Re: [CAD_CAM_EDM_DRO] Weird Temperature problem

kimvellore wrote:

>Hi,
> I built a CNC controller with a torroidal transformer at the power
>supply end. Everything works fine (almost). The Problem I have is when
>the garage is cold (I have the setup in my garage) around 57F or less
>I keep blowing the AC fuse to the transformer. I normally run fine
>with a 3A fuse but when cold it blows a 6A fuse as soon as the power
>switch is flipped.
>
>To debug I disconnected the transformer from the diode caps etc.. so
>it was just open and still I kept blowing the fuse. Now I heat up the
>transformer with a hair dryer and after it is warm I turn it ON and it
>does not even blow up a 1A fuse. So on warmer days (>65F) when I was
>using the power supply it was working fine…
>
> My question is has anyone seen this kind of problem and do you have
>any recommendations for a solution.
>
>

This is REALLY, really wierd. is this a ferrite toroid, or is the core
wound with steel
tape? If a ferrite, I think your ferrite is cracked, and thermal
stresses open up the air
gap (where the crack is) when it is cold. You might be able to make it
work fine by
putting some king of plastic strap around the OD of the core to hole it
tightly together.
Does it make a clunk or thump when it is turned on? That might be the
core pieces
pulling together.

If this is not the problem, then you may have a defective winding
somewhere, and at
the lower temperatures, two turns somewhere touch through a scratch in
the insulation.

Jon