Re: [MendelMax] Heat bed shutting off.

[Sean Mitchell]

Does the heated bed actually shut off (lose temperature), or does it just reach its peak for temperature?

Is it still trying to heat (check the LED on the RAMPS that corresponds to your heater - does it stay on?)

How do you reset it so you can turn it on again?  

On Fri, Apr 5, 2013 at 8:28 PM, Gerhard Picou <gerhar...@gmail.com> wrote:

Hello my heat bed will turn on for awhile and then turn off and not turn back on.This happens usually around 70 degrees.I have checked the solder on the bed for cracks but there was nothing.The highest it got to was 80.

What could be wrong?

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Sean Mitchell

echo "zvgp...@tznvy.pbz" | tr '[a-m][n-z][A-M][N-Z]' '[n-z][a-m][N-Z][A-M]'

[Jordan Miller]

is your MOSFET overheating? what board are you using? prolly you want to switch to an AC relay with a silicone pad

jordan

[Larry Knopp]

Also check the large fuse on RAMPS (the big "cheez-it") for over-heating...

[Printer]

I had the exact same problem, I ended up just hitting the reset button the the side of the card. Haven't had any trouble since.

[Printer]

****WARNING****, I believe this will reset your stepper settings, best jot them down first and will have to plug them back in..

[Caanon]

If you ask it to hit 90 degrees but your heater isn't powerful enough to hit that mark and only can hit 70 or 80 after a while, it will time out and turn off (on Marlin firmware at least).

[Arnaldo Garcia]

Hello Gerhard, were you able to solve this issue?...I'm having the same problem...thanks.

[Sean Mitchell]

Hi Arnaldo,

Can you expand on your issue, for example does the heated bed actually shut off (lose temperature), or does it just reach its peak for temperature?

Is it still trying to heat (check the LED on the RAMPS that corresponds to your heater - does it stay on?)

How do you reset it so you can turn it on again?  

What electronics do you have, how many W is your bed and how many W is your power supply?

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[Arnaldo Garcia]

Thanks for reply.

- The heated bed turns off after it reaches between 60 and 70 degrees and the LED stays on.

- I have to wait about 10 minutes and I turn the heated bed on from the repetier and it stars heating againg until it turns off again.

- Im using a 24V RUMBA Board, the heated BED is 360W and the PSU is 15A 360W.

- I have tested by using two different RUMBA Board and I have the same issue.

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[Sean Mitchell]

It sounds like what Larry Knopp pointed out, the fuse on RUMBA is the same as RAMPS; the bed fuse is rated for 11 amps. 

You might want to consider driving that kind of load from a solid state relay - they're quite cheap and handle huge currents.  For example, this one will handle up to 40 amps (though leave a safety margin, see below).  You can get these in lots of places, the important things to look for is that it's DC-DC (most are DC-AC, so you can switch a wall plug / mains current from a low voltage, but in your case you want to switch DC voltage). Because the input voltage is 3-32v, you can either hook up directly to the pin on the microcontroller (5v = on) or hook up to the heated bed output (12v/24v = on) and it will work fine. I would prefer the microcontroller direct (less to go wrong, no need to switch the high voltage side on), but I'm not sure if the RUMBA has the pins easily accessible. 

You should always leave a safety margin when working with these currents - for example I have a 200W heater and have calculated around 100W for other things (hot end, motors, lights, etc).  My power supply is 600W, which gives me a 50% safety margin.  One could argue 50% is a bit much, but you should leave at least 20% - in your case I would use a 450-500W for the bed alone (if you're driving your hotend and other stuff, add more!).  

Also make sure your wires are big enough - 15 Amps requires at least 18 gauge wire, and don't forget a safety margin so I would be using 16 Gauge