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Heatbed Not Reaching Temperature

Posted by matrix4721 
Heatbed Not Reaching Temperature
May 12, 2013 09:15AM
Hello everyone, well my printer is built and ready to rock and roll, my problem is i can only get the headbed to reach around 90 degrees which is far from enough when printing with abs (Doesnt stick to the bed) im running a 500w atx rated at 30 amps, ramps 1.4 and the mk2 heatbed, ive used an external temp probe to test the bed and it is reaching the 90 degree mark but no higher. Any suggestions would be greatly appreciated. kind regards
Re: Heatbed Not Reaching Temperature
May 12, 2013 09:36AM
Update: ive measured the output of the psu and when its not under load it reads 11.56v, when the heatbed is turned on it drops to 10.38v and when both the hotend and bed is on it drops to 10.20v, not sure if this has any meaning
Re: Heatbed Not Reaching Temperature
May 12, 2013 10:17AM
That's too much of a voltage drop. Have you tried placing a load on the +5v rail (like an old CD drive or something)?
Re: Heatbed Not Reaching Temperature
May 12, 2013 10:49AM
Hi, thanks for your reply, i havent tried putting a load on the 5v rail, im assuming you mean the 5v rail from the atx psu and not the 5v rail on the ramps board? i have plenty of cd drives laying about, if i attach on what am i looking for? am i still measuring the voltage output of the 12v from the atx psu?
Re: Heatbed Not Reaching Temperature
May 12, 2013 10:51AM
Also out of curiosity i notice theres 2 sets up 12v inputs on the ramps board, would using 2 psu's help at all? at the moment im using 1 psu for both sets of inputs
Re: Heatbed Not Reaching Temperature
May 12, 2013 10:54AM
Yes, connect a CD drive or old hard drive to one of the molex connectors on the PSU and then measure the 12v output with your heaters turned on. Some PSU's require a load on the +5v in order to properly regulate the +12v. Do NOT connect it to the +5v on the RAMPS board unless you want to release the magic smoke.
Re: Heatbed Not Reaching Temperature
May 12, 2013 11:59AM
okay, i connected an old cd drive and the voltage without the headbed was 12.02v and when i enabled the heatbed it dropped to 10.52v, i set the heatbed to 120 degrees and after an hour it was holding at 108.8 degrees (previous high was 94 degrees)
Re: Heatbed Not Reaching Temperature
May 12, 2013 12:23PM
That's an improvement, but that voltage drop is still to high. I have the same heatbed and can get it to 110 degrees in about 6 minutes or so with no insulation under it. Are you measuring the voltage at the power supply connector or at the heatbed? Do you have a different pair of wires connected to the 11A and 5A connectors on the RAMPS? What kind of wire are you using to supply power to the heatbed? Does the connector on the RAMPS board get hot when you turn the heatbed on?
Re: Heatbed Not Reaching Temperature
May 12, 2013 01:02PM
hi, i was measuring from the connector end, im using the standard wires used in atx power supplies (same used in molex), its the same pair of 12v wires split into 2 pairs, the ramps board doesnt appear to get hot
Re: Heatbed Not Reaching Temperature
May 12, 2013 01:26PM
You should try to use a different pair of wires from the PSU for each connector pair. Look at the ratings for your PSU and chances are it does not have just 1 +12v rail, it probably has several. Each +12v rail can only provide a fraction of the PSU's total output power. You might have selected a weak rail. Try using the wires on the ATX 12v connector or the PCI express power connectors. Also, it might be overkill, but I actually use 2 pair of wires for the 11A connector on the RAMPS. The reason there are so many +12v and GND wires on your PSU is that they really can't carry much current on their own, so they use several pairs.
Re: Heatbed Not Reaching Temperature
May 12, 2013 06:24PM
hi, thanks for your reply, ive tried it using 2 seperate wires for each pair and i still cant get past 107 degrees, i will try doubling up the wiring like you say you have, im not that experienced with electronics, but if im following you right then i should end up with 4 x 12v wires soldered into 2 pairs going into the 2 12v inputs of the ramps board? also i have removed the heatbed and will double up the wiring on there to see if that helps, please let me know if ive got any of that wrong and i'll keep you posted on my progress. Kind regards
Re: Heatbed Not Reaching Temperature
May 12, 2013 07:58PM
No need to solder, just twist them together. Also, I have 2 yellow and 2 black wired to my 11A connector and 1 yellow and 1 black wired to my 5A connector. Doubling up the wiring on the heatbed wouldn't hurt, but since the voltage drop was measured at the power connector I don't know if it would help any. By all means, do it though since it can only help even if only a little. Just out of curiosity, what make and model is the PSU you're using?
Re: Heatbed Not Reaching Temperature
May 13, 2013 02:45PM
im using a 500w q-tec atx psu, ive had to ditch the last one cos it kept cutting out, ive doubled the 12v wiring up on and replaced the wiring that goes from the ramps board to the heater with wire out of a mains lead, voltage now reads 11.93v when idle, 11.11v when the heater is running (tested from the ramps connectors) and 10.33v (measured at the heatbed,been running for 20 minutes so far and only at 83 degrees, i was thinking, i know its overkill, but to prove a point is there any reason why i couldnt connect 2 atx psus to the ramps board? 1st atx psu to the 11amp input and the 2nd psu to the 5a input? any thoughts?
Re: Heatbed Not Reaching Temperature
May 13, 2013 03:44PM
Update: after an hour its upto 116 degrees, thats its limits, might have to try 2 psu's idea
Re: Heatbed Not Reaching Temperature
May 13, 2013 06:51PM
If you have another sacrificial PSU sitting around, then go for it. If you have to buy a second one, then forget it, buy another quality PSU and run with just that. Actually, a PSU running at a higher voltage would be even better. The only reason I can think of to use an ATX PSU is if you already have one lying around.
Re: Heatbed Not Reaching Temperature
May 14, 2013 06:06AM
matrix4721 Wrote:
-------------------------------------------------------
> im using a 500w q-tec atx psu, ive had to ditch
> the last one cos it kept cutting out, ive doubled
> the 12v wiring up on and replaced the wiring that
> goes from the ramps board to the heater with wire
> out of a mains lead, voltage now reads 11.93v when
> idle, 11.11v when the heater is running (tested
> from the ramps connectors) and 10.33v (measured at
> the heatbed,been running for 20 minutes so far and
> only at 83 degrees, i was thinking, i know its
> overkill, but to prove a point is there any reason
> why i couldnt connect 2 atx psus to the ramps
> board? 1st atx psu to the 11amp input and the 2nd
> psu to the 5a input? any thoughts?

No way,

It's not the power supply at this point. Heat Bed with a 11v+ supply should heat up quickly.

Is there anything else you are heating the bed up with? Large metal plate? Glass? etc?

What is your themsistor for the bed attached to? Are you verifying the temperature with another source?

Check to see if you have any PID settings enabled in the firmware for the heater bed.

EDIT: You also keep saying degree. You talking Fahrenheit or Celsius?

Edited 1 time(s). Last edit at 05/14/2013 06:10AM by ShadowRam.
Re: Heatbed Not Reaching Temperature
May 14, 2013 08:25AM
Hi, im using glass with a top layer of kapton tape, ive verified the temperature with the probe on my multimeter and it matches, im measuring in celsius. PID settings are as follows

// PID settings:
// Comment the following line to disable PID and enable bang-bang.
#define PIDTEMP
#define BANG_MAX 256 // limits current to nozzle while in bang-bang mode; 256=full current
#define PID_MAX 256 // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 256=full current
#ifdef PIDTEMP
//#define PID_DEBUG // Sends debug data to the serial port.
//#define PID_OPENLOOP 1 // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
#define PID_FUNCTIONAL_RANGE 10 // If the temperature difference between the target temperature and the actual temperature
// is more then PID_FUNCTIONAL_RANGE then the PID will be shut off and the heater will be set to min/max.
#define PID_INTEGRAL_DRIVE_MAX 255 //limit for the integral term
#define K1 0.95 //smoothing factor withing the PID
#define PID_dT ((16.0 * 8.0)/(F_CPU / 64.0 / 256.0)) //sampling period of the temperature routine

// If you are using a preconfigured hotend then you can use one of the value sets by uncommenting it
// Ultimaker
#define DEFAULT_Kp 22.2
#define DEFAULT_Ki 1.08
#define DEFAULT_Kd 114

// Makergear
// #define DEFAULT_Kp 7.0
// #define DEFAULT_Ki 0.1
// #define DEFAULT_Kd 12

// Mendel Parts V9 on 12V
// #define DEFAULT_Kp 63.0
// #define DEFAULT_Ki 2.25
// #define DEFAULT_Kd 440
#endif // PIDTEMP

// Bed Temperature Control
// Select PID or bang-bang with PIDTEMPBED. If bang-bang, BED_LIMIT_SWITCHING will enable hysteresis
//
// uncomment this to enable PID on the bed. It uses the same ferquency PWM as the extruder.
// If your PID_dT above is the default, and correct for your hardware/configuration, that means 7.689Hz,
// which is fine for driving a square wave into a resistive load and does not significantly impact you FET heating.
// This also works fine on a Fotek SSR-10DA Solid State Relay into a 250W heater.
// If your configuration is significantly different than this and you don't understand the issues involved, you proabaly
// shouldn't use bed PID until someone else verifies your hardware works.
// If this is enabled, find your own PID constants below.
//#define PIDTEMPBED
//
//#define BED_LIMIT_SWITCHING

// This sets the max power delived to the bed, and replaces the HEATER_BED_DUTY_CYCLE_DIVIDER option.
// all forms of bed control obey this (PID, bang-bang, bang-bang with hysteresis)
// setting this to anything other than 256 enables a form of PWM to the bed just like HEATER_BED_DUTY_CYCLE_DIVIDER did,
// so you shouldn't use it unless you are OK with PWM on your bed. (see the comment on enabling PIDTEMPBED)
#define MAX_BED_POWER 256 // limits duty cycle to bed; 256=full current

#ifdef PIDTEMPBED
//120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
//from FOPDT model - kp=.39 Tp=405 Tdead=66, Tc set to 79.2, argressive factor of .15 (vs .1, 1, 10)
#define DEFAULT_bedKp 10.00
#define DEFAULT_bedKi .023
#define DEFAULT_bedKd 305.4

//120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
//from pidautotune
// #define DEFAULT_bedKp 97.1
// #define DEFAULT_bedKi 1.41
// #define DEFAULT_bedKd 1675.16

// FIND YOUR OWN: "M303 E-1 C8 S90" to run autotune on the bed at 90 degreesC for 8 cycles.
#endif // PIDTEMPBED

EDIT: i have tried it without the glass attached and it still doesnt reach peak temp
Hope this helps, kind regards

Edited 1 time(s). Last edit at 05/14/2013 08:45AM by matrix4721.
Re: Heatbed Not Reaching Temperature
May 14, 2013 09:36AM
>EDIT: You also keep saying degree. You talking Fahrenheit or Celsius?

He'd have a really big problem if it took his heat bed 1 hour to reach 116 degrees fahrenheit.

EDIT: Config looks fine for the bed power. Do you by any chance have a fan running near the bed, or is your machine near an AC vent?

Edited 1 time(s). Last edit at 05/14/2013 09:44AM by sheck626.
Re: Heatbed Not Reaching Temperature
May 14, 2013 09:32PM
UPDATE: Okay, so using 2 atx psu's did the trick (to a point) the bed can now reach 120 degrees C but it took 24 minutes to reach it (from cold, room temperature is 17.5 degrees C) im not sure if it should take this long but seems abit excessive to me.

sheck626 - Thanks for your reply, in answer to your question, theres no fans pointing in the printer (only fans are from the psu / ramps fan which are facing away

im considering trying to make a cardboard enclosure to surround the machine (back/sides and top, not front) to try and and ensure the temp stays stable, was also thinking, i have a spare piece of glass from a large scanner laying about, wondered about putting some foil on the desk with the glass on top with the printer sitting on the glass, thought perhaps it would help reflect the heat back up and also keep it level, might not back any difference but might be worth a try. 2 psu's isnt ideal, is there anything else i can try now that the bed has been proved to be able to get to that temp? or anything i could try to get it to heat up quicker? any advice would be great, kind regards
Re: Heatbed Not Reaching Temperature
May 14, 2013 09:56PM
17.5C room temp is cold as hell where I'm from (Florida). No wonder we have such different results! I'd recommend insulating the bottom of the print bed. Also, I've never needed to print at 120C. I find ABS sticks to Kapton tape at 110 degrees just fine so I've never even taken my print bed to that temp before (115, is the higest I've tested it).
Re: Heatbed Not Reaching Temperature
May 15, 2013 12:19AM
just ditch the atx psu, they drop voltage like no other. get a good 12v 30a regulated power supply, they have much less noise and are fully self regulating so they will stay at 12v or higher if you so choose to do. if all else fails this is a post i made a few days ago to someone else with a bed issue. Someone really needs to get rid of the suggestion to use an atx psu, they are not properly regulated to run a steady stream of current at constant voltage, they are made to provide power for a computer which is constantly changing the amount of current it needs, and they only use max current for a short amount of time, unlike a printer which is using it the whole time to heat the bed. also it turns it self on when you plug it and the fan only turns on occasionally when the heatbed is on, otherwise its dead quiet.

first, check to see if the connections to your wires are getting hot, if they are, you need to find a better way to connect the wires, more secure you know.

second if the wires are still hot, go up in gauge

third take a piece of cardboard a bit bigger than the bed. take some fluffy cloth staple it to the cardboard, then staple aluminum foil on top. if you are afraid of shorts cover the foil with a thin layer of tape.

now ive recently discovered a method for blowing the fan full blast on the print to increase precision of filament. after you have printed a few layers, take like some napkins or whatever you have and cover up the rest of the bed with the napkins. now the bed will keep hot, and use less energy, and you can blast your fan.

I plan on making a sort of cardboard camera iris to cover up the bed more easily, if you can cover up most of the bed you can just blast the fan and this would be much better than the napkins. ill post the link from instructable on how to make one, its kind of a cool thing to have too.

edit:[www.instructables.com]
Re: Heatbed Not Reaching Temperature
May 17, 2013 03:34AM
Update: thanks for your help, i will get a 12v 30amp regulator when i have some spare cash, for right now tho i'll have to stick with the atx psu. my heatmat sits directly onto the ply bed, with this setup it reaches 120 degrees C in around 24 minutes, however, if i lift the heatmat off the bed by acouple of mm it heats up to 110 degrees in 8 minutes and to 120degrees in 15 minutes, it seems as tho the ply is sucking all the heat out, with that in mind im going to try what aduy suggested and use foil to reflect the heat back up, i will let you know the results
Re: Heatbed Not Reaching Temperature
May 17, 2013 04:39AM
UPDATE: First attempt with single layer of foil still took 24 minutes to reach 120 degrees C, im going to try and cut off segments from the ply bed to see if that helps
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