingroup\$ There are nice high-current relays that are thru-hole mounted on PCBs. In either case (MOSFET or relay) the PCB traces would require reinforcement with some copper wire to handle 60A without overheating. \$\endgroup\$
    – jpc
    May 14 '10 at 1:03
  • 2
    \$\begingroup\$ If you are using a PCB, which I don't recommend, I suggest a trace width calculator, for example [1]. Sixty amps is a serious current. Using a service like BatchPCB, which uses 1oz copper, means a very wide trace. [1] home.comcast.net/~pcb.george/trace.html \$\endgroup\$
    – Dirk
    May 14 '10 at 12:29
  • 1
    \$\begingroup\$ 60A is serious current, but if it's limited to a particular duration (e.g. 1msec) then it's not quite as much of an issue. But you have a point. \$\endgroup\$
    – Jason S
    May 14 '10 at 13:39

I would suggest a mechanical relay. There are relays for automotive uses that can handle your load. You will typically need a small MOSFET or BJT to drive the relay coil (connect one end of the coil to +12V and drive the other to ground using the MOSFET/BJT).

You could use a high-current MOSFET but I don't think you can beat the price and low losses of the relay.

edit: JustJeff is right that when switching full 60A (especially if the load is inductive or the wires are long) the relay will need additional protection from inductive spikes to prevent arcing at the contacts (which may result in a permanently-on relay). With a MOSFET you could try making the turn-off slower (the dissipation should not be an issue if you rarely switch) by increasing the gate resistor.


Interrupting 60 A is a non-trivial task. I'd use a DC contactor, like those used in electric vehicles. McMaster sells a pile of them: http://www.mcmaster.com/#dc-voltage-contactors/=72v7eh

In particular, I think part 7995K42 would work.


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