Can't get to 120° on the bed. PSU problem?

Hi, i'm an inch away from finishing my prusa i3. I own a printrbot simple too and modded it to support a heated bed so i can print with ABS.
Some months ago i got a prusa i3 kit, but i can't get the bed to 120° no matter how long i leave the thing on. It just gets to <110.
I'm using old PC PSUs for both printers, and while it works fine with the printrbot, i think it's not doing the trick with the prusa (presumedly because of the larger print bed).
I can measure the 12V when the bed is off, but as soon as i turn it on it drops to 11.5 and remains there.. I've tried adding a 2Ohm 20W base load to the 5V rail too but the voltage drop was reduced at most by 0.2V, which didn't make much of a difference.
Could someone reccomend me some power supply or help me make my psu work as it should?
thanks

Why would you want it to go to 120?

Many people print with it at 110 and I found much less warping at 95. If there is a reason you must have it at 120 then you need more voltage, maybe a 24v supply instead of 12v.

But I think most of the heated beds are basically designed to be at 110 @ 12v with no controller.

I've measured some voltages, maybe it's useful

Voltage with bed off (with base load) : 11.98
Voltage with bed on (with base load) : 11.54
Voltage with bed off (w/o base load) : 11.85
Voltage with bed on (w/o base load) : 11.52

Did you put cork under the bed for insulation?????

As Tmorris said, "Why do you want 120C?"

---

_______________________________________
Waitaki 3D Printer

110 is enough for ABS, why go higher?

hey
first of all, i thought 120 was the temperature for ABS.. There are so many opinions on the internet i guess, and since 120 worked for me on the printrbot i thought it was a must.
I printed a cellphone case @ max temp (~110) and one corner lifted a little bit. I presumed it was the temperature, but my bed was probably dirty..

And yea, i got a piece of wood under the bed for insulation. That part is covered.

Anyhow, i measured the voltages wrong last time.. after checking the Voltage levels at the bed i found out that it drops to 11V.. is that ok?

I'll give it a shot with 110 and report.

Thanks for the replies

i'm printing at 100 degrees right now and it's all coming well for now.
BUT
the bed still takes like 25 mins to heat up..
i'll keep on trying to get those 12V from my PSU, but now i know that i can keep on printing for now
thanks

Thats where a nice adjustable PSU comes in handy. I can bump mine up if needed.
Yes printing while printing ABS, heating the plate takes a LONG time compared to PLA. Its just one draw back among many.
Im debating switching to PLA after this roll of ABS I have is gone.

does PLA stick better? at what temp?
i have a roll of PLA left there forgotten from the time i had no heat bed on the printrbot. ABS parts just look a lot better, the opacity it has does a lot for the looks in contrast to the glassy style of PLA. And it was a struggle to get PLA stick to the bed... i had to rely a lot on hairspray.

I print abs at 120, I find abs sticks much better and releases much easier when cool too. However I use 15v to get it there, which takes about 10 mins.

I find it hard to keep a stable 110 with 12v.

PLA on painter's tape at 60 degrees is magic. I have yet to have a single issue not related to be leveling for sticking.