Bed not heating up

I have a RAMPS 1.4 board coupled to a Taruino classic with marlin configured and uploaded.

I can read the temperature from the bed thermistor and if I warm that up with a lighter the temp increases however commanding the bed to heat up does nothing.

I have 12v going in to each power connector on the RAMPS board if I measure the voltage between each bed lead and ground I get 11v at each which doesn't seem right?

Thanks

Ben

I think it's probably that the atx power supply I have is not up to it

I connected the bed thermistor to the position for extruder 1 and then hooked up a heater cartridge to D10 and tried to set the hotend temp which caused the psu to turn off.

I grabbed a 12v 4a psu hooked up to just the right hand power input on the ramps board and the cartridge heated up as expected.

Will have to get a better psu and try again.

Ben

Quote
plexer
I have a RAMPS 1.4 board coupled to a Taruino classic with marlin configured and uploaded.

I can read the temperature from the bed thermistor and if I warm that up with a lighter the temp increases however commanding the bed to heat up does nothing.

I have 12v going in to each power connector on the RAMPS board if I measure the voltage between each bed lead and ground I get 11v at each which doesn't seem right?

Thanks

Ben

That is the correct reading when the bed is not switched on. When it is on, the negative pin will go to ground (0v).

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Waitaki 3D Printer

Make sure whatever PSU you get can deliver ~20Amps at 12V. You could probably get by with less amperage, but it's good to have a buffer.

Quote
plexer
I have 12v going in to each power connector on the RAMPS board if I measure the voltage between each bed lead and ground I get 11v at each which doesn't seem right?

The D8, D9, and D10 screw termals all always supply 12v to whatever they are powered. The negative lead that would normally be connected to ground passes through a MOSFET which acts as the switch. When the microcontroller pulls the particular pin high, it allows the current to flow through the mosfet to ground, completing the circhut. By pulsing it on quickly, it can control the temperature or fan speed.

If the MOSFET overheated, a common occurance with the standard one they use for the bed, then it may have destroyed it not allowing it to switch to ground. Did you have a fan blowing on the MOSFET and/or a heat sink attached?

If you hook up the bed directly to one of the two grounds connected to the ramps board, does your bed heat up then? Obviously don't leave it connected this way, but that will tell you if your bed is wired correctly and functioning, buy eliminating the MOSFET from the equation.

"bed thermistor and if I warm that up with a lighter"

so you applied 2000C to a device that is rated for 300C?

I would be amazed if this thermistor is still ok.

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Dust
so you applied 2000C to a device that is rated for 300C?

I would be amazed if this thermistor is still ok.

A butane TORCH might reach 1500C. A bic style lighter is probably closer to half of that, and that's at it's hotest point. It's not advisable to hold a thermistor under a flame, but quickly passing it through a flame a few times to raise it isn't going to damage it.

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Dust
"bed thermistor and if I warm that up with a lighter"

so you applied 2000C to a device that is rated for 300C?

I would be amazed if this thermistor is still ok.

No I allowed the heat from the flame to radiate and warm up the thermistor.

Ben