SSRs in unvented plastic enclosures?

[julianf]

After yessterdays entertainment, im keen on making a new control box.

My last unit was a metal case, with an integrated heatsink on the rear of the box -



It does not look like that now though!  It was a desktop unit, and got oil spilt on it too many times.


I have a wall mounted plastic enclosure.  I dont really want to cut oil channels (vent holes) in it, so how should i handle the SSR - is it possible?

Ive never noticed the SSR even getting warm on my exising setup, but its got that heat sink attached.  Ive got plenty of heat sinks, but how much dissipation is really needed?  I would say that the box im considering is probably 2.5ltrs in volume.

[knighty]

fix the ssr to the side of the box, put a hole under the base of it, then a washer or something else to pack it out, and the heat sink on the outside ?

[julianf]

I considered somthing along those lines - cut a hole for the heat sink to stick out of.

I need to look through my box of heatsinks to see if there's anything suitable for that idea.

It would, of course, be easier to have it all inside though, so im still keener on that plan, if its possible.

[Rotary-Motion]

nice neat front panel there julian

[lozzzzzz]

Wow, there is a first time for everything.  I can in fact offer some help on this one. 

I tested my finished rig today and I have a set up much like you describe Julian, I've just a 4.4l clip top lunch box from Wilkos.  I screwed the lid to the frame of the machine and mounted all the electrics in the in the base of the lunchbox, so when it is clipped in place it faces outwards. 

I cut slots in the box to allow 3mm ali sheet to poke out.  At the time of making it I thought this is hardly worth it, the SSR's can cope with 40A and I'll be giving them 13A max.  I'm glad I did though.  After just 10 mins they were all at 70 degree C so I riveted bigger bits of ali sheet on and they seem to be staying at 50 degrees C now. 

See my video in my thread for some inspiration. 

[Mickindashed]

It's about 17w of heat when switching a 3kw heater.

[Manfred]

It's about 17w of heat when switching a 3kw heater.

  If that's the case, to get an idea of the heat potential grab hold of a low energy light bulb say 11 watt after an hour on.

[Tony]

After yessterdays entertainment, im keen on making a new control box.

My last unit was a metal case, with an integrated heatsink on the rear of the box -



It does not look like that now though!  It was a desktop unit, and got oil spilt on it too many times.


I have a wall mounted plastic enclosure.  I dont really want to cut oil channels (vent holes) in it, so how should i handle the SSR - is it possible?

Ive never noticed the SSR even getting warm on my exising setup, but its got that heat sink attached.  Ive got plenty of heat sinks, but how much dissipation is really needed?  I would say that the box im considering is probably 2.5ltrs in volume.

That's cool

My SSR is mounted inside an ally box, it barely gets warm (heatsink paste between PID and box).  I suspect the dissipation of heat depends very much on the PID though.

[julianf]

I forgot about this thread.

In the end, i concluded that it would be easier to mount the existing job somwhere where it did not get covered in oil, than remake a case.

And i set about the job quickly...

...so, currently, the box is still under the reactor with half its guts hanging out : (

[julianf]

Speaking of which -

K-type thermocouples - whats the rules with joining the wires?  Twist, but not solder - is that right?

[Tony]

You can solder, the only reason it is avoided is that close to the hot end it limits the thermal range (solder melts!).  It should have no effect at constant temperature elsewhere down the wire.

The argument is that the solder blob forms a chromel-solder-chromel interface; the first chromel-solder interface will add a voltage, but the next solder-chromel interface will take the same voltage away - so long as there is no thermal gradient across it.

[therecklessengineer]

I make it about 20W at 13A.