My heated bed never gets past 80C

So I purchased this from Amazon [www.amazon.com] and it came with a MK2B heated bed. This was intended to be an upgrade for my Prusa i3. So far the heated bed that came with this just can't cut it past 80C even after 30 minutes. I thought it was my RAMPs board so I hooked it directly up to the power source (the one that comes with a Folgertech Prusa i3 is 12V/30A) and it still read that the temp was only getting to 96C after a 30mins.

To test if maybe my firmware selected thermistor was wrong, I attempted a test cube and sure enough the ABS would not stick (I have the aluminum plate perfectly covered in kapton tape, not printing to bare aluminum).

I'm so confused. I'm just now trying to get to ABS. (I'm using green from MeltInk) but the Folgertech printer claims it can print ABS. Also, the printer seems to get to 60C relatively easily when I have the power hooked to the RAMPS 1.3 board, but try to get to 70C and it's a sloooooow crawl. like hitting a wall.

Do you have a multimeter? Can you check the voltage when directly connected? Can you check the resistance of the bed?

If you don't have a dedicated 24V pad check if it is connected correctly.
Most allow for 12 and 24V input - if connected to 24V you won't get any proper heating.
And I would measure the current draw of the pad to see if it is in spec or not.

> And I would measure the current draw

Sorry, but how many people do you think have the ability to measure 10A+ current ?

Can you measure the bed resistance? If its 1.5ohms then the performance you describe can be expected. Put insulation under the heater so the energy goes into the bed and doesn't heat the air. Cork, corrugated cardboard or wood are useful. Increasing the PSU output wont help. I have 4mm of cork and it still takes 25 mins to get to 100.

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MCcarman
..... takes 25 mins to get to 100.

room temperature ?

4mm of cork is what i intend to use with some fiberglass.

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amigob
> And I would measure the current draw

Sorry, but how many people do you think have the ability to measure 10A+ current ?

All of them that are interested in building a 3D printer. Any basic multimeter will measure up to 20A with appropriate cables. Taking on a reprap style 3D printer without a multi-meter and a soldering iron would seem 'strange' to me.

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amigob
> And I would measure the current draw

Sorry, but how many people do you think have the ability to measure 10A+ current ?

1. I would not suggest to measure if I would fear it could be too complicated or too expensive
2. Even a cheap 20$ multimeter from the hardware store can measure 20A DC, if not check the 15$ one right next to it.
3. In case you really can't get anything to measure these high currents:
Get a standard 1Ohm shunt and measure the voltage drop across it (while the shunt is connected in series with supply/load)

I'm trying to measure the resistance but I'm getting nothing o.O The heater bed is completely turned off but I'm not getting a reading. I checked my meter by measuring the resistance of a resistor and it was spot on. Is there a special way to measure it?

The heatbed has a pretty low resistance of about 1.3 Ohms - it can be tricky to measure accurately. If you touch the probes of your meter together you will get an idea of the minimum resistance your meter can show. It will probably vary quite a bit depending on how well surfaces of the probes touch and if there is any dirt in the way. That will give you a feel for how you will need to press fairly hard on the heat bed pads when you are trying to get a measurement, and if you twist the probes a little at the same time it will help scrape away any surface contamination.

Okay, I will keep at it. Also, I purchased an infrared thermometer. It's saying the aluminum plate surface is actually around 87.6C when the thermistor says it's 92.3C. My aluminum plate is coated in Kapton tape, so could that throw the heating measurement off?

... any shiny or reflective surface can show wrong values - paint a spot black and measure it, if it's showing different values.

But your thermistor can be not properly calibrated and reading off numbers too, so hard to say, which of them is more precise ...

---

Viktor
--------
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Okay, so I managed to get a resistance from it. It's hovering at approximately 1.3-1.5 Ohms which was nice to see. But now that I have that, how can i measure the current through the PCB without shorting? I got some cork board and adhered that to the bottom and the hottest it got after an hour was about 98.7C(Measuring directly from the surface of the PCB with the infrared thermometer). Also, I'm getting about 11.45 V from my RAMPS board to the Heated bed. My power source is strong at 12.1V

Edited 1 time(s). Last edit at 02/20/2016 09:53PM by WalkerMaker.

What resistance does your meter show with the leads shorted to each other? You have to subtract that to get the actual resistance of the circuit.

This performance doesn't sound odd for a ~1.2 ohm bed on ~12V, especially with a heat spreader and an un-insulated back surface. There's a reason 24V mods are popular.

Edited 1 time(s). Last edit at 02/21/2016 09:18PM by IMBoring25.

On just 12V any added resistance between power source and bed will affect the performance.
Do a check with good quality speaker cables - the extra thick and flexible type.
I play quite a lot with hot wire cutters of all lengths, even at work now, and I have to say it really matters how thick the supply cables are if serious power levels are required.
On a lot of printers I have seen that the cables to the bed are often quite thin and as a rule of thumb I always double the cable diameter for high power applications if the cable gets warmer than the surrounding temps.

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IMBoring25
What resistance does your meter show with the leads shorted to each other? You have to subtract that to get the actual resistance of the circuit.

This performance doesn't sound odd for a ~1.2 ohm bed on ~12V, especially with a heat spreader and an un-insulated back surface. There's a reason 24V mods are popular.

Well, if that's the case do you really suggest upgrading to a 24V system? I just ordered a smoothie board 5X which can handle a 24V system...
And if I do up to a 24V system, can I only use 24V regulated heating beds or do I have to use 12V only? (Or boards that can be soldered accordingly of course)

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Downunder35m
On just 12V any added resistance between power source and bed will affect the performance.
Do a check with good quality speaker cables - the extra thick and flexible type.
I play quite a lot with hot wire cutters of all lengths, even at work now, and I have to say it really matters how thick the supply cables are if serious power levels are required.
On a lot of printers I have seen that the cables to the bed are often quite thin and as a rule of thumb I always double the cable diameter for high power applications if the cable gets warmer than the surrounding temps.

They're nice thick 18 gauges cables and I don't read any resistance from them. I think I'll just jump the hurdle and do the 24V system if heated beds for 24V systems are that much better.

Just checked you Amazon link and through to the heater spec and it says its resistance is about 1.5 ohms so at 12V you should get 96wats. A max temp of 80C is very low. If you get different response when you ran it direct from the PSU and got to 96 in 30mins that's about the same as mine. But indicates your Ramps is limiting the current somehow. I don't know much about the Ramps boards so don't know if they have a current limiter like the stepper drivers do.
Using the same Heater on 24V has a resistance of over 5ohms so power goes up to around 110wats. That's not a huge leap. And you will have to use a relay as you can't put 24V into the Ramps board. If you really want performance and are going to buy a PSU for the bed then it may be worth looking for a 15V supply as suggested on the Amazon site and leaving the heater connected for 12V (1.5ohms) that will give you 150wats. If its a variable supply you can turn it down so as not to cook the heater to much.
Im not convinced just going 24V will solve your issues with this heater board.
If you watch the thermistor output on the temperature screen (if using RH) is the temperature rise smooth or does it at any point jump or flatline - errors in the temperature table can cause it to be incorrectly reported. Was your ABS test print on Kapton at 80C or 96C? I would have expected it to work at 96C but probably not at 80C but I am not an expert.

If you are using Marlin try running auto-tune I believe its called. I had a similar problem and found my PID numbers were way off. Mine would heat up to almost what ever I had it set at then would stall out about 4 to 5 degrees short ie if I set it to 95 it would heat right up to 91 or 92 then s-l-o-w-l-y go to 91.1, 91.2, etc. but if I set it to 80 it would stop at 74...after running auto-tune and changing the PID numbers which were way different heats right up.
I found the auto-tune instructions in the Marlin configuration.h file

I had similar problems with my bed not heating on 12v..
I just had to crank up the output from the psu to 13.5 to fix.
Though if you have a cheap ramps like i do, you'll have to upgrade
the fets.