Heated bed cannot reach temp

[gajtguy]

I rec'd the Rev3 board, and then got the Rev2 board from support. They both measure 1.4ohm. I've got the Rev2 in there now, and upgraded the power supply to a 600watt, but it still takes 9mins to get to 90 degrees. Frankly I'm okay with that (for now).

[EyeBee]

I've been having a similar issue with my Rev3 bed on the RoMAX v2. It took close to 40 minutes to get up to 90C (with a towel on the bed). I had always preheated the bed via Repetier Host. I just used the LCD menu to set bed temp to 90C and it got there in less than 15 minutes (still with a towel). Is there some setting in the software that we should be changing?

[nitewatchman]

I rec'd the Rev3 board, and then got the Rev2 board from support. They both measure 1.4ohm. I've got the Rev2 in there now, and upgraded the power supply to a 600watt, but it still takes 9mins to get to 90 degrees. Frankly I'm okay with that (for now).

I just got my Rostock up and running a few hours ago. It came last week with a Rev. 2 Bed. My bed comes up to 90C in 4-1/2 to 5 mins.

What I have done: 1) used a Corsair RM750 modular power supply, 2) used #14AWG Fine Stranded wire (speaker wire), 3) BT60 connectors on the bed supply wires, 4) used Wago 222 - 5 pole termination blocks to gang the 4 P/S wires to the single #14.

The P/S output measures 12.10VDC at idle at the P/S and 12.10VDC on the bed terminals when the bed and the extruder are running at full load. I don't have any concerns about the ability of the P/S to deliver full output to the bed.

nitewatchman

[nitewatchman]

I've been having a similar issue with my Rev3 bed on the RoMAX v2. It took close to 40 minutes to get up to 90C (with a towel on the bed). I had always preheated the bed via Repetier Host. I just used the LCD menu to set bed temp to 90C and it got there in less than 15 minutes (still with a towel). Is there some setting in the software that we should be changing?

There may be a good reason for this. If you look at the Temperature Curve Screen on Repetier's main page, does the green zone go all the way to 100% on the "Output Bed" display when the bed is heating up and controlled by Repetier? If not, the power output may be held down by the Firmware Setting - "Bed PID max value[0-255]". Reducing this number can have the effect of throttling the power to the bed down by controlling the Pulse Width Modulation of the Rambo controller applied to the bed power.

Long shot but worth looking. Since the LCD/Rambo can heat the bed faster this would seem to rule out P/S and wire size. Problem is this number actually resides in the firmware and should control in either mode unless it has been changed and never updated to the EEPROM.

nitewatchman

[JohnStack]

650W Corsair, modular taking 45 mins to get to 90 on the original Onyx - but I have a 3/32 spreader as well. Maybe a weigh-in by @SeeMeCNC guys when they get back from having fun at Makerfaire...

[EyeBee]

If you look at the Temperature Curve Screen on Repetier's main page, does the green zone go all the way to 100% on the "Output Bed" display when the bed is heating up and controlled by Repetier?

Yes

If not, the power output may be held down by the Firmware Setting - "Bed PID max value[0-255]". Reducing this number can have the effect of throttling the power to the bed down by controlling the Pulse Width Modulation of the Rambo controller applied to the bed power.

No, I checked that and its set to 255.

Long shot but worth looking. Since the LCD/Rambo can heat the bed faster this would seem to rule out P/S and wire size. Problem is this number actually resides in the firmware and should control in either mode unless it has been changed and never updated to the EEPROM.

Thats what has me scratching my head.

[Steve123]

Same problem here! Bed will go to 60, stay there for a bit, then dives down to around 35/40. I have not heard a word from support, going to buy a new power supply and try that. Are they sending new beds out?

[Demolishun]

I have a Rev 3 and could not get above 80. The resistance measured 1.2 ohms (my meter is not very accurate though). However, I have since changed to a 20VDC (24VDC dialed down) power supply for just the heated bed. I now no longer have issues with heating the bed. I modified the max PID output of the bed to be 72% duty cycle. This averages to about 12 amps at 20VDC which is 240 watts. 12 VDC will put out 120 watts at 1.2 ohms. I would recommend moving to a 24VDC power supply rather than using PC power supplies in future versions of the Rostock Max series. This will require other changes, but it would completely eliminate issues like this.

What is the max temperature of the heated bed anyway? (max safe for equipment temperature that is)

[ThatDirectorGuy]

I am having the same problem. It is going into almost an hour now to try and reach 90 degrees. I ended up taking poster board and encircling the whole printer for a make shift enclosure. That gets it up to 90 degrees only slightly faster. Windows are closed.. I have the v3 bed also

[geolupulus]

Same problem here! Bed will go to 60, stay there for a bit, then dives down to around 35/40. I have not heard a word from support, going to buy a new power supply and try that. Are they sending new beds out?

They are definitely sending replacement beds to those with this issue. We had to call them a few times, but we got a bed and now I can print at 100C without a hitch. Keep on them! FWIW I have had much better luck calling them on the phone to get assistance than using email. Online chat is also better than email.

[Demolishun]

So what is wrong with the current beds? Is there a manufacturing defect? I don't want to find out six months from now I should have asked for a replacement and have it fail.

[Polygonhell]

So what is wrong with the current beds? Is there a manufacturing defect? I don't want to find out six months from now I should have asked for a replacement and have it fail.

I doubt it will fail, the issue in general with using PCB's for heated beds is that the copper depth on a PVB is not critical dimension, so it tends to vary by manufacturing batch and when you're trying to get something in the 1-2 ohm range that can be significant, and given the size of the Onyx and the thickness of the glass plates we use, it doesn't take very much to end up with a bed that won't hit 100C on 12V.

I have a Prusa MK2 bed around somewhere that will blow the poly fuse on a ramps board as it heats the bed, it just happens to have slightly thicker than normal tracks.

[Demolishun]

Okay, so if the bed is just copper then I am not too worried. I surely do not want to go back to using 12V just because of the speed issue. My bed appears to be at 1.2 ohm or close to that.

Ooh, can we buy some of those out of spec beds from SeeMeCNC? I might want to get a second one so I start building another machine...

[ThatDirectorGuy]

Rev3 bed on the RoMAX v2
Takes a long time to reach 90 degrees enclosed and with the pot lid on. Once the lid is removed it plummets down to 80 degrees and never climbs again.
Waiting on support's response.

[CaptInane]

If you're having trouble with your heat bed, definitely get sold of their support. Like a few other people, I contacted them and I'm waiting on the replacement. I was told the week before Memorial Day that they should be getting the new ones in. So, yup, I'm still waiting.

On a slightly related topic, through all this testing to make sure it was the heater and not some fault of my own, I noticed that the stock PSU has an issue with not being able to hold 12V when a load is added to it. As a former PC tech, I'd never seen a power supply do that. Granted, I always utilized all the various voltages. After loading the 5V bus with a light bulb burning about 9-10W, the voltage output was a solid and steady 12V. Although the bed is certainly faulty, I am able to get it up to 80C within 20min with a towel.

I am getting a bit antsy for th replacement though. But, I still bet the voltage will continue to run under 11V either way.

[Hansen]

I have the rev5 Onyx, and I think it has the same problem. I am not able to get any higher than approx. 83 degrees, and it takes forever. I measured the voltage to the heat bed on the RAMBO. Also, I was wondering about the rather thin wires going to the heat bed - it carries some 12 A! - so I took the printer apart and measured the voltage directly on the soldering points on the heated bed - 10.93 V. All in all that is power lost. Power which should have gone to the bed.

Measured:

Voltage on the RAMBO: 11.12 V (ideally it should have been 12.0 V)
Voltage on the heated bed: 10.93 (so there is a voltage drop across the wires going to the heated bed)
Heated bed resistance: 0.8 ohms

Roughly speaking I get a temperature increase of approx. 60 degrees with the power supplied to the bed. The power currently supplied to the bed is about 149 watts, but with the ideal 12.0 V it would have been 180 watts, meaning that I would get an temperature increase of approx. 72 ideally. This is still not enough for the heated bed to reach 110 degrees, which I think it is supposed to achieve.

I am wondering about the assembly with the heated bed lying on top of the "star" shape, which again is lying on six nylon spacers. The heated bed has to heat up the star shape as well as the glass plate on top. I'm thinking that maybe it would be worth trying to add more nylon spacers, so instead of this:

Code: Select all

------- BED -------
--- STAR SHAPE ----
-- NYLON SPACERS --

It could be this:

Code: Select all

------- BED -------
-- NYLON SPACERS --
--- STAR SHAPE ----
-- NYLON SPACERS --

The added nylon spacers might reduce the thermal loss through the star shape (??). It might, however, introduce an increased risk of the heated bed "twisting" without the mechanical support underneath (??).

[Tincho85]

It's an issue of current. Solder an extra wire onto the wire going into the Rambo and the one going to the bed. Recommended by John Oly. I have done 3 wires from Rambo to Bed. Went from only being able to get up to 85 degrees to being able to get to 125 degrees and heating up much faster.

Also don't use a pot holder...you a pot LID! A glass pot lid with the approximately circumference of the actually bed works beautifully.

First of all, excuse my english


Im having troubles with my bed also. But I've Rev2.
It takes 20 min to get to 90ºc and can't reach 110 even after an hour.

So I tested the output current from Rambo to the Bed:

It should say 12v right? So the solution is to add 1 more black and yellow wire?

The wire from Rambo to the bed is a 2,5mm silicone wire, so I think theres no need there to add another.


Thanks, Martin

[nitewatchman]

Martin,

Looks like you are testing directly from the Rambo output with no load being applied. In this case the voltage should reflect very little if any drop due to conductor size. My opinion which is sometimes correct, is that the voltage should be floating high to match the output potential of the power supply. Is the power supply voltage generally low? Or said another way what is the voltage when measured at the Rambo Heated Bed inputs, the place where propose to place the additional two wires? What are the two measured voltages when the Hot End and all other external devices are switched off.

By the way I really like your wiring, connectors and labeling.

nitewatchman

[Tincho85]

Martin,

Looks like you are testing directly from the Rambo output with no load being applied. In this case the voltage should reflect very little if any drop due to conductor size. My opinion which is sometimes correct, is that the voltage should be floating high to match the output potential of the power supply. Is the power supply voltage generally low? Or said another way what is the voltage when measured at the Rambo Heated Bed inputs, the place where propose to place the additional two wires? What are the two measured voltages when the Hot End and all other external devices are switched off.

By the way I really like your wiring, connectors and labeling.

nitewatchman

Hi thanks for your reply. Lets see if I got it right.
So what you say its that I should meassure the voltage directly from the plate?

Hot end and peek fan OFF:
Bed: 9.76 volts

Hot end and peek fan ON.
Bed: 9.56 volts.


Thanks.
Martin

[nitewatchman]

I think that your measured voltage shows a serious voltage loss and is reducing the wattage available to the bed. I also have a Rev.2 bed and performing the same voltage test from a cold start, which is the worst case, the measured voltage is 11.55VDC. As the bed heats the resistance increases and the voltage will rise but the heating rate will also slow.

Timing my bed without the copper heat spreader plate, it has taken 4+ minutes to reach 75C and 6+ minutes to reach 90C. At 85C the voltage across the terminals had risen to 11.62VDC. Replacing the heat spreader will cause the bed to heat slower due to the greatly increased thermal mass but it still takes about 9-10 minutes.

The wire you are using, 2.5mm, is between a #14 and a #12AWG so I do not think that this should be an issue (I use a #14AWG) but I think that the 2.5VDC+ voltage loss is. Suggest that you follow the voltage back to the supply and try to isolate where the drop occurs. If it goes all the way back to the supply, it may just be overtaxed.

There have also been discussions regarding some brands of power supplies than have difficulty in supplying full a 12VDC output unless the +5VDC rail has some load applied to it. I have no first hand experience but this has been discussed by people whose opinion I respect. An easy way to check this would be to hookup a PC disk drive to one of the spare output cables and apply that load across the +5VDC rail, measure the voltage and see if it helps.

nitewatchman

[Mac The Knife]

I am currently running a separate power supply to my heat bed. The power supply was one designed for Recreational Vehicle 12v power system, and charging the R.V. batteries. It outputs 13.7 volts at 30 amps, and with a jumper, will output 14.2. My bed heats up to 90C in 7 minutes, and most importantly, maintains the temperature within 6 degrees. Come winter time, that will probably drop. Here is an example of what I'm referring to. http://www.rivergatedist.com/bulldog_30_amp.htm

[Tincho85]

I think that your measured voltage shows a serious voltage loss and is reducing the wattage available to the bed. I also have a Rev.2 bed and performing the same voltage test from a cold start, which is the worst case, the measured voltage is 11.55VDC. As the bed heats the resistance increases and the voltage will rise but the heating rate will also slow.

Timing my bed without the copper heat spreader plate, it has taken 4+ minutes to reach 75C and 6+ minutes to reach 90C. At 85C the voltage across the terminals had risen to 11.62VDC. Replacing the heat spreader will cause the bed to heat slower due to the greatly increased thermal mass but it still takes about 9-10 minutes.

The wire you are using, 2.5mm, is between a #14 and a #12AWG so I do not think that this should be an issue (I use a #14AWG) but I think that the 2.5VDC+ voltage loss is. Suggest that you follow the voltage back to the supply and try to isolate where the drop occurs. If it goes all the way back to the supply, it may just be overtaxed.

There have also been discussions regarding some brands of power supplies than have difficulty in supplying full a 12VDC output unless the +5VDC rail has some load applied to it. I have no first hand experience but this has been discussed by people whose opinion I respect. An easy way to check this would be to hookup a PC disk drive to one of the spare output cables and apply that load across the +5VDC rail, measure the voltage and see if it helps.

nitewatchman

Hello again
I've connected a fan to the 5VDC output, and it seems to be working good:

When Hotend, bed and peek fan are on, the voltage increases a little bit.


Then I tested the bed here, with everything turned on:

result: 9.8 (an average really, it changes from 9,7 to 9,9 overtime)


Will this help?? I don't want to buy another PSU
My knowledge of electronics is very low, so I'm scared to burn something up by doing this. If someone can confirm this wiring change it would be really appreciated.

I am currently running a separate power supply to my heat bed. The power supply was one designed for Recreational Vehicle 12v power system, and charging the R.V. batteries. It outputs 13.7 volts at 30 amps, and with a jumper, will output 14.2. My bed heats up to 90C in 7 minutes, and most importantly, maintains the temperature within 6 degrees. Come winter time, that will probably drop. Here is an example of what I'm referring to. http://www.rivergatedist.com/bulldog_30_amp.htm

Wish I have the ability to do that

[Polygonhell]

The output pins will read less than 12V even with the best PSU in the world, the MOSFET circuit is not 100% efficient and depending on EEPROM settings, you might be measuring a none cconstant output.
The place to measure for PSU droop is on the input pins to the RAMBO, with the Hotend and bed heating, it will probably drop some but you should be within spitting distance of 12V.

[nitewatchman]

Martin,

Adding the wires from the Power Supply where you so in your photo is correct to increase the ampacity of the Heated Bed circuit.

Your proposed wiring change can certainly do no harm. Adding the extra wires at the location you show will increase the wire cross section in the supply circuit to the bed and lower the total resistance therefore lowering the voltage loss. If you already have three or four 12VDC wires connected there however, the resistance is likely already pretty low and you may not see much change. But it is worth a shot.

As long as you match colors and polarity you should be fine and there is no down side. Just be sure to check the selected wires to be sure that the voltage is correct and that the color and sign (+/-)of the measured voltage of the wire you are adding matches the original wires.

Best of luck.

nitewatchman

[nitewatchman]

The output pins will read less than 12V even with the best PSU in the world, the MOSFET circuit is not 100% efficient and depending on EEPROM settings, you might be measuring a none cconstant output.
The place to measure for PSU droop is on the input pins to the RAMBO, with the Hotend and bed heating, it will probably drop some but you should be within spitting distance of 12V.

Yeah, I get about 0.5 to 0.6VDC drop across the MOSFET's. The Rambo input is always 12.2VDC +/- the Rambo outputs about 11.6VDC.

That is why I suggested early in this string to measure the voltage at the Rambo Inputs also.

nitewatchman