How long does it take for the mk2 heatbed to heat up

I have been printing exclusively in PLA, but I've been concerned that it takes up to 5 minutes to reach 60 degrees. So today, I tried to heat it to 110 for ABS. Not to print just yet - just to see if I could reach that temperature. After about 25-30 minutes, I was up to about 104. It was still climbing, but ever so slowly.

This is my second bed, and this one heats up noticeably slower than the first. I'm using the same wires, but I'm a bit suspicious of the solder joints. I think I'm going to remove the wires, clean out the holes, and re-solder.

One other thing I am doing that's a bit different. I am not soldering the resistor/LED to the board. Instead I am soldering them directly to the feed wires just where they project from the bottom of the board. I assume its just a simple parallel circuit with the bed itself, but maybe I'm taking too much current through this path. I am using the called-for resister (10k I believe).

if your wiring was suspect it (the wiring) would get very hot very fast, and likely melt the insulation on it because it (the wiring) would contribute a significant amount to the resistance.
The bed resistance should be ~1.2 - 1.5 Ohms.
It's more likely your PSU isn't outputting enough power. If you have a meter, measure the voltage from the PSU when the bed is heating, it shouldn't drop voltage significantly. If the voltage is dropping and you are using a converted ATX supply, you can try putting a load on the 5V line or increasing the existing load if you are using one to see if that helps.
You can also try insulating under the heated bed, it'll help a bit.

For point of reference my heated bed hits 110 in about the same amount of time as it takes my hot end to hit 240, and I have no insulation under it.

I am not using a PC power supply. I am using a 12v 30amp power supply, but I will check the voltage.

Would the wiring heat up if the issue was the solder point?

It WAS the solder connection. I removed the wire, cleaned out the hole, and re-soldered. Now I not only reach 60 in 1/3 the time I used to, but I can get all the way up to 110 in about 7 minutes.

Now I need to tinker with the z height and level to get it back to printing as well as it was before the surgery...

Do you have glass on top of your PCB heat bed? My mk1 with 3 mm glass on top of it takes much longer than my hot end to heat up to 110C.

Yeah - I have glass on top of the board.

There is no comparison between the heat up times of the heatbed and the hot end. The hot end is definitely the rabbit - it heats up significantly faster than the bed. Usually I don't even preheat my hot end until the bed is fully up to temperature.

Quote
Polygonhell
For point of reference my heated bed hits 110 in about the same amount of time as it takes my hot end to hit 240, and I have no insulation under it.

What would that time be? The actual time would actually be useful. How about if everyone posts the time it takes to heat up their mk1 or mk2 heated bed from room T (20C) to 110C? I guess we would need to indicate where the temperature measurement is being made and what's on top and bottom of the heat bed.

My time is 17 minutes from 20 C to 110 C measured in the middle under the PCB (heating trace). I have a 3 mm glass with PET tape on top and no insulation.

Between 5 and 7 minutes for my Mk2 to 110 measured with an IR thermometer on top of the glass.
My thermistor measures about 20 degrees cold because of placement, but the values are repeatable.
It should be noted that my Mk2 has somewhat low resistance and the thermal fuse on the ramps board will trip if I don't have a fan on it.

A Z axis problem is stopping me progressing on my own build (feel free to check my post and tell me what I'm doing wrong), in the mean time I've tested heating times on my heated bed for something useful to do

Mk II bed with insulation directly under bed and 2mm glass above bed:

Initial room temp 15.5C
Time to 60C 4.0 mins
Time to 100C (cumulative) 21.5 mins
20 mins later it still hadn't got above 104 C

Hotend which wasn't switched and was about 20 cm above the bed had risen to 21.5 by this time

I have an insulating cover I've made for the bed so when it's got down to ambient again I'll try again and post those results...

Time to 60C 3.5 min
Time to 100 C 8 min (cumulative)
Time to 110 C 9.5 min (cumulative)

Hot end showing 16.5 C at this point but bed dropping to 104 quickly after I take of the heated bed cover.

Hope this helps

Edited 1 time(s). Last edit at 10/23/2012 04:58PM by Logrod.

I am having problems with my heatbed too. It´s a MK-1 and it does't get hotter than 90o and takes about 20 minutes to come to this temp. I checked other posts and the main discussion is the power supply but I have a 250w 12v 20A power supply that should be enough. So I bought a muiltimeter to check resistance and it´s marking 3.5 ohms (I read above that it should be 1.2-1.5 ohms). The voltage in the bed while heating is about 11.2V (In the output of sanguinololus mosfet its 12v sharp) so what can it be? The problem is with the PCB itself?

Edited 1 time(s). Last edit at 10/25/2012 02:29PM by edu_gomes.

Did you check the resistance on the MK1 terminal or at the end of the wires? From your voltage measurements, it should line you have too much resistance on your connector or wires. You might need thicker wires, perhaps 14 gauge, to your MK1. Also, for a Sanguinololu, you should search for Nophead's post on how he connects the wires to the MOSFET tab instead of the terminal.

I checked both (at the terminal and at the end of wires) its about the same. I have a preatty thick cable connecting it. I will check this post. Thank you


brnrd Wrote:
-------------------------------------------------------
> Did you check the resistance on the MK1 terminal
> or at the end of the wires? From your voltage
> measurements, it should line you have too much
> resistance on your connector or wires. You might
> need thicker wires, perhaps 14 gauge, to your MK1.
> Also, for a Sanguinololu, you should search for
> Nophead's post on how he connects the wires to the
> MOSFET tab instead of the terminal.

Has anybody tried the new MK2a PCB? It has much larger pads for soldering on the feed wires. This might help eliminate the problems many are having. It doesn't matter how thick you feed wires are if there is a poor solder connection.

I'm here because I'm trying to get my bed to heat up more quickly, too. I haven't been particularly successful.

I've got 3mm kapton-covered glass over inverted MK2 PCB (i.e., trace up), and the thermister taped to the non-trace side. I've got a silicon insulator under the PCB (but it's about 15mm smaller than the PCB at every edge). I've got 18 gauge wire to RAMPS 1.4, (with a molex connector in-between) and an ATX power supply that is giving me a solid 12V (with load on the 5V rail).

In 20 minutes, I go from 21C to 101C (as measured at the thermistor).
At 25 minutes, I get to 105C.
At 30 minutes, I'm at 108C, and tired of waiting.
At 37 minutes, I'm finally at 110C.

It's starting to sound like this is pretty typical, and that thermister location (trace side or not) matters quite a bit. So that's my experience. Advice welcome.

Verify what the actual temperature is on the glass, depending on placement the thermister can be miles off.
Measure the PSU voltage when the bed is heating, it could be dropping under load.
Measure the resistance including the wires, you'll have to disconnect the bed from the ramps board to do this.
I'm not using a converted ATX PSU, and I have no insulation under the board, and I manage a lot faster than 20minutes.

@Karmavore:

In addition to measuring the voltage at the PS when the heater is on, you also want to measure the voltage at the Mk2 terminal to verify that you're not losing too much from the wire or connector. Also, you should measure the resistance of the Mk2. If it's much larger than 1.1 ohms, then it will be slower in heating up unless you use a higher voltage power supply

@jbernadis:

I have two MK1 and I've never had any problems with the solder joint on the terminal pads. But they are small and you do need to have good soldering technique to make a good connection.