540 Motor as a generator

I've got a few 540 motors from the boys RC car projects (as soon as they upgrade the motor a perfectly good 540 DC brushed motor gets consigned to the scrap bin, otherwise known as my come-in-handy box) and I was thinking of using one as a DC generator so my little Stuart 10H would actually do some work for a living. I've read somewhere that they are not the most efficient generators, but as I'm not too worried about optimum efficiency I wondered if anyone has had any experiences of using them as generators?

You will find that the kv of the motor is pretty high....A typical motor will give around 8-9 volts at a fairly high speed...8-9000 rpm...

If you have the patience to rewind you could get the voltage up and required speed down.

The current you can draw depends on wire gauge and how powerful the magnets are, but dont expect a lot..

Edited By John Rudd on 09/01/2019 10:05:09

Thats interesting, thanks. I've enough spares to mean if I have a go and make a mistake its not a problem.

I have used similar small permenant magnet motors as generators for my IC engines. You may find you need to use a belt drive to increase the speed, this was common in full size steam generating stations.

As a quick check you could drive one of the motors with your lathe of drill and see what output you can get.

This video is my 3cc engine lighting a few lamps:

**LINK**

You can often improve the performance as a generator if you are able to rotate the backplate slightly to find the optimum position. Motors usually are optimised to run in both directions at many speeds, but as a generator runs only one way and usually at a near-constant speed you can make useful gains this way.

Neil

I'v used small motors as generators on my hot air motors.

Ian S C

These motors would be a pain to rewind for more volts out. The simplest way would be to use a simple op-amp circuit to boost the voltage driving you meter. This would also have the advantage of reducing the load on the motor (generator).

Ed

Can you explain this "simple op-amp crcuit" please? Perhaps you mean a boost mode switching regulator. A boost regulator will give you a constant output at higher voltage but there are limits to what it can do.

Cheap chinese version

https://www.ebay.co.uk/itm/MT3608-2A-DC-DC-Voltage-Step-Up-Regulator-Boost-Converter-Like-LM2577-XL6009/132860039749?

Robert G8RPI.

Hi Robert, a boost mode regulator would work, but tends to be configured to supply a constant output voltage.

I believe that this unit is to be used as a tacho generator and drive a voltmeter calibrated in RPM.

If you look at op amp (operational amplifier) circuits, (the 741 is a typical device) it can be configured with 2 resistors to have a gain of 10, 20 etc. The output of the op amp then feeds a voltmeter calibrated in RPM.

With most modern voltmeters or "meter LCD modules" the load taken is small so little power is used.

Cheers, Ed

Ed, Jon's original enquiry was for the generator to do 'some work'. I understood that he would want to light some bulbs, drive a pump, or in some way show that the engine is producing power. With the very best circuit design, and with power opamps its going to be a self defeating goal.

If the opamps needed an external power supply then it would be like cheating, if the motor generates enough power to light bulbs then it could power the opamps too!

Ian P

Earlier, Neil mentioned rotating the 'backplate'. To clarify (for anyone not familiar with motor design), the backplate is what the brushes would be mounted on. Rotating the backplate, so the brushes actually, relative to the field magnets allows the motor (or generator) characteristics to be fine tuned for torque/voltage/speed (all interrelated here). On a typical DC motor nowadays the brushes are in the moulded end cap so some ingenuity might be needed if you want to do any adjustment.

Ian P

Easy with a plastic backplate, but a crimped in metal one will need the crimps removing with a dremel grinder or similar.

@Ed, I don't think the way it would be used was specified just 'do some work'. My choice would be to daisy chain some LEDS and see how many it will run.

Neil

Hi Gents, I misread the original posting, possibly best way to proceed is to run the motor at about the proposed speed and see the output voltage. Depending on type LEDs often need about 1.5v per device. It should then be possible to see how many you can fit in a string. Several parallel strings could then be operated as they typically need about 10mA or so peer string.

Ed

I have just seen a device that would be brilliant to show the capabilities of your engine and generator set. My granddaughter has been given a 'Plasma Ball' that was one of the items in the shop at the London Science Museum.

I have not examined it closely enough to find out any details but its about 60mm diameter and it can only contain a very small battery which it runs off for long periods before it is charged via the micro USB connector. (probably contains a 3.7V Lithium cell). I am sure a 540 motor will easily provide enough energy to create the plasma.

So a demonstration of old and new technologies, Live steam to live plasma

Ian P

Go on.......... make the generator from scratch yourself! Early M. E. magazines have several nice designs. It would look 'proper' coupled to the Stuart!

Hallo Jon,

it is a good idea to discribe where you want to use the generator.

For example for my son, as he was younger, we made a Wilesco setup and then he want to have a generator for his small radio. I looked the same way as you , but you need with this type of motors a very high speed. We ended with an old printer stepper motor. This was used as a printer with 20 to 30 Volts or similar. Stepper motors are putting out as a generator ac volts , but with a simple diode and capacitor circuit and a voltage protector for the radio, it was possible to run the radio by about 500 to 1000 rpm of the wilesco steam engine. And that works fine. He had a lot of fun with it.

Werner

Even a fairly small Stirling Engine will turn over a small DC motor to give enough volts, and current to power a small transistor radio, or light up a few LEDs.

This little motor has a power cylinder bore of 5/8", and a stroke of 1/2". The motor used as a generator came from an old cassette tape recorder. The hot air engine is based on a design by JustenJones and was featured in ME vol 178/4038 P 158. There are two versions of the motor GAMA, and BETTA, my one is the GAMA type which I suspect may have a slight power advantage. This design won the Gnat power competition 1996 (I think).

Ian S C

To revive this thread, I finally got around to seeing what a 540 would put out. Unloaded at 1000rpm I saw 2.8v. Running in the opposite direct got a negligable difference.

I stlll plan to build a generator, or rather, some period looking mounts to make the generator look like an old school generating plant.