Slow getting to 110C bed target on 10" i3v

[printbus]

The 8" bed, in theory, should only require 64% the energy needed by the 10" to maintain a given temperature. Something I did not consider before pulling the trigger on the 10"!

What's interesting is that the heat bed on the new 12-inch printer just released by MakerFarm should likewise require 144% of the energy needed by the 10-inch. The product page for the 12-inch heater, however, says it needs 20 amps, which isn't all that much more than the 10-inch.

[old man emu]

I found that my heater pad was warped in a similar way to yours. I forget whether I did anything about it or not since I figured that I was printing on a glass sheet anyway and that would be flat as it appears to be. I didn't consider any effect that lack of contact with the glass would have. I was more concerned about getting a level print surface.

One thing I would consider is attaching the thermistor to the glass plate to obtain a more accurate reading of the temperature at the actual print surface. That could be difficult as it is hard to find a space between the heater pad and glass.

How have you secured your thermistor to the heater pad? There was a tip in relation to fitting the extruder thermistor of setting it in place in is hole with a blob of auto muffler putty. I wonder if that would work with the heater pad and be better that kapon tape.

Don't forget that going from 18AWG to 14AWG is like going from a fire hose to a garden hose. There's a mighty big constriction to flow. I think you did the right thing by struggling with the 14AWG all the way to the pad.

Old Man Emu

[JimG]

I applied some of that white silicone heat sink grease to the underside of the heater, then plopped the thermistor in and on top of the grease. Taped it down with kapton.

The other thing I did was glue a very fine wire thermocouple to the underside of the bed so that I can independently monitor its temp. Just to keep the thermistor honest.

I found that the thermocouple reading and thermistor readings never vary by more than 4C. This would be very crude for a lot of applications, but I think is just fine for this one.

Jim

[usarmyaircav]

I just bought and installed 12 AWG wires to go between the PS and the heatbed relay. I also forgot that I need to remove the glass and heatbed and cut out a hole in the corkboard where the thermistor is. I think between the two of those I should be in good shape for heating my bed. A cloth over the top of the bed is a good idea. slight fire hazard I would think.

[JimG]

I just bought and installed 12 AWG wires to go between the PS and the heatbed relay. I also forgot that I need to remove the glass and heatbed and cut out a hole in the corkboard where the thermistor is. I think between the two of those I should be in good shape for heating my bed. A cloth over the top of the bed is a good idea. slight fire hazard I would think.

If you are OK with the corkboard below the heater, then you should also be OK with the cloth on top ;-) The biggest problem with the cloth, or anything else on the top, is that you have to be there to remove it when the bed is warmed up. 'Membering things like that when I am working in the "lab" is not my strongest skill.

I have cardboard below mine. The piece of silicone foam rubber I bought for this turned out to be too thick.

Jim

[usarmyaircav]

If you are OK with the corkboard below the heater, then you should also be OK with the cloth on top ;-) The biggest problem with the cloth, or anything else on the top, is that you have to be there to remove it when the bed is warmed up. 'Membering things like that when I am working in the "lab" is not my strongest skill.

I have cardboard below mine. The piece of silicone foam rubber I bought for this turned out to be too thick.

Jim

DOH! I didn't really think about the cork underneath LOL.

[usarmyaircav]

so after changing the wires from the power supply to the relay my bed heated to 110c in 8 minutes. I still need to make a small hole where the thermistor is in the cork but much better!

[JimG]

OK, reporting back with the results of the great wire swap of 2014.

Before starting the exchange, I measured voltages at the PSU and at the solder joints on the heated bed while the system was in its "stock" configuration: 12.06V at the PSU; 11.24V at the heated bed. Total power loss from wire resistance around 13% (but remember I already had pretty heavy 16AWG wire for everything except the heater board leads).

I completely removed the 18AWG leads from the bed by unsoldering them. Next time, I would NOT do this (see more below). I soldered new 14AWG lead wires directly to the solder pads on the underside of the heater. I ran the 12V side of the heater circuit from the bed to the relay board, and from the relay board to the PSU. I ran the ground side of the circuit directly from the heater to the PSU. All wires now 14AWG.

Result: 11.59V at the heater. Approx. 7.5% loss of power due to wire resistance.

I don't know yet how this will translate into warm up times for 110C ABS printing. Along the way I also discovered that the heater is very slightly warped: the top surface is very slightly concave across the X direction. It is most noticeable on "my" end of the bed. I built a flexible shim from printer paper and pushed it in between the plywood and the underside of the heater. This was just enough to bring the heater up into contact with the glass, but not enough to interfere with bed leveling. Paper? Well, my cardboard insulation hasn't caught fire yet so I figured why not.

If I did this again, I would proceed along my original mental plan, i.e., leave short pieces of the original 18AWG leads in place, and solder the new 14AWG leads to the remnant stubs of the 18AWG. But I do a lot of soldering on PCB's, and the 14AWG wire is VERY flexible, so I felt confident and decided to do a complete leadectomy. Mistake.

The physical thickness of the 14AWG poses some difficulty in securing the wires to the plywood bed because the little holes that Colin provided for a wire tie are too close together for 14AWG. So I had to unsolder the new 14AWG leads and point them toward each other rather than 90 degrees to the back of the heater. Even doing this left a wire bunch that was too thick for the small spacing between holes in the plywood. I eventually got it all sorted out and got the wires secured well, but it took a bit of doing.

Did I mention the part about pulling the solder pad off of the PCB? Yup, applied a little too much heat on one of the new leads. I had to scrape length of solder resist off of the main trace on the board, clean and tin the now-exposed copper, and resolder the new lead.

Did I mention the part about how well 14AWG wire conducts heat away from the tip of your soldering iron? If you attempt this, dig around and find a nice heavy tip for your iron. The little tips I use for most PCB work didn't stand a chance!

Jim

[old man emu]

​Bar-b-que at Jim's place this weekend! He's supplying the salmon.

[TechMasterJoe]

i cooked 2 eggs sunny side up as a joke once on my schools Airwolf HD2x
it's about the only thing it's good for


i got a 12in i3v on the way and i picked up 12ga silicone wire for this reason
I'm going to be using a .075in thick sheet of stainless steel that i machine polished at work for a bed at first just to try it out
i don't really like that mini relay that they come with so i got a 50amp SSR and heatsink.
another thing using relays and or mosfets it's always best to put them on the ground side in case of internal failure
they just stop working