Help with heat reading problem with custom heated bed

[hampzter 1]

Hey.

I bought this kit from eBay:

http://www.ebay.com/itm/Heated-Bed-Kit-for-Ultimaker-Reprap-3d-Printers-MK2-PCB-Aluminium-plate-/161157442118?ssPageName=ADME:L:OU:GB:3160

(There is a "primitive" wiring description on the bottom of the page. And yes, I know it uses a relay instead of MosFET. Will change that later! :wink: )

Now to my problem. Whenever my Ultimaker needs more heat on the bed and starts it, the temperature on the nozzle plunges about 6 degrees.

This is REALLY annoying and I can't really figure out where the power thief is that is.

Is there anyone out there that has any idéas?

Regards,

</Jonas>

 

[tommyph1208 55]

Did you solder in a resistor on your board as described here, as well as in the bottom of the ebay listing:

http://wiki.ultimaker.com/Heated_Bed

What do you use to power the bed?

 

[hampzter 1]

Yes. I have solder the 4.7kOhm resistor there. I tried measure it (though while solderd) and got 4.7kOhm through it also, so I think that part should be ok.

I power it with a switched power supply (this one: http://www.aliexpress.com/item/250W-24V-Small-Volume-Single-Output-Switching-power-supply-for-LED-Strip-light/628583985.html ). Though I had to take it down to 20v instead of 24v or otherwise it hit the limit of 10A.

 

[hampzter 1]

Now I have tried building a mosfet-controller for the on/off of the bed and I still get a big dip in the heat reading when the bed activates and a big jump up when the bed stops loading.

Is there anyone that has an idea on what I can do to make this not happen?

Or any idea of where I should search for the error in temperature reading..