I've got a robot powered by a 12v SLA battery. I'd like to build a discharge protection circuit to kill things if the battery dips below 11V.

In the event of low voltage, the brain of the robot (Raspberry [email protected] logic levels) will turn off everything it can, but I need to cut power to things that eat power at idle (like the Raspberry Pi itself) so the battery doesn't over-discharge when accidentally left on.

If I put a relay*** between the battery and the relevant boost and buck converters that change the battery voltage into 3.3V, 5V and 18V rails, I'm looking at switching about 14V@11 amps max or around an amp at idle when the cut-off would be needed.

Is there a low-draw circuit that can switch an 11 amp circuit? I'm kind of lost researching between mechanical relays, SSRs, and MOSFETs as far as which wastes the least power, and am not sure the best way to trigger one of those at 11V.

I know enough to run with a general idea if I can get a general direction (I.E. Use an SSR with a comparator), but I certainly won't turn down a link to a relevant schematic. I just don't know which road to go down.

Budget is low to moderate. (I'm trying to prevent ruining a $40 battery)

*** I say relay here, but am totally open to whatever makes sense to do the switching.

  • \$\begingroup\$ You can use latching relay. The coil energized only at changing moment. \$\endgroup\$
    – user263983
    Commented May 10, 2021 at 0:55
  • \$\begingroup\$ A suitably rated MOSFET and a comparator will meet your need. | A relay will too with a higher current drain. | A latching relay will draw minimal operating current but they are usually more costly. \$\endgroup\$
    – Russell McMahon
    Commented May 10, 2021 at 5:20
  • \$\begingroup\$ @user263983 I do like that idea, especially if I can fire the "Off" pulse from the Raspberry Pi. However, I've never used latching relays and don't know where to buy them in small quantities at a reasonable price, or what models to look for. Any suggestions? \$\endgroup\$
    – SvdSinner
    Commented May 10, 2021 at 18:00
  • \$\begingroup\$ Just quick search amazon.com/… secure.sayal.com mouser, digikey. \$\endgroup\$
    – user263983
    Commented May 10, 2021 at 20:38


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