SSR cooling fan switch-on surge

[chastuck]

I've got a 240v AC fan fitted to my PID controller case. The fan switches on via a normally open thermal switch mounted on the SSR heat sink. Everything works fine, but when the fan kicks in it causes a momentary loss of power to to the PID. It's so quick that you can hardly see it, but you can just see the PID reset to the switch-on display and then return to normal. The motor on the fan is obviously causing a power surge when it switches on. I guess I'm worried about the spike harming the SSR or affecting settings on the PID. Does anyone have a suggestion as to how the fan switch-on surge can be stopped?

 

[bobsbeer]

You could disable the thermal switch and leave it running all the time. Or change to a 12v fan.

 

[chastuck]

Just in case anyone else ever has this difficulty, I have cured the power spike problem. I fixed a snubber (contact suppressor) across the thermal switch contacts (http://www.maplin.co.uk/contact-suppressor-498) and a MOV across the power input to the PID (http://www.maplin.co.uk/transient-suppr ... lateditems). Not sure which of the two was the solution, or maybe both, but now the display on the PID does not flicker at all when the fan kicks in.

 

[asd]

Hi Chas,

What sort of thermal switch did you use, and where from? I'd like to put one into my PID controller to cool down the SSR heatsink.

Simon

 

[Kevin Wood]

Just in case anyone else ever has this difficulty, I have cured the power spike problem. I fixed a snubber (contact suppressor) across the thermal switch contacts (http://www.maplin.co.uk/contact-suppressor-498) and a MOV across the power input to the PID (http://www.maplin.co.uk/transient-suppr ... lateditems). Not sure which of the two was the solution, or maybe both, but now the display on the PID does not flicker at all when the fan kicks in.

That's a good solution. :thumb:

Incidentally, I put an MOV across each of my SSRs to add a little protection to them. I had one go pop in a dramatic way when my HERMS kettle was a little loose in its' base and the contact there arced while driven by my temperature controller.

 

[chastuck]

Hi Chas,

What sort of thermal switch did you use, and where from? I'd like to put one into my PID controller to cool down the SSR heatsink.

Simon

Here's what I bought. http://www.ebay.com/itm/ws/eBayISAPI.dl ... OC:GB:3160
Works well. After fitting it I tried it out first in situ by using the wife's hairdryer.