Motor Conversion

Simply provide enough torque and speed at the input to enable the required voltage and current to come out at the terminals. Escap instrument motors are really good at this sort of thing.

So, no physical conversion is needed? I spin this thing fast enough and I will see measurable voltage on my input wires? I have 3 wires going in.

Yep.

<....I have 3 wires going in...>

..........except as a generator they are now 'coming out'!

Only two of these are connected to the brushes and the commutator on a DC permanent magnet motor. It is entirely possible that the third is connected to the frame of the motor so as to act as an earth. Check using a multimeter set to ohms, and make sure they are all connected correctly to the circuits downstream.

Small instrument motors and those that are intended for model construction typically run at 12VDC, and an earth wire is not generally provided as the voltages are too small to be worth the bother. Higher voltages require an earth connection for personal protection, and the betting that the third wire is an earth is 7-4 on, favourite.

It is worth getting the completed rig checked out by a competent electrical tester before using it (the nature of the questioning in the post suggests that the original poster doesn't have the Ace of Spades in hand) so as to ensure safety.

It is not quite as simple as just spinning a motor to make electricity. You will make some, but the efficiency and the amount of sparking that will be reproduced will probably cause an early life failure.

This is because the optimum point for the position of brushes to supply the motor with electricity is widely different for the optimum point to take off power at the brushes as a generator!

If you can add some rotational adjustment to either the brushes or the fields, you can by turning the motor (with another motor for test purposes) at a constant speed, monitor the output voltage and observe the brushes for sparking. Use some sort of dummy load to draw some current, up to the running current of the motor had when working as a motor.

Rotate the brush assembly or the fields relative to another and find the point where the sparking is minimised and the voltage output maximised. Better to have a slightly lower output voltage if you can erase all sparking at the same time.....

Now you have a generator!

With a permanent magnet motor, you may have still the problem that at different loads, sparking may still happen either side of your optimum position load wise.....if your load is variable, set for a middle value., constant loads will be OK once the brushes have been set correctly.....

Proper DC generators have extra inter-field poles to put the optimum position for the brushes always to the same physical point, depending upon the load.

I personally would never use a brush motor for anything else than as a motor and if I wanted to generate say 12 or 24 volts, I wold use an alternator from a car or truck, which can be obtained on the web for up to 5 KW loads!!! Already made and with electronics for battery charging built in (often)...

But every car/truck alternator I have seen & worked on has brushes- perhaps you meant a PM alternator- such as can be obtained by utilising a F&P washing machine stepper motor(normally driven 3 ph by 100v d.c.) as an alternator & rectifying the a.c output to d.c.- & also rewiring as to the e.m.f. required?. Happy christmas to all.

It is true, most have brushes as you say, but (which is what I should have said) NOT a commutator! Sorry for the confusion....entirely my fault. My apologies.....

Though some more modern versions have their magnets on the rotor and the fields are in the stator and therefore no brushes are needed at all.....I have not looked around, but these later types are probably not so easy to find and identify. If anyone out there knows a good way to do this, I am sure that I would not be alone in being most grateful for any infos.... Then the wear and tear from usage would be even further reduced....

The usual types have (as you kindly pointed out) only slip rings, which are far less affected by usage than a commutator is. I have had Car Alternators with slip rings work for longer than 350,000Kms in what can be very adverse conditions under the hood/bonnet of a car!!!

I hope that you can forgive my silly error as it is Christmas!! And best wishes to you and yours.

Good interesting post, thanks.

I have used Niehoff brushless alternators on commercial fishing vessels. They are soooo reliable that you just dont think about alternators anymore. It is just there year after year with no maintenance, no failures and no hassles. They are mega expensive, like about $2300 for a 14 volt 250 amp model, but worth it if an alternator is mission critical in your application. I have used Motorola and Leese Neville brushed alternators which are a lot cheaper. They make more radio noise than the brushless type. They are good alternators, and a good value, but not as good as a Niehoff brushless if you value reliability highly. The bearings are not as long lasting, brushes wear down and they are just not as tough (occasional diode failures). If you dont have the bucks and do have the space, just use two cheaper brushed alts. They run just fine in parallel without having to do precise load balancing or matched voltage outputs. Better if you do all that, but OK if you dont.

Mark

Now lets say I took one of those permanent magnet DC servo motors rated for 1500RPM at 24 VDC, and turned it at 700RPM or less using a wind turbine, would I be able to charge a battery if I feed a multi-range voltage converter set with an output of 14V?