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Heated bed not reaching temp

Posted by Jerms.a320 
Heated bed not reaching temp
April 16, 2014 10:31PM
Hi guys, so my heated bed won't reach 110 for ABS, I can get it to around 80 degrees Celsius but the plastic wont stick well,

The voltage coming into my RAMPS board is 12.11V (with the heated bed on) (I have loads on both the 3.3V and 5V rail), but the voltage across the heated bed wires is only 11.21V .... I am using very heavy gauge wire for the heated bed -- its was leftover from some solar panels we had installed , before I measure the voltage I though it could be my poor soldering , I tried to take the wires off and resolder them but they are near impossible to take off - they are not too bad

any ideas about why the voltage is lower -the hot end isn't on at the moment-.... and the hot end reaches 230 perfectly within a few minutes

is there any settings that need to be changed in the firmware, I am using sprinter



Edited 1 time(s). Last edit at 04/16/2014 10:32PM by Jerms.a320.
Re: Heated bed not reaching temp
April 16, 2014 11:24PM
you can switch to bang bang method and turn off pid for heated bed, also double wire make 2 wires for gnd and 2 for pos connection on heated bed.

also insulate the bottom of the bed. have the top of bed with sheet of glass.
Re: Heated bed not reaching temp
April 16, 2014 11:30PM
Hi James,

where is this Bang Bang method in the firmware ? the wire I am using is really thick, I couldn't fit two of the wires in the headers for D8 (im not sure it is D8, but the heated bed port on the RAMPS board)

Ive insulated the bottom of the bed and have some glass on top

thanks heaps
Re: Heated bed not reaching temp
April 17, 2014 12:16AM
So I commented out the #definePIDTEMP 1 , then uploaded the firmware then attempeted to heat the bed up to 110, the voltage is at 11.20V and temp only 80 degrees sad smiley

the resistance of my bed is 2.1Ohms , so as V=IR does that mean I=11.20/2.1 = only 5.33A ? the heated bed needs more like 12A doesn't it ?


Edited 1 time(s). Last edit at 04/17/2014 12:49AM by Jerms.a320.
Re: Heated bed not reaching temp
April 17, 2014 01:47AM
Is your whole bed getting hot? 2.1ohms is about twice what the normal heatbed would measure -- see [reprap.org] . Maybe one of the copper traces is broken?
Re: Heated bed not reaching temp
April 17, 2014 02:32AM
The whole bed gets hot, it seems fairly even,

looking around I cant see any damage to the traces (they are just the lines right ?) .... my soldering is not great, but how much would that increase the resistance by ? I am using a ribbon cable that is then attached to some thicker wire -- but that wouldn't have any effect on the resistance of the bed

any more help would be great --- I was so close to printing the other night - I had a good first layer partially down but then the hotend picked it off the bed as it moved past sad smiley

open | download - Bed.jpg (587.2 KB)
Re: Heated bed not reaching temp
April 17, 2014 02:46AM
You have a 12/24V MK2B board

If you look on the board you will find a little table

for 12v operation you need

pin 1 +12v
pin 2 gnd
pin 3 gnd

you have nothing on pin 3 from your picture.. you need that for 12v operation or the resistance is to high....

Edited 1 time(s). Last edit at 04/17/2014 02:46AM by Dust.
Re: Heated bed not reaching temp
April 17, 2014 03:23AM
You're brilliant Dust !!

I thought you could just pick ahahaha

..... I will have to replace the ribbon cable and then for ground I will just halve the wires , 7 wires each

I tried to desolder the wires (my method was flawed, I had not suction gun or wick) is there any easy way to take them off - or should I wait to buy some wick ?

thanks so much smiling smiley

Re: Heated bed not reaching temp
April 17, 2014 04:16AM
Just jumper the grounds from pin 2 to pin 3 and don't desolder.
Re: Heated bed not reaching temp
April 17, 2014 04:25AM
Btw - if you are having problems de-soldering that (mess :-) ) - you are using too small a soldering iron. You need around a 40 Watt iron for that job. A 40W will have the wires off in a second. No need to remove the solder.

I struggled for years with just a 12w small iron. The day I bought a 40W for larger jobs I realised I'd suffered for years for no reason! I use both the 12w and 40w a lot. I have an 80W that destroys anything it goes near unless it's huge.

Oh, and about 4 or 5 of those wires on each side is easily enough.

Edited 3 time(s). Last edit at 04/17/2014 04:28AM by Dodgey99.
Re: Heated bed not reaching temp
April 17, 2014 12:25PM
Thanks heaps guys !!!

Got it printing , finally, tonight ... bed reaches 110 in 20min, mind you the voltage was only 10.9 ish V

I had a few sticking issues, but it seemed that spraying hairspray on the bed then cleaning it off seemed to work ---- ahahaha - I keep doing that so long as it works smiling smiley

there was also some warping - but the bed fan turned on after the third layer so I think leaving the fan off will rectify that problem

Thanks so much ! Reprap forums are the best !

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