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Old 28th Apr 2015, 12:48 am   #1
EF80TVVALVE
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Default Transformer for pianola vacuum box

Not too sure which section this should go in!

I have recently bought a vacuum box for my pianola but I am unsure of which transformer to get for it. I have opened the unit to find the spec of the motor (similar to a vacuum cleaner motor) and it states 110v AC 60Hz. I have shopped around a bit and have come across a few transformers but they all seem to be 50hz. Would the pump still work okay at 110v 50hz or is this likely to cause a problem with the unit? Also does anyone know what suitable wattage transformer I should get to power it?

Kindest Regards
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Old 28th Apr 2015, 7:37 am   #2
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Default Re: Transformer for pianola vacuum box

Is the motor a cap start cap run type?.
If it is, then the 60Hz motor will run a lot slower when ran on a 50Hz supply. A 2 pole 50 hz motor has a speed of 2800rpm, a 60Hz motor will have a speed of 3600rpm. When buying a Transformer for a motor there is a very large current needed to start the motor untill it is up to its speed, this may be upto 8 times the run current for the first m/sec.
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Old 28th Apr 2015, 8:40 am   #3
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Default Re: Transformer for pianola vacuum box

Does the motor use brushes?

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Old 28th Apr 2015, 10:22 am   #4
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Default Re: Transformer for pianola vacuum box

If the motor is similar to a domestic vacuum cleaner motor then it will have brushes. I have never seen an induction motor on a domestic vacuum cleaner, but Bobdger is correct regarding starting current on induction motors. Regard the transformer rating, can you run the motor via a Variac and measure the current . Current times 110 volts plus 5% will be near enough I think.Ted
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Old 28th Apr 2015, 10:40 am   #5
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Default Re: Transformer for pianola vacuum box

Probably the easiest and cheapest is a 110v tool transformer as use on building sites. Nice and safe in its yellow box, well rated and tested, only 55v to earth on each 'phase'.
Loads for sale secondhand on auction sites.
I have used them to power 115v USA dishwashers in the past, they cope well with short time overloads.
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Old 28th Apr 2015, 12:06 pm   #6
broadgage
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Default Re: Transformer for pianola vacuum box

A tool transformer should be fine as regards the voltage but wont alter the frequency.
If the motor is a brush type, as seems likely, then frequency is of little importance and 50 cycles will be fine.
In the less likely event that you have an induction motor, then it will run slower and perhaps fail to give the required output, it would also draw more magnetising current and run hotter.

As regards the size of the transformer, I would borrow or hire one of any standard size and then measure the running current to determine what size transformer need be purchased.
Be aware that the stated wattage of most tool transformers is for intermittent use only, the continuous capacity will be half or less of the short term or tool rating.
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Old 30th Apr 2015, 9:59 pm   #7
Brigham
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Default Re: Transformer for pianola vacuum box

I've been thinking of buying one of these. Is there provision to stop it ripping your rolls off the spindle at the end?
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