Diode On Small dc Toy Motor: Why ?

[Bob]

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

 

[Phil Allison]

Bob wrote:

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.

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


> For some reason, they have a diode in one of the leads to the motor.

** You are sure it is a diode because ?

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

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

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

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


.... Phil

 

[Baron]

Bob prodded the keyboard with:

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

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]

On 04/08/2015 13:01, Bob wrote:

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

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

 

Bob <rgsros@notme.invalid> wrote:

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

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

 

[M Philbrook]

In article <mpq9hf$1cg$1@dont-email.me>, rgsros@notme.invalid says...

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

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

 

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