Need a step-up transformer. What wattage?

[KurskKnyaz]

This is not related to computer power supplies but this is seems the most appropriet section to post this in. A medical office I work with just imported some equipment that was made in 1972 Soviet Russia. The equipment is intended to run on 220V and the amperage is rated at 3.18A.

Had this been a DC current device; multiplying the amperage and voltage would tell me that I would need a step-up transformer capable of handling 699.6W (seems ridiculously high at first but keep in mind that this was made in 1972 and uses very inefficient vacuum tubes). However, this is an AC device and AC is not as efficient as DC and so that Power = Voltage x Amperage equation does not apply.

These are my questions:

1. are my estimates that I would need a step-up transformer capable of at least 700W correct?

2. What capacity (in terms of Watts) step-up transformer would I need given that this is an AC device (just an estimate)?

 

[Aluvus]

Originally posted by: KurskKnyaz
A medical office I work with just imported some equipment that was made in 1972 Soviet Russia.

:shocked:

However, this is an AC device and AC is not as efficient as DC and so that Power = Voltage x Amperage equation does not apply.

The issue is not efficiency, per se. AC "apparent power" (in volt-amps) is composed of both "real power" (in watts) and "reactive power" (in volt-amps reactive). People tend to try to equivocate real power and apparent power, which occasionally gets them into trouble. But it generally creates trouble when they start with real power and need apparent power. You are not in that situation.

2. What capacity (in terms of Watts) step-up transformer would I need given that this is an AC device (just an estimate)?

It's late here, but if my train of thought is correct...

For a wattage of 3.18 amps, times an input voltage of 220 V, your load would draw 700 VA of apparent power, which translates to no more than 700 W of real power. To be on the safe side, I would buy a transformer that is rated significantly higher; 1 kW is a nice, round number.

If this is a long-term installation, it may be worth your while (and safety) to have an electrician install a 220 V line like you would use for a dryer.

Note that in the off case your device expects a power frequency other than 60 Hz (I don't know what the Soviet bloc was in 1972, but today it is 50 Hz), a power transformer will not solve your problem.

 

[KurskKnyaz]

Thanks. I got everything to work, just needed some fuses. They decided, against my advice, to stick with he current 500W transformer.

 

[mpilchfamily]

I would alsop have to suggest going with an electritian installing a 220V line.

 

[KurskKnyaz]

I received a phone call two days ago from the medical office:

"Hi, Michael the fuse on the transformer blew out like you said it would. Can you help us find the right one."


I love it when people word service requests like that. The doctor at the office said I should install a "stronger" fuse even though I previously explained to him the purpose and function of a fuse in an electrical circuit.

...anyway, they ended up getting them a 1KW step-up transformer after more explaining.

 

[Zepper]

How would they expect to get the equipment serviced if it fails? Pretty soon all the older fellows who have the tube circuitry mojo in their bones will be gone... How long ago was it refitted with a new set of electrolytic caps? The best of those generally have a working life of 7 to 10 years. I can't imagine getting an over 35 y.o. piece of tube gear and still expect to have much in the way of useful life. Personally I can't believe it is still working properly at all...

.bh.

 

[KurskKnyaz]

I dunno....

...I wouldn't even bother importing heavy shit that old all the way from Ukraine. Its not just 35 years old; it's also made in the U.S.S.R.