RAMPS1.4 - Heatbed wont heat up to 100C

Hi,

I'm trying to figure out what when wrong here, I bought a aluminum heated bed from a local vendor here in my country but I can't seem to get it to heat up to 110c it just hover at 88c, some people suggested to change the mosfet which I did change it with this one

IRLB8743PBF [my.element14.com]

but it does not fix the problem, my setup currently using 12v 30A Led power supply and while heating I can confirm that the mosfet did not overheat it just stay around 35C-40C, the polyfuse are at normal tempeture too, would it safe to assume that the alunimum heatbed is the culprit here? I bought 2 of them the second one on my prusa i3 only manage to get to 98C max it can't go any higher than that, firmware already set to 255 the pid max setting

FYI I get 1.8ohm when I measured the resistant of the copper trace while my old mk2a pcb heated bed is 1.2ohm

Edited 1 time(s). Last edit at 02/10/2015 10:03PM by skelator.

1. Measure the voltage appearing on the heat bed. If it is much lower than the 12V from your power supply, then you are losing too much in the cabling and/or the mosfet.

2. You didn't say what size the heated bed is. If it is about 200mm square then a resistance of 1.8 ohms is rather high and you will need more voltage to get it hotter.

3. As you have a LED supply, you can turn up the supply voltage. Caution: if you are using Arduino/RAMPS and you have an LCD screen attached with the backlight powered from 5V, then the voltage regulator on the Arduino will already be getting very hot, and you should use an external 5V regulator before you increase the voltage. Otherwise, you can turn the voltage up to 14V.

4. Insulation under the bed will help.

---

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].

Quote
dc42
1. Measure the voltage appearing on the heat bed. If it is much lower than the 12V from your power supply, then you are losing too much in the cabling and/or the mosfet.

Will do that when I get home but my heat bed is wired with 16AWG silicon wire normally used for RC

Quote
dc42
2. You didn't say what size the heated bed is. If it is about 200mm square then a resistance of 1.8 ohms is rather high and you will need more voltage to get it hotter.

my heated bed are 200x200 standard size

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dc42
3. As you have a LED supply, you can turn up the supply voltage. Caution: if you are using Arduino/RAMPS and you have an LCD screen attached with the backlight powered from 5V, then the voltage regulator on the Arduino will already be getting very hot, and you should use an external 5V regulator before you increase the voltage. Otherwise, you can turn the voltage up to 14V.

noted I will need to look up on on how to do this, maybe I can just disable the backlight

Quote
dc42
4. Insulation under the bed will help.

my alunimum bed is mounted on a MDF plate

Edited 1 time(s). Last edit at 02/11/2015 04:38AM by skelator.

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skelator

Quote
dc42
3. As you have a LED supply, you can turn up the supply voltage. Caution: if you are using Arduino/RAMPS and you have an LCD screen attached with the backlight powered from 5V, then the voltage regulator on the Arduino will already be getting very hot, and you should use an external 5V regulator before you increase the voltage. Otherwise, you can turn the voltage up to 14V.

noted I will need to look up on on how to do this, maybe I can just disable the backlight

The funny thing is, some people scream that you shouldn't feed more than 12V to the Arduino Mega (which is rated at 20V maximum) for fear of overheating the regulator; but they are quite happy to power a 12864 graphic LCD from the 5V rail - which causes the regulator to get hotter than is wise even with 12V input.

I would disconnect the backlight anode from the 5V supply and connect it through a series resistor to +12V (which is about to become +14V). If it is a 12864 mono graphics LCD, then the backlight needs about 100mA, so a 100 ohm 2W resistor would be about right. Depending on how good the PSU regulation is, you may see the backlight dim slightly when the heated bed is on.

The LED supply will have a voltage adjustment pot near one end of the terminal block.

Edited 1 time(s). Last edit at 02/11/2015 05:14AM by dc42.

---

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].

If you want to eliminate the controller from your suspect list, just wire the heatbed directly to your 12V power supply for testing. If it can't reach 110C wired directly to the power supply, you know what the problem is.....

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vreihen
If you want to eliminate the controller from your suspect list, just wire the heatbed directly to your 12V power supply for testing. If it can't reach 110C wired directly to the power supply, you know what the problem is.....

An excellent suggestion. You can also turn up the voltage to 14V with just the heat bed connected to the PSU, to see if additional voltage fixes the problem, before you make any changes to the printer electronics to accommodate 14V input.

---

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].

ok did some check

power getting to the heatbed is 11.5v power measured directly from the power supply are 11.85v not actually 12v or maybe it my multimeter but my Watt Meter does said it 11.85v so I guess my multimeter is correct, If I turn up my power to 14v I need to find a resistor to drop my voltage to 12v as I have a fans running directly from the 12v source not sure the can can handle 12v and will my stepper motor run fine with 14v? I dont see any label on the stepper motor indicating working voltage

The stepper motor drivers are constant-current and can take much higher voltages than 12V (AFAIR they are rated at 35V). The capacitors on the RAMPS board may be rated at 16V, 25V or possibly 35V depending on your board. A simple way to drop the voltage to the fans from 14V to 12V is to put three 1N4001 or similar diodes in series with them.

---

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].

Quote
dc42
The stepper motor drivers are constant-current and can take much higher voltages than 12V (AFAIR they are rated at 35V). The capacitors on the RAMPS board may be rated at 16V, 25V or possibly 35V depending on your board. A simple way to drop the voltage to the fans from 14V to 12V is to put three 1N4001 or similar diodes in series with them.

ok noted I put some diode for the fans or maybe hookup and one of my stepdown regulator for fans and LED

UPDATE:

Bumped the power supply to 14v, finally barely heated up to 105c, if my calculation are correct with 14v and 1.8ohm resistance on the board, it need 25A just to heat the bed up!

I did also wired the heated bed directly to the power supply and adjusting the voltage while at it with 13.95v it can go up to 105 and stuck there unless I bump the voltage even more

Edited 1 time(s). Last edit at 02/11/2015 09:08AM by skelator.

Ohm's law: U(volts) = I(amps) x R(ohm). ==> I = U/R ==> I = 14/1,8 ==> I = 7,77 Amp.
Have measured the actual temperature, maybe your thermistor is misreading.

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gforce1
Ohm's law: U(volts) = I(amps) x R(ohm). ==> I = U/R ==> I = 14/1,8 ==> I = 7,77 Amp.
Have measured the actual temperature, maybe your thermistor is misreading.

the thermistor is acurate, only -/+ 5 degrees as I also measured with my IR thermometer just incase, but 1 thing for sure with 12v the bed will never ever heat up to 100c that for sure

You could bump the supply voltage to 15V if the PSU will go that high and has enough spare current capacity, but if the capacitors on your RAMPS board are only rated at 16V that leaves very little margin unless you replace them with 25V capacitors. Otherwise, I suggest you look for a different heat bed.

---

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].

Just to check before you replace any more hardware, you did check that PID is correctly tuned, didn't you?

If the heatbed has an LED it is easy to check, the LED shouldn't flicker before you get close to your target temperature. If it flickers that is PID switching the current on and off, when it hasn't been tuned PID can cut in way too soon, meaning you are not getting full current to the bed when you need it.

EDIT
Just noticed you already tried hooking directly to the PSU, so that eliminates PID from the equation.

Edited 1 time(s). Last edit at 02/12/2015 05:45AM by plankton.

Ok,

did my first print on ABS I keep my voltage to 14v as dc42 suggested, can't go to 15v as check the capasitor it only rated to 16v I don't want to risk it, bed will take a while to reach 100c but it can..

now having problem with my marlin, I already enabled BED Pid in firmware configuration but M304 wont give me anything, so can't really set the PID for the bed need to figure out why. Plus I need a new ABS spool the one I have already exposed to moisture quite long time getting popping sound while printing, maybe I'm going to bake the filament to dry it out when My wife is not around :p

You don't need to use PID control for the bed, and using it may make the mosfet run hotter. Leave it as bang-bang instead.

---

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].

Quote
dc42
You don't need to use PID control for the bed, and using it may make the mosfet run hotter. Leave it as bang-bang instead.

ok I'll leave the bed as default for now, reason enabling was I'm expecting a Solid State relay to arrive anytime soon now , but first thing first I need to dry my filament

Edited 1 time(s). Last edit at 02/16/2015 03:34AM by skelator.

Using a SSR with that heat bed will probably reduce its output, because an SSR will have a higher voltage drop than the mosfet on the RAMPS board.

---

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].

Quote
skelator
...but first thing first I need to dry my filament

Instead of waiting for the absence of adult supervision, put your heatbed to work while you're testing it. Put the spool in the center of your heatbed, and cover it with a small cardboard box. I do not know how it will work, but plan to try it myself sooner or later because my kitchen autoclave^H^H^Hoven is only 6 months old and cost me over $1,200.....

just wondering, I have no fan on the ramp board, only fan thats working is in the psu, other than that, none, I did have a fan on D9 but now D9 has no current, both the heatbed and extruder are getting less than 12v when heating, anything I need to look out for when cranking up the voltage?

thanks

D9 should not be powered until an M106 commands it on, and is used for a layer fan, not the hot end fan, which should be wired to 12v directly. What voltages are you seeing? Supply out, board in, and heatbed out? Check also that you are not using too small a wire to the heatbed/board . . . 16ga would concern me, 14 may be OK, myself I'd use 12ga or 10ga to minimize losses.

- Tim

Edited 3 time(s). Last edit at 07/29/2015 02:20PM by tadawson.

supply to board is only 12.06v when nothing is on, once heatbed is on, supply in drop to 11.6v output to bed only 11.49v I cracnked up the voltage on PSU to 12.6v, now with extruder and bed both switched on they are both getting 12.03v, you are correct on the fan, but my problem there is m106 does nothing, the output is dead, it was working, but just went dead all of a sudden, I have 35v caps on this board, and I bought a new one in the post, but just checked the new one I order, has only 16v caps not sure the wire ga, I use household electrical wires, the one came with it was 16ga, I swapped that out few weeks ago and gave me more temp, 16ga I was struggling to get 95c nevermind 100c or above, after switching out the wires, I got just 100c but I need another 10c to 20c more, even at 11c and able to keep up 100c while printing would be a big improvement

just testing the bed now, at 94c at the miniute, but only took few minutes to get that instead of 30mins and moving up slowly from here on

its stalling at 99.1c struggling, thats almost 10c improved

cranked it up another bit, still below 13v from psu to board in, heating faster now, dropped to 86c when I turned it off to up the voltage, and its back to 93c in seconds

would you think it be safe to crank it to 12.95v without step down, I'm not familiar with these electronics, I only go by what I know with cars...

Edited 4 time(s). Last edit at 07/29/2015 03:25PM by deaconfrost.

At this point, if you have not already done so, insulating the bottom of the bed may do the trick. I couldn't getbover 95 on my Kossel, but with about 1/2" of foam under the bed, I hit 100 withot any trouble.

And you have not changed any firmware or anything along those lines? Perhaps a MOSFET has failed . . . there really isn't much on the RAMPS between the Arduino and the FET.

Oh, and only dropping .1v supply to the bed isn't enough that I would worry myself . . . looks like the power supply regulation is a bit soft, though . .

- Tim

yep I have reprap sheet under the bed and printer is in a chamber

I have the voltage at 12.94v to the board, bed and extruder now keeping above 12v and bed holding 105c during print

Edited 1 time(s). Last edit at 07/29/2015 07:50PM by deaconfrost.

a bit of update on bed temp in regards to curling, I just printed out this 20mm cube at 84c starting bed temp, how did that managed? it wasn't completely glued to the bed when print was finished but it did have some hold on the bed..... but that's after everything I've done to the print in this post [forums.reprap.org]

straight to glass no tape no abs juice nothing. not a very clean print, was just doing it at rather a bit high speed just to see if I got the offset and servo angle right



not sure if its the thermistor at faults, but last time I waited the bed to hit 105c, then start print, and the first layer was curling like there's no tomorrow

Edited 2 time(s). Last edit at 08/10/2015 12:24PM by deaconfrost.

At those high printbed temps an open window or a person passing by have a lot more effect on the print. That's why the ABS printers should be enclosed. ( That and the cancerous fumes from ABS )
-Olaf

Hi, sorry to ask, as i'm not a electrician so i not sure, the step to change the voltage of the motherboard to 12.95V, can you write in detail on the step so everyone can use it ? would be grateful for you to do this! thanks you and appreciate your notes!

Hi. I know this thread is old.
But I just registered to say THANK YOU

for all of the discussion. Every step. I managed to sort my problem. Just a bit of context: Mine couldn't heat past 82C.
So I measured the heat bed terminals while it was heating up. It was showing 10.45V and the input voltage was 12.02V.

So I recrimped the connectors and put solder on the end lugs and plugged them into RAMPS. Then I got better bed voltage. I also upped the voltage from the PSU to 13.3V which made it 13V when the printer is turned on. The voltage at the bed when heated is now 12.75V.

@evetanlm I unscrewed the power supply housing, opened the lid and carefully turned the potentiometer inside with a screw driver. Have to be very careful because this its dangerous (240V source) and there's lots of capacitors if you slip