Looking to temporarily remove the dead man switch from my electric mower, while I wait for a replacement switch.

I have connected the black (negatives) together, as the switch connects them together when the plunger is pushed in. However, it seems the white and red wire that goes to the output of the bridge rectifier is normally closed, i.e., the opposite. Have confirmed blade spins without the white and red connected, but want to know what those connections are for before actually uses the temporary setup.

Is it for some kind of flyback resistance, or to nullify the voltage across the bridge rectifier so it doesn't damage the motor, or blow a fuse sometimes?

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  • 6
    Disabling the deadman's switch... I hope you have some spare fingers and toes lined up. Commented Oct 8, 2022 at 15:44
  • 4
    @MichaelHarvey Have used this mower, and others with dead man switches, for many years and never had a situation where me letting go of the handle would be advantageous to my safety. But this isn't really the point. The part is on backorder, and the stupid rules in our area means I can't put off doing the lawns any more. Maybe if this is the time I need to use it I can sue the government for rules that are forcing this course if action ;)
    – user66001
    Commented Oct 8, 2022 at 20:55
  • @Ecnerwal Typo. Fixed.
    – user66001
    Commented Oct 8, 2022 at 20:58

1 Answer 1


Probably electronic braking, to stop the blade faster. Particularly being it's in the deadman switch.

Presumably the output of the rectifier is also (more relevant to this use) the input of the motor. Depending on details, there might be a braking resistor somewhere on the white or red wire, or it may not be required.

Would be nice to think it's connections for regenerative braking, but that seems...unlikely. Too complex for a simple consumer item that's never all that far from a plug-in.

Amusingly (to me) the stack your question was migrated out of has this Q&A explaining it: https://electronics.stackexchange.com/q/16654/33670

(I guess they managed not to mention "lawn mower" so it flew under the radar...)

  • Thanks. Funnily enough before I came to look for answers to my question, this possibility came to mind, after remembering the free spinning that happened in my test just contacting two of the four wires, and what I recall from prior use. Yep, second picture shows wires going from the bridge to the motor. It would be cool to have regenerative braking, but not sure the increased part count would justify the recovered energy in this application. That is funny that a question that could have the same answer was migrated, especially as the bridge is a electronics device!
    – user66001
    Commented Oct 8, 2022 at 21:05
  • You have to stick to the electronics and not mention the consumer device at EE, usually. Of course, it probably would have been closed as a duplicate, then ;^)
    – Ecnerwal
    Commented Oct 8, 2022 at 22:02
  • I've noticed the EE folks throw electronics questions this way simply for mentioning that it's an appliance and not a "pure" design question. :/
    – FreeMan
    Commented Nov 1, 2022 at 16:17

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