DC motor supply

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Bob Engelhardt

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Oct 11, 2021, 1:39:56 PM10/11/21
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I have a 24v DC motor that I'm using with a PWM controller supplied by a
24v SMPS. I want to be able to briefly switch the motor to 48v with a
relay. I don't have a 48v supply, but I do have a 24v transformer &
bridge. I know that the following will give me the 48v, and I think
that the Motor Control will be OK with it. But I'd like to know if I'm
missing something. The relay will disconnect the Motor Control from the
motor before connecting the 48v.

Thanks, Bob

___________________________ +48v
_________ | _________
| +|______________|______| Motor |_____
| 24vdc | |Control|
| SMPS | | |
| -|_______________._____| |_____ Motor
|_______| | |_______|
|
_________ _________ |
| 24v |____| Full +|__|
|Xformer| | wave |
| | |bridge |
| |____| -|________________________________
|_______| |_______|

Phil Allison

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Oct 11, 2021, 7:10:38 PM10/11/21
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bobenge...@gmail.com wrote:
===========================
>
> I have a 24v DC motor that I'm using with a PWM controller supplied by a
> 24v SMPS. I want to be able to briefly switch the motor to 48v with a
> relay.

** Bad idea.
Doubling the DC input to a brush motor will quickly destroy it - it may last only a few minutes of such abuse.
Over voltage creates severe acing across the segments of the commutator.

A good rule is to have no more than 2.5V for each pole of a DC motor.


..... Phil

amdx

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Oct 13, 2021, 8:12:43 PM10/13/21
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 I had a 28V 2hp motor on a go cart and ran it on 48V. Ran it for a few
years, and never saw any commutator problem.

 But we did have an especially long, hard run and it came back with the
windings smoking. It would draw over 250 amps untill you got up to speed.

I will admit it was a motor designed for a military application, so
probably had some good specs.

Mikek


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ehsjr

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Oct 15, 2021, 12:30:17 AM10/15/21
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On 10/11/2021 1:39 PM, Bob Engelhardt wrote:
> I have a 24v DC motor that I'm using with a PWM controller supplied by a
> 24v SMPS.  I want to be able to briefly switch the motor to 48v with a
> relay.  I don't have a 48v supply, but I do have a 24v transformer &
> bridge.  I know that the following will give me the 48v,

Your 24V xformer + bridge will give you peaks of
over 36 V

Ed

Bob Engelhardt

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Oct 21, 2021, 10:06:06 AM10/21/21
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Phil thanks - I didn't know that. Nevertheless I'm going to proceed
with my arrangement:
- it's for my own use & not a customer's, nor a product
- the "briefly" is 5-10 seconds and a duty cycle of maybe 5-10%
- I have a few of these motors and if one is destroyed I'll use another
and have learned a lesson

Phil Allison

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Oct 21, 2021, 8:41:51 PM10/21/21
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boobenge...@gmail.com wrote:
===========================
>>>
> >> I have a 24v DC motor that I'm using with a PWM controller supplied by a
> >> 24v SMPS. I want to be able to briefly switch the motor to 48v with a
> >> relay.
>
> > ** Bad idea.
> > Doubling the DC input to a brush motor will quickly destroy it - it may last only a few minutes of such abuse.
> > Over voltage creates severe acing across the segments of the commutator.
> >
> > A good rule is to have no more than 2.5V for each pole of a DC motor.
> >
> >
> Phil thanks - I didn't know that. Nevertheless I'm going to proceed
> with my arrangement:

** So you did not want our advice - did you ?

> - it's for my own use & not a customer's, nor a product
> - the "briefly" is 5-10 seconds and a duty cycle of maybe 5-10%
> - I have a few of these motors and if one is destroyed I'll use another
> and have learned a lesson

** Did you count how may poles on that motor?
It matters just a tiny bit ......


..... Phil

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