Certainly looks like a rotary converter, probably WWII aircraft (is that an
air ministry crest on the terminal box?) where they were used to provide the
various voltages required for radio and other electronic gear from the basic
aircraft supply. The ID plate puzzles me though as all the ones I have come
across have been DC to DC devices.
Well spotted Nick, yes, it's Air Ministry. Only a mains motor as far as I
can see, there is no provision for a current take off.
I've got another similar thing somewhere - I'll dig it out, but I'm certain
the other device really is a rotary converter as it will light a mains bulb
from a 12 Volt battery ;o))
I've also got a 300 AMP dynamo from a Canberra and a phase converter from a
Shackleton. The latter is fan cooled and sound just like a gas turbine
Looks like a step-up ratary converter for radios in aircraft.
Radio valve HT voltage is 250V DC or so, the aircraft only has 24V DC
so they used these for jumping up the supply volts. Some also had a 6V
feed for the valve heaters as well, and a few had AC output so you
could run a mains tranny off them.
But it says "1/8th horsepower, 4000 RPM, WARNING the frame of this motor
should be efficiently earthed." The operative words here being, of course,
"motor" and "horsepower" ;o))
On my rotary converter it says "12 volts input, 240 volts output". Other
ones I've seen have a comm. at one end and slip rings at the other. None of
them have "motor" on the label.
Good-o, an interesting problem! I think I'll go and play with it through a
RCD. If there is a power cut in the SW tonight, you know who to blame.
In message ,
I have something very similar with just two commutators languishing at
my mum's house. I had it as a schoolboy (30 years ago) and it did run
on 240V - I can't remember the output.
Right then. My curiosity piqued, I delved amongst my bench corner where I
keep Interesting Electrical Devices Wot I Will One Day Use and found the
Three AC motors, a 1920's 50V dynamo and the ex-Canberra dynamo.
The ex Shackleton inverter (24/28v to 115 v. 770 watt, 400 CPS)
An Electro Dynamic Construction Company Converter (12V DC to 230V AC at .521
A "Transformer rotary, HT 20 watt, No. 2. Volts, 11/480. Amps, 3.4 to .04"
The latter certainly seems to fit the radio slot that Peter came up with.
And of course, this weekend's purchase. Having sat down with it, I am more
than ever convinced that it is some kind of electric motor. It says so and -
unlike all the rotary converters - has a pulley and drive shaft sticking out
of the end. Having cleaned all three comms. I feel that it has never had
much use, all the segments are sharp edged and the insulation deep cut on
both end comms. The two end brush holders accept the same kind of (unworn)
brushes, but the inside brush holders are smaller and the comm. is much
The Air Ministry terminal box is a red herring (well spotted!) and my
feeling now is that it is an electric motor from some kind of fairly
sophisticated device - perhaps a business machine of some kind - from the
1940's. Off now to my Science museum contact and my mate Tim who is as nuts
about old electrical stuff as we are about old engines!
Updated pics at
I'd rather have a free bottle in front of me
than a free frontal lobotomy!
I've been lurking for a while and couldn't resist this one as I have
probably burnt my fingers on most of the rotary devices in pictures
posted by Kim :
1/ Bought one of these (similar) from an ad. in Wireless World back in
the late 60's 'Mains Power Anywhere'? - thought I would supply the whole
house from a car battery! I was only about 11 years old at the time!
2/ Fairly standard HT rotary transformer - used one to power a
'portable' valved transmitter in the 70's. Funny how your brain lulls
you into a false sense of security with 12v derived equipment - 200V DC
really does hurt !
3/ I think that this may be a motor generator
i.e. shaft power for driving say a gramaphone turntable and HT/LT from
the commutators for a valve amplifier. The number of segments on the
comms give a clue to the voltage.
4/ The dreaded Rotax 108A rotary - normally mounted on a chassis along
with associated control gear and stuffed in some hard to get at corner
of a military aircraft. VERY heavy and a real pig to set-up on a cold
windy airfield with a noisy smelly Houchin GPU beside you supplying the
28V DC. The 108A was (still is ?) used to supply 115V 400cs (Hz) for
TACAN etc (Hunter,Canberra)
Thats my input - any errors are down to middle-aged brain fade.
As Mr Dingley states in his reply - transformers are not a lot of good
for DC. Motor generators were very popular before and during the war for
both battery and mains powered equipment requiring various voltages.
108A inverter :
It's the sort of thing that one tries to forget really - never had a
bench test rig so testing was 'live' on the aircraft.
From your photographs, you only seem to have the inverter. A control
panel is also required to control the voltage and frequency (Type 26 ?)
This was pre solid-state and used carbon piles to control the stator
windings along with a separate resistive "soft-start".
If you have the control unit, I can probably find the connection info.
I think that the box on top only contained the filters.
It is probably not aircraft unless 28V DC running voltage, but there
were plenty of other applications for these things.
Regarding carbon piles, Newton-Derby were still making these to go
with big DC dynamos in the 1970's, and the Cub gennies all have carbon
pile regulators, a move on from the Isenthal rotating contact ones
that were used previously.
Sorry, no. I was still thinking of that other motor.
Yes, the Rotax set is clearly aircraft kit. If I had more bookshelves,
I could find the magic Book For Training Erks on aircraft electrics of
(actually Kim, you're welcome to a loan or a photocopy)