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I want a hard power switch for some battery-powered BLDC motors, but the currents (5A, up to 20A transients) and voltages (up to 60V) limit the kinds of switches I can use.

Because I want some small pretty switches that have the same effect of a hard switch, I've come up with this design with a voltage regulator and solid state relay:

enter image description here

The DPDT switch controls flow to the coil of the SSR as well as the ground of the voltage regulator, resulting in 0 standby current, ideal for my batteries. Because the electrical requirements are less demanding on the coil side of the SSR, I cam less constrained to the switch I use.

Are there any reasons why this design wouldn't work or should be avoided?

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    \$\begingroup\$ What's a "7824TV"? Normal LM7824s are only good for 40V input (Absolute Maximum). 60V >> 40V. I presume that internal schematic for the SSR is totally wrong and that it's a DC output type (not a triac as shown) that directly accepts a voltage on the input (not a current as shown). \$\endgroup\$ Apr 2 '15 at 15:33
  • \$\begingroup\$ Usually a flyback diode is recommended when using SSR, especially with inductive loads. \$\endgroup\$
    – Eugene Sh.
    Apr 2 '15 at 15:43
  • \$\begingroup\$ Nice catch. As for VT, it's some prefix the part author included to signify it sits vertically on the board. No significance otherwise. \$\endgroup\$
    – BB ON
    Apr 2 '15 at 18:54
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You have probably discovered this by now but ...

Are there any reasons why this design wouldn't work or should be avoided?

The big problem is that you are using a triac to control a load on a DC supply. This won't work. Once the triac is turned on it will remain on until the supply current is switched off.

You need a DC SSR.

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The first and most obvious problem you have is your SSR input. If the input is rated for operation at 24 volts, fine. Otherwise, you need a limiting resistor to keep from killing the SSR LED.

The second problem arises from your statement that you're using DC motors. The current transients will translate into voltage transients which will feed back to the regulator input, and may very well destroy it. You need (at the least) transient protectors on the regulator input. Actually, you can incorporate a voltage dropper into the protection circuit, as well - see Spehro's comment.

Finally, with these current and transient levels, you'll need to be careful about current routing and layout.

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The first problem with your design is that, the 24V voltage regulator will fail when you exceed 36V in practical sense. I therefore recommend that you use a step down or buck converter as shown here http://helpersalone.blogspot.com/2016/08/simple-dc-to-dc-step-down.html

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