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Old 14-11-17, 07:14 PM   #1
modelengineer
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Default DC motor as a generator

Hi
I have a small 24v DC motor that I was hoping to use as a generator.
Its a BTH unit and from period adverts Ive seen I think its compound wound, it works fine as a motor but spinning the shaft with a drill produces less than .5 of a volt
Can anyone advise whether this will need wiring modifications to make it work?
Thanks
Dougie

Last edited by modelengineer; 14-11-17 at 07:24 PM.
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Old 14-11-17, 07:45 PM   #2
chrismac
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Hi, you could have a search through this thread, I have seen this mentioned a few times before,
http://www.stationary-engine.net/for...tor+conversion

Hope this is of some help.

Chris
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Old 14-11-17, 08:33 PM   #3
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What connections does it have? Internal as well as external.

Peter
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Old 14-11-17, 09:12 PM   #4
modelengineer
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Thanks for the replies
At the moment all I can tell is it has the standard two leads for power
I can take it apart to have a look inside but what should I be looking for?
Dougie
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Old 14-11-17, 09:32 PM   #5
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You need to establish which leads go where.

There will be two brushes in its simplest form and a set of main field coils and a set of auxiliary coils if you theory is correct about being compound-wound.

So, potentially 6 wires, but some will be interconnected, so try and work out in words what you have and where they go. any colours or labels are important.

Peter
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Old 15-11-17, 03:53 AM   #6
Lucien Nunes
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Are you spinning it in the same direction as it runs as a motor? In the opposite direction (aside from possible brush damage) it will only generate a minute voltage as the shunt field will oppose the residual magnetism instead of adding to it. In the correct direction, you will probably need to get close to motoring speed before the voltage builds up.

Small compound motors are unusual. What was its application? If its offload speed when motoring rises much above its full load speed, or it is universal (AC/DC), then it will probably turn out to be series wound and will not function as a practical fixed-voltage generator. Again the likely effect when only a meter is connected would be to generate a very low voltage.


Supposing it is compound, and can be made to produce the proper voltage. You may want to make a couple of adjustments. One is to reverse or disconnect the series field coils. The required polarity relative to the series field is opposite for generating compared to motoring, so instead of helping keep the voltage steady they will make it sag at high load. Another is to set the brush rocker to a new neutral point for the same reason. Neither of these have much effect off-load so don't worry about them until you have obtained full voltage.

Please post pics and any relevant data!
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Old 15-11-17, 06:24 PM   #7
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Here are some pics of the wiring inside the motor along with the data plate
I have no idea of its original use but it looks old but unused
More pics in next post
Dougie
Attached Images
File Type: jpg SANY0289.JPG (136.1 KB, 31 views)
File Type: jpg SANY0292.JPG (139.9 KB, 26 views)
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Old 15-11-17, 06:25 PM   #8
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Here are more pics
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File Type: jpg SANY0291.JPG (140.2 KB, 20 views)
File Type: jpg SANY0293.JPG (143.2 KB, 20 views)
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Old 15-11-17, 06:49 PM   #9
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Looking on the inside the power cables go to the coils, one to each then the other end of the coil is attached to the brush holders so only four wires
this link to graces guide is what led me to think it was compound wound, its all the info I could find
https://www.gracesguide.co.uk/File:Im19370205EE-BTH.jpg
I hope this helps clarify things
Thanks again
Dougie
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Old 15-11-17, 07:02 PM   #10
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Your description of the wiring indicates a series wound machine.

NHH
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