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50hz to 60hz using an Inverter

N

Nama

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Joined
May 22, 2009
Messages
854
Location
New Zealand
I'm trying to do is run my dual 801 Shugart drives in New Zealand at 60hz.
New Zealand power is typically 50hz, which means my drives spin at 300rpm as opposed to 360rpm. So I was thinking to do the following:

1) NZ Mains 220vac 50Hz into a 12vdc converter (a PC power supply will probably do for this)
2) 12vdc into a '12vdc to 120vac' 60z inverter
3) 120vac at 60z into the Shugart drives.

Is there any problems that could arise from doing this with vintage equipment?
Also, does anyone have know approximately how may Watts a dual Shugart 801 setup will draw?

Just thought I'd ask before going ahead and purchasing an inverter, don't want to waste any money if this direction is problematic.

Cheers

Phil
 
The table on page 29 of the 'SA800/801 Diskette Storage Drive - Theory of Operation' manual indicates an allowance of 0.5 amps at 110 VAC (i.e. approx. 55 Watts)

Note that the frequency tolerance is tight.
 
Great!
Thanks for the info.
I just checked that out.
+-0.5Hz...yes, that does seem tight!
 
I had the reverse problem with one of my drives. 220V 50Hz in the US 60Hz. The 220V was easy enough and came as a freebie with the linear PSU, whose primaries could be configured to supply 240V. Of course, the drive motor spun too fast. So I started digging around and located a small flanged timing belt pulley that fit the motor shaft perfectly (small allen-head setscrew) at my local surplus shop. It worked a treat. Now, this was 30 or so years ago and the 8" drive was brand-new and offered for a trice because of the 50Hz nameplate rating.

Nowadays, you could probably print a pulley of the right diameter or have one machined up for you if you know someone with a small lathe. The original pulley of course, is crowned, but a flanged one works just as well.

This would let you run the drive motor from a transformer and not worry about the frequency difference.

FWIW, the drive was a Qume DT/8. Great drives, those.
 
If you do go the inverter route, be aware that the cheap ones don't produce a true sine wave. They put out a "Modified" sine wave that some electronics don't tolerate very well. You'll need to spend some bucks to get one that makes a "True" sine wave.
 
> +-0.5Hz...yes, that does seem tight!

I remember servicing the early reel-reel audio tape machines had an AC motor with the large capacitor tied to the third winding. The AC frequency IS the rotational speed reference. There is no other speed servo
so the tolerance is very tight.

Larry G
 
Those disks worked also at 220/240V/50hz, so I dont understand why using 50Hz at 110V could be a problem. Am I missing something ?
 
retrogear said:
> +-0.5Hz...yes, that does seem tight!

I remember servicing the early reel-reel audio tape machines had an AC motor with the large capacitor tied to the third winding. The AC frequency IS the rotational speed reference. There is no other speed servo
so the tolerance is very tight.

Larry G
Click to expand...

A year or two ago, it was announced that the local (!) power company would no longer hold a tight tolerance on frequency. They said that dips in frequency would be compensated for in the future by surges in frequency so that synchronous clocks would keep time.

But, what does that do to disk drives, tape decks, and turntables?

Forget the oxygen-free cables, you need your own genset.
 
It's been going on for a long time--the changes in frequency are very slight and long-term.

Consider that the average PLL data separator has a capture ratio of +/-10-20 percent and it doesn't matter in the case of reading or writing.
 
>It's been going on for a long time--the changes in frequency are very slight and long-term.

Yea and with audio tape the music would just go up or down half an octave :)
 
>Don't most modern (yes, modern) turntables use a crystal-stabilized drive?

Most later model turntables, tape decks actually used DC motors. Many of them the speed control was actually built into the motor and had a hole to insert a screwdriver and adjust.

PS - expensive "direct drive" turntables had speed control servos based on DC not AC and the speed tach reference was actually a physical pattern in the turntable itself.

Never saw the inside of the modern usb turntables

Larry G
 
Last edited:
Nama said:
I'm trying to do is run my dual 801 Shugart drives in New Zealand at 60hz.
New Zealand power is typically 50hz, which means my drives spin at 300rpm as opposed to 360rpm. So I was thinking to do the following:

1) NZ Mains 220vac 50Hz into a 12vdc converter (a PC power supply will probably do for this)
2) 12vdc into a '12vdc to 120vac' 60z inverter
3) 120vac at 60z into the Shugart drives.

Is there any problems that could arise from doing this with vintage equipment?
Also, does anyone have know approximately how may Watts a dual Shugart 801 setup will draw?

Just thought I'd ask before going ahead and purchasing an inverter, don't want to waste any money if this direction is problematic.

Cheers

Phil
Click to expand...

Hi Phil,

your approach is reasonable, except most very modern pc power supplies are way to low a current capacity on the 12v output. maybe an 1 amp, as there is so little that uses 12Vdc. Biggest current O/P is 5vdc supplies, so you may not get the grunt you need.

Better of looking for a stabilized 12 battery charger, hook it to a 12v battery then use the output of battery to power your 12 to 110vac 60hz inverter.
The battery in middle will give you output stability if and when your NZ ac mains frequency fluctuates, or more correctly browns out.

My suggestion however is look at picking up a "dual conversion ups".

They do come up on ebay quite a lot.

Often with dead batteries.

The better ones have full sine wave output. If your good with electronics you can change the internal frequency reference to give the 60Hz output you need.

I converted one to give 240v 50hz in to 110V 60hz out. Removed the automatic bypass circuit.
left the battery in and that aided the stability of output during power line dips.

The other way is a make a small rotary HZ converter.
get a 240v 50hz synchronous motor connect it to small alternator via pully and belt with a bit of a flwheel in middle to take care of the mains frequency variations.

by choosing the pulley sizes correctly you can end up with the ratio you need for 50 to 60hz conversion.
And use toothed the pulley say from cars that you may find at wreckers.

I can even recall seeing this sort of Hz conversion setup done in a 3rd world country using a truck alternator, that had the rectifier section removed.
Gave 3 phase AC out.

so there are some options for you

regards
David
 
Thanks guys,
lots of great suggestions, and pitfalls to watch out for.

I think the ultimate solution would be to have some new pulleys machines, and some new belts purchased. Although even something as simple as that sounds, is probably going to be quite a process.

I was hoping the inverter direction would be an easy(er) solution, however after reading David's post, it doesn't seem as simple as I first thought.
However I do have all my equipment behind an isolating transformer, and I was hoping that would smooth out any peaks, troughs and ripples in the NZ AC line...so maybe this direction is still on the table if I could source a powerful enough 12V source???

Thanks again

Philip
 
Another option is to find someone with a junker SA-80x drive with a 220V 50Hz motor that can be swapped in to your unit. Many PSUs have jumpers to set for 220/240 volt operation.
 
I guess there is no harm is asking on the 'Vintage Computer Items Wanted' section of the forum.

Cheers

Phil
 
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