Slow getting to 110C bed target on 10" i3v

[AbuMaia]

glass is more conductive than water, wood, and even salmon

Have you been cooking on your print bed? :-P

[JimG]

Have you been cooking on your print bed? :-P

Now, there's an idea ....

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

[JimG]

The AC SSR's I use for controlling nichrome heaters drop around 0.6V across the switched terminals when conducting. They are spec'ed at around 1.6V drop, but in my applications I only see around 0.6V.

When dealing with mains voltages this is not a big deal. I will be curious to know what kind of voltage drop you see across your SSR? The relay, although a little noisy, at least does not drop much voltage when it is switching.

In AC heater circuits I have seen far more SSRs fail in a shorted condition than an open condition. It would be a lot better if they failed open, but Murphy's Law is at work, I guess.

Jim

[printbus]

I agree on the voltage drop. A 50A SSR will likely have more on-resistance than a relay. The heat bed on the 12-inch printers is apparently lower watts-per-area than on the 8-inch and 10-inch, so I won't be surprised if we start hearing owners of the new 12-inch printers bemoaning long warm up times. Eliminating all the voltage drop you can could become real important on the 12-inch printers.

I've also grown to appreciate the click of the relay. It makes it easier to be doing something else while the bed is heating up. As soon as I hear the relay start to cycle off and on, I know I've got about a minute to get to the printer to check/wipe the priming of the extruder as the print starts.

For anyone wondering, the Omron G8QN relay used on the MakerFarm heat bed relay is rated for 30 amps.

[JimG]

For anyone wondering, the Omron G8QN relay used on the MakerFarm heat bed relay is rated for 30 amps.

According to the spec sheet for the Omron G8QN, the electrical contacts are rated for at least 100,000 operations. Assuming around a 5 second time base for the PID routine*, then the relay would be good for at least around 70 hours of operation. I guess I should have a plan for replacing mine at some point ;-)

Seems like a power MOSFET that uses the bed as a heat sink might be worth exploring?

Jim

* This was not immediately obvious to me in the Marlin code. Does anyone know what the default value is, and where the code is located?

[TechMasterJoe]

i tested and i see .6103v drop and have sense built a mosfet board based on
http://www.newark.com/international-...-7p/dp/28W1167
this will be a ground switching setup with a real mosfet driver feeding Gate voltage + opto-isolated
apx RDS will be under .0008ohm (test board .000691)
this i think will get the volt drop to stay under 0.02v at the switch
2 mosfets in parallel each rated for 260amps, 300amps pulsed
this will come with 10ga wire apx 3in long soldered on with XT60 connectors as i have tested them and see less then .01v drop at 30amps
i plan on making a few if anyone wants one PM me
test done with 200mhz Tektronix oscilloscope, Fluke 87-5 + i 410 amp clamp
I will include tested RDS with finished part and a thermal photo under 35amp load
test board is 1in by 1.15in 1.5oz copper PCB with 10ga wire soldered on temp on mosfet cases is 6.3c above ambient without a fan under 45amp static load
apx cost for each board will be around 11$ for 15$ i can include an extra 6ft of 10ga silicone wire (842 strands) + apx 3$ for shipping US only for now
this will cover just about any hotbed install i think

hey if anyone is bored hook your hotbed to a audio amp and place a magnetic on on the bed (best to take the glass off so it don't get broken)
it plays music (act's like a voice coll)

i just did some numbers based on the wire i have 10ga silicone ultra flex and yes it's true 10ga but even true 10ga will net a 2.5~3.5% loss in only 6 feet
i can cut this in half if i drop down to 8ga but price might go up a buck

[JimG]

Very nice solution.

Jim

[dacb]

Here is a data point... On my 10" MF, when it was in the garage, and ambient was > 20 degree C, I could reach 110 without a lot of struggle. Below that, it was constant on and problematic although I was well below the rated PSU wattage. I don't print a lot of ABS anymore so it isn't much of an issue and the printer is inside where 22 C is pretty close to the norm. Heats to PLA 70 deg by the time the extruder is hot. I like that ABL lets the bed warm thoroughly while probing. My sensor is mounted below the heater PCB per the directions. I use a cardboard spacer which doesn't reflect heat upward as I'd like. I tried (briefly) a silicon potholder and found it the same as cardboard. So now we use the potholder in the kitchen. I've wondered: How do Al beds do? I occasionally come across a slice of Al that would work but I think about adhesion. The sensor below doesn't really reflect what is actually going on at the glass surface. Particularly hardware store glass like I run. I always figured a drop in thermal transmission through the glass so the extra time lets the temperature penetrate and as glass is an insulator this can take some time vs. what the probe reads.

IIRC, some, like maybe clough42, don't use a heated bed for PLA? I also recall 200mm bridges from his masterpiece, so I aspire.

Not a 12in so YMMV.