Mk3 Alu Bed High resistance

ixlix

Mk3 Alu Bed High resistance
November 02, 2015 07:25AM

Registered: 9 years ago
Posts: 49

Hi guys, ive got a mk3 aluminium heatbed that wont get past about 85c (covered) or 73c (uncovered). Ive just measured the resistance at the soldered connections at the base of the heat bed (im running it on 12v) and im getting 3.2ohms! Thats on the 200 setting of my multimeter. Now im not a electronics guru so am i way off here? When i touch the probes i get 0.05ohms which would be about normal for cheap probes right? Have a got a dud bed? Or am i measuring it incorrectly. Im running a old 22a atx powersupply but have a 33A 12v psu on its way.

Any advice would be greatly appreciated.

Alex

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J-Max

Re: Mk3 Alu Bed High resistance
November 02, 2015 08:50AM

Registered: 10 years ago
Posts: 722

Hi,

3.2 ohms is a bit high for 12v powering. It should be around 1.5 ohms.
Maybe you should ask your reseller for a proper one. I would.
Otherhand it should work better under 24v if you own that kind of PSU.

Maybe big cables may help it to get higher temperatures.
Make sure your PSU delivers enough amperage too.
A proper MK3 needs 8 amps for 96 watts consumption.
If I'm not wrong, with 3.2 ohms, you should need 18 volts and 5.6 amps to reach the same temperature.

++JM

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ixlix

Re: Mk3 Alu Bed High resistance
November 02, 2015 09:47PM

Registered: 9 years ago
Posts: 49

Thanks JM. Im using cables aroun 8-10 gauge, they only just fit into the terminal blocks of the ramps. Ive tried two psu's and i get the same result. Ive contacted the seller and he's asked for a photo of the wiring but said if it all seems fine then he'll replace it.

Heres hoping.

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WZ9V

Re: Mk3 Alu Bed High resistance
November 03, 2015 11:44AM

Registered: 11 years ago
Posts: 293

Bigger wires are not going to help this situation, the resistance is limiting your current at 12V to 3.75A or 45W.

The pictures I've seen for a Mk3 show multiple inputs with a grid printed on top for 12/24V, are you sure you are using the 12V input and not the 24V one?

The 12V input should have half the resistance of the 24V one which would double the current/wattage at 12V to about 90W assuming 1.6Ohms.

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ixlix

Re: Mk3 Alu Bed High resistance
November 03, 2015 05:06PM

Registered: 9 years ago
Posts: 49

You are actually correct WZ9V, although i had soldered the GND to both pad 2 and 3, upon closer inpection it had lifted enough to lose contact. I have resoldered it and the resistance is down to 1.8ohms, which may be a little high due to my cheap multimeter leads. The bed now heats up to 95c pretty quickly and stays there during a print. thumbs up

Pity i went and ordered a new psu! Oh well, it will fit better in my corexy machine's box.

Cheers for all the help!

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elwood127

Re: Mk3 Alu Bed High resistance
November 04, 2015 12:55AM

Registered: 10 years ago
Posts: 705

That is still high. Mine is 1.2 ohms and I wish it were 1.0.

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ixlix

Re: Mk3 Alu Bed High resistance
November 04, 2015 04:04AM

Registered: 9 years ago
Posts: 49

Well I'm measuring it with a cheap meter which reads .5ohms when you touch the probes, so its probably not quite 1.6.

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o_lampe

Re: Mk3 Alu Bed High resistance
November 04, 2015 04:22AM

Registered: 9 years ago
Posts: 5,232

You better read voltage and current ( if possible with your DVM ) and go from there.
-Olaf

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WZ9V

Re: Mk3 Alu Bed High resistance
November 04, 2015 05:09PM

Registered: 11 years ago
Posts: 293

Glad I could help. You can always use that "spare" power supply for the next printer.

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ixlix

Re: Mk3 Alu Bed High resistance
November 09, 2015 07:55PM

Registered: 9 years ago
Posts: 49

Ok just to follow up on this, with the new 33A psu, my bed hits 100c in a few minutes and never leaves it during a print. The mk3 alu is a great bed after all. thumbs up

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deaconfrost

Re: Mk3 Alu Bed High resistance
November 09, 2015 08:13PM

Registered: 9 years ago
Posts: 312

i was about to reply, and yes the mk3 is great, I dont even use a glass, straight on the bed, when I tried the glass theres a 5c different, lower ofcos, but it stay above 100c all the way no problem, mk2.5 i had before was struggling to get 90c let alone 115c, mk3 has reached 115c, thats the highest I've ever tried

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MechaBits

Re: Mk3 Alu Bed High resistance
November 10, 2015 06:40AM

Registered: 9 years ago
Posts: 1,671

So are you using one psu for arduino & bed or are you running two?
I have a 33a psu was thinking of getting the MK3 but might run at 12v for pla

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deaconfrost

Re: Mk3 Alu Bed High resistance
November 10, 2015 07:07AM

Registered: 9 years ago
Posts: 312

i'm running single 12v 30a psu

Edited 1 time(s). Last edit at 11/10/2015 07:07AM by deaconfrost.

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MechaBits

Re: Mk3 Alu Bed High resistance
November 10, 2015 07:51AM

Registered: 9 years ago
Posts: 1,671

Cool...can you confirm hole size & spacing they are listed as 5mm holes and cant remember spacing but remember it wasnt 209mm, slight redesign needed for it.

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deaconfrost

Re: Mk3 Alu Bed High resistance
November 10, 2015 08:08AM

Registered: 9 years ago
Posts: 312

I use 3mm screw on mine, fit well, dont think a 5mm screw can fit through it, i think it is 209mm cant remember exactly, can't measure it now its printing smiling smiley

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ixlix

Re: Mk3 Alu Bed High resistance
November 10, 2015 05:52PM

Registered: 9 years ago
Posts: 49

Yep running a single 33a psu for everything. I can measure the holes tonight.

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