Author Topic: Old electric motor conversion  (Read 630 times)

Offline RayW

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Old electric motor conversion
« on: November 16, 2019, 12:36:09 PM »
For some years now, I have had this old American Dictaphone electric motor sitting on my workshop shelf waiting for me to find a use for it. Since first typing this post, I have discovered that it is from an Edison Dictaphone shaving machine, used for erasing recordings on wax cylinders and re-facing them for being re-used to record. In practice these machines were a bit like a small lathe with a very thin layer of wax being removed from the surface of the cylinder by an auto-feed cutter. One advert states that the cylinders could be re-used up to 100 times.

As can be seen from the attached photos, it seems to have various adjustments possible to cope with voltages from 110 - 220 and with various cycles.
The whole brush assembly can be rotated to adjust its position and the ring is marked in two places "Extreme throw this way". One section is stamped "25-50 cycles Or Direct" and the opposite section "90-133 cycles". The nameplate also states "To be used with proper resistance"
When coupled to mains voltage (240volt UK), the motor runs at very high speed.
My question for all you electronics experts out there is could I convert the motor to a generator to be powered by one of my engines? If so, how would I do that?
I did try connecting the leads to a voltmeter and spinning over the motor with an electric drill and thought that there was a tiny movement on the needle but nothing definite.
« Last Edit: November 16, 2019, 12:59:23 PM by RayW »

Offline BillTodd

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Re: Old electric motor conversion
« Reply #1 on: November 16, 2019, 02:25:33 PM »
Seems a pity to mess with it but...

You may be lucky and it will have enough residual magnetism in the field core to 'self-generate' when loaded  , i.e. just put a small load (a bulb) across the input an spin it up . You might just be able to add a small magnet to the field to get the thing started.

If that doesn't work ,to make it in to a dynamo you'll need to separate and excite the field windings (i.e. drive some current through the windings) while taking the power out of the armature via the brushes.

[edit] I'm assuming this is a DC or Universal motor. It could be a brushed induction motor (do the brushes connect to each other only or - as  in a DC motor are in series with or shunted across the field?)   Just seen the  'Universal' in big letters across the label. :facepalm:
« Last Edit: November 16, 2019, 02:34:32 PM by BillTodd »
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Offline John Rudd

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Re: Old electric motor conversion
« Reply #2 on: November 16, 2019, 02:53:52 PM »
It is basically a 220v ( nominally....) universal motor, the field coils will be in series with the armature....

The field coil resistance will be around 6-9 Ohms each....wound with fairly thin wire and the armature as well. if you were to excite the field coils externally ( disconnect the ends that go to the brushes and join together)  with a small dc voltage- try 3-4 volts...remember the dc resistance will be small so the current will be a few hundred milliamps....keep the volts low, or else the coils will get hot...then try spinning the armature with a battery drill and see what comes from the brushes...

Be aware, with the armature being wound for mains ac you wont get a lot of power from it, the limiting factor being the gauge of the armature windings....
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Offline Stuart

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Re: Old electric motor conversion
« Reply #3 on: November 16, 2019, 03:16:15 PM »
Rule of thumb

One com seg forward for motor one back generator

You need to find the null point for the brush gear , to do this disconnect the field coils from the rest of the motor and apply a low 2 volt current limited AC  voltage to them use a lamp in the circuit to do it

Then put a volt meter on the brush gear ( brushes on the com ) and rock them till you find the null ,then adjust as required

Enough of the proper way as itís a motor now no power connected  :zap: hold the armature still and move the brush gear against the normal rotation start with one seg. but two may be better if the gear allows it

Have fun
Yes I used to wind dc armatures and ac stators , but your unit is a bit twee


Ps just find out the way it would motor and turn it the other way it should work
« Last Edit: November 16, 2019, 03:19:36 PM by Stuart »
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Offline RayW

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Re: Old electric motor conversion
« Reply #4 on: November 16, 2019, 03:32:42 PM »
Thanks John and Stuart for your replies. I would definitely be well out of my depth here and would probably ruin what is a perfectly good motor at the moment, so I think I'll leave well alone, especially as it doesn't sound as if it would produce much output anyway!
Shame, because it has the appearance of an early dynamo. As far as I have been able to find out, it dates from the early 20's.