Custom PID

robs · August 21, 2006, 07:32:46 PM

Quote from: TomG on August 21, 2006, 07:29:41 PM
Nice job. Let it run for a couple of hours and you'll probably find that it's barely warmer than ambient. Were you having heat problems with the SSR mounted inside the box?

No heat problems before the heatsink. I added it because I got a few emails regarding it and also Auber Instruments recommends one.

I don't know if it needs to be on there. I put it on to be safe.

Thanks!
rob

robs · August 21, 2006, 07:48:39 PM

Quote from: iceman on August 21, 2006, 04:15:14 PM
Robs; I just wanted to say thank you very much for all the hard work you've put into this project. For that matter I would like to thank everyone for the input and information supplied here.
I noticed you used a 25 amp SSR. I'm running dual 1500 watt elements in my smokers. Do they make a 40 amp SSR?
All you folks have certainly given me the desire to tackle this project.
Again, THANK YOU.
Regards; Patrick :) :) :)

BTW TomG Very nice job on the heat sink!!! ;)

Iceman,
Auber Instruments sells a 45a and a 50a.
http://auberins.com/index.php?main_page=index&cPath=2&zenid=215411ad7761e233301fadbb4b25749a

begolf25 · August 22, 2006, 04:19:48 AM

QuoteThanks to begolf25 for answering my questions and all of his help. I couldn't have
done this without his help.

I was glad to help Robs. But I just wanted to say that this PID design came from TomG and he deserves the credit. I just passed all of the help and information he shared with me onto Robs. That is what is great about this forum, there is never a shortage of help from its members.

I also don't want to take credit for work that isn't mine. The pictures of the PID on the recipe site thread labeled as mine are TomG's, not mine.

Oldman · August 22, 2006, 05:15:15 AM

Quote from: begolf25 on August 22, 2006, 04:19:48 AM
QuoteThanks to begolf25 for answering my questions and all of his help. I couldn't have
done this without his help.

I was glad to help Robs. But I just wanted to say that this PID design came from TomG and he deserves the credit. I just passed all of the help and information he shared with me onto Robs. That is what is great about this forum, there is never a shortage of help from its members.

I also don't want to take credit for work that isn't mine. The pictures of the PID on the recipe site thread labeled as mine are TomG's, not mine.

No problem I will add credit and re-lable the images.

TomG · August 22, 2006, 08:18:26 AM

Come on guys, you're making me blush. This was a joint effort and a fun project, and without Bubbagump's thoughtful, patient input it would have never gotten off the ground. Thanks to Robs, Olds, and Beogolf the info is now in a simple, easy to locate and understand format.

iceman · August 22, 2006, 10:01:43 AM

You guys sure make a great team!!! ;D Thanks!!! ;)

Oldman · August 22, 2006, 10:22:00 AM

Quoteand without Bubbagump's thoughtful, patient input it would have never gotten off the ground.

You know I wonder about him... it is like I either do not see his postings or he has moved on... if he has moved on then we have lost one great library. That would be a one real cotton pickin' shame too.

bubbagump · August 22, 2006, 11:51:11 AM

Quote from: Oldman on August 22, 2006, 10:22:00 AM
Quoteand without Bubbagump's thoughtful, patient input it would have never gotten off the ground.

You know I wonder about him... it is like I either do not see his postings or he has moved on... if he has moved on then we have lost one great library. That would be a one real cotton pickin' shame too.

Thanks Olds, I'm still around from time to time. Been running six different directions lately.

Rob - Great work!! It's nice to see everything condensed to one thread with links to the originals for reference. The time you put into this will pay dividends for others looking to go the PID route. :) :)

Bubbagump

robs · August 22, 2006, 11:59:13 AM

Quote from: bubbagump on August 22, 2006, 11:51:11 AM
Rob - Great work!! It's nice to see everything condensed to one thread with links to the originals for reference. The time you put into this will pay dividends for others looking to go the PID route. :) :)
Bubbagump

Thanks. The real test will be someone creating a temp control box based on this (I've done it over and over to make sure), and them posting results, sugestions, etc.

I really just want to make it as easy as possible, as I wanted to do it myself for along time, but didn't have the guts until befolf25 said to go for it.

rob

Habanero Smoker · August 22, 2006, 12:53:43 PM

I am not interested in building a PID, but I need to say good job Rob and Bubbagump. These instructions will be helpful to many.

Arcs_n_Sparks · August 22, 2006, 02:01:31 PM

Rule of thumb for cooling electronics: if you cannot keep your thumb on it, it is too hot and needs to be cooled.

If you want to do some math and size the heat sink correctly, you need to know how much power is being dissipated in the SSR. This will be its voltage drop switched on times the current being switched. This will be watts, and the SSR package will have a certain degree C/watt spec. A heat sink will have its own degree C/watt spec. Say you are switching 15 amps and have a 1 volt drop across that SSR, that will be 15 watts of dissipation. If you have a 5 degree C/watt heat sink impedence, then the heat sink would get to 75 degrees C above the ambient temperature. This puts you very close to 100 degree C, which is really too hot. (all of the above assumes a 100% duty cycle on the SSR).

Note the heat sink rating may be for either convection or forced-air cooling, so you have to examine the spec with some care.

The Edisonian approach will be to put something together and see if it burns up or smells bad (or you notice it gets hot prior to the above happening).

Arcin' & Sparkin'

iceman · August 22, 2006, 03:06:20 PM

You could always do what's done at the fab shop. Just hand it to Stumpy and if he screams and drops it and starts calling you unmentionable names you know it got to hot and it's back to the drawing board. :o :D ;D ::)
They still get him with the ole "Grab that wire Stumpy and tell me if it's a live one will ya?" Gotta love him but ya just can't fix stupid sometimes. Heck of a friendly guy but................. ;)

robs · August 22, 2006, 07:38:48 PM

Ok folks, I think this thing is done. I feel bad about skimping on the heatsink instructions, so please keep the ideas coming regarding the subject. There's alot of creative people here.

I'm still thinking that the optional aluminum cover this box comes with could be used as a heatsink. From what I understand, heatsinks need to be made of copper or aluminum. If I could change anything about this project, I think it would have been trying to use the cover. Attach the heatsink to the cover with epoxy. Done. Maybe drill a couple of small holes for airflow, maybe not.

I may do this on my next project box.

Thanks again to everyone. If anyone sees anything wrong with the post, please let me know so I can correct it.
rob schmit

MRH · August 23, 2006, 05:35:08 AM

robs,
Wouldn't using epoxy to glue the ssr to the aluminum insulate it and keep it from transfering the heat as well? I figure that is why the ssr has a aluminum plate for mounting. I have mine screwed to the side of the box and haven't had any trouble yet, but i only used the 10 amp ssr.

MRH

robs · August 23, 2006, 05:55:34 AM

Quote from: MRH on August 23, 2006, 05:35:08 AM
robs,
Wouldn't using epoxy to glue the ssr to the aluminum insulate it and keep it from transfering the heat as well? I figure that is why the ssr has a aluminum plate for mounting. I have mine screwed to the side of the box and haven't had any trouble yet, but i only used the 10 amp ssr.

MRH

I don't think so. I'm not an expert in the area but the research I've done suggests otherwise. Are you questioning the use of JB Weld as the thermal epoxy? I followed these instructions http://maximumpc.com/forums/viewtopic.php?p=512175&sid=c5a1238a05c1723c0c5eee42d2e8699f and it seems to be working fine.

rob