DC motor voltage rating?

G'day all

Slightly odd question, perhaps - is there any method of determining the correct operating voltage for a DC motor. I have some little motors manufactured by Escap Motion (Porte Escap predecessor?). I have run them on voltages varying from 3 to 15 and they operate smoothly and with rpm (apparently) relative to the applied voltage. The case markings on the trial motor are:- escap 22c 17 205E34 v22411-z1003-e13. Would the 22c and v22 parts indicate intended 22v operation or is there anything else which would point out appropriate power input?

TIA

Rgds

Bill

Hi There

You can probably download the spec sheet if you search online.

regards David

Thanks David.

Have searched, no useful result, hence question.

Rgds

Bill

Would the 22c and v22 parts indicate intended 22v operation

More likely an indication of the motor frame size, I suspect. That is usually the case on larger industrial motors.

Sorry can't be of more assistance, as I have no experience of dc motors of that size.

Regards,

Nigel B.

Hi

If you open the Portescap website, under "contact us" you'll find an enquiry form - might be worth a try

Keith

Hi There

22 is almost certainly the motor diameter.

Escap codes do not appear to indicate the voltage.

I found one on Ebay where the diameter was 35 and the motor code started with 35.

regards david

Nigel, Keith, David thank you. A quick caliper would seem to agree with the motor diameter suggestion.

I was wondering (from a position of total ignorance) if there was some sort of formula for working out the intended operating voltage - other than applying increasingly high voltages until the 'magic smoke' issued forth? Used to think that 'wiggly' amps were the difficult ones - maybe not so!!

Rgds

Bill

Bill, most of the Escap motors I have come across in my work are low voltage and in the Drives of theodolites they run on 6vdc.

Clive

I seem to remember this make of motor being popular for model railway applications, although I lost touch with that aspect of modelling some years ago.

The link below will take you to some ESCAP data sheets in PDF format, I think they are for the current range but do seem to explain how the case markings are arrived at.

I think page 7 on the first one is probably most relevant, but have not been through it all to see if the voltages are featured.

**LINK**

Edited By V8Eng on 14/08/2012 22:25:31

Thank you Clive and V8 - The motors I'm querying have been run on various voltages from 3 to 18 so far and the only noticeable variation is the speed (surprise, surprise!!) Haven't run them for long so no overheating observed. Escap voltages vary, apparently, from 3 to 24 or possibly more. I'll keep searching.

Rgds

Bill

On this Portescap page, there are five ranges of Brushed DC motors in the 22mm diameter.

There are downloadable details for each of them ... so the best bet would probably be to start with a visual comparison of what you've got with what they now sell. ... Even if the product code has changed, I suspect you will recognise the famly.

MichaelG.

I've done a lot of work with dc motors and control in much larger sizes so here are a few of my thoughts.

On a dc motor, voltage and no load speed are very very nearly proportional so a motor rated 250 vdc 1000 rpm could just as well be rated 125 vdc and 500 rpm. The limit on voltage at the high end is how much the commutator can stand before a flashover or how much speed the motor can stand before it flies apart. At the low end the brush dropand under load and the IR drop become significant so the volts/speed characteristic will depart from linearity but this happens at only a few volts. In your case you will be nowhere near flashover. In your case with a small motor put a test voltage on it and measure the speed at no load then calculate the voltage you need for the speed you want and use this plus make an allowance for speed drop under the load you intend to apply.

In other words for small motors you can pretty much invent your own voltage rating to get the speed you want. Of course, for the load rating (hp, watts, or current) you will have to try a few increasing loads, give it some time at each load and stop when it gets uncomfortably hot on your fingers.

Ken

As Ken said, the voltage depends on the speed you require. What is probably more important to consider is the power you require (proportional to torque x speed). At a given speed the current through the motor is proportional to the applied torque. Most of the heating power is caused by the current x the winding resistance squared.

If you don't want to do the measurements and calculations, Ken's finger test is the way to go.

Russell.

Russell

I'll assume you meant to say "current squared X winding resistance".

A handy formula to remember is "T=5250XHP/N

where T is in lbft, HPis in horses and N=RPM or

HP=TXN/5250

I guess lbft and HP date me but I'll get around to converting some day

Ken

Just an afterthought:

Actually at any speed right down to standstill the current is proportional torque as long as the field is kept constant which is the case with most small dc motors as they use a pemanent magnet field.

The lbft per amp and voltsper radian per second are key constants in designing a speed control

Ken

Just remember, if doing the finger test suggested by Ken, that the motors are coreless; having no core laminations, the thermal inertia is very low, so they can overheat to the point of destruction very quickly.

In general, permanent magnet motors are not killed by too many volts unless they go so fast as to cause mechanical failure; the no load speed rises until the back emf cancels the current flow. It is excessive current flow which kills them, and this is almost entirely dependent on the load. However, it is possible that a coreless motor could overheat while the motor is reaching no-load speed if you cycle it too frequently.

David

Edited By David Littlewood on 15/08/2012 20:05:41

Michael, Ken, Russell, David - thank you all.

I'm starting to get the feeling that I'm into "How long is a bit of string ?" territory! I don't have a specific project for the motors, just a desire not to ruin some rather nicely made bits of electrical gear through my ignorance. Measuring rpm might be tricky as the output shafts are tiny - 1 -1.5mm perhaps. Anyway, your responses have given much food for thought. I shall ponder and test and, if any sensible results accrue, report back

Rgds

Bill

Ken,

Yes that's what I meant - perhaps Altzhimers is setting in

If you're feeling dated you may be interested in the lab I learned about electrical machines in:

No worries about health and Safety then!  Three phase supply on open brass terminals, open rotating machines.  It taught you respect

Russell.

Edited By Russell Eberhardt on 16/08/2012 15:52:58

Russell

Actually that looks somewhat like the rotating machines lab at the university where I learned such things. Some of my work was in steel plants both here (Canada), Italy and France and they use the same sort of setup for line panels, both power breakers and DC relaying. However, most of the MG sets, amplidynes, etc have been replaced by solid state power electronics in cubicles and many DC relaying functions have been replaced by PLC's. Anymore the safety people are hot to lock everyone out of such places, even those who must track down problems which actually makes it more difficult to stay safe when tracking down a problem

Anyway it's nice to talk to someone of my vintage.

Ken