# Brushed DC Electric Motor Used as a Generator

## Main Question or Discussion Point

I was wondering whether there was any literature on brushed DC motors used as a generator or whether you know anything of the sort? I know that DC motors behave differently when used as a generator instead of a motor. However I have not been able to find anything about it so I was wondering whether there is any information about it? Thanks for the help.

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yes you could if you can spin it fast enough. But you notice how hard it is to spin the big ol thing? wouldnt produce to much power. you can make it power your workstation LED lights

jim hardy
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look up "dynamo"

in general there is no difference between a DC generator and DC motor

a small permanent magnet motor will make near its nameplate volts and amps if you turn it in its operating range

if it's a wound field motor it needs to be provided with field current

there's plenty of tutorials about at many levels of sophistication, let a search engine be your friend.

look up "dynamo

a small permanent magnet motor will make near its nameplate volts and amps if you turn it in its operating range"

My experience is a little bit different.
Small motors are maybe 50% efficient.
So if a small motor is being used as a generator, it's output is 50% of nameplate and efficiency is 50%, then output is only 25% of nameplate.
Above is based on tests of only one motor/generator.

I used my dremel to test my brushed motor. 8000rpm it makes about 4volts. @35000 rpm it made 11 volts

jim hardy
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I used my dremel to test my brushed motor. 8000rpm it makes about 4volts. @35000 rpm it made 11 volts
how much field was on it?

how much field was on it?
not sure how to test for the field

jim hardy
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how many terminals does it have?
what does it do if you apply 11 volts (12 probably close enough)?

There's two basic formulas for DC machines

Volts = k X flux X rpm
where k is a constant for the motor's physical design
flux is magnetic field inside, either from a permanent magnet or the combination of all its field windings
rpm is of course rpm

Torque = 7.04 X k X flux X Iarm
k same as determined from open circuit speed test (which you did with Dremel)
flux same as above
Iarm is current through armature

If it has only one terminal, try connecting a lamp to it while spinning with dremel. If voltage goes up, lamp lights and dremel slows down, it's a series field
if voltage collapses it may have a defective field.

its a vintage titan motor. has 2 terminals pos & neg. Cant read the lable any more on it.