Instructables

Electric Lawnmower tripping circuit-breaker, Motor still runs.

I know you folks must have seen this question many times, but I still have to ask: my electric lawnmower tripped the circuit breaker (I suspect due to excessively long grass), and kept tripping it after I reset the breaker. The weird thing about it is that each time I reset the breaker and restart the lawnmower, the motor would actually start and run for half a second, before the breaker trips again. I infer that means the motor itself is not shot, and possibly not the rectifier either? Can anyone help with this? Thanks in advance!?

Sadly, its quite possible that the motor MIGHT run for a fraction of a second, even if its dead, but its unusual.

Have you checked the power cord for problems ?

Is this an earth leakage circuit breaker ?
Probably the circuit breaker is not rated for the right amperage?
Baboony (author)  blkhawk1 year ago
I have used this mower for 3 years and never had a problem before, so I don't think it's the breaker.
iceng Baboony1 year ago
Keep an open mind !

The fact is the E-mower fails after a moment tripping the breaker..
..... The unknown cause can be ....:
The mower could be the Current cause
But the breaker could also be the oversensitive cause.
Or the momentary high current start winding does not self disconnect.

Any chance you could plug into another circuit with a different
breaker with an equal amps or greater capacity ?

A
Baboony (author)  iceng1 year ago
I did, yes. In fact I tried it on three different plugs, and all three breakers tripped. That's why I thought it was the mower and not the breaker(s).
iceng Baboony1 year ago
Well done,  I concur with you...

A bad ( shorted ) rectifier diode leg is the most common fail scenario.

A simple test if you can reach and disconnect one of the armature
brush wires is to then turn the power on and see if you still pop that
breaker confirming a bad diode.

A

BTW I assume you know to un-plug the mower when you go in to set this up !

Baboony (author)  steveastrouk1 year ago
That is definitely interesting to hear! I was pretty sure if the motor burnt out it won't run at all.

Anyway, I tested the power cord with another appliance (trimmer, in this case) and it seems to work just fine. But I do plan on borrowing a power cord from the neighbour to double check, just in case.
Vyger1 year ago
If it is 3 years old and had a lot of use it is possible that the brushes are bad or just worn out. The brushes are the little carbon blocks that "brush" the power onto the armature. Besides normal wearing they can break and get crumbled pieces in the holder. Brushes can usually be replaced. Often appliances like a mower have an extra set shipped with them. Check your manual and see if yours can be replaced and if they provide them. In liquidhandwash's picture you can see were the brushes make contact. Its the area on the left. As the armature spins the 2 brushes make contact with the copper plates. There is usually a blue continuous spark seen there when the motor runs. If the motor draws more power the spark gets bigger and will give off an ozone smell. Higher draw (like when the motors works harder) will wear out the brushes faster. They literally burn away.
I suspect that the motor has overheated and burnt out some of the coils in the armature, this will make it draw excessive current, and possibly run at a slower speed. A good way to tell is does the motor have funky burnt smell, and if you can see the brushes do they spark excessively when it runs?
Screenshot-10.png
Baboony (author)  liquidhandwash1 year ago
Thanks for the response. I didn't really detect any burnt smell, but I'll open up the mower and try to take a look at the coils this weekend.