PID Temperature Controller SSR Fan Problem

[alecount]

Below is a picture of my recently built PID driven temp controller. I have a fan attached to the heat sink of the SSR. I want the fan on when there is power to the SSR. So I attached it to the DC input side of the SSR. And this works, almost. When the fan is attached in this way, the PID (Mypin ta4-ssr) intermittently shuts off, then immediately powers back. When the FAN is not attached it works fine. Although the SSR doesn't get the cooling it needs. The fan is DC24V 0.18A. Any ideas as to why this is happening?

 

[doug293cz]

The PID is not designed to provide enough current to run a fan. You are overloading the output of the PID. Get a 120 V AC fan, and connect one side to the SSR AC output (on the heater side) and the other side of the fan to neutral. However, there is really no reason to switch the fan. They don't use a lot of power, so I would have it come on when the panel is powered.

Also, it looks like your heatsink is inside a sealed box. You would get much better cooling if you had some airflow thru the box. EDIT: just noticed the grill on the side of the box. Is there another vent for exhaust/makup air?

Brew on

 

[atoughram]

Also, it looks like your heatsink is inside a sealed box.

Yea - inside a sealed box wont let the heat our or cool air in.

My favorite way of adding ventilation in this case is to drill a hole in the side and add a drain cover over it.

 

[BrokenHorn]

However, there is really no reason to switch the fan. They don't use a lot of power, so I would have it come on when the panel is powered.

+1 on this for two reasons. Turning the fan on/off that frequently will wear it out faster. Also, heat transfer isn't instant, so once the SSR switches off, it is still transferring heat to the heat sink. Having the fan on full time would be better to help dissipate all the heat.

You could get a 120v fan and wire that in or the way I would go is getting a 24v power supply in case you want to add other 24v components down the road. The 24v power supply wouldn't cost to much more than a 120v fan.

 

[alecount]

Currently, I just have one small hole drilled in the back. I was going to see how much heat this thing generated before I figure out air flow. At 120V, I didnt expect it to get too hot with the current setup. It did run on my BIAB rig for about 20 minutes before it started shutting on and off and the SSR was cool enough to touch.

Thanks guys. 115V fan on the way and I will be taking a trip to Home Depot shortly.

The only reason I built this thing is because I ordered the parts a couple years ago and was bored. I currently use a Johnson Controller to run my rig. What keeps them cool? Just low amperage?

 

[BrokenHorn]

A Johnson controller isn't going to flip on/off nearly as quickly or frequently. The frequent on/off shifting is where SSR's build up most of the heat.

 

[alecount]

Also, the only reason I wanted the fan to shut on with the SSR is I also use this to sous vide. That rig employs a cooler (my old mash tun before I saw the light and convert to BIAB). With that system, once at temp, the cooler only looses a degree or two per hour and the RIMS tube is only on for a minute or two to get it back to temp. And, something like ribs, cook for 24 hours. Cycling a fan 24 times vs leaving it on for 24 hours will take less a toll. But the more I think about it I will probably use the Johnson Controller for that. No worries concerning a failed fan.

Again, thanks guys.

 

[atoughram]

If you only using it for 120V, I'd mount the SSR directly to the ammo can with some thermal grease - the ammo can is more than enough of a heat sink for 120V operation.