PAPST Capstan motor

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PAPST Capstan motor

Postby gary » Thu May 22, 2014 4:21 pm

Hi, I was wondering if anyone had any more information regarding this motor or if anyone can decipher the wiring info on the label. Cheers.
(BTW a very comprehensive Google search has turned up very little).
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Re: PAPST Capstan motor

Postby Steve Anderson » Fri May 23, 2014 12:09 pm

Gary, how many wires/terminals does it have - ignoring any that may be chassis/earth? It would seem like it's a 3-phase motor going by the Delta and star symbols in each line. Another clue to this is the reference to 380V - the voltage between phases on a 3-phase 220V supply.

Other than that I can't really help much further...

Steve A.

Be thankful you're not in the Philippines where it's 220V - that's OK - but at 60Hz - whacky!
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Re: PAPST Capstan motor

Postby gary » Fri May 23, 2014 1:35 pm

Hi Steve, hope all is ok for you over there?

Yes I think there is no doubt that the motor is constructed as a 3 phase external rotor motor - but therein lies the rub.

capstan terminals.jpg
capstan terminals.jpg (77.41 KiB) Viewed 4169 times


These motors, apparently, can provide the 2 tape speeds 3-3/4 and 7-1/2 by "pole changing" - i.e. changing the wiring configuration similar to this:

bapst wiring.jpg
bapst wiring.jpg (35.82 KiB) Viewed 4169 times


In addition I am assured by the donor of this motor that it is run from a single phase supply (with the cap providing the phase difference).
Whilst I know this can be done with a two phase motor I am not aware of how that works with a three phase motor - the best I can come up with is a "fake" 3-phase supply whereby on coil is supplied by the active, another coil is supplied with the same active but reversed (i.e. 180 degree phase shift :shock: ) - the donor says via the neutral but that is what he must mean by that - and the third is supplied by the active through the cap - apparently this CAN work (although I remain sceptical) but the motor runs poorly and gets hot - maybe for low torque applications this is OK - this is all news to me so I am groping for more info.

In particular I would like to know (if there is anyone who is familiar with this motor):


Things I can't figure out:

What do the letters to the left of wye/delta symbols refer to?
Why is there a dash under the uF column heading for the first 2 options and what are the numbers immediately to the right of those?
Why is the rated wattage different for the third option? (I am assuming that the cap is performing some p.f. correction perhaps?)


BTW apparently these things CAN be run off 60 Hz and the correct speed is then obtained by changing the pulley diameter.

Anyway just a little more info (and a lot of pure uneducated guesswork on my part) that may strike a chord in someone's memory.
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Re: PAPST Capstan motor

Postby Steve Anderson » Fri May 23, 2014 4:58 pm

With the commoning of the three terminals it would appear set up for a 'star/wye' configuration. If you remove the cables and the commoning bar do you end up with three isolated windings? Presumably all very similar in DC resistance. You've taken a photo so you can always restore it back to the way it was.

Was it originally in a tape-recorder?

Steve A.

I'm flying back to Bangkok this evening. I just hope I get through immigration/customs/baggage claim, into a taxi and arrive home before the 10pm curfew.
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Re: PAPST Capstan motor

Postby Steve Anderson » Fri May 23, 2014 5:14 pm

A quick Google and I unearthed this, which you probably did as well, perhaps one of our German speaking members could translate..the motor in the photo appears to be from the same origin and basic design...

http://www.elektrikforen.de/motoren-sch ... toren.html

Steve A.
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Re: PAPST Capstan motor

Postby gary » Fri May 23, 2014 6:07 pm

Steve Anderson wrote:With the commoning of the three terminals it would appear set up for a 'star/wye' configuration. If you remove the cables and the commoning bar do you end up with three isolated windings? Presumably all very similar in DC resistance. You've taken a photo so you can always restore it back to the way it was.

Was it originally in a tape-recorder?

Steve A.

I'm flying back to Bangkok this evening. I just hope I get through immigration/customs/baggage claim, into a taxi and arrive home before the 10pm curfew.


I was going to mention that but I came to the conclusion that the links were placed that way for shipping purposes only - the motor is unused so it is impossible to determine what the machine was it was destined for - Papst themselves no longer produce or support AC synchronous capstan motors (not surprisingly) - I only know it is a capstan motor as the donor indicated it was so, and because I found a specification that indicated so (alas no further information).

Yes that is a good call re measuring the windings - I should have already done so I suppose although I was already convinced that it was 3 separate windings (as it is) - so no centre tap as indicated on the wiring diagram I posted.

All 3 windings have the same dc resistance so a starter winding is unlikely.

I suppose the capacitor could be a starter cap rather than a run cap - but the literature indicates they are usually run caps.

The only thing curiouser (to quote Lewis Carroll) than the motor text is the lack of information regarding capstan motors on the internet - I suppose the most likely encounter people have with them is a simple replacement when one goes faulty. In recent times DIY turntables have become popular and I see many are using capstan motors for that purpose - but they tend to be the modern DC type (i.e. the commutation is done electronically), what we now refer to as DC brushless motors - and interesting thing I have discovered from my research into this is that these (Papst AC synchronous motors) were the forerunners of the modern DC brushless motor and indeed were the first to produce same.

I may be wrong but the clue to the operation of this motor appears to me to be in the interpretation of that blasted E - what could it be?

Steve that's not a great situation to be coming home to, the only good thing is that the military seem to be keeping things calm, for now... my best wishes are with you.
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Re: PAPST Capstan motor

Postby gary » Fri May 23, 2014 6:10 pm

Steve Anderson wrote:A quick Google and I unearthed this, which you probably did as well, perhaps one of our German speaking members could translate..the motor in the photo appears to be from the same origin and basic design...

http://www.elektrikforen.de/motoren-sch ... toren.html

Steve A.


Yes, a Google translate of that thread indicates that the main issue is about motor dismantling - so no additional info there - although you can interpret the motor text to be pretty much the same as my motor - what is that blasted E!??? - Note the text in the column to the right of the capacitance value - totally nonsensical!

Edit: sorry I originally wrote mounting rather than dismantling.
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Re: PAPST Capstan motor

Postby Steve Anderson » Fri May 23, 2014 6:33 pm

I'm treading dangerously here, but I assume Delta is the same in both English and German. Which to me means a three-phase arrangement.

'E' is often used to denote voltage which in these cases may mean a single-phase supply whereby the capacitance value quoted is required to give the correct phase-shift. 7uF at 50Hz comes out to around 450 Ohms...seems reasonable. Phase shift will depend on winding inductance/resistance.

I've used AC syncronous motors in the past whereby they required a 'run capacitor' of a couple of uF. These were small affairs and if indeed this were a capstan motor the 7uF value seems 'about right'.

I would be tempted to try it in a star/wye arrangement with 220/240 across two of the arms, ignore the common/centre connection and add said capacitance between one of the energised terminals and the remaining free 'arm'. If feeble or doesn't run at all try the same in a Delta arrangement.

That's just the way I would have a go at this....don't get it too hot. But having said that many motors do run quite hot, even lightly loaded...there's no Silicon inside...I assume.

Steve A.

Anyway, gotta fly...literally!
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Re: PAPST Capstan motor

Postby gary » Fri May 23, 2014 6:53 pm

Yes I agree that seems to be the most likely arrangement, although all my training and experience tells me a 3 phase motor won't work (properly) unless there is a 120 degree phase difference between the windings, but I have been surprised before...

<blinding flash>

Oh dear have I just had an epiphany? If the first winding is fed with a single phase supply (0 degrees) and the second winding is fed from the single phase supply through a capacitor such that the phase shift is 120 degrees, and the third winding is fed from the same source as the second winding but in reverse (240 degrees) then... Oh dear time for me to retire... oh wait I already am... ;-)

Yeah - not quite but this should do it...

proposed wiring.jpg
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Edit: Alas a little more thinking and a bit of analysis and my "epiphany" was short lived, however the approach should work - just:

My "pseudo 3 phase" is hardly ideal...

pseudo3P.jpg
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Cheers Steve, have a great flight, and if I wasn't an atheist I would pray that all is well back there despite the situation, none-the-less I wish you god speed - good luck!
Last edited by gary on Fri May 23, 2014 11:12 pm, edited 1 time in total.
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Re: PAPST Capstan motor

Postby Steve Anderson » Fri May 23, 2014 10:01 pm

You got it..time to board...see you A.M...assuming the 'net hasn't been cut...

Steve A.
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