PCB Heatbed Temperature

Hi,

I'm new to electronics.

I have a Prusa Mendel kit that came with a PC power supply, a PCB Heatbed MK2, a thermistor, an MDF plate, and ribbon wires.

Sandwiched together, from bottom to top, I put the MDF, a piece of cardboard, the thermistor, the PCB, and then a piece of glass. I attached 2 yellow and 2 black wires from the PSU to the 11A part of the RAMPS terminal, peeled wires from the ribbon and soldered them to the PCB, and set the bed temp in Pronterface to 110.

However, the highest temp it'll reach is 95, and it takes about 45 minutes to reach that temp. Anybody know what I might be doing wrong?

Thanks.

What gauge wire are you using between the ramps and the PCB. You need a decent gauge for the amps being sent here. I'd say 18 or larger.

Measure the voltage at the PSU. If it significantly less than 12V you may need a dummy load on the 5V.

Measure the voltage across the bed terminals. If it significantly less you need thicker wires. I use all the black and yellow wires from an ATX PSU. Cheap ones skimp on the wire gauge and 2 is nowhere near enough for 10A.

---

[www.hydraraptor.blogspot.com]

I dunno what gauge the ribbon wires were. There's no numbers printed on it, and the website that sold them didn't say. But I bought some 18 gauge wire, and it seems to work okay now.

Thanks.

Hi,

My heatbed has been working well enough for the past month, until today when I tried to set the bed temp higher than 110C. I set the bed temp to 120C, but it seems that the highest it will reach is 113C. So I tried to print at 113C. After several minutes of printing, the bed temp started falling. I tried to reset the temp to 110C, but it didn't work. I restarted Pronterface and restarted the PSU, and set the bed temp to 110C again. But it would reach around 55C and then drop again.

Did I fry something? The hotend and the motors still work fine.

Thanks.

at this point i think its a waste for anyone to use an atx psu, you can get a readymade 12v 30a psu for 35 bucks, it will run at 12v without mods and the voltage is adjustable up to 15ish. just my two cents. also they are aluminum so they look better.

It's possible you just have a bad solder joint or bad connection to the controller board (whichever you may be using). Measure the voltage at the print bed and at the power terminals. If there is a signifigant difference, then you have a problem with either the wiring or the mosfet that switches the bed power. Test at the heat bed connector on the controller to rule out the mosfet. You're going to get some voltage drop across the wiring, but it should be minimal.


Wait, I just read your post further, are you using the ribbon wires to supply power to the heated bed? If so you need to replace them, they can't carry enough current. I just use 16 gauge speaker wire that I wired my car stereo with (not pretty, but it works). The heat bed and the extruder heater should be wired with heavier gauge wire, not the ribbon wire they gave you.

One thing to check is that your slicer is set to 0 on "minimum bed temp" otherwise it will automatically kill the bed temp when you start the print. And by default it's always set at 5, which is lame.
If your power supply isn't up to the task of heating the PCB, which mine wasn't, it might also get too taxed when you are printing, and do an auto-shutoff until the load reduces.

What is the best way to sink heat possible? A wide thin hot plate exposed to open air convection.
OF course there is not enough power to keep this thing running really hot. By comparison it is like running your induction cooktop on lower than the lowest setting. Anything over 115C is difficult, but possible.

Try insulating with fiberglass instead of wood.
Also, running the other hot end with drain more power away from the ATX, running my printer hot end can lower the printer bed temp from 105C to 60C. That means there is a current limit with the ATX.

"What is the best way to sink heat possible? A wide thin hot plate exposed to open air convection.
OF course there is not enough power to keep this thing running really hot."

If that were the case then CPU's would not require a heatsink/fan since the open air convection of the bare chip would be the best way to cool it. Stagnant air is actually a very good insulator. Which brings us to another issue that is air flow in the room the printer is in. If there are fans or AC vents, that will affect the properties of the HBP. I have a PCB heatbed using glass I cut from a picture frame and I have no trouble getting it to 110 degrees (and I've even gone higher) using an ATX power supply. If there is a fan on in the same room, it does affect the max temperature I can reach though. If I want to go even higher, then I would insulate the bottom of the PCB heatbed before messing with the PSU.

Quote

My heatbed has been working well enough for the past month, until today when I tried to set the bed temp higher than 110C. I set the bed temp to 120C, but it seems that the highest it will reach is 113C. So I tried to print at 113C. After several minutes of printing, the bed temp started falling. I tried to reset the temp to 110C, but it didn't work. I restarted Pronterface and restarted the PSU, and set the bed temp to 110C again. But it would reach around 55C and then drop again.

Did I fry something? The hotend and the motors still work fine.

How do I measure the bed voltage? If I measure directly from the PSU, I will get 12V. But if I measure from where the wires are soldered to the pads on the PCB, nothing happens. Does that mean something's wrong with the RAMPS?

Or did I measure it wrong? I turned the PSU on, calibrated the multimeter, turned the knob to 50 DC V, then touched the pads (negative to negative, positive to positive). But the needle didn't move.

Is it possible for a soldered connection to degrade over time? A month ago, I replaced the ribbon wires on the bed with 18 gauge wire. And the bed would heat up better and faster. But I wasn't able to clean out the old solder. So maybe the conductivity got weaker?

Edited 1 time(s). Last edit at 04/12/2013 09:48AM by Axis.

It's possible you created cold-junction solder joints, a routine thing with folks who are new to soldering, especially when using inexpensive soldering irons from places like radio shack. May people make the mistake early on of thinking that apply a blob of solder is enough. It's not. It MUST wet thoroughly both parts being joined

1) get a small sponge, wet it, shake (don't squeeze) the excess water.
2) heat up your soldering iron
3) wipe the tip repeatedly on the spnge to clean off crud
4) apply some solder directly to the tip. It should stick. If it doesn't, clean the tip and try again. If it doesn't, you may need to consider getting a new tip
5) if it does stick, wipe it off again on the sponge.
6) reapply a bit of solder to the "good tip.
7) Apply the solder iron to the solder junction making sure that the are of the tip with solder stuck to it contacts the junction
8) apply a bit more solder, right into the wedge of space between the tip and solder junction
9) if it wets (flows onto both) apply more solder until the joint is filled.

When I measure from D8, nothing happens.

If I connect the bed directly to the PSU, the bed is able to heat up.

When I pulled the wires out of the green terminal on the RAMPS, I noticed the ends of the wires were blackened. Only the wires from the 11A side were blackened - the wires from the 5A side were fine.

Is it possible to make a table/bed like as a flat surface with bent edges facing down, like a metal tray up side down.
Than to attach some ceramic insulators to the underside and wind a nichrome wire across them to heat the air under the table/bed.
This way hot air will be trapped under the table.
Am I correct?