Running USA 60Hz motors on UK 50Hz mains

[shawthing]

Hello All, first proper post from a new member, been lurking and learning a while though... ...I'm looking to run a couple of 115volt US reel to reel machines here in the UK, and have the two problems of the speed being wrong and of the motors overheating; I'm new to electronics (though with many years as a recording engineer behind me), but from the little I've learned so far, I understand the motors have the correct number of windings for 60Hz and when running on 50Hz, they overheat (and I have found this to be the case!). Can anyone offer any advice: 50Hz to 60Hz converters are available I've found, but at huge sums (and sizes), so not an option unless unavoidable; I'd also prefer not to swap out the motors for UK ones, though if nothing else will work...
Re. the incorrect speed, I'm hoping to correct that by changing out a wheel / pulley for one of a different size. Also, BTW, I searched the forum before posting this, and found a previous thread which touched on the overheating problem, but hadn't offered any solutions...
Any help gratefully received, Chas

[paulsherwin]

Presumably you're already using an autotransformer to drop the voltage and still getting these problems. The cheapest and simplest solution is probably to buy a US 12V-115V 60Hz inverter and run this from a high power 240V-12V PSU. If you're planning to use the decks for high quality recording you may have problems with RFI though.

A post to uk.tech.broadcast may yield more info.

HTH, Paul

[shawthing]

Hello Paul, many thanks for your reply - sounds like a solution, hadn't though of this! You're right that I've been using a 240V-115V step-down transformer, but I'm afraid I'm on a steep learning curve here - could you please explain what an inverter is/does? How would the 50HZ of our UK mains not be transmitted through this combination? Is this because the 12V ends of both units are DC? (Re. your point about hi-end work and RFI, not a problem - this is mainly just for fun; I do use vintage kit to 'dirty up' instrumental and vocal tracks in recording work, but in that situation, the more dirt the better!)

Wow - if this is a workable (and affordable) solution, I shall be forever in your debt: I'd been losing hope of ever seeing these machines working properly.....best wishes, Chas

Paul - just googled inverters - Aaahhhh, now I understand! Many thanks for the suggestions, looks like a goer! You're a star, all the best, Chas

[scotty29]

Chas.
Do you know what type of motor it is ?
If it is a split phase induction Cap. start., the windings could well be the same.
The difference being in the motor run capacitor being a differant value for the 50 hz system.
Also the capstan size will have to be changed to take care of the slight change in speed that will come about with the change in frequency.
If the motor is a shaded pole type, then you will have to follow the path that Paul suggests.
Best of luck
Harold

[Ed_Dinning]

Hi Gents, be aware that some of the cheaper 50Hz inverters do not produce a sine wave but a modified square wave. This can cause your motors to overheat and fee alsorts of noise onto the audio. The sine wave types are of course much more expensive.

Ed

[jim_beacon]

Chas,

an inverter is a device that takes in DC, normally from a battery, and converts it to AC at a higher voltage, for example, 12V DC from a car battery to 240V AC for use in a caravan.

As Ed says, most cheap inverters produce a poor output waveform, as they switch the DC with a sqaure wave, this is then fed into a step-up transformer to provide the output. This relies on the inductance of the transformer, and sometimes a capacitor at the output to turn the square wave into a very distorted sine wave. The problem is a high harmonice content (remember Fourier analysis?). The harmonics will cause heating in the motors and transformers, and may well cause interference to the rest of the cicuit (I've measured significant output at 130MHz!! from this kind of inverter).

Jim.

[paulsherwin]

Originally Posted by jim_beacon

(I've measured significant output at 130MHz!! from this kind of inverter).

I did warn him there might be RFI problems

Best regards, Paul

[shawthing]

Hello gents, many thanks for various replies ;

To Jim_Beacon & Ed_Dinning: I've located a decent quality inverter that produces a pure sine wave (well, claims to, I'll have a look at the output when it arrives...) and is rated at 320W, made by Driftgate 2000 (www.dg2k.co.uk in case anyone wants one) plus a 240V to 12V PSU (300W) from Stontronics (http://www.stontronics.co.uk/product...?lproductid=34 ), so hopefully these will do the job.
FYI, this is to run two vintage USA machines: a 1950 Magnecorder PT6A and PT6J combo (rated at 185W running together in REC mode, so I've allowed for system losses), and a late 1950s Voice Of Music 750A. The V-M machine is intended only for playback (of staggered stereo tapes) so hopefully less critical; the Magnecorder I'd like to use to record as well as playback, but we'll have to see if RFI problems make that impractical...
If anyone can see any reason why these units (suitably encased in some kind of outer box, for safety reasons) shouldn't work for this purpose, please let me know - failing that, I'll try it out and report back with results!
To scotty29 Re. motor type: as I mentioned in an earlier post, I'm a bit of a beginner in electronics, can you advise how to tell motor type? Or is this the kind of info that's contained in Service Manuals etc. (I have some documentation on the Magnecorder, very little as yet on the V-M). Would the age of the units (early to mid 1950s) give any clue, e.g. if certain types of motor were simply note available before a certain date?
Thanks once again to all who replied, best wishes, Chas

[paulsherwin]

I'm no expert, but Driftgate seem to make high quality professional kit. The cheap inverters which produce a square wave output are *much* cheaper than the stuff on their website.

Best regards, Paul

[Dave Moll]

Originally Posted by shawthing

I've located a decent quality inverter that produces a pure sine wave (well, claims to, I'll have a look at the output when it arrives...) and is rated at 320W, made by Driftgate 2000 (www.dg2k.co.uk

Looking at their advert, the ones I found claimed to be quasi sine wave, so it would certainly be interesting to see a 'scope trace of the waveform. Incidentally, the lowest rating I could find was 500W.

[GMB]

"quasi sine wave" is what the cheapish ones do. I have one, and I think it generates a square wave with a step added in the middle. Some electronic things like it and some don't.

[Mike Phelan]

Originally Posted by shawthing

To scotty29 Re. motor type: as I mentioned in an earlier post, I'm a bit of a beginner in electronics, can you advise how to tell motor type?

AC motors of this sort are either synchronous or not. Synchronous motors have permanent-magnet rotors, and run at a speed dependent on how many poles and what the mains frequency is - 2 poles 50Hz 3000 RPM, 4 poles 1500 RPM etc.
Non synch (squirrel cage) motors have alloy or copper rotor conductors and they generate slippage - in the above example, more like 2850 and 1425 RPM; this can vary slightly under load.
To make the motor start, there are various devices:
(1) Two sets of windings with different inductances
(2) Two sets of windings with a capacitor in series
(3) Pole pieces split and copper shading rings across half
(4) Synchronous only - soft iron spider with different reluctance from rotor
(5) A completely separate starter motor - Hammond organs.

(1) and sometimes (2) have a centrifugal switch to turn off one set of windings.

HTH

[shawthing]

Hello, you're quite right that the page on their site for Inverters only shows 'quasi sine wave' models and only down to 500W; they tell me they haven't yet got the pure sine wave model up on the website, it's a new product, various power ratings from 350W to 3kW, definitely pure sine wave, £150, from memory (ordered it last week - to Paulsherwin: is that the kind of price you were referring to? ).
They're normally supplied with UK 3pin plugs, he had to go check they'd do one with US style plugs and apparently you can have any type of plug you need by special order.....In any case, when it arrives, I shall hand it to the Service Department at work, and ask them to check it out - and post the results here, of course!
Many thanks to all for your replies and interest; I'm going to check out the Magnecorder tonight, see if I can see what type of motor it has.
It's funny, I'd have thought there'd be lots of people here in the UK running (or wanting to run) US reel machines, turntables etc., and who must have come up against this problem - or is it not a popular thing to do? I've noticed a certain amount of US radio sets talked about in the radio forums, but I'm guessing mains frequency is not such an issue with radios?
Best wishes, Chas

[GMB]

US reel machines, turntables etc. that had any thoughts of export have some kind of switchable rubber wheel or belt so they can work on either frequency. I certainly have one like that. The only minor issue with other things is that US transfomers contain less iron where they were not considering 50Hz operation and so run rather hot on 50Hz.

[shawthing]

Originally Posted by Mike Phelan

AC motors of this sort are either synchronous or not. Synchronous motors have permanent-magnet rotors, and run at a speed dependent on how many poles and what the mains frequency is - 2 poles 50Hz 3000 RPM, 4 poles 1500 RPM etc.
Non synch (squirrel cage) motors have alloy or copper rotor conductors and they generate slippage - in the above example, more like 2850 and 1425 RPM; this can vary slightly under load.

Hello Paul, many thanks for this, I'm going to investigate as to exactly what motors are used in the Magnecorder and, when it arrives, in the V-M too.
However, I've assumed that as both these machines were originally designed to run on 60Hz, they'll both be happier on 60 rather than 50, regardless of the type of motor - is this a safe assumption? (it's certainly the case that the Magnecorder motor gets too hot to rest my hand on after about 30-40 mins, which I understand is a good test to try...).
best wishes, Chas

[paulsherwin]

Originally Posted by shawthing

they tell me they haven't yet got the pure sine wave model up on the website, it's a new product, various power ratings from 350W to 3kW, definitely pure sine wave, £150, from memory (ordered it last week - to Paulsherwin: is that the kind of price you were referring to? ).

I've seen consumer oriented 240V 300W inverters for about half that price, but I'd be surprised if they were suitable for this job.

Best regards, Paul

[jim_beacon]

Valradio in Hounslow make pure sine wave inverters, but the last on we got (1kW model, around 8 years ago) was £700 ex-VAT. Having said that it has performed faultlessly since. We also have a 24V input one, which has given no trouble in over 20 years.

For the low powers you require, it wouldn't be too difficult to build one, though I would suggest a crystal derived frequency source, as this is your most important factor.
Jim.

[shawthing]

To GMB - yes, I've seen this too (e.g. on some Akai consumer machines). This Magnecorder however was not intended for export; in its time (from 1949 to about 1958) it was a pro unit - you either had this or an Ampex (or, for consumer use, a Brush Soundmirror) until about 1951, but they hadn't considered export I don't think, it was all a bit new. I'm hoping the Voice of Music machine that is on its way will be a little more forgiving - that one's very much a consumer unit!
To jim_beacon - circuit building is a skill I am shortly going to try for the first time, and I didn't want to risk a mains adaptor as my first project; I felt safety was worth the cost - bit cowardly perhaps , but I also have a very inquisitive 7yr old to consider!
The overheating of both transformers and motors was certainly evident when I first tried both the pre-amp and the transport units (they're separate) so you're right there - hopefully giving it 60Hz will make things much happier.
I've attached some pics, they show the two units out of their cases, powered up (still on 50Hz, so not for long!), best to all, Chas

[shawthing]

Just thought here are a couple of pics of the main (drive/capstan) motor and its name-plate, plus one of the only info shown on the smaller motor for the suply reel/rewind...

[reel-to-reel-man]

A Magnacorder Lovely reel to reel, I won one from the states about 2 years ago for $50 but had just lost my job and couldn't afford to get it shipped, the reason for my one and only - feedback