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Hotbed not working!?

Posted by flemish4

flemish4

Hotbed not working!?
October 10, 2012 05:17PM

Registered: 11 years ago
Posts: 8

Hey all!

I have RAMPS1.4 with a PCB Hotbed v2

I've measured its resistance at 0.002ohms and its voltage at 0.3volts meaning it should have 150 amps through it?!

does this sound right? also it will only head to 30degrees!

HELP sad smiley

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Polygonhell

Re: Hotbed not working!?
October 10, 2012 10:51PM

Registered: 12 years ago
Posts: 939

Resistance should be in the 1.2-1.5ohm range and the voltage should be whatever your supply voltage is probably 12V.
Resistance that low implies you have a short, or you're measuring it wrong.

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lol

Re: Hotbed not working!?
October 11, 2012 05:56PM

I've never seen resitance that low in my life, I work with a multimeter every day... meter leads are more than .002 ohms..

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flemish4

Re: Hotbed not working!?
October 12, 2012 01:05PM

Registered: 11 years ago
Posts: 8

CORRECTION! I misread my multimeter the resistance is close to that which it should be! So what could be causing the low voltage?

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flemish4

Re: Hotbed not working!?
October 12, 2012 03:35PM

Registered: 11 years ago
Posts: 8

Okay more info! The resistance is correct and the voltage is too until the bed hits 30 or 40 degrees, then it suddenly drops to 0.some volts!? Also the yellow capacitors(?) get really hot is this normal? Thanks

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Polygonhell

Re: Hotbed not working!?
October 12, 2012 10:43PM

Registered: 12 years ago
Posts: 939

The yellow "capacitors" are resettable fuses.
The odds are the resistance of the heated bed is marginal (on the low side) what did it measure?
If it's inside the normal range you can try a small fan blowing over the fuses, I have a 80mm fan blowing over mine.

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flemish4

Re: Hotbed not working!?
October 13, 2012 07:56AM

Registered: 11 years ago
Posts: 8

It's hard to tell my multimeter only seems to go down to 1 ohm -.- so it flicks between 1 and 2. Will cooling the fuses help the bed then?

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flemish4

Re: Hotbed not working!?
October 13, 2012 08:40AM

Registered: 11 years ago
Posts: 8

FIXED! A fan over the ramps board seems to have stopped it cutting out smiling smiley