TRK-8180 Perdisco Japan model, AC power supply rated for 100v AC. What happens if plugged into 120v AC?

[Chuck M.]

What mods if any will be needed to run on 120V AC, I am going to disconnect wires to board from power supply and put a meter on it and plug it in, You know the old smoke test. The box is dissembled for cleaning, repair and waiting for belts. My guess is secondary voltage will be too high on 120V. Chuck.

 

[caution]

Replace the transformer.
According to the service manual it's nothing fancy, just a single secondary winding. The manual says it takes 12V for batteries (8 D cells)so I would imagine a transformer that gives out 15V would be ideal, the main rail's regulator circuit should be able to handle that. I don't think a transformer that outputs exactly 12V would be enough. I've typically seen 3-6V higher than the stated voltage for DC/batteries on the incoming side when testing a box plugged into an outlet. The fuse inside is rated for 2.5 amps, so make sure the transformer can support at least that.

 

[Superduper]

I agree, change the transformer. However, I do not recommend starting out with a 15V transformer. Transformers voltage specifications are based on the rated current draw, at AC. When at no load or a quiescent state, it will be much higher. You can expect a 12.6V transformer to actually test at about 15V with zero load directly at the secondary before the rectifier, at least this is my experience. Additionally, boomboxes don't use AC, they use DC and the type of PS circuitry makes a difference (full-wave, half-wave, capacitor or inductor filtered, etc. The final voltage peak will be different from the AC voltage once rectified into DC. For example, if it uses a full wave bridge rectifier and is capacitor filtered, you can expect final DC output to be approximately 1.41x higher from the original AC voltage. Unregulated with no load. That brings the DC output from a 12.6V transformer probably somewhere around 19V which is about all that most 12V boomboxes can handle. If you start with a 15V transformer (or 14.4V which is probably more common), you're going to almost certainly end up with well over 20V unregulated after rectification and filtering. See the following circuitry by Hammond Transformers.... note the formula for calculating output voltage. For your information, I had a perdisco, one of those colored ones, and I promptly blew my music search system including the LED digits by connecting it to 120v. Can't undo that, so keep that in mind.

 

[hopey]

that's over 16% difference in line voltage so would be risky as you never know how much fluctuation in your street voltage. 10% is fine and have used many boxes' rated at 220v on 240v. I don't think it would matter on the secondary its the primary winding you are risking.

20 is 16.67 percent of 120.

 

[Chuck M.]

Thanks for the help guy's, I am going to try a 120v ac to 12v dc transformer going through the rectifier board and see what volts will be under load.

 

[caution]

Transformers voltage specifications are based on the rated current draw, at AC, at no load or a quiescent state, it will be much higher. You can expect a 12.6V transformer to actually test at about 15V with zero load directly at the secondary before the rectifier, at least this is my experience. Additionally, boomboxes don't use AC, they use DC and the type of PS circuitry makes a difference (full-wave, half-wave, capacitor or inductor filtered, etc. The final voltage peak will be different from the AC voltage once rectified into DC. For example, if it uses a full bridge rectifier and is capacitor filtered, you can expect final DC output to be approximately 1.41 the original voltage. Unregulated with no load. That brings the DC output from a 12.6V transformer probably somewhere around 19V which is about all that most 12V boomboxes can handle. If you start with a 15V transformer (or 14.4V which is probably more common), you're going to almost certainly end up with well over 20V unregulated after rectification and filtering.

That's really good information, thanks for clarifying that!

 

[Chuck M.]

I looked at the original transformer and it is 100vac to 10.3vac through a full wave rectifier filtering circuit. My wife is an Electrician and said you will end up with to high a voltage at 12vac into that circuit. I am a Mechanic and said aaaah 12 volts in should be 12vdc out, She said you will see. She is right I am wrong. I found a 120vac to 10.3vac on eBay and it should do the trick.

 

[Chuck M.]

Thanks for the help guys, especially Superduper for the info and diagram. Chuck.