QU-BD heating pad setup

In order of your questions:

DC-to-DC SSR rated for at least 20-30amps and of the 12V variety. with the switch side connected to the sang and the outputs across the positive of the power supply to the bed.

Dell Powersupplies as referenced on board already, or Meanwell power supplies like lawsy has if you want glossy product.

It will trip the power supplies over-current protection.

You will need to change the thermistor in firmware if you want to avoid problems - its a single number in a file, and uploading it. its not overly complicated and far safer.

Since I work for a computer company and I have access to computer equipment, I went with the server power supply option.  I found a few power supplies laying around, including a 750W Delta DPS-750EB and a 850W Astec DS850-3.

I liked the Astec a lot, as it's physically smaller, but I didn't like that the fans are running all the time the AC cord is plugged in.  Even though the power switch is off, and the PS is not outputting any power, the fans are still running, and they're not exactly quiet (it's a server after all)

So I decided to go with the Delta.  Its fans only come on when the power is turned on, so once you turn it off, it's quiet.

Anyway, I will post a few pics as I go along with this rebuild.

It will 'work'... it will even report a tempreature, and you'll be able to type 95°C and it'll 'report' 95°C...

Its just that the heated pad will be MUCH higher than 95... Because you have placed the thermistor so far away and on the otherside of a metal plate.... there will be anywhere up to 20°C difference between the top side of the QU-BD and the bottom side of the aluminium plate.

Seriously - you are cutting a corner that will end in a huge troubleshooting headache... Not to mention it will cause you QU-BD to run much hotter, and harder, than it should.. and will introduce a massively wide PID cycle as the distance the tempreature has to travel from where its created to where its measured is so much larger than it should be and thus the on/off cycles will be increased in duration... longer to (apprently) heatup and longer to (apprently) cooldown... 

Its just like on the stock SD Extruder, why you have to 'add 30°C' to the reported tempreature to know what the Actual Meltzone tempreature is.  That 30°C Delta is from a realtively short distance of brass, that transmits heat quite nicely. Do you know what the delta is between the top side of your QU-BD and the bottom side of the aluminium plate and the *side* (the standard thermistor is side mounted not center mounted) of it ? Its going to probably be a lot more than 30°C and you're the only one who can work out what that temp delta is because you don't have the benefit of the research that gave you that 30°C figure in the first place You're essentially suggesting that its 'ok' to set the Tempreature on an Airconditioner to control a room to a precise tempreature by employing a thermostat down the corridor and in an entirely different room

So unless you want the center of your bed running at 120°C, the sides at 105°C and the 'reported' tempreature to be 90°C... (which it will duly report) then deal with the fact you have to make a tiny change in firmware that 100's of people have made already to "great success" (to quote Bruno...). Or accept that you are cutting a serious corner that you really haven't examined the ramifications of and feel free to disregard the advice offered and go along your merry way  

But I just can't get my head around doing all this effort to skimp on one line in firmware... that will give you nothing but negatives in return ?

Are you thinking I'm putting the bed on top of the aluminum plate and the thermistor at the bottom? 

I'm not, I have it setup the same way as the original pad, at the bottom, with the thermistor sandwitched between the pad and the bottom of the plate

Not on my machine.  The thermistor was mounted dead center in the bed.  There's even a drilled n indentation at the bottom for the thermistor head to sit flush with the surface, it's just that they didn't route a groove for the wires, but they're fairly thin.

Wow...I can see you feel quite strongly about this.  I never said I won't do the firmware change, only that I wanted to try this setup .  I don't think I'm cutting any corners, it's just a different approach.  If I find the readings to be erroneous (after I check them with a heat gun), then I'll do the change.

I have no problems with firmware changes, but man, cut me some slack, I'm not and idiot with a soldering gun....

Today I borrowed the heat gun from work and ran a few tests. 

The following readings and findings seem to go against the conventional wisdom as it pertains to the installation of the thermistor, at least for a QU-BD heater pad.

I heated the pad to 70°C, and read the temps in a few different place, including the bottom of the pad, and top of the print bed. 

Take a look at the following 2 images.  The one with the high reading is taken at the spot where the QU-BD thermistor is, the other is in the center of the pad, where I placed the original thermistor.  Notice the difference between these reading which were taken a couple of seconds apart.  I also flipped the bed and took a reading on top, but forgot to snap a picture of it, the top read about 67.5°C.

The QU-BD thermistor is built into the pad near the place where the wires are soldered to the coils.  For this reason, the readings are much higher than the rest of the pad.  Not only that, but the temps build up a lot faster in that area compared to the rest of the pad, giving the false impression that the pad heats up super fast, when in fact it takes a lot longer for the entire pad to heat up evenly.

So, at least for my setup (and I think this would probably apply to anyone upgrading the original heater to a QU-BD model), reusing the original thermistor instead of the one built-into the QU-BD heater, is in my opinion a more accurate solution (sorry, Adrian).

After the earlier tests, I heated the bed up to 95°C, and tested the temps across multiple points across the print bed, to check for evenness.

First of all, while the thermistor reading got up to 95°C in a little over 3 minutes, the top of the printbed never actually reached those temps, it actually topped out at about 91°C in about 6-7 minutes.  Additionally, while the readings around the center of the bed were around 90-91°C, the edges (about 1" in) read between 86-88°C.  I also took a few readings of the bottom of the heater pad, and the average was 113°C.

I cranked up Repetier to 100°C, but the actual bed temps only went up to 90°C around the edges and 92-93 in the middle.

Since we are talking heatbeds I was wondering if anyone had some info on the nichrome from the stock pro beds. I'm mostly curious about the pattern and the ohms. I haven't felt like pulling mine apart to find out but i figured people who have done replacements might know.

The reason is I just found out that autodesk gives away free student copies so I've been modeling some parts from my sd2 to try and learn inventor (and also play with simulation CFD which I know nothing about, but seems pretty cool). I added some files to the wiki for the extruder and the heatbeds even though I know no one uses the glitchy wiki.

Hey Pirvan - looks good.

I've been away for the weekend, so just catching up. Will post details for you re my setup later on.