Diode On Small dc Toy Motor: Why ?

Question

Hi Folks,

I'm not an EE, so would really appreciate someone educating me a bit on this.

Trying to fix kids toy.

Very simple electrically, just a battery going to one of those small, cheap, probably a PM type, dc motor that does nothing but spin a pointer.

For some reason, they have a diode in one of the leads to the motor. (in series with one of the leads)

The Diode must be defective, for if I by-pass it, the motor spins just fine.

Can't imagine why the Diode.

Hard to believe that it is for any RF suppression due to the brushes that are apparently on this really small dc motor ?

Anyone have any thoughts perhaps as to for what purpose the diode was included ?

Thanks, Bob

Baron · Accepted Answer

Bob prodded the keyboard with: To ensure that the motor spins in the right direction and not to spin at all if the battery is reversed. --  Best Regards:                       Baron.

N_Cook · Answer

There seems to be a few types of small diode constructions that are guaranteed to fail an overcurrent by going open circuit. Cheaper than a wire-ended fuse , and as a plus, battery reversal protection

Phil Allison · Answer

** I guess the " pointer" does not spin at the same rpm as the motor, cos there is a gearbox ?

** You are sure it is a diode because ?

** What if you reverse the cell in the holder ?

** I have a possible theory in mind, but you need to describe the gadget a lot better.

... Phil

M Philbrook · Answer

My guess would be maybe to prevent charging of the power source? That would happen if you hand spin the pointer. But it could also be suppressing noise by not allowing current to flow on EMF back voltages.

Jamie

mroberds · Answer

Depending on exactly what kind of diode it is, it will drop around 0.3 to 1.1 V or so.  Without the diode, and with fresh batteries, maybe the motor ran too fast for the application. Matt Roberds

jurb6006 · Answer

Most likely because the mechanism would bee damaged or desrtroted by revers rotation.

Diode On Small dc Toy Motor: Why ?

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