Hotter heated bed possible?

Hello,

I have the Mk2 PCB for my heated bed but It's difficult for it to get hotter than 95 degrees. I has to put my printer into a box so it could go to 103.

Has someone made an AC bed or something like that?

Thank you

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Ernesto Pareja

dcctrains.netne.net

Try insulating with corrugated cardboard, or foam board underneath, and glass on top. Both cardboard and glass are poor conductors, but glass is better, so it will draw most of the heat from the board, and prevent it from radiating downward. Keep the solid copper facing up.

Make sure the thermistor is mounted directly against the bottom PCB surface with at least three strips of kapton. Don't put it in the hole if your board has one of those. It does not have to be right in the center, but close to the center is probably better than too close to the edges.

Also check the resistance value of the board. If the value is too high (3,4,5,6+Ohms), it will not get very warm with a 12VDC supply. Not sure what the exact value should be, but it's near 1 or 2 Ohms. Should be drawing about 6-7 amps when fully heated.

I would ensure that your thermistor is coupled really well to the heated bed that you are using. The PCB beds that we tested were all able to get to high enough temperatures for ABS printing without an issue. Another issue may be that your power supply can't get enough amperage to the PCB.



***Blatant Self Promotion***

We have silicone rubber heaters that can get quite a bit hotter and can get to temperature a lot faster than normal. The only downside is they draw a lot of power so you need a fairly strong power supply (400w+) or a dedicated 12v supply. They have been tested hooked up directly to Azteeg and RAMPS electronics with no ill effects. A 100k thermistor is embedded in them for temperature monitoring.

8"x8" (15amps @12v)
[store.qu-bd.com]
12"x12" (20amps @ 12v)
[store.qu-bd.com]

Chelsea - QU-BD

Chelsea - QU-BD Wrote:
-------------------------------------------------------
> They have been tested hooked up directly to Azteeg
> and RAMPS electronics with no ill effects. A 100k
> thermistor is embedded in them for temperature
> monitoring.
>
> 8"x8" (15amps @12v)
> [store.qu-bd.com]
> 12"x12" (20amps @ 12v)
> [store.qu-bd.com]

20 amps will kill a RAMPS board if run directly. The connectors are not meant for it, and the fuse is only rated at ~12 amps. I've tried it. If you want to run that much power to a heated bed, why not use AC current? That's what I do. I use a SSR to control it, which works fantastically. You also don't need nearly as heavy gauge wire, since the amperage will be far lower. And you don't need a super beefy power supply. The only disadvantage is that you can't PWM control it - at least not at high frequency. That doesn't really matter though considering the thermal mass of the bed.

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Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

We do recommend a dedicated power supply with both of the silicone rubber heaters, however we have 2 RAMPS 1.4 boards (from Ultimachine) that are powering it without any problems. The Azteeg X1 and X3 electronic's MOSFETS are heavier duty than the spec RAMPS and work well with the silicone rubber heaters.

-Chelsea

Why did you increase the wattage? For example if the 8x8 took 10A, (as the original Prusa does) bed it would work with all electronics and it would get a lot hotter and heat faster than the PCB bed because its resistance does not increase as it gets hotter. The current drops to 7A at 110C on the PCB bed and that limits the temperature.

12x12 @ 20A makes sense as it is proportional to area, so that is a bit low compared to the original.

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[www.hydraraptor.blogspot.com]

K, I'm a little conserned now, as I have an 8x8 mat on the way...
I was under the impression that I could plug it into the RAMPS 1.4 without issue?

I guess I should not do this?
I'm not sure how to wire it then?

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--------------------------------------------------------
Custom all metal CoreXY
- Duet 2 Wifi w/ PanelDue 7i
- 330mm x 360mm x 500mm
- 750w Silicon heater

Custom Mendel90
(Backup printer - Old reliable!) - Sold

15 and 20amp is to much fore the ramps so i think we need make it separated of the ramps Bord.
pin7 pwm is not used on the ramps i think.
like this id.
[reprap.org]

Edited 2 time(s). Last edit at 08/31/2012 01:43PM by michel pet.

Thanks to all.

I isolated the printer in a cardboard box and now I can get the bed to 110 degrees.
I think I will give the silicone rubber heat bed a try. The overhead time to get the bet to temperature is very high with my MK2 PCB (around 25 minutes).

Anyone has used the silicon rubber bed?

Thank you

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Ernesto Pareja

dcctrains.netne.net

You should check your PSU isn't dropping voltage when the heated bed turns on.
My uninsulated MK2 hits 110 about as fast as my Hotend hits 230.

Also I assume you are using a thermometer to read the temperature and not going off the thermistor reading?
My thermistor is about 25 degrees off at 110, and it purely because of placement.

Edited 1 time(s). Last edit at 09/01/2012 12:32PM by Polygonhell.

The thickness of your wires can make a difference too. If you're using cables that are too thin some power is wasted in your cables instead of going to the heated bed. (hint: if your heated bed cables are hot chances are they are too thin).

this is the schema .
a have made a test print and it works fine.
a have set the pin from the head bed to pin 5 this is a servo pin and ik works .

Wat kind of tape wood be the best fore the head bed.
i want to stick it under a alu bed

I am using kapton tape on top an Alu bed. It works pretty well.

i need to tape it under here.

oops, you stated under the bed, I missed that.

What about a piece of cardboard below the heated bed to provide some thermal isolation?

Hello all!
(I posted this on the QU BD Forum, but there is more traffic here)

I have the 8x8 silicon heater pad.
My original plan was to plug it directly into my Ramps 1.4 board, but having the heat pad pull upwards of 15 amps,
I don't want to take the chance of killing the board. Now I'm thinking about using a SevenSwitch.

I have a Master craft MultiMeter(Canadian Tire) and I tried an Amp test on the pad...
it only pulled a max of 7amps. Not mind you, the leads on the tester
just about got as hot as the bed!! So I'm sure that affected the test..! (I have new leads good for 20A on order...)

Another issue I'm having is finding the correct thermistor setting in the Marlin firmware to read the correct temps... (Configuration.h)
I've tried all the settings, and nothing scales with the temps; verified with an IR Thermometer.

Does anyone else have the pad plugged straight into thier Ramps board without issue?
and what thermister settings are you using?

Thanks!
Chris

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--------------------------------------------------------
Custom all metal CoreXY
- Duet 2 Wifi w/ PanelDue 7i
- 330mm x 360mm x 500mm
- 750w Silicon heater

Custom Mendel90
(Backup printer - Old reliable!) - Sold