Marlin Setting for Heatbed - 24V

Just see if anyone is in the same situation.

Using direct 24V to the heatbed, I give up to 100 in about 5 mins.

But using the 24V thru RAMPS1.4 it will take up to 15mins.


Is there anything I need to change in the firmware so that it draw more current?

I have try using the M303 auto tune but it always time out.

thanks
Daniel

How many amps does your 24V heat bed pull? The Ramps board may not be happy with your current.

More likely - There is a firmware setting for heat beds that limits the max current for low resistance heaters. You may have it turned on.

Using a 14 A 24V switching power supply.

Any idea on the firmware setting?

The Ramps board is only rated for 11 amps. If your bed pulls more than that, you will have an issue.

// If your bed has low resistance e.g. .6 ohm and throws the fuse you can duty cycle it to reduce the
// average current. The value should be an integer and the heat bed will be turned on for 1 interval of
// HEATER_BED_DUTY_CYCLE_DIVIDER intervals.
//#define HEATER_BED_DUTY_CYCLE_DIVIDER 4

Thanks.

I think because it is a switching power supply, the current depend on consumption. This is just my assumption

I believe this is the reason that direct attached is faster compare to via RAMP board.

But no complain for now. At least it is working.

Probably will try other method. Try the relay way but the clicking is killing

A properly designed power supply should put out a constant voltage right up to it's maximum current point. That's true weather it's a switcher or an analog regulated supply.

Check the wiring with a DVM and see where your voltage drops are. This is just DC electronics. There's no magic in it. If the supply is putting out 24 volts and there's 24 volts on the heater all the time, the results will be the same no matter which way the wires run. If you have a major voltage drop somewhere, then yes your will not heat up as fast.

Remember that the Ramps will only handle about 11 amps, so your setup needs to be under that limit. A one ohm heated bed (the official spec on them) would pull 24 amps at 24 volts. Of course an in spec heated bed will get to 110C in 7 minutes at 12 volts...