DC Motors as Generators?

DC motors with permanent Magnet work only as a dynamo,excluding Brushless,As it has an electronic in between that work only one way.

I don't think wound field DC motors no matter what type is it can work as a generator.unless there is some excitation like in alternators.

Thank you.

Yes you can.The neutral axis wil shift so you need to repossition the brush gear in neutral axis to ensure black commutation.

Regards

Absolutely correct....but many motors do not have the physical possibilty to do this, furthermore, few understand how to set it up even if it does have the adjustment.......

DC motors as generators...

Series= yes, but you have to get an excitation current started and output current cannot drop to "0"

http://www.tpub.com/content/doe/h1011v2/css/h1011v2_93.htm

Shunt= yes, but you have to get an excitation current started and then limit it so the shunt winding doesn't burn up

http://www.tpub.com/content/doe/h1011v2/css/h1011v2_91.htm

PM= yes, DC output as-is

PM Brushless*= yes, multi-phase ac output will need diode bridge for DC

*Brushless motors that use EXTERNAL phase drivers. The tiny ones, like those used in muffin fans, have integrated drive electronics and need modification to work as an alternator. The hobby brushless will work as an alternator, but output voltage will be low until you hit higher RPM's
http://www.horizonhobby.com/Products/Default.aspx?ProdID=LOSB9430

Hi,

brushless with electronic disconnected is in reality an AC motor/generator.

So to be used without problems as a generator.

RHABE

No motor, even the ones that can generate, do it well.Simply because they were designed first and foremost as a motor. On brushed motors, the brushes are not in the right position for maximum power.....as a generator.....

An exception is a permanent magnet stepper motor, it does quite a good job and provides two AC outputs, a few diodes and you have lumpy DC......a cap and you have level DC......

Output is almost directly linear to RPM.

Hi,

not only steppers, any permanent magnet AC motors.

Best are the motors that are used in machine tools to drive the axes.

Depending on iron- and eddy-current losses I would assume that steppers are worst, AC-servos are medium and AC with iron-less-coils are best.

Brushes will wear, but brushed motors/generators will have finely divided collectors, so ripple on DC is small whereas brushless (= magnets are rotating) usually have two to three pole-pairs only, so diode rectification is ok but will produce 30% ripple at 2 phase and 15% ripple at 3 phase.

RHABE

You will be surprised at stepper motor outputs and due to having really high quality bearings, lifetime......

Finding stepper motors is easy, find permanent magnet AC motors will be like looking for Rocking Horse shit!!! Let alone possible prices....

By the way, you can make a good alternator from a car alternator if you replace the coil on the rotor with a permanent magnet. (You do not then need the slip rings anymore or the brushes!)

It can also be used as a giant powerful stepper motor too if required!!!

There is even a DIY video of that change on YouTube somewhere.....

Here is the stepper version:-

http://www.youtube.com/watch?v=rrNYIqhkTQc

And to an AC Alternator here:-

http://www.youtube.com/results?search_query=Alt+Conversion+from+DC+to+AC&search_type=&aq=f

There are dozens of videos on how to do this, great for home windmills......

I agree completely.
RHABE

Sherline laths use stepper motors and I was wondering if they can really do any hard mechanical work to force tools to cut metal but they seems to do all that with precision. Getting a right stepper motor may be the problem. Those used in printers are very flimsy.

Then build a stepper motor from a car or truck alternator, the way to do it is shown on YouTube. Its a relative coarse 60° per step (if I remember correctly) but really powerful, and if geared down for better accuracy, would give even more effective torque....How much do you need...

Also you can see how to make a simple but effective alternator (basically in an identical manner, as steppers make reasonable alternators too!), for a home built windmill for example, by simply replacing the rotor coil with a permanent magnet.....

I thought I recently posted the link(s) here on this blog for the YouTube flash films, but it might have on another blog, so if anyone is interested, just ask me and I will post the links again (or search for yourself!). Very interesting indeed.

Yes I did, Post #12....

I am also a bit scared of low voltage and very high DC current of stepper motors. Perhaps this may be helping in getting greater magnetic field strength with less coil counts. I have not done much on 2-3V 100A switching circuits.

http://www.schneider-electric-motion.com/download.php?file=NDk0MmQwNWFhZTM0My9MZXhpdW1fU0QzX0VOLnBkZg==

Dear Shyam,

we use (since 1995) the now renamed stepper: BRS3AD, 20Nm torque in 10,000 steps/rev, so only 2Nm available to drive the sliding axis of our self-built ultra-precision turning machine. 4 sliding axis (Moore), 1 turntable (Moore), mainspindle with airbearing (Dover) and direct drive (Infranor).

Above link is a brochure of the motors and drives, page 43 shows the relevant motor data.

The motors are designed by Berger-Lahr, later this company sold to SIG and now Schneider Electric.

The slides are only slightly lubricated, one step is equivalent to 0,3µm and this is done within 10% and a maximum error of 1 step as the leadscrew has a 0.3µm/rev periodic error.

High currents as you indicate are only valuable if very fast switching/stepping is necessary.

RHABE

You can also use a stepping motor and diodes from each winding to get pretty smooth DC. This is because each winding produces its own phase. I did this with a four winding stepper with one common. This is useful for small power generation as there are not many big stepper motors.

Hi Ron

I suppose that with some alteration, most any DC motor can be used to generate power. However, just how fast you must turn such motor will determine it's effectiveness, as not all will be equal in performance capability. A good example of this is the home made wind generator that uses PM DC motor salvaged from a home owner type of treadmill. I have salvaged two, though I am not sure just when I might assemble them into wind powered generators. One is rated at 3/4 HP and the other is rated at 1 HP. I will likely just use a flat ribbed belt like the one that is used to rotate the treadmill and a larger pulley to speed up the revs. to increase output.

Automotive alternators modified to produce voltages like 18/24/36/48 volts are available on the web. If wind powered electricity is what you are searching for, there is lots of info available on the internet.

TMF

Thank you all for your input. Now I pop the question. I'm building a model of a diesel electric locomotive in 1:8 scale and want to couple a small gas engine (weed eater?) with a DC motor acting as a generator, feeding small DC motors on the wheels. Will a DC motor/generator provide adequate power? If so, what will be the best motor to use?

I guess that all depends on how fast you want this locomotive to move and will it be pulling any load. There are a variety of toy cars and trucks that are powered by 6/12 volt batteries depending on the size child that may be driving it. The motors for these toys are about 1 1/2" dia. and 2 1/2" long. If you are looking for real power, I suggest tread mill motors. I am unsure just what 1:8 scale relates to. Diesel electric locomotives came in a variety of sizes, therefore so may your "1:8 scale version. Without having seen your drawings, I vision going the easiest route. Maybe use lawn tractor trans axles powered by the treadmill motors and controllers from the same equipment. This would permit you to make turns with putting the wheels in a bind.

By the way, there are several string trimmer models on the market with 4 cycle motors today, and there are small generators already on the market that will do just what you are describing.

TMF

1:8 ? Pretty big project. And pretty demanding when it comes to power. I would suggest a small automobile alternator with modified exciting so you're able to control speed etc. In all other solutions you 'll propubly nead DC/DC conversion or messy motor combinations. But I think gas engine doesn't add much to lealism. A diesel wouldn't either. Sounds for one won't have any resemblence with the real thing. I'd use just cheep lead bats supported by a charging system and recorded sounds from a real beast. Could even reproduce the combustion smell and smoke easily if you had to.

I thought the same thing at first. BIG project!

However, I believe the hobby railroad scale "1/8" means [1/8 inch per foot] ?

OP should confirm.

Dear Mr. ronseto,

Yes. A it should be a SHUNT WOUND MOTOR - which can work as DC Generator also.

I am afraid - SERIRS WOUND MOTORS will have limitations.

DHAYANANDHAN.S

Thank you all for your input. FYI, 1:8 scale means 1-1/2" = 1'-0". Wheel gauge = 7-1/2".