Phebe HeatBed not getting up to temperature

[kilroyo]

For the life of me I cant figure out why I cannot get the temperature above 70 degrees celius on the heatbed. This is the first time I have been finally able to used it. I have 2.6 ohms on both sides of the board (I dont know if this is correct). I have tried it straight from the power supply to limit the possibility it being an issue with ramps. I have removed the glass, fans, etc and anything that I think could affect it, but when taking the temp with a meter it will go no higher. My extruder works fine and it gets up to temp. I have the Board wired parallel like its called to be. The LED works fine and lights. But with the temperature as it is, my prints pull up from the bed. Just wondering if anyone has run into this issue with the board also and how you fixed it. I did go back over and solder my joints again to make sure. But Im stumped

[michaellatif]

I have two of them and they both work well, temps get up to 150C easily. I have wired my board to run the traces in parallel, I get something like 3 Ohms? Someone mentioned a problem with their Phebe but their resistance on one of the sides was either low or way to high.
Have you checked the resistance from the board at the board and at the end of the wires?

[stienman]

What gauge wire do you have attached? What is the resistance of the whole assembly including the wire? What is the voltage at the heated bed when it's connected to the power supply?

[kilroyo]

1.3 ohms with it all wired up,,, 12.25 V coming out of the power supply ,, using around a 14 guage wire from power supply ,and 2 positive and 2 negative strands of 16 gauge coming from ramps to the heatbed, using ramps I get about 10.88 to 10.93 V to the board.

well I decided to test if one side was hotter then the other side , and the left side is getting much hotter than the right , about 20+degree difference, wiring tested good, now I gotta look at the board again , just wierd because I get the same resistance thou

[stienman]

Keep in mind that 120W is not that much, and if you are in an air conditioned environment or with fans running nearby, you might only see a 20-40C difference between the board and air temp if the board is hanging out in free air.

Put the board on an insulated surface, and make sure no air currents are blowing across it, and see if that changes your results.

[BrainSlugs83]

How many watts is your PSU rated for on the 12V rails? How many watts are you trying to draw from them? (in DC, W(atts) = V(olts) * A(mps). A = V ÷ R(esistance). So for 2.6 ohms of resistance @ 12.25V, you're sourcing ~56.5 watts for each 12V trace (~113 watts total if you're running them in parallel -- call it ~60W or ~120W just to err on the side of caution). What about your hotend? Etc... Add all the 12V watts up, and check and see how many your PSU is rated for (or if it's rated in amps, do it in amps -- make sure your PSU can handle the amount you're trying to source on the 12V rails specifically -- there is usually a table on the PSU itself).

If you're getting a voltage drop, and the voltage drops are different for each of the two heating circuits (are they being powered from the same MOSFET or by two different MOSFETs? Sorry, I'm not familiar with the Ramps hardware yet) that could explain the uneven heating issue you have.

Edit: Secondly, if you're running them in parallel up the same wire, make sure that your wire is of a large enough diameter to handle ~120 watts (if you're running them up two strands of wire to be powered in parallel by two different MOSFETs, make sure each strand can handle the ~60 watts you'd be pumping through each of them).

[kilroyo]

Well I was able to solve the issue with only one side heating up ,, the screw type connector that I had solder to the board for running the wires to was bad, soldered a new one on , now both sides heat up, what was throwing me off, was the fact I forgot to account for the resistance from the led resistor. It works, but it just doesnt seem consistant enough. Its working and gets close, granted I dont get a 100 degrees celius each and every time, but atleast its somewhat close.