Hotend Temp off by several degrees

[atoff]

Mine's actually the same way. I have to set it to about 215 to get to 209-210c, the bed is rock steady. The Nozzle fluctuates quite a bit.

[Barefoothurst]

The problem is that when I print fast and need heat, the hot end can't keep up even though it's being supplied with 100% power according to the repetier host graph. It's like 20c low at times.

[Polygonhell]

Mine's actually the same way. I have to set it to about 215 to get to 209-210c, the bed is rock steady. The Nozzle fluctuates quite a bit.

This can be the result of a P value that is too small or an I value that is too small, or a D value that is too large.

PID autotune is at best a starting point.

I find PID autotune in repetier to give bad results, especially with the 40W heater cartridges that are common now, and Aluminum heater blocks. If I autotune my E3D without a cooling fan running, the resultant PID's will end up with a 10 degree temperature variation at 240C, I can tweak the PID's by hand and get that down to less than 1C.
With a cooling fan running it's a lot better because some of he efficiency of the heater is lost, so it's less prone to overshoot.

When I change plastic from PLA to Nylon (I run the latter without a cooling fan) I change my I value form 2.5 to 0.5.

[Barefoothurst]

i have been researching to try and learn how to adjust the PID values to try and get a better result. According to Repetier host graph, its applying full power to the hot end but it just can't keep up while printing, leaving me to believe that i have a bad resistor.

[geneb]

If you've got a cracked resistor, it's done. It needs to be replaced.

g.

[Barefoothurst]

If you've got a cracked resistor, it's done. It needs to be replaced.

g.

ok then. Im down until my 40w heater arrives.

[Polygonhell]

If you've got a cracked resistor, it's done. It needs to be replaced.

g.

Agreed

But if your interested this http://www.flitetest.com/articles/p-i-a ... a-nutshell is IMO a very clear explanation of PID's without disappearing down the mathematical rabbit hole, it's describing motor gains for quadcopters, but the principles are identical.

[Eaglezsoar]

If you've got a cracked resistor, it's done. It needs to be replaced.

g.

Agreed

But if your interested this http://www.flitetest.com/articles/p-i-a ... a-nutshell is IMO a very clear explanation of PID's without disappearing down the mathematical rabbit hole, it's describing motor gains for quadcopters, but the principles are identical.

A very interesting and easy to understand read. Thank you for posting the link.

[Barefoothurst]

Well I installed my 12v 40 watt cartridge heater and the difference is amazing. Printing nylon at 235c the heater is only running at around half power. This is a good and bad thing. I love the power and speed of warmup but I am worried that a eventual thermistor fail will see me with a fire on my hands. I would like to lower the max voltage applied to the heater so that I can dial back the power to just enough. This way if a thermistor fails I have less of a chance of a fire. Where in the firmware can I find the voltage setting for the hot end?
Thanks again for all the help

[geneb]

There IS no voltage setting for the hot end. You might be able to limit how much power it's fed by changing the max PID value, but someone else more knowledgeable than I needs to comment on that.

g.

[Polygonhell]

There is a setting called
EXTR1 PID Drive MAX in the EPROM, it sets the maximum PID on time the firmware is allowed to apply.
128 would be roughly half on, half off.
It doesn't modify the maximum voltage, but given then PID frequencies involved it behaves much the same way.
Now having said that I doubt that would prevent a fire in he case of a run away Hotend, but in practice the only way that happens is if the thermistor is pulled out of the Hotend and still functional. If it falls it usually results in an error state and shutdown.

[seanriddle]

Well I installed my 12v 40 watt cartridge heater and the difference is amazing.

Did you have to enlarge the hole in the hot end to get the cartridge heater to fit? What did you do with the other hole?

Thanks!

[Eaglezsoar]

Well I installed my 12v 40 watt cartridge heater and the difference is amazing.

Did you have to enlarge the hole in the hot end to get the cartridge heater to fit? What did you do with the other hole?

Thanks!

You can leave the other hole empty, cut a small piece of copper or brass for a little bling, or use it to heat your salami.

[Barefoothurst]

thanks for all the info guys. The hole was actually a little oversized for the heater so I inserted the heater and used a vice to carefully squeeze the outer wall to hold the heater in place. The otter hole remains empty. I wrapped the whole assembly in high temp tape to insulate and hold everything in place. its been printing for a whole day now and it works great! well worth it.

[smiley]

I love the power and speed of warmup but I am worried that a eventual thermistor fail will see me with a fire on my hands. I would like to lower the max voltage applied to the heater so that I can dial back the power to just enough. This way if a thermistor fails I have less of a chance of a fire. Where in the firmware can I find the voltage setting for the hot end?
Thanks again for all the help

If you are running .91 firmware like I am and your thermistor fails like mine did, the printer will go into dry run mode, which means it will cut all power to the hot end heater and the extruder stepper.