I just inherited a heated snowboard/ski press, with large silicon heat pads controlled by an arduino. I don't know who wired it up, but there is no documentation and it is a complete rat's nest. The unit runs of 120V AC and I see 4 SSRs in the power box, which is strange because I only have two heat pads. It looks like they are using little ceramic RTDs for sensing... I'm looking to start over with what I have, or possibly purchase some new equipment if it makes my life a bit easier. I can add photos and a parts list if anyone is willing to help!
Thanks for the reply, the last time it was used it overheated on one side (there is a pad on both the top and bottom of the press) and ruined the board. I'll be checking out the code later this evening.. I need to get my hands on the cable to connect to the arduino.
Okay if you're new to arduino but have "good" experience with electricity, go ahead.
But if you're new to electricity, what I can recommend is that you don't work with voltages like 120VAC. They can be deadly.
Any carelessness could cause an accident with serious consequences.
If you don't have experience, hire a professional.
You could be on to something here.. the pads are quite large. I'll double check the wiring, and see if I can't find out where these things were ordered from to try and get more information. The pads themselves look very generic. I'll upload some pictures after my next shop visit.
SSRs are typically either on or off. So you may find in the software some kind of slow PWM drive. The SSRs are probably zero crossing types so turning them on or off doesn't cause spikes. And the heating elements will change temperature very slowly in repsonse to the SSR being turned on or off. So you might have for example a 10-second period, and the heating is raised or lowered depending on what percentage of the 10 seconds the SSR is turned on.
If the thing overheated, that could be a failure of the sensing circuit that's supposed to tell the Arduino what the temperature is.
A parts list or BOM, bill of material, is essential to unwinding your project and documenting it's construction. Include ALL part numbers if you can find them.
Thanks, I finally got some time to play with this (I work a normal job, and this is a hobby thing..) The heat pads heat up VERY quickly, and my RTD temp sensors can't catch up to them. The control mechanism is exactly what you had mentioned.. heats up to a temp, then shuts off until it is below a temp and kicks back on. The problem is, the sensors (which responded very quickly when calibrating) don't tell the pads to shut off until they severely overshoot. The problem is not as bad on the way back down, but after they fall below the 'kick on' threshold they overheat again before turning off.
Is there a way around the on-off control mechanism? I can't find much for a PID style control for high voltage systems. A friend suggested ditching the arduino and controlling through inkbirds.. any thoughts on this? Thanks again for your time.. adding photos to another reply shortly
Are you sure? Could it be that the overshoot occurs after the current has been shut off?
Well, I described another approach in post #10, which is to turn the power on for only part of the time, anticipating that it will continue to warm up. The closer it gets to the desired temperature, the shorter the duty cycle. Then hopefully you don't overshoot.
I don't think you can get away from the full on or full off situation. Your SSRs wouldn't like that.
I'll do my best to sketch up a diagram soon. The yellow connectors come from the SSRs, through some in line fuses, and ultimately to outlets that the heat pads plug directly into.
Next time I fire it up, I'll use a multimeter to check when the current to the pads is turned on/off. I'm heating to around 80 degrees C, and in the current configuration the temps go over 100 C before the sensors read the target temp of 80 and tell the system to turn off. You're saying I have some control over the percentage of which the pads are turned on over a specified time window? I'll have to dig deeper into the code and see about adjusting this...
The temp sensors are mounted to the pad using what looks like liquid electrical tape.. I'm thinking there has to be a better way, any advice is appreciated.
They responded almost instantly in the cold bath / boiling water bath calibration... they are ceramic, so I had them in plastic bags, but even so I was impressed with the response time.
