1 Topic by aonomus

  • aonomus
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Topic: PCB Mk2a Heatbed Upgrade Advice?

So I have a SD3, and I recently tried using ceramic tile on the buildplatform.
- The good news is that centre to edge deltaT is ~1degC.
- The bad news is that the thermocouple distance from the tile means that I can't get the bed temperature much higher than 60degC when the thermistor reads 100degC

So I have a PCB mk2a heat bed, that I'd like to use, but I don't know whether the mosfet will handle it (unheatsinked).
- 12V input, resistance is ~1ohm on the heatbed, so 12A current.
- MOSFET is IRLB8473 on the printrboard variant of the SD3; Rds(on) = 3.2mohm, Pdiss(calc) = 4.6W
- degC/W for junction to ambient is 62degC/W, which makes it seem like I would absolutely need heatsinking?

The heatbed has some kind of duty cycle or PWM to control the temperature, so its not ALWAYS putting out 4.6W, this is where I can't figure out whether I need heatsinking or not. Any advice?

As for mounting the PCB heatbed, I was planning on maybe making fiberglass standoffs out of scrap PCB to raise the heatbed up just enough to let me slip the thermistor wires under the bed and to the centre hole. Hold it all together with binder clips. Thoughts?

2 Reply by Tomek

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Re: PCB Mk2a Heatbed Upgrade Advice?

Getting your thermistor closer to the hot bed won't change your effective temperature you can get the bed to, with a limited heating source..

If you upgrade the bed heater, make sure you have a powersupply that can handle it.

I reckon the bigger issue with the mosfet is that you'll want to beef up the source to sink traces on the sanguinololu

3 Reply by adrian (edited by adrian 2013-08-16 09:51:16)

  • adrian
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Re: PCB Mk2a Heatbed Upgrade Advice?

Yes you need heatsinking.. and I haven't examined the PCB tracks on the new boards, but you may want to add some low-gaugeish wires on the heater mosfet.

Re the thermistor - I just poked it through the hole in the middle and drilled a small depression in the back of the tile and then used binder clips to hold the whole thing to the existing alu build plate... works fine..

Tomek wrote:

I reckon the bigger issue with the mosfet is that you'll want to beef up the source to sink traces on the sanguinololu

His got the printrboard clone version... but it would still pay to upgrade unless you've looked at the traces and confirmed they are indeed 'high power' as claimed in the propaganda... I mean marketing wink

4 Reply by aonomus

  • aonomus
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Re: PCB Mk2a Heatbed Upgrade Advice?

Alternatively I can just use an exteranal PID controller meant for 12VDC, and put it on a big 700W power supply.

This all got started because I put in the jigsaw filament feeder upgrade and found that I'd have to move the Z home screw all the way up, and even then it wouldn't make it to the bed. Might as well add all the stuff in between to get the upgrade done then!

And as a final note it seems like I miscalculated and forgot a zero. 0.0032ohm x 12A^2 = 0.07688W ==> 4.76 degC raise in temp from ambient.

5 Reply by RavensCrest

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Re: PCB Mk2a Heatbed Upgrade Advice?

Hello,
is it too late to suggest my build to you? http://www.soliforum.com/topic/2544/my- … eated-bed/

Solidoodle2 with Ceramic tile heated bed http://www.soliforum.com/topic/2544/my- … eated-bed/
"1kg should last for an while" is a lie!

6 Reply by Damon550 (edited by Damon550 2013-08-19 09:35:56)

  • Damon550
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Re: PCB Mk2a Heatbed Upgrade Advice?

im struggling with my heat bed getting it up to temp.

is there any way to give the stock heat bed some more herbs?

i have heard that when you use a relay for say the QU-BD beds the relay goes off its head.

could i get better results by changing the gcode or just direct connection to 12v?

i it takes about 30 to 45 min to get to 80C but 3 hours to get to 90C

would a bigger power supply help any?

i have a SD3 with the alu carriage and glass

7 Reply by aonomus

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Re: PCB Mk2a Heatbed Upgrade Advice?

So as an update to this thread:
I set up the PCB heatbed by just placing it ontop of the kapton/aluminum heatbed (traces up) and placed a ceramic tile ontop. I broke my thermistor when I tried to run thin enameled wire under the PCB heatbed, but I still wanted to test. Using the original thermistor on the stock aluminum heatbed I found the temperature between the PCB heatbed traces and the stock thermistor were small, but the tile temperature was much slower to rise and even after 30 minutes it wouldn't come up to temperature. The greater thermal mass plus the heatbed levelling off much sooner than the tile means the PID thinks its at temperature when it really isn't.

I'll have to try installing a thermistor in the tile again soon, but for now I think that with an enclosure this could actually work. If the tile isn't dropping heat from 100degC to 20degC ambient, and only going to 60degC air temperature in the chamber, then the tile will probably reach temperature sooner.