Q. If I have an AC power source of 100 volts at an odd hertz of something like 250 Hz is there any reason why I cannot build a transformer with this input on the primary and 14 VAC on the secondary? I would be using a salvaged core from an old transformer to wind new transformer wire after stripping the old winding from the used core.

This 14 VAC would then be rectified to DC to be used to charge a battery bank.

The only transformer information I have seen has to do with either 50, 60 or 400 Hz. Is there some reason why only these frequencies are mentioned other than they are the standard ones used by countries or military? Is there some sort of electrical "rule" that would prevent the project above?

Mac

 

There z no restriction for the frequency. And i know that a normal transformer can operate for different frequencies.
But for a very low/high freq.,, core losses vary and hence efficiency reduces.
worldwide the supply operating frequencies are 50 & 60Hz. Thats y most of the trnsfrmrs are designed so.
In smps (switched mode power supply) the transfrmers are subjected to very high frequency pulses.

 

If it's an old 400 Hz transformer, then the core won't be efficient at 60 Hz. Which is not to say it won't work, but you might not get the expected result, and power handling might be puny.

 

Some interesting information from another specialized forum:

Interference Technology reader Dennis Hennigan writes:

"I knew this many years ago but forgot. Can I run a 120VAC to 6.3VAC 60Hz filimant transformer at 120VAC 400Hz? "

Reader Ken Javor responds:
"The answer is yes. You cannot do the reverse, however."

Another useful response from reader Orin Laney:
"Turns ratio and voltage will be OK, but transformer dissipation is likely to be excessive. Most 60 Hz transformers use laminations that are too thick for effective eddy current suppression at 400 Hz. If the lams are ~.014 thick, its not a good bet. Thinner is better for this purpose, and some 60 Hz designs will work OK or are even deliberately designed to work as high as 400 Hz. So, it depends on the transformer shop around. And for those new to this: NEVER try to run a 400 Hz transformer on 50/60 Hz! "

I wonder why! If the core can take hysteresis losses at 400Hz, wouldn't it be able to handle 60Hz. The copper losses should be less because of more skin depth, if that is even applicable. Maybe it has to do with the eddy currents and too thin of laminations.

Anyone know the reasoning? I'm curious!

Steve

 

Some interesting information from another specialized forum:



I wonder why! If the core can take hysteresis losses at 400Hz, wouldn't it be able to handle 60Hz. The copper losses should be less because of more skin depth, if that is even applicable. Maybe it has to do with the eddy currents and too thin of laminations.

Anyone know the reasoning? I'm curious!

Steve

I think it's because the primary (magnetizing) inductance on a 400Hz transformer will likely be less than that of a 60Hz transformer. Put 60Hz into the 400Hz transformer and the current will be excessive, causing excessive dissipation (heat) in the primary winding resistance.
I have a Triad isolation transformer that runs at 140°F with no load. I think it's because they used less copper to save on cost. My point is that the magnetizing inductance is low, which makes it run hot.

 

FYI for you younger types , most of the 400hz transformers were used (still are?) in aircraft applications in WWII. For the same power wattage output a 400hz transformer is significantly lighter then a 60hz transformer, and in aircraft use weight is everything.

 

FYI for you younger types , most of the 400hz transformers were used (still are?) in aircraft applications in WWII. For the same power wattage output a 400hz transformer is significantly lighter then a 60hz transformer, and in aircraft use weight is everything.

As far as I know most military aircraft still do. My dad retired from the airforce in the 70's, where it was still the standard. Don't know about commercial, but I suspect it is there too.

 

FYI for you younger types , most of the 400hz transformers were used (still are?) in aircraft applications in WWII. For the same power wattage output a 400hz transformer is significantly lighter then a 60hz transformer, and in aircraft use weight is everything.

That's because they don't need as much wire to achieve the required inductance.

 

The Navy was using 3 phase 400 Hz in electronic equipment at least until 1974.