MakerBot Industries

I did measure the resistance on the board. I get 2 Ohm.

Ya, he asked about resistance and he wanted me to check the wires voltage, to see if maybe I have a frayed wire, or some other connection problem.

I think 2 ohms is too low. I'm sure someone else can check theirs.

I know at 2.5 ohms an extruder takes AGES to heat up.

Ya, I would like it if someone can check what their Heater Board V 1.1 reads for resistance on the heater leads. Anyone?

So my heater board resistance is fine at 2 Ohms at room temp then?

Ok. With the heater board on, my red lead from the multimeter plugged into the back of the connector in heater power red and the other black lead from the multimeter plugged into an unused molex connector ground. It reads 11.1 V. So there is a difference of .7 volts.

Now, with the red and black wires disconnected from the heater board, but the thermistor wires still connected and the heater ON…. testing at the heater board cable connector I get 12 V. From the phoenix clip, with no wires connected TO the phoenix clip, I get 12V DC. I am using a I think 16 AWG wire and I don't think my multimeter has a high enough resolution to pick up the differences between the two. So, this means I cannot calculate the resistive drop.

So…. Ed, are you telling me that reading 11.1 volts at the heater, while the heater is on…. does that mean there is something wrong with my heater…. or not?

It seems to be getting faster every day…. is it possible that these heaters have a break in period? Probably not, huh? Because with the default setting of 130 C, there would be a lot of new users complaining about how their bots NEVER start printing. Because on the first day I couldn't get above 110 C. Now I can get to 130C and beyond. Also, my speed has been gradually increasing. As of my last test, I am just shy of beating the extruder to its operating temp.

That means, 130 C at 6:30 seconds, last tested. This seems acceptable, considering, when I was getting 4:30 second start times, I was using a glass platform. Which has very different thermal properties from aluminum. The glass would of course reflect alot of the heat back to the board, where the thermistor is. With the aluminum, it is constantly spreading and dissipating heat. So of course it would take a while longer to reach temperature.

Oh, and btw, I am not the one with discolored connectors. I think that was someone else!

So, my board may be almost functioning normally now…. however, I feel I must mention, my PID settings are P !00, I 0, D 0…. so maybe my board isn't functioning close to 100% after all?

It reads 11.1 V

Ah! Numbers!

Your earlier reading of 10.4 V across the heater says it will draw 10.4 V / 2 ohm = 5.2 A and dissipate about 55 W.

Dropping 0.9 V from the +12 V supply to the heater seems excessive; that means there's 0.9 V / 5.2 A = 0.175 ohm in the wiring / connectors / whatever.

The switched wire to the Extruder Controller drops 11.1 - 10.4 = 0.7 V in the wire and the MOSFET. I think the MOSFET accounts for 0.1 V of that.

Stranded 16 AWG wire has about 4 m-ohm/ft resistance, so 5 ft of wire will drop about 0.1 V. Stranded 18 AWG is 7 m-ohm/ft and will drop nearly 0.2 V. You're seeing more than that, which suggests there's more resistance in the connectors than you'd like. However, that's the nature of Molex connectors and the wiring (which we're ignoring) from the power supply to the EC.

It seems to be getting faster every day…

The heater should be pretty stable. What with all the fiddling around you've been doing, I suspect you're rubbing some crud off the connectors. At 5 A, it doesn't take much corrosion / dirt / oxidation to build up a little resistance and with a 2 ohm load, a little excess resistance goes a long way.

my PID settings are P 100, I 0, D 0

All that does is turn the heater fully on until the thermistor reaches about 2 C over the setpoint. After that, the EC switches the heater on & off with a +/- 2 C deadband around the setpoint temperature; the plate's thermal mass smooths out the small oscillations and the plastic part never notices anything.

Remember that the thermistor temperature applies to the bottom of the heater PCB. Glass is a better insulator than aluminum, so I suspect the top of the plate is now much closer to the thermistor temperature than it was before. The glass may have seemed to heat faster, but the top may have actually been cooler.

Incidentally, IR thermometers aren't useful on glass or metal surfaces, due to their low emissivity. Kapton tape has a surprisingly low emissivity, alas. Black electrical tape is good, but turns into slime at 120 C. Blue painters tape seems passable. Measure a consistent surface and make sure it fills the thermometer's field of view…

Anyhow, I'd say you're getting about as much performance out of that poor heater as can reasonably be expected…