I'm fairly new to electronics, but still have a basic understanding (1st year Electrical Engineering Student).

I've started a project of repurposing a used treadmill I found online for $20 as a variable speed pottery wheel for my girlfriend. When the treadmill arrived it had a blown fuse and after replacing the fuse it continues to trip the RCD.
I began debugging the circuit and think that I have isolated the problem to the transformer (I disconnected all of the components with terminals off the main PCB and started reconnecting them from AC forward until the RCD began to trip. The transformer was the connection that caused this to occur).

Attached are some photos of the transformer unit. I don't have too much experience with transformers so my question is - is this a single transformer with 3 windings (1 in and 2 out) or is it two separate transformers packaged as a single unit.

Transformer Markings

Bonus Question - if theres any advice or other methods I could use to bestconfirm that the transformer is the circuit issue?

  • 3
    \$\begingroup\$ It's three windings on a single core. "In" and "out" are relative. \$\endgroup\$ Commented Jul 5, 2016 at 12:35
  • \$\begingroup\$ Thanks for the clarification @IgnacioVazquez-Abrams. I am aware that it's relative, my slip was mainly due to my interpretation of the intended use of this transformer in it's 240v (Mains) step down configuration inside the treadmill. Will be more careful with wording in the future. \$\endgroup\$
    – James
    Commented Jul 6, 2016 at 12:11

2 Answers 2


Yes, you have a transformer with three independent windings. The picture is showing you how it is intended to be used, which is that 240 VAC is applied to the upper left winding. That results in 22 VAC out the one depicted at lower left, and 10 VAC out the one at right.

What that really tells you is the turns ratio and the maximum voltage that should ever be applied to the top left winding. There should be no problem at all to apply a lower voltage to the top level winding. For example, if you applied 115 VAC instead, then the lower left winding would produce 10.5 V, and the right winding 4.8 V.

Unfortunately, the label does not tell you anything about the current capabilities of the windings. However, it should certainly be safe to connect the top left to 240 VAC while leaving the other two open. This should not cause excessive heating in the transformer, nor should it cause a fuse to blow.


From the looks of it you have a low current transformer with a 240 VAC primary input winding and two low voltage output windings. Test by checking for shorts from any lead to frame. Then check for shorts from winding to winding. In a transformer like this the primary winding should show some DC resistance but the winding could be burned and put an almost direct short across the 240V leads.


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