Building an oven, SSR confusion

Thread Starter

bmklawt

Joined Dec 27, 2013
8
I know very little about electronics, that being said, I am building a temporary oven to bake some painted (Cerakote) parts.
I have 3, 1100 watt heating element controlled by a MYPIN TA4 controller, at first I ran all three heating element through a MYPIN SSR-25 DA relay but burned up the SSR in a few minutes.
Now I an trying to run each heating element through a OPTO-22 240D45 SSR, the 12vdc input is running parallel to the three SSR's inputs and the output from each SSR is running to the 3 separate heating elements, this did not work, somewhere I read hook a light-bulb up to the output for testing and that did work so I hooked up the light bulb in series with the heating element and the light bulb comes on but not the heating element, if I hook the light bulb in parallel with the heating element then both the light-bulb and heating element work.
Whats going on here, is there a proper way to do this? searching google just muddies the water for me.

Your help is greatly appreciated,
Bruce
 

MaxHeadRoom

Joined Jul 18, 2013
25,636
The lamps will light as the elements represent a solid conductor as far as they are concerned.
What voltage are you operating the elements at? So it sounds as they are working with the SSR's ?
 

crutschow

Joined Mar 14, 2008
30,454
I have 3, 1100 watt heating element controlled by a MYPIN TA4 controller, at first I ran all three heating element through a MYPIN SSR-25 DA relay but burned up the SSR in a few minutes.
At 120V, the three elements draw 27A, so why did you think a 25A SSR was sufficient?
And at that current the SSR likely needs to be on a heatsink.
 
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You must have a heatsink with SSR's! Rule of thumb is they dissipate about 1W per amp. So 27A of heater load, you need a large heatsink to dissipate 27W without overheating the part.
At those currents and higher, a mechanical relay starts to get more practical.
 

Reloadron

Joined Jan 15, 2015
6,826
You have three 120 VAC elements at 1100 watts each so you have a 3300 watt load. Elements wired in parallel. So you get 3300 watts / 120 VAC = 27.5 amps. While I haven't a clue what SSR you are using my personal observation is the imported inexpensive units off the boat seldom meet their specifications. That said you initially used a MYPIN SSR-25 DA relay which is a max current 25 amp relay.

Some considerations you need to think about. You want an SSR which has some overhead for your maximum load. Your load is 28 amps so you really want about a 40 amp SSR. Next as was mentioned you really want a good SSR heatsink to remove heat. When it comes to the actual SSR I like manufacturers like Gordos, Crydom, Omega and several others. Buy once and cry once. Consider using some thermal compound between your SSR and heat sink. Really only need a pea size dab spread on the bottom of your SSR. The link is merely an example. Finally since you mention 120 VAC elements I assume you are in N. America. US residential wiring is typically AWG 12 wire with 20 amp service outlets. You will need a minimum of 30 amp service Each element will do fine using AWG 12 wire but your mains service to your SSR should be a minimum of 30 amp service using AWG 10 wire. Even that is cutting it close. A standard 120 VAC US outlet simply will not support your load.

P.S. You also may want to consider a small fan to remove heat from your heat sink.

Ron
 
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OP there are many low cost chinese SSR's, copies of Fostek etc. that simply can't take meet their current rating and have no safety approvals. "MYPIN" is a generic name. Across the Internet, there are chinese SSR's failing and counterfeit internals, they cook and burn up just due to poor quality alone.
Be careful because a burnt up melted SSR can be dangerous if hazardous live shorts to the input side.

The Opto-22 240D45 is superior quality - but still needs a big heatsink or it will quickly burn up.
 

Thread Starter

bmklawt

Joined Dec 27, 2013
8
I first tried with a 20 amp circuit but keep tripping the breaker so I switched over to a 120V 30A circuit.
I did something wrong the first time through, I tore everything apart and wired it up with one SSR with a light bulb as the load and got that to work then added the 2nd SSR and got that to work then added the 3rd SSR, after getting that to work I replaced the bulbs with the heating elements and it all works now
 

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Reloadron

Joined Jan 15, 2015
6,826
Well alrighty then and long may it work. :) I have used Cerakote on gun parts, works just fine and last a long time. :) About 250 ~ 300 F. While I am not a big fan of the stuff plenty of people like it. Nice touch with the old Simpson 260 meter.

Ron
 
I checked and the heatsinks are smaller than this chart, your pictured heatsink plus SSR are about 4.2°C/W so ~10A through just one SSR would give about 67°C operating temperature. With no heatsink, the 45A rating becomes about 5A! But in parallel the three should work well.
I would also ensure the oven chassis is earth grounded, enough to survive a ground fault at say 30A if wiring melts or heating element fails.
If you don't get the oven heat expected, you might add a convection fan to stir up the heat off the elements into the space.

opto22 HS.PNG
 
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