Transformer from a Xpelair heat recover unit

[mouse2130]

Hi all

So my Xpelair Xcell 150 heat recovery unit stopped working on the slow speed.
I've taken it to bits and it looks like the transformer has gone, but it's an odd beast. It looks like a normal multi tap but I can't work out how the primary and secondary coils work, the only transformer I can find with a common ground is a buck transformer, is it ok to share the ground on a multi tap and just turn an isolating transformer into a non-isolating one?

I get increasing resistance readings from 0 to all the tap points, but it's open between 0 & 240 on the bottom.

I rang Xpelair and was forwarded to their 3rd party parts line, but they have no record of this unit or that transformer (I've also logged a ticket direct with them, but I'm not holding out)

I only really need the 100v one but if I try googling for 100v transformer its convinced I want a site one.

Can anyone shed an light on this, I'm out of my depth now.

Cheers
L

^ I'd already unplugged neutral

 

[Lucien Nunes]

It appears to be an autotransformer as one would expect. There is no secondary, just one tapped winding shared between the input and output circuits. The input is between 0 and 240, and the output between 0 and whichever tap is selected. An autotransformer obviously does not provide isolation, but is smaller and more efficient than a double-wound transformer as only part of the load current flows through the full length of the winding.

The fact that you have continuity from 0 to the top 240V terminal but not the bottom one that is designated as the input, suggests that the latter connects via a thermal fuse within the winding that has gone open circuit, either through overload, insufficient cooling or sometimes just bad luck. It may or may not indicate that the transformer itself is kaput.

If you can snap the plastic bobbin cover off (it's probably stuck on with varnish) you might see the fuse and even be able to replace it, or it might be completely embedded and inaccessible. You have nothing to lose by looking. If you wanted to replace it due to having difficulty sourcing a replacement transformer, there is a simple test with a light bulb that can fairly reliably detect faulty windings.

OTOH somebody must have made it, and it could save a lot of hassle if they could just pop one in the post...

 

[mouse2130]

Wow, thanks, I never knew. I'll try and prise it open, as you say, nothing to lose.