Dead SSR or Bed Heater?
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Thanks for the reply and observations...I know this has to be something stupidly simple, but what a puzzler it is.
I'll try bumping up the dead time variable as that makes sense. You are correct that this is a big honking piece of aluminum bed and as we all know...aluminum is one of those metals that heats quickly and cools quickly, hence why it's used for most heat sinks.
As far as I know all the hardware checks out and for the record- the Thermistor is mounted right in the center of the bed and it does function.
Next basic test I'm going to do is the old pre-heat the bed with a cast iron skillet right on the bed, with print mat removed.
I'll use my infrared laser thermometer to make sure the pan is not too hot and see what happens.
The heat should wick from the iron to the aluminum fairly fast and maybe get past this icy road block.Thanks again for the suggestions!
-Cheers! -
@Electriceye what happens when you try an tune your bed heater rather than turning it on before its tuned?
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I'm going to try that tonight. I think I did this already after I PID tuned the hotend, as it was my next logical step.
Sad that I can't remember...
I broke out my FLIR One infra red camera today and took some pics...the bed heater simply does not not to heat up...at all.
Also gave me a nice idea where the hotspots on my printer are- power caps on the Duet and the Pi3B+ looks a little warm, but certainly within operating limits. I'll post some pics later when I retry the PID tune on the bed heater.Thanks again for the suggestion!
-Cheers!
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@T3P3Tony
Well..I did try this before and got the same result...notta.Here's the command I used:
M303 H0 S105
Auto tuning heater 0 using target temperature 105.0°C and PWM 1.00 - do not leave printer unattendedAfter watching it sit there for a half hour and not budge, I cancelled it.
I also dbl- checked the voltages at the SSR:Top portion: (AC)
118.50 voltsBottom Portion (DC from Duet)
24.0 voltsSo, the SSR appears to be doing it's job, but the bed heater simply will not heat up one iota.
beginning to think this is a defective bed heater, bummer since it is brand new and never been used.I'm going to have fun arguing with the RatRig guys about an RMA since the printer kit is a few years old now and I've only recently started to put it together. Just my bad luck I guess.
I ordered a new Keenovo 1000w bed heater, in case RatRig cannot replace mine, but the very slow boat from China says it won't get here until late February... ugh.
Thanks again for the suggestion!
-Cheers! -
@Electriceye what resistance does the bed heater measure?
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Resistance is still the same as my original post. I disconnected the leads from the Power supply neutral and SSR and measured them stand alone (not connected to anything else)
-Resistance check of bed heater leads shows 14.4 ohms (120^2)/1000 = 14.4 ) when checked with multi-meter
So...how can the resistance be within tolerance or expected levels and the bed still not heat?
voltages in and out of the SSR all look good still.I'm going to go through the wires involved and dbl check connections, but I have done that already once, maybe second time is the charm? I have upped 2 images of the wiring I have done. Not my best work, try not to laugh.
-Cheers! -
My FLIR camera doesn't show any obvious issues either.
Pics of the heater bed are stone cold...as one would expect from a 6.5 mm thick slab of aluminum that isn't heating up.
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@Electriceye If you are confident in doing so, I would bypass/short your SSR and see if the bed heats. BE READY to kill it. Current is clearly not flowing or there would be a kilowatt of energy showing up somewhere. Obviously this is not a solution, but could be diagnostic.
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Have you tested your bed output with something like a fan to confirm that it's switching correctly?
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Yeah, I thought about that and remembered the circuit breaker in this room is only 15A so that would probably trip right away and might not even be enough time to see what, if anything happens.
Since this is a 120 volt mains bed heater, I'm a bit reluctant to push things too far.
Without cycling or pulsing the AC to the bed I'd be afraid it would just melt it instantly.Oh and I HATE electro shock treatments, they just ruin my day.
Thanks for the suggestion, though!
- Cheers!
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Now that's an idea... now what to hook up? Would a small appliance type fan rated at 120 volt suffice?
I have a small ULINE desktop fan I wouldn't mind sacrificing to the AC gods if need be. -
I'm suggesting you test the Duet output directly, not the SSR outputs. A DC fan that matches your VIN voltage.
Though if you're measuring the correct 120v from the SSR output already and it's switching correctly then testing the Duet output is moot.
I'd be more inclined to suspect the SSR rather than the heater itself.
What are the specs of the SSR? Do you have another to test with?
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Yep. All good points.
This leads me back to my original post findings, voltages are there...but that little LED indicator light on the SSR has never turned on, that I have seen. That puts us full circle...is it the bed heater or SSR?
Now I'm thinking you are right...it might just be the SSR.
I have a new one (different brand) and the bed heater on order already...just have to wait until they arrive. Sigh.
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@Electriceye A 1000W heater should not trip a 15amp breaker; it only draws about 8.5 amps. If your heater matches your bed mass appropriately it should not be melting instantly, either. Everything is pointing to the SSR not working.
But as @Phaedrux notes, you can attach something else to either side of the relay to test function, so long as that something else is rated for the appropriate voltage and won't pull too much current.
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Well in that case it may be a good idea to test the Duet output with a fan, just to ensure it's working properly.
For testing the 120v side you could wire up a light socket, but only if you're absolutely comfortable working with 120v.
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24 v DC fan works perfectly connected to the 24 volt side of the SSR, turning on and off as commanded by the Duet output.
Light bulb test coming up! This is really getting old, many thanks to all for the input & suggestions!
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@Electriceye looking at your picture the input wires on the SSR from the duet are reversed you may want to try reversing the polarity,
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WINNER WINNER!
Fried Chicken dinner!
You sir..are correct!
The clue I should have guessed was that the LED on the SSR was not illuminating...LEDs are polarity sensitive!The image I was going by (duet3_mini5+_v0.5-v1.02_d1.5_wiring.png) was upside down as viewed on the screen, as opposed to the direction I have it mounted. GREAT CATCH!
Board now heats up (quickly I might add) and the LED on the SSR is aglow!
jumpedwithbothfeet wins the internets today!
Thanks to ALL who had tips, suggestions and input. You people ROCK!
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