PCB Heatbed

Has anyone wired in the Prusa MK2 Heatbed yet?

I bought mine brand new and I can't get it to turn on at all.

I am running Ramps v1.4 board (factory built), Sprinter and Pronterface.
When I try to set the heat it tells me the Bed temp is at 295.

I tried putting my fans as a load on the D8 connections to see if I could turn them on and off but the light does not come on for the heat bed and the fans don't start.

Any ideas?

Windcatcher

1) have you measured the bed's resistance?
2) after this step, and if the measured resistance is within 1.2 to 10 ohm, have you tried connecting the bed to a 12v power supply directly?

windcatcher Wrote:
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> When I try to set the heat it tells me the Bed
> temp is at 295.
That suggests it isn't turning on because it thinks it's already too hot. Check that you selected the correct type of thermistor in the firmware, and check for short/open circuits on the thermistor connections.

Thanks for the responses,

No, I have not measured the beds resistance but its a factory built board so I didn't think to try that. (I will now though)
Shouldn't the circuit turn off and on with any load attached?

As for the Thermistor, I got mine from Avnet and special ordered the Epcos 100k one and set my thermistor type to 6 in the config.h file.

EPCOS (TDK), B57560G 104F, NTC THERMISTOR G560 /100 K/F 1 %

// 6 is EPCOS 100k
// 7 is 100k Honeywell thermistor 135-104LAG-J01
#define THERMISTORHEATER 7
#define THERMISTORBED 6

I had the same problem with my extruder mosfet and it turned out to be in the Sprinter config.h and pins.h files which leads me to believe that this too is just a wrong setting somewhere.
Is there anywhere else I need to define it?

OK, I measured the board and I get 1.2 at the leads where I would connect it to the Ramps board.
Tried connecting it to a different 12v supply and it doesn't short out but the leds on the Heatbed don't light up either.

Any ideas why?

windcatcher Wrote:
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> I had the same problem with my extruder mosfet and
> it turned out to be in the Sprinter config.h and
> pins.h files which leads me to believe that this
> too is just a wrong setting somewhere.
If nothing (heaters or motors) was working correctly, check that the firmware's pin settings are for the right version of RAMPS: 1.3/1.4 have different pin assignments from earlier versions.

> Tried connecting it to a different 12v supply and
> it doesn't short out but the leds on the Heatbed
> don't light up either.
Was this directly connected to 12V (as opposed to via the RAMPS), and did it get hot?

Never assume brand new commercial stuff comes devoid of flaws.

Your heated bed should be pulling some 10 Amperes @12V, and when directly connected to a capable 12V power supply, should heat up. Does it?

Try inverting the + and - terminal cables: do the led light up?


Also, with the bed disconnected, please measure at the terminals the thermistor resistance at ambient temperature. You should have some 100 KOhm at room temperature, and decreasing with heating.

Thank you both,

I will try all of the above when I get home and let you know what happens.

Windcatcher

Ok, so I tested the PCB Heatbed on another power supply and it heats up right away but the led lights do not come on.
This is weird because I have one mounted each way like the wiring diagram says here; [reprap.org]
I guess they might be cooked so I will have to unsolder one and test it.
The important thing is that the bed heats up just fine.

So now that leads me to believe it is either my thermistor or the thermistor setting that is wrong.

//// Thermistor settings:
// 1 is 100k thermistor
// 2 is 200k thermistor
// 3 is mendel-parts thermistor
// 4 is 10k thermistor
// 5 is ParCan supplied 104GT-2 100K
// 6 is EPCOS 100k
// 7 is 100k Honeywell thermistor 135-104LAG-J01
#define THERMISTORHEATER 7
#define THERMISTORBED 6

I set it to six before because it was called EPCOS 100K like the part number I ordered from Avnet.

EPCOS 100K Thermistor (B57560G1104F)
Supplier: Mouser
Part Number: 871-B57560G1104F000

Upon closer inspection I noticed that the thermistors shipped to me are part number (B57560G 104F) not 1104 like Mouser PN.
I am going to call Avnet in the morning and make sure I have the same part as the Mouser one.

I'll let you all know how it goes.

Windcatcher

PCB Heatbed problem solved.

Problem 1 - The thermistor from Avnet needed to be set to 1 in config.h.
It now reads correctly and is very reliable.

Problem 2 - The led was burned out, don't know how that happened but I soldered on a new one and it lights up just fine now.

Problem 3 - And this was the big one, Not enough power in the computer power supply I used.

A word to the wise, buy a new 500 watt power supply and you will avoid a lot of problems.

I tried 3 used ones from various computers and although they supplied 12v they lacked the amperage required to run the extruder and the Prusa PCB Heatbed at the same time.

Hope this helps someone else.

Windcatcher

Many PC power supplies require a load on the 5V rail to give substantial current on the 12V rail. 12V/50W light bulbs connected to 5V are commonly used to get this load.

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