Need Help- PID Smoker controller on fritz

[ibebirdman]

Ok, I am a little over my head. I built a PID controller using those directions from Rob at Old's Place to control a finned strip heater in my smoker. It has worked great for months. Now on my last smoke, something when haywire. Now when I turn it on and I barely get any heat from the heater. It it cool enough to touch. What would be the most likely problem? Fried heater? Thermocouple?

Any help would be much appriciated.

Joel

 

[justpassingthru]

Hey Joel,

I'm not an expert, but I would guess you SSR Relay is burned out, when I was doing research for mine what I found was to use a 40A SSR Relay with a Heat Sink, from what I read the Relay is the weak link, what amperage SSR do you have?

To test the thermocouple just turn on the PID and the PV should be ambient, then hold a lit match or lighter under the it (not too close or too long) to see if the PV increases, to test the heating strip check the terminals with a  volt meter to see if you have line voltage.

Hopefully some of the PID guys here will see this and respond,

Gene

 

[ibebirdman]

You may be on to something. I  have a 25A SSR with a heat sink. I pulled the strip heater  and connected it directly to a plug. It headed right up. I put a match under the thermocouple and it readout on the PID shot right up. I guess that means the SSR is the only other part that could go out. I don't have a inline fuse, would that have prevented this? I am just a bit confused at how a 15A strip heater could burn out a 40A SRR  But then again, I really don't know my way around electricity, so I am sort of flailing around in the dark here.

Any explination would be enlightening.

Joel

 

[justpassingthru]

Joel,

First you say you have a 25A SSR, then you ask how could a 15A heater could burn out a 40A SSR, which one do you have?

All of the strip heaters I've seen are rated in watts, what is the wattage of yours?

If your SSR is a 25A it is probably operating too close to optimum, another question, did you use the glue between the SSR and the heat sink?  I was told it helps with the heat transfer.

Does the box that holds all of the pieces have ventilation, mine has ventilation slots and I mounted the heat sink over them, this helps with the heat dissipation and prolongs the life of the SSR.

I don't have a fuse in mine, in my schematic the fuse is placed in the 'Line In' voltage before the PID to protect it.

Looks like you have diagnosed the problem, the final test is to check the voltage out of the SSR when it is in the Ramp mode, but that is probably not necessary if the other components are working.

Gene

 

[ibebirdman]

Ok, I miss spoke, I have a 1250W heater, this one to be exact:

http://www.grainger.com/Grainger/TEMPCO-SS-Heater-2XDX4

Which I miss remembered as being about at large as you want on a 15A circuit (I think). 

I didn't use glue between the SSR and the heat sink. I can fix that. I really don't want to vent the box unless absolutely have to. Where the units sits it is partially exposed and I don't want spiders and stuff getting on.

i will order a new SSR, this time 40A on monday and see if that fixes the problem. Thanks for the expertise, I really appriciate it.

Joel

 

[justpassingthru]

So you have a 1250w/120v heater strip.

The formula for amperage is watts divided by volts...   1250w/120v=10.42amps, which your 25A SSR theoretically should handle, but the people at Auber Instruments advised me to go with the 40A SSR to avoid any problems.  When you buy the next one I would recommend using the 'special' glue that comes with it, they told me why but it was over my head, what I remember is they said to use it liberally.

As for venting why not drill a few holes and cover them with some stainless window screen, you think you have problems with spiders, I have to deal with geckos and they can squeeze into the smallest places. 

This is from the Aubers site for their 25A heat sink:

This heat sink is for 25A SSR. It allows the SSR to handle up to 15 Amp without forced air cooling (in an open air environment).

You have 10.4 amps running through the SSR without any ventilation.

When I touched the area where my heat sink is attached it is warm, not so warm to burn, but I can imagine how hot that could become inside of the box if left unvented, which is probably the reason for the SSR failure rather that the amperage.

You probably know this, but when you order the 40A SSR don't forget to order the 40A SSR heat sink, ...the 25A heat sink is too small.

I'm glad I could be of service,

Gene