12 v dc dynamo

[sparky1962]

Has anyone out there any ideas on how or where I can get a double ended dc dynamo or motor for the front dynamo of our 4 inch scale Burrell showmans engine?
It has the casing and just a plain shaft at the moment but it would be nice if it actually worked and generated .
Any thoughts?

[Tufty]

It's been a long time but I seem to recall dynamos only generate one way unless you muck about with the (I think) field windings. Can you fit a small alternator in? Another advantage being self governing at 12 (or 24)V.

[the highwayman]

The alternator idea is probably the easiest route to take, alternators need to spin fairly fast, so could be 'geared up' from the through shaft within a 4" scale body, but would probably need a battery to 'excite' the alternator. As Tufty pointed out the voltage is self regulated, so the engine revs could rise and fall a bit without blowing bulbs, there is also a pamphlet available describing various modifications to car alternators to perform different duties. If the engine is a scenic it would be fairly easy to arrange 'gearing up' via belts putting a car alternator on the exciter platform and using the existing 'casing and shaft' as a countershaft, worth a thought?

[sparky1962]

yes plenty to think about as there wqs an alternator in the exciter body but it didn't work so I put in a landroverr dynamo
I dont think it would matter too much about which way it spun if it had a shaft either end you could swap the dynamo round.
I thought about a dc motor but cant think of any double shaft ones

[steamy1]

Front mounted vehicle engines usually run clockwise looking at the front so the Dynamo would also run in that direction.


What is wrong with crossing the drive belt ? excuse my ignorance.

[weidner]

If things are symmetrical at the commutator end of the dynamo then it would likely run either way . Whichever way it runs then you will still have a + and a - , just that they will not be the same way around . The two wires to the dynamo are one of the main output wires , and the other is one end of the field circuit . In both cases , output and field ( marked D and F by Lucas ) , the earth connection completes the circuit .

On an automotive dynamo you will need a CVC box to control the voltage , otherwise it will rise too high if you over rev the engine , and then it will blow the bulbs . There are two coils and some points in the CVC box . The coil with the points on top cuts in when the dynamo voltage reaches charging speed , about 12+ volts . This can be jammed closed with a matchstick if you are not connected to a battery . If you are , then the battery will try to drive the dynamo as a motor if you hold the points closed when not up to charging speed .

The other coil will start to vibrate when the voltage rises too high , This intermittently puts a resistance in the field circuit to reduce the voltage and hold it steady at about 14 and a bit volts .

If your dynamo will not charge then you may have it connected with the wrong polarity . The simple answer to this used to be to touch the cutout points together momentarily , when the battery will reverse the polarity of the dynamo . The same applies if the dynamo has lost all its residual magnetism , which will mean it will not charge until you energise the field coils by touching the points in with a battery in circuit .

This is from memory of old Lucas Magdyno sets on motorcycles , and Morris minor electrics .

No responsibility accepted !

[steamy1]

I seem to remember, long ago someone was selling end castings for car dynamos to make them look more realistic on miniatures.

[iain]

Might be worth contacting STW as they had castings and had working dynamos on their kits.

[tasker tractor]

VW aircooled beetle you can get 6v or 12v dynamo's the shaft is long enough to put a pulley on either end. they do need a voltage regulator though.
Mike

[sparky1962]

Thanks for that the dynamo from a vw beetle seems the way to go as you say just run it through a voltage regulator
Can you tell me is that how the full size things work?
Never really thought too much about it until now