Broken 240/120 switch on Transformer

After soldering together a bridge rectifier to make a 12vdc power supply from a 120/240vac transformer, I was having trouble getting anything to happen once I plugged this in. It turns out the 240/120 switch was in pieces inside its housing. There were tiny ball bearings and springs and a number of paper clip looking pieces of metal. I took apart two other, similar switches, but neither looked the same. Then, tested the transformer with a multi-meter but I get buzzing sound any combination of touching the wires.

My question is... What two input wires should plug into a 120V outlet? Or should I put two wires together on one lead and the other two together on the other lead (if so, which ones)?

Thank you!

T

When the primary side has four wires it usually means there are two 120V windings. For use on 120V you wire them in parallel (across each other so you join two pairs of wires and feed power to both) and for use on 240V you wire them in series (two wires joined and power fed across the other two).

Your only problem might be getting the windings the right way around. If you reverse one pair of wires with respect to the other, you generate two opposing magnetic fields in the transformer and (almost) nothing comes out at the secondary winding. You want them to cooperate and generate a magnetic field where one reinforces the other.

If you haven't removed the wires from the switch, and you want to use 120V, the photographs suggest you should link the green to the black and the blue to the brown.

The switches are usually quite simple to repair. The 'paper clip' is the bit that touches the center tag to one of the end tags. It pivots on the center contact from one side to the other and is pushed into position by the ball bearing rolling over it's back surface. The spring keeps pressure on the ball bearing. Hint: straighten the four tabs on the switch body first then after you reassemble it, bend them inwards through the four recesses on the back of the switch. A dab of silicone grease on the ball bearing helps to keep it in place on the end of the spring while you handle it.

Brian.

It should be the green/black and the blue/brown like you said. I tried it the other way before posting and the two opposing magnetic fields were generated (i.e. it didn't turn on). I wanted to check here first before experimenting live again.

Thank you!

T

Well, I put the Black/Green together and the Blue/Brown together and then plugged it in. It was silent and then a loud "pop" and I unplugged it. I guess it is all over.

Thayne said:

Well, I put the Black/Green together and the Blue/Brown together and then plugged it in. It was silent and then a loud "pop" and I unplugged it. I guess it is all over.

Click to expand...

In your first post you said you had continuity between any combination of wires. Did you mean that if you had one probe on say the black wire you had continuity between each of the other three separated wires.

- - - Updated - - -

Example -
Black to green
Black to blue
Black to brown
All showed continuity

Yes. My multi-meter was buzzing on all connections -- but two connections buzzed louder than the other two (across the switch orthogonal sounded different than the diagonal connections (switch in pic above)). I never heard my multi-meter buzz like this (the transformer was not live).

Now, I get climbing resistance with any combination of connecting wires with the multi-meter.

Thayne said:

Yes. My multi-meter was buzzing on all connections -- but two connections buzzed louder than the other two (across the switch orthogonal sounded different than the diagonal connections (switch in pic above)). I never heard my multi-meter buzz like this (the transformer was not live).

Now, I get climbing resistance with any combination of connecting wires with the multi-meter.

Click to expand...

You shouldn't have continuity from one wire to the other three. But since you checked it through the switch I wouldn't be able to say. Theres only two ways that I can think to have continuity from one to the other three if they are separated. Either the two primary's are shorted together. Or the transformer is actually a 120/208/240 volt transformer.
It may also be that the problem is in the secondary. The reason I say this is because if there were a short in the primary it should have shown itself when you had the polaritys backward. It was only when you connected the transformer correctly that voltage was induced on secondary. I may be completely off base with this assumption. Hopefully the moderators will weigh in and confirm or deny this.

Hello Thayne,
That switch doesn't look like it can handle 110 or 240V AC, especially current wise.
Does it have an imprint or markings on it that its suitable for mains AC operation?
Sorry to be a worry wart, but the switch looks like it resides as a low voltage DC
on/off switch.
Regards,
Relayer

Relayer said:

Hello Thayne,
That switch doesn't look like it can handle 110 or 240V AC, especially current wise.
Does it have an imprint or markings on it that its suitable for mains AC operation?
Sorry to be a worry wart, but the switch looks like it resides as a low voltage DC
on/off switch.
Regards,
Relayer

Click to expand...

It has no marking, but it was inside a metal box that said it was a car battery charger. It had a plug to the main and to clips (red/black) to the battery. Inside was only an LED and a 6A10 diode. I plugged it once and it worked. I checked with multi-meter and it was 12vdc. It then died. I opened it up and the wires were falling apart, connections coming undone. I was trying to reuse it by making a power supply.

I got my Arduino Mega to build a 3D printer and a CNC. I also got a few ESP32s setup for another project. I was hoping to use this transformer as a (small, portable) power supply. I already have 3.3 and 5v supplies and an S-250-12 (mounted to a frame).

Transformers seem to not like me. I have three that I cannot get working. This one seems to have hope. Can anyone help? I would greatly appreciate it. If I order one it has to come from China and it takes six months.

Thanks.