Hi All,
I have a number of old items of US test equipment that I've never really used at all. Think about testing electrolytics under working load, is it ok to use US 110v equipment with a 250v to 110v 500w step down transformer given that there is a 20% difference in the mains cycle? The testing will only be for a short time too.
Best Regards
The problem, that you're probably aware of, is frequency. A transformer designed for 60Hz will saturate more easily at 50Hz. US mains is nominally 120V so running at 110V will help. But measure to make sure it is 110V or less. You can measure if a transformer is going into saturation using a variac and ammeter. Ideally take all load off the transformer under test. Often done by unplugging all valves. Wind up the voltage and see when the current suddenly starts to increase. This may take some judgement as some transformers will enter saturation more suddently than others.
Also a saturating transformer gets hot! Some transformers only have a problem on 50Hz vs 60Hz when on load.
As Jeffrey says, use minimum mains voltage, which can even be 100V (series antiphase 10V or 20V transformer on primary is better than a resistor).
Some gear has well spec'd transformers and is OK.
The equipment I am thinking about is such as a Solar CB160 or Cornell Dubilier BF50 capacitor analysers both made during the 1940's.
The saturation problem happens at zero load just as much as at full load. Both iron and copper losses rise as the core saturates and the transformer can get too hot even at no load. Obviously under full load there are additional copper losses.
its sound like I would be better swapping out the old transformer for a 250v primary version??
Plenty of US kit is fine with 50Hz. You just need to be aware of the potential for problems. The few bits of US kit that I've used at 50Hz have been OK.
Hi, these transformers can have the primaries rewound for 240v, but the issue can also be the frequency/ flux density, so either a bigger stack is needed or you need to try and get 20% more turns in.
If it is a standard lam style it may be possible to change from a Stalloy to a Unisil lamination.
In practice the lam thickness makes little difference.
In some cases, providing there is space, it is better to get a purpose built new transformer
Ed
It would be a shame to destroy the originality of what by now is rare and moving towards historic. I would just run it up at 110v, possibly via a variac and see if the transformer gets hot. Older quality equipment did not suffer so much from the need to cut corners with the pricing and production cost. I have a number of such 117v items and I tend not to worry too much.
A lot of HP equipment allows for different voltage selections (I mean the big rack gear and high end stuff you can now get rather inexpensively).