Transformer for pianola vacuum box - UK Vintage Radio Repair and Restoration Discussion Forum

EF80TVVALVE · 28th Apr 2015, 12:48 am

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

Bobdger · 28th Apr 2015, 7:37 am

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.

Radio Wrangler · 28th Apr 2015, 8:40 am

Does the motor use brushes?

David

ex 2 Base · 28th Apr 2015, 10:22 am

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

Boater Sam · 28th Apr 2015, 10:40 am

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.

broadgage · 28th Apr 2015, 12:06 pm

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.

Brigham · 30th Apr 2015, 9:59 pm

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

28th Apr 2015, 12:48 am	#1
EF80TVVALVE Octode Join Date: Feb 2010 Location: Leicester, UK. Posts: 1,433	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

28th Apr 2015, 7:37 am	#2
Bobdger Hexode Join Date: Jan 2015 Location: Rustington, West Sussex, UK. Posts: 384	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.

28th Apr 2015, 8:40 am	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: Transformer for pianola vacuum box Does the motor use brushes? David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

28th Apr 2015, 10:22 am	#4
ex 2 Base Heptode Join Date: Nov 2009 Location: Scarborough, North Yorkshire, UK. Posts: 510	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

28th Apr 2015, 10:40 am	#5
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	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.

28th Apr 2015, 12:06 pm	#6
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,130	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.

30th Apr 2015, 9:59 pm	#7
Brigham Octode Join Date: Mar 2006 Location: Co. Durham, UK. Posts: 1,118	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?