Motor for use as a generator on miniature traction engine
Motor for use as a generator on miniature traction engine
(OP)
Hello everyone. I've joined this forum as I'm in need of some help from a sparky!
I'm building a 3" scale Fowler Showmans road locomotive and I need to make a generator to go on the front to power 12 or 24V lighting etc.
I have been told that the best way to do this will be to use a 12 or 24V permenant magnet shunt-wound motor. Is this right and can anybody help me with one as I've looked without success. The motor needs to be about 6" diameter.
The below shows the sort of thing I'm looking for:
I'm building a 3" scale Fowler Showmans road locomotive and I need to make a generator to go on the front to power 12 or 24V lighting etc.
I have been told that the best way to do this will be to use a 12 or 24V permenant magnet shunt-wound motor. Is this right and can anybody help me with one as I've looked without success. The motor needs to be about 6" diameter.
The below shows the sort of thing I'm looking for:





RE: Motor for use as a generator on miniature traction engine
I'd look for a standard vehicle alternator and incorporate it into a custom housing to make it look like a period DC machine. Alternators for a modern vehicle have high output for their volume and have the regulator built in so the voltage is constant regardless of rotation speed. Size-wise they're about right too if you can fabricate a sheet metal casing to disguise it. Alternators for earlier vehicles tend to be a bit smaller than current ones because the electrical load of modern vehicles is considerably higher than in the old days.
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If we learn from our mistakes I'm getting a great education!
RE: Motor for use as a generator on miniature traction engine
BUT a permanent magnet motor will generat just fine.
I do like Scotty's suggestion though. It will save you a lot of burned out lights.
The output voltage of a PM motor or generator is directly proportional to the speed of rotation and hard to control.
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor for use as a generator on miniature traction engine
RE: Motor for use as a generator on miniature traction engine
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor for use as a generator on miniature traction engine
I have never seen an automotive alternator keep generating once the external battery gets below a certain point. The internal or external regulator chokes and the field is shut off. It has happened to me many times.
I would suggest that you do go the alternator way but that you add to the 'camouflage can' a small battery. A motorcycle battery or similar. This shouldn't be too hard as alternators have a radically different form factor than older generators. They are very short. This gives you the area behind the alternator which has to be be there anyway to provide a realistic exterior look.
BTW the scheme would free you to make the exterior look identical to your original model.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor for use as a generator on miniature traction engine
I have found that jump starting with a completely dead battery, the alternator would run the ignition as long as the revs were high enough. If you let the revs drop before the battery had enough charge for the ignition,you were hooking up the jumpers again. (And again, and again, usually. Always had to try it too soon. LOL)
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor for use as a generator on miniature traction engine
I worked in an auto shop for a while and saw exactly that many times, and my Renault taught me that too.
I suspect that if you somehow ran with no regulator you would actually get something but being the regulators have integrated circuits or relays that need X voltage or Y current to get into their operating regions it's a no-go.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor for use as a generator on miniature traction engine
Thanks Trevor.
RE: Motor for use as a generator on miniature traction engine
Go to a junkyard and pull the alternator from a Mazda Miata. All the engine accessories are cute as a button and just the right size. I don't know if it uses an external regulator or not; if you find one, pull that and the charging harness too. Conceal a 12V motorcycle battery somewhere, wire it up, and you've got a nice 12V lighting system.
Mike Halloran
Pembroke Pines, FL, USA
RE: Motor for use as a generator on miniature traction engine
Anyway! I had a quick look on eBay and there are a few permanent magnet DC machines intended for exercise treadmills which are good for 1HP at about 4000 rpm. The 180V output might be an issue but if you run it at a more reasonable speed of 500 rpm then you'll get 24V or so. The output will be very sensitive to speed and load changes, which is generally bad news for lighting circuits as they aren't very tolerant of over-voltages.
A small shunt wound DC machine will be an expensive thing to buy new, and there aren't that many around surplus simply because they aren't that common. You would need some form of field controller which you could do manually - pain in the ass - or get involved with some moderately complex auto controller. I still think the alternator is the best solution even if you have to conceal a small lead-acid battery. An alarm battery would be adequate - the field doesn't take much current.
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If we learn from our mistakes I'm getting a great education!
RE: Motor for use as a generator on miniature traction engine
A quick search on ebay might show up a picture to look at.
RE: Motor for use as a generator on miniature traction engine
Forget the DC PM shunt-whatever solution. It's going to end up being a major undertaking for you. If you are serious about constructing this model you should spent your creative time and energy on other aspects.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor for use as a generator on miniature traction engine
But, having said that, go with an alternator and make a dummy case.
If you are really good in the fab shop, you may consider making a new drive end end bell that looks like the generator you are trying to copy. The new end bell could support the alternator and some dummy sheeting back to a similar ND end bell.
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor for use as a generator on miniature traction engine
RE: Motor for use as a generator on miniature traction engine
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor for use as a generator on miniature traction engine
Or you might find an old 32 volt generator from the lightplant days.
RE: Motor for use as a generator on miniature traction engine
A couple of other hacks.
There used to be kits available to generate 120 volts from an alternator. There was a Voltmeter, a manual throttle pull and a switch that reconnected the output of the alternator to a receptacle and put unregulated 12 volts to the field. You pulled the throttle until you had about 90 or 100 Volts DC. That was enough for 120 VAC rated power tools. I guess someone discovered the high voltage ratings on the diodes and insulation needed to cope with load dump.
There were some good old boys making welders. They would install a 60 or 100 amp alternator in a pickup. They would buy a box of diodes and "match" the characteristics with an ohmmeter. They would then parallel enough "matched" diodes to carry the welding current. Of course they also used a throttle pull. At the engine RPMs needed to weld with these, cooling was not a problem. I met one of the fellows building the welding conversions. They were very popular in remote ranching operations.
Both these conversions were back in the days before solid state Voltage regulators and gas was cheap. It took a lot of Revs (and gasoline) to either weld, or run a power tool with these conversions.
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor for use as a generator on miniature traction engine
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Has anyone any ideas where I can get one from or can anybody help me with one? Thanks.
RE: Motor for use as a generator on miniature traction engine
What's wrong with the one on eBay - £23 looks like bargain of the week!
I have an old 3HP AC motor made by BTH nearly seventy years ago lying in the garage - it's the original from my own lathe. No direct use as a generator but would make a lovely housing to hide something more modern inside to get a period look. You want it, you can have it: it's up in the North East.
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If we learn from our mistakes I'm getting a great education!