Slow heating up on MK3 dual power heat bed

Quote
aFrazatto
What bother me as hell and no one seams to have a good explanation, is why temperature drops to 75º every time the printing fan turns on.

Have you checked that there is no short between pins D8 and D9, i.e. the gates of the bed and fan mosfets? (These are the pins from the Mega just outside the "2A" and "2B" labels of the E0 motor connector.

Also make sure that the metallic top of the bed mosfet does not touch the top of the fan mosfet.

Quote
aFrazatto

Quote
dc42
Does the indicated temperature drop immediately the fan turns on, rather than over a period of a minute or more? If so, then that suggests a noise, grounding, or firmware issue.

It's not immediate, since the heat must dissipate, but it is quite fast.
I found another person with the exact same problem, if it was firmware, it would be more common.
I believe it's something with the generic/cheap chinese RAMPS I bought.

In that case I think my diagnosis was correct: the heater power in the configuration you are using is insufficient once the fan has turned on. RAMPS is IMO an outdated solution with several design flaws - especially when you buy cheap Chinese RAMPS clones (as almost everyone does). But I have also seen several reports of under-powered PCB bed heaters. Perhaps they were made with thinner copper than the original design called for.

If you have a multimeter, try measuring the voltage across the bed heater when it is running at full power, and compare it to the voltage going into the RAMPS. If the difference is more than about 0.2V, measure the voltage drop across the heated bed mosfet on the RAMPS and the voltage drop across the 11A polyfuse, to see where the voltage is being lost.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Well, i have the same problem...my alu heated bed os not heating as it shlould, initially it just reached to 65 celcius, just read that thin wires heat up so its resistance rises too, so now im using an old lamp wire that used to work at 220 volts, im still testing it but i just reached 80 celcius in 20 min...also i read that for alu heated beds its recomendable to use 15 volts , but since im using a ramps 1.4 i dont know how to acomplish that...

Hi there,

I am working with a prusa i3 right now and I am facing the same issue: my bed takes too long to heat up. I haven't tried all the solutions presented above, except checking the voltage which is ok.

My question is: would PID alone get the problem solved? I really would like to avoid changing the wires and other devices unnecessarily.

PID only kicks in, when the temp is close to the setpoint.

The easiest thing you can do is to put some insulating stuff on the bed, like cork or MDF / Cardboard. Even old newspaper works.
Don't worry, they won't catch fire.

Edited 1 time(s). Last edit at 04/27/2017 01:53AM by o_lampe.

Hello, I just bought myself an chinese MK3 aluminium heated bed .
I want to use this on my Printrboard .
Yesterday I run a first test with it, I connected it as the hotend, also the thermistor as the hotend thermistor, and tried to heat it up to 40 deg C from the hotend manual comand .
It went to 40 deg C pretty fast, I didn't try it at 60 deg C as it was quite late and feared not to have some short as my PSU is only the original 8 A from Printrboard .

I measured the resistance at 12 V and it is a wapping 2.5 Ohms ... so double what it should ...

I have a new 30 A 12 V PSU so no problem with that I think.

Ok now I want to configure the firmware for the Printrboard, but I see there is suggested PID parameters for the MK3 .
Do you have any suggestions ?

Another problem is that the connectoars for the heated bed on the Printrboard are really weak, so I would like to limit the current to maybe 5 A .

So I will use this line #define MAX_BED_POWER 200 // limits duty cycle to bed; 255=full current

M303 E-1 C8 S90 will this work on the Marlin for the MK3 heated bed ?