I have a 110VAC input, 24 VAC output transformer that includes an Elsen WA128 fuse on the 110 v input side. I accidentally momentarily shorted the 24v. This blew the fuse. I want to replace the fuse with an equivalent, but I need to know if this is a slow or fast acting fuse.
This transformer supplies power to a skylight window controller. The window is opened and closed with a DC motor.
The description of where slow and fast acting fuses are used is confusing: fast for electronics, slow for motors. But this application does both.
Thank you for your responses. I admit that I was a bit sloppy - I said the transformer was 110 v, it is actually 120 v, I apologize. For further clarification, I have had this transformer in use for over 10 years without problems. It is rated at 55 VA. I accidentally touched the 24v lines together momentarily. A day or so later I realized that the skylight no longer worked. I found the problem to be the transformer. A VOM test showed that the secondary had continuity, but the primary winding was open. I drilled out the rivets and unwrapped some tape around the primary winding. I then found the Elsen fuse, connected in series with the primary winding. A VOM test shows continuity through the primary winding is good, but the fuse is open.
Although I am not certain about this, from the comments above, and other comments on the web, it appears that the Elsen fuse is both a thermal fuse, AND a current fuse. I am not sure about this, but it appears that the Elsen part is no longer made. I was able to find a possible replacement on eBay, but that is when I started thinking that a suitable replacement might be a better approach.
To my surprise, the momentary short circuit of the transformer also caused the skylight electronic circuit board to fail. This is a different problem, and also one that I have not yet solved, but a different subject.
The transformer is mounted in an open area in the basement, and the duty cycle is really really trivial. The skylight had not been used for several days before my momentary short circuit mistake. I seriously doubt that the fuse blew due to transformer heat over 128 deg C. I think it was due to a few milliseconds of secondary short circuit.
The part referenced above, thermal fuse NTE8070-8242, will pass up to 15 amps. I have not been able to find the current rating of the Elsen WA128.
My guess is that this transformer was NOT made specifically for this skylight, and therefore the fuse in the transformer was intended to protect the transformer PRIMARILY from over temp, and only secondarily for over current. But I seem to have blown the fuse by over current. A 55 VA transformer at 24 v translates to a load of about 2.25 amps (ok, 2.29). I think the NTE part would not protect against a transformer current overload.
So, my questions are:
- have I analyzed the problem correctly?
- Should I pursue the NTE (15A) thermal fuse, or try to find the obsolete Elsen part?