UPS Transformer for bucking?

[martinihenry]

I have a salvaged power transformer from an Uninterruptible Power Supply that I've been saving for years, hoping to find a good use for it. Well, I think I may have one. I'm restoring an old RCA 810K1 floor radio, and I need to buck my 124VAC line voltage down by about 12 volts. I'm sure most folks here are familiar with the notion of wiring a 2-3amp low voltage transformer so as to buck or reduce line voltage. What I'm uncertain of, is whether my choice of this transformer is a prudent one. Data for these Lei built transformers doesn't seem to be widely available, but it appears to be a standard 120V to 12V, center-tapped step down transformer. Now, I know these are used reversed in the UPS, so a low voltage, high current can be stepped up to a lower current, 120VAC to power the peripherals.

My question is whether or not such a transformer can be used with 120VAC as a bucking transformer? Power draw by the radio would be probably around 100 watts at 112VAC. I know I could buy a filament transformer for about $20 to do this, but I'd much rather do this for free with my existing transformer. Any thoughts are greatly appreciated!

 

[cowboybob]

Don't see why not.

Assignment of Primary and Secondary labels is arbitrary.

Only concern might be current capacity. Since your circuit ought to be fused anyway, you'll find out soon enough if there isn't adequate current capacity.

 

[martinihenry]

Ha! Yes, fusing. It's a good thing...definitely! Will assemble it tonight, and give it a shot. Will post results here.

 

[KMoffett]

.....
My question is whether or not such a transformer can be used with 120VAC as a bucking transformer? Power draw by the radio would be probably around 100 watts at 112VAC. I know I could buy a filament transformer for about $20 to do this, but I'd much rather do this for free with my existing transformer. Any thoughts are greatly appreciated!

This is not a good idea. This is a dangerous idea. Yes you "can" use the secondary of a transformer in series with the line to buck (or boost) the line voltage. With your attempt to power an old 12V radio directly off the power line, you stand a good (50-50) chance of placing the live side of the power line on the radios chassis. Touch the chassis and a ground and your wife can collect on your life insurance.

Just get a 120Vac to 12Vac step-down transformer.

Ken

 

[Diver300]

This is not a good idea. This is a dangerous idea. Yes you "can" use the secondary of a transformer in series with the line to buck (or boost) the line voltage. With your attempt to power an old 12V radio directly off the power line, you stand a good (50-50) chance of placing the live side of the power line on the radios chassis. Touch the chassis and a ground and your wife can collect on your life insurance.

Just get a 120Vac to 12Vac step-down transformer.

Ken

It's a 112 VAC radio, so it will need to have a supply that is dangerous if touched. Therefore it will be designed to well insulated. Running it with one of the supplies at 124 V should be safe.

I would suggest putting the 12 - 0 - 12 V winding in series with the 120 V winding, and running the whole lot from your 124 V supply. That will make sure that the transformer is not saturated so the iron losses will be less. You should be able to tap off about 112 V from the centre tap.

 

[KMoffett]

Opps! Missed that. Got to retake that speed reading course.

Ken