Welcome! Log In Create A New Profile


Resistance on the Heated Bed Heater Wires

Posted by Garry Bartsch 
Resistance on the Heated Bed Heater Wires
October 27, 2013 08:53PM
It's the most clueless guy on this forum with another question. Since I've never used a multi-meter and knew nothing about electricity before starting this project I hope I'm doing my measurement properly. Red goes to Ω and black to COM on the machine. I set the dial to 200Ω. I measure the ends of the large red and black wires to the heated pad by pressing them against a piece of glass with the probes.

I get 2.2Ω. This is almost double the ~1.2Ω mentioned in the manual. Is this way too high? I think the higher resistance is because of a dodgy connection between the twelve ribbon cables and the red wire. We ended up with a twisted joint that had some empty spaces between the wires (because they were 'kinky' after taking them apart after the first attempt to twist them together) and as a result we applied more solder to this joint to make it solid. We applied sufficient heat so there is no problem with the joint being cold.

Any slaps for me confused smiley? I'd sure do better building a second machine after making so many mistakes the first time around.

(P.S. This is how the arrangement turned out with the wires pointing out.)

I measure 2.1Ω directly on the pads on the heated bed. So 0.1Ω difference between that and the 2.2Ω measured on the end of the wires. Maybe all is OK?

With the multi-meter dial set on 200KΩ the thermistor measures 92.8. Is this 92,000Ω and thus acceptable?

Edited 1 time(s). Last edit at 10/27/2013 10:53PM by Garry Bartsch.
open | download - arrangement.jpg (398.5 KB)
open | download - joint.jpg (294 KB)
Re: Resistance on the Heated Bed Heater Wires
October 28, 2013 05:39AM
You need to subtract the resistance of the meter leads when measuring small resistances. Short them together and subtract the reading you get. My meter leads are only 0.2R but perhaps yours are more.

If you get 92K from the thermistor it implies your room is hotter than 25C is that the case? Another possibility is if you held both connections with your fingers skin resistance can lower the reading.

Re: Resistance on the Heated Bed Heater Wires
October 28, 2013 08:08PM
Aha! Thank you Chris. The shorted probes were the trick. smileys with beer

The meter read 1.6Ω when the probes were shorted. Then 2.8Ω for the heater wires for an actual value of 1.2Ω for the heated bed. Yippee!

Today with a room temperature of 25.5C the heated bed thermistor read 937,000Ω.

The extruder heater was 6.8Ω at the extruder motor PCB for an adjusted 5.2Ω.

I hope the last two are OK.
Re: Resistance on the Heated Bed Heater Wires
October 28, 2013 08:40PM
Yes I think those are all good. Very thin meter leads and a warm room!

Re: Resistance on the Heated Bed Heater Wires
October 28, 2013 10:19PM
Sweet! Thank you Chris. Two computers, two monitors and other devices make this room warm always. I think this multi-meter is not the best. It was cheap on ebay ... LOL.

Onward! Getting near the end of the build.
Sorry, only registered users may post in this forum.

Click here to login