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Seeking help with 12v dc motor controller on golf buggy #2

tezzarina

Dec 30, 2021
3
Joined
Dec 30, 2021
Messages
3
Hi all
I'm a newbie here and this is my first post - so go easy!
I realise this thread finished over two years ago but I recently had the exact same problem onedog had way back in Nov 2019.
I bought the same golf buggy from a recycling shop ($20) with the idea of making an electric billy cart for my grandkids - which I did.
Went beautifully for 1 or 2 hours then suddenly took off. I had installed emergency switches on the bumper bar and on top of the seat so I could quickly stop it. The control knob made no difference - in fact didn't make any difference if it was plugged in or not. Whenever the battery was applied it was full throttle, without any control. Since the I've checked the plug-in speed unit and it appears to be working normally on testing - resistance varies with turning the knob. I then took the speed control unit apart. No obvious burns/blisters or anything abnormal looking. Since I had ordered a new speed controller I thought I had nothing to lose so took the top off the relay - all looked normal there too. I have only superficial electronic theory knowledge (but I'm very curious) so I have no idea what caused the failure. I hope the new controller will get the cart back in motion.
 

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Alec_t

Jul 7, 2015
3,590
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Jul 7, 2015
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Welcome to EP!
It sounds as though either Q1 or Q2, or both, could have failed short-circuit. Note that they, and D1, all need to be in good thermal contact with their heat-sink(s).
 

tezzarina

Dec 30, 2021
3
Joined
Dec 30, 2021
Messages
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Thanks Alec_t
Would it be too embarrassing to explain to me what Q1, Q2 and D1 actually are?
Their heat sinks are well attached.
Thanking you.
 

Alec_t

Jul 7, 2015
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I'm not familiar with that controller board, but I would guess Q1 and Q2 are power MOSFETs and D1 is a power diode (or pair of diodes in one package). Perhaps another forum member knows that board and could confirm. It is quite common for MOSFETs to fail short-circuit.
 

tezzarina

Dec 30, 2021
3
Joined
Dec 30, 2021
Messages
3
Thank you Alec_t
I will do more research to enlighten myself.
Thanks again.
 
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