Heat Bed not heating

Not sure if this is the correct place to ask this question, but I'll ask anyways.

I'm building sort of 3D printer/CNC machine and I'm having problems with the heat bed. It is a 400x400 heat bed of 12V and dimensions 410x410x3mm (www.amazon.es/gp/product/B07DN8P2HG/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1)

I also putted a relay (www.aliexpress.com/item/32663806352.html?spm=a2g0s.9042311.0.0.60aa4c4d7yJgV2) for safty reasons. The thermistor indicates correctly room temperature and when I preheat the heat bed (using repetier) a led next to D8 turns on and the led in the relay also turns on.

I dont think the problem is the power supply (30A 3600W 3CH), so I don't know what can be the problem.

I also checked al the wiring and the soldering of the cables connected to the heat bed.

For the wiring I followed this diagram (not excactly, because my power supply has 3 channels, so the wiring was easier)

The solid state relay is for 24-380volt AC heated beds you have a 12v DC heated bed

Use an external mosfet eg [www.aliexpress.com]

You can get SSR that can switch DC, but they have to be designed for it... eg [www.aliexpress.com]

I would be interested to know the resistance of that bed, with it you can calculate the current it is going to use since I (current) = V (voltage) / R (resistance)

Edited 4 time(s). Last edit at 08/03/2019 08:59AM by Dust.

What a mistake (facepalm). Didn't see it was for 24V.

Thank you very much for the fast answer.

I'll buy the MKS then.

Today I received the MKS MOSFET. Still not heating up....

I checked voltage with the multimeter and when I preheat the bed, not voltage goes out to the heat bed (also the led doesn't turn on). It is a faulty MOSFET or I'm wiring something wrong?

I followed this scheme



Also the hotend is not heating up. I tried to preheat the hotend to calibrate it, and also not working. In both cases the thermistors are fine (I measured 115k Oms in both of them) and also I measured 12V in all the inputs and outputs of the RAMPS (also the leds of D10 and D8 turn on when I preheat).

I checked the heater cartridge wiring and seems also fine.... Can be de RAMPS damaged? 3 axis motors work fine.

The RAMPS has 2 power circuits, on the board they are marked as 5A and 11Amp power plugs

You need to supply 12v to both of these

The 11amp power plug supplies 12v to the d8 mosfet
The 5amp power plug supplies 12v to everything else (hotend, stepper motors, and the mega)



Re the hot end. If the D10 LED lights the ramps is probably fine.
Yes the electronics can die... the mosfets can be damaged by static electricity, but the fact the the LED turns on, indicates it is fine.

Edited 2 time(s). Last edit at 08/06/2019 11:55AM by Dust.

Quote
Dust
The RAMPS has 2 power circuits, on the board they are marked as 5A and 11Amp power plugs

You need to supply 12v to both of these

The 11amp power plug supplies 12v to the d8 mosfet
The 5amp power plug supplies 12v to everything else (hotend, stepper motors, and the mega)

2e436a102020cd87e55cb7a4aaf2b683_preview_featured.jpg

Re the hot end. If the D10 LED lights the ramps is probably fine.
Yes the electronics can die... the mosfets can be damaged by static electricity, but the fact the the LED turns on, indicates it is fine.

I have the RAMPS wired as in the image you attached and also checked if both power inputs were receiving 12V. Maybe the MKS MOSFET arrived already damaged and thats why the MKS light doesn't turn on when I try to heat the heat bed (pretty bad luck if that's the case).

And respect the hotend.... Do you recommend me to substitute the cartridge in case they sent me a 24V one instead of a 12V or is damaged?

Stop guessing.. measure things.

Check with a multi meter you are getting power

For the bed
plug the -ve probe into D8 - plug (you have to use this -ve pin as this is what is switched on and off)
plug the +ve probe into the D8 +plug

Set the meter to DC voltage, if it doesn't auto scale set it to a voltage higher than 12v

It should read 0 volts dc when off and 12v dc when on.

For the hotend
plug the -ve probe into D10 - plug (you have to use this -ve pin as this is what is switched on and off)
plug the +ve probe into the D10 +plug

Set the meter to DV voltage, if it doesn't auto scale set it to a voltage higher than 12v

It should read 0 volts dc when off and 12v dc when on.


Check your cartage resistance.
Unplug the cartage from the controller and measure the wires it should read about 3.6 ohms for a 12v 40watt cartage.

[reprap.org]

The screws on the terminals don't make it a mechanic problem. Do they ?

Dust, I admire your patience !
Luckily (or is it ?) the heating element is not in 220V

Edited 3 time(s). Last edit at 08/07/2019 02:36AM by MKSA.

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Also to eliminate the firmware as a cause use the RAMPS test code

[reprap.org]

This code need no modifications

It moves all steppers back and forward, repeating forever
It turns all mosfets on and off, repeating forever

NB it does not look at endstops and it does not check thermisters.
It will just keep heating forever.

Quote
Dust
Stop guessing.. measure things.

Check with a multi meter you are getting power

For the bed
plug the -ve probe into D8 - plug (you have to use this -ve pin as this is what is switched on and off)
plug the +ve probe into the D8 +plug

Set the meter to DC voltage, if it doesn't auto scale set it to a voltage higher than 12v

It should read 0 volts dc when off and 12v dc when on.

For the hotend
plug the -ve probe into D10 - plug (you have to use this -ve pin as this is what is switched on and off)
plug the +ve probe into the D10 +plug

Set the meter to DV voltage, if it doesn't auto scale set it to a voltage higher than 12v

It should read 0 volts dc when off and 12v dc when on.


Check your cartage resistance.
Unplug the cartage from the controller and measure the wires it should read about 3.6 ohms for a 12v 40watt cartage.

I already checked D10, D09, D08 outputs and 5A and 11A inputs before, but I re-checked today. When I turn on the power supply I receive in all of them 12V (checked in the screws) even if the hotend and the heat bed were not preheating. Anyways when I preheat them, the leds from D10 and D08 turns on.

I checked the cartridge cable. Continuity was fine, but in one of the cable there was an area with some melted plastic. I checked that conection and the cable was burned in that area. Fixed. Now it heats fine and with a reasonable speed.

I also checked the MKS voltage. From the power imput I receive 12V, as well form the conections that goes to D08. In the outputs that goes to the heat bed, unfortunatelly, I measured 1V and then lower values until it reached 0. Also, as I said, the led that indicates that is theorically working the MOSFET, is not turning on.

P.S: Sorry for being a pain in the ass.... I had some knowledge in this things, but it is the first time that I had this problems (my ANET A8 worked amazingly well for the cost, 3 years old, arround 500h printing and only had to change one fan and clean the extruder once). First time building by myself one 3D printer.

Maybe the heated bed is actually dead?

You can wire this directly to the power supply.. does it heat up then? (this will continue to heat up uncontrolled till you unplug it)

can you take a few photos oh how you have the bed to the external mosfet to the power supply connected? (have to check your wiring... as we are missing something)

Quote
Dust
Maybe the heated bed is actually dead?

You can wire this directly to the power supply.. does it heat up then? (this will continue to heat up uncontrolled till you unplug it)

can you take a few photos oh how you have the bed to the external mosfet to the power supply connected? (have to check your wiring... as we are missing something)

Wired directly to D08. It heated correctly.

The wires are fine, and I followed the instructions of the conections (polarity and port's name was very clear on the MKS MOSFET pvc board) and double checked if I wired correctly.

Decided to return it (that's why I don't attach a photo, it is already packaged) and buy a different MOSFET. It arrives this Friday, so I'll see if I can finally print.

Edited 1 time(s). Last edit at 08/07/2019 12:04PM by adrian_rg.