I bought a 500 VA Sola constant voltage transformer off ebay, new surplus.
I hooked it up and it works exactly per spec, from 100 to 500 watts (resistive) load.
I only had it on about 30 minutes and it did not get warm, but its got lots of mass.

But it hums and buzzes. The sound changes with applied voltage
and load. I've used lots of these before, but the largest was 120 VA.
There's a modern new one outside my office, a 120VA one, and it hums
but not a lot, which is my prior experience.

What's your experience with these?


Is it normal for these big industrial ones to hum?

No. I've got the wired-in Sola CV transformer, good for 1800VA, a DoD surplus buy. I have high line voltage... My transformer never hums, but did make some noise when I inadvertently hooked up a 400Hz transformer once.

Some slide into a plastic housing - others have through-bolts holding the EI core together - perhaps something is loose?

Any power-factor correction in the stuff plugged in?

EDIT: One thought - I'm nearly deaf, and wear hearing aids, so I'll have my daughter listen to the Sola to see if I'm just deaf to it's audibles....

Try tightening bolts holding the core together. Varnish may be needed to stop vibrations which cause hum.

I assume the resonating capacitor is still good?
Rich

Those things usually hum. Some of them pretty loudly.

Beware, they also draw power, as well as current, as long as they are humming. So you want to turn it off when not in use.

It is also normal for them to get pretty warm, even without a load.

Ted

+1

I have never seen one that didn't hum, and the level of hum does change with the load. The temperature may also surprise you. Often you can hear them from several feet away depending upon the size of the transformer.

I'll try tightening the core. Also, the shell is humming due to magentism. I had that
problem in my NC-400 radio as its transformer core was too close to the case.
I'll try rubber damping between the case and a steel bar.

As to the caps, they must be OK since it generates a nice sine wave at all
loads. The common mode waveform of the output is terrible however ... I need to ground it.
A 2.2K resistor works fine.

They do hum ..... some of them loudly. I have one and had to move it to the next room. I read in some of their literature that it’s normal but I cannot recall the exact document

Then all is well. I found the "buzz" due to the magnetic action of the core on the shell,
and fixed it with a piece of cardboard jammed between them. Now it just hums.

This ruins my idea, already beautifully enacted, of attaching a power strip
directly to the thing to plug radios in. Oh well ... the power strip cost
no more, not a penny, than an equivalent extension cord to cut up for the
in and out of it. It took 20 MINUTES of my and the Lowe's electical man to
find proper fixtures to put on it for the leads! We kept looking for a simple
1/2 inch fitting of the clamp type .. and could not find it! Finally he looked
in their supplier's catalog and they make every size except 1/2 inch. I finally
found a waterproof fitting that works nicely. At $2.78 a pop.

It will have to be mounted in the utility closet.

And I found why the first time I tried it it did not get hot ... my brain should have
realized this. It started out at 25 degrees F. Now it gets barely on the warm-hot border.