PID Tuning help needed
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@deckingman Hi, I get 4.1ohm. I don't know if this can be correct, as it 'feels' too little?
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@Reefwarrior typical resistances
P\V --------------------- 12V---- 24V
40w (Red Leads) 3.6Ω 14.4Ω
25w (Blue Leads) 5.76Ω 23.04Ω -
@Reefwarrior said in PID Tuning help needed:
@deckingman Hi, I get 4.1ohm. I don't know if this can be correct, as it 'feels' too little?
So, if my maths serves me correctly, V=IR, so I=V/R = 24/4.1 = 5.8536Amps. Wattage = VI = 24 x 5.853 = 140.48 Watts !!
If the voltage was 12, then the current becomes 2.9 Amps so the wattage would then be 12 x 2.9 = 35 Watts.
So it looks you have a nominal 40 watt \ 12V cartridge so when you put 24V through it, you get roughly 4 x the heating power.
Note. A 40 Watt/24V cartridge would have a resistance of about 14.5 Ohms.
Edit. A 40W/ 24v heater cartridge would draw about 1.65 Amps which is perfectly safe to use with the onboard MOSFETs - no need to use an external one.
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Thank you all for the feedback. Yes seems I am running a 12V then at 24V. I take it I can't just put in a power factor of P0.25 to fix this? Or will it be better to rather just swap it out for a 24V cartridge?
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@Reefwarrior said in PID Tuning help needed:
Thank you all for the feedback. Yes seems I am running a 12V then at 24V. I take it I can't just put in a power factor of P0.25 to fix this? Or will it be better to rather just swap it out for a 24V cartridge?
Running 25% PWM is bad idea IMO. The problem is that, if a MOSFET fails, then you could end up with the full ("permanent" as in non PWM switched) 24V which could be a fire risk.
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@Reefwarrior swap it. it will be unsafe until you do so
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Cool thank you. I will swap it out this afternoon then, and see if it is better.
With regards to the temperature measurement. Is it normal for it to jump up and down a few degrees? The graphs show spikes, instead of a normal flat line....
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@Reefwarrior said in PID Tuning help needed:
Cool thank you. I will swap it out this afternoon then, and see if it is better.
With regards to the temperature measurement. Is it normal for it to jump up and down a few degrees? The graphs show spikes, instead of a normal flat line....
I think you'll find it's a lot more stable with a cartridge that is a better match to the hot end. The PID control can only do so much and when you have a heater that is over powered by a factor of 4 then you are likely to get overshoots when it turns on.
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@Reefwarrior said in PID Tuning help needed:
Is it normal for it to jump up and down a few degrees?
No, check your wiring. Either it's picking up interference (usually from stepper motor or endstop wiring), or there's a poor joint. It will also cause the PID tuning to fail, as it can't get a consistent reading, and it's probably why it's taking so long to tune.
Are you using a thermistor PT1000, PT100 or thermocouple? There are ways to make the last two more reliable, by using four wires rather than just two.
Ian
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@droftarts Hi Ian,
It looks like one of those little glass bead thingies that measures the temperature....
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@Reefwarrior Sounds like a thermistor. Check your wiring, and make sure the leads of the thermistor aren't grounding on the heater block, and that the thermistor bead is making good contact with the heater block (ie not flapping about in a big hole!). Cartridge thermistors, or PT1000, are generally easier to use and get good contact with. What kind of hot end is this?
Ian
Cartesian bed-slinger with Duet 3 Mini 5+ WiFi and 1LC : RRP Fisher Delta v1 with Duet 2 Maestro : TronXY X5S with Duet 3 MB6HC and Roto toolboard
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@droftarts E3d v6 clone. I will take a look at the hotend too....
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@droftarts Did you check the earlier posts? It transpires the OP has a 12V cartridge and a 24V system. So around 140 Watt instead of 35. Methinks, that's more likely to cause the oscillations.
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@deckingman Yes, read the whole thread. @Reefwarrior said "The graphs show spikes". While I'm sure the heater can create a spike up in temperature, it probably can't create a drop as quickly! But a dodgy thermistor can, though I guess it could be a power drop across the board when the heater switches on, if the PSU isn't up to it.
@Reefwarrior A screenshot of the temperature graph misbehaving would go some way to disambiguate the cause of the "spikes". Try wiggling the thermistor wires, see if that causes the spikes, too.
Ian
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@droftarts I guess it depends on the definition of "spike". I read this (quote)
Other strange thing is, there are quite a lot of oscillations with regards to the temperature being sensed. (Up to 3 to 4 degrees up and down)
As you say, we need a picture of the graph......
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A picture of the graph would be nice, but don't don't run that 12v heater at 24v just to make a graph for us. You're liable to melt something. Just replace the heater with a 24v version before you do anything else.
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Hi all,
OK so I swapped the cartridge for a 24V one. Did the PID tuning... results:
Warning: heater behaviour was not consistent during tuning
Auto tuning heater 1 completed after 4 idle and 25 tuning cycles in 1494 seconds. This heater needs the following M307 command:
M307 H1 R3.064 C165.3 D10.06 S1.00 V24.3
Send M500 to save this command in config-override.gBothers me a bit with the 'warning'. Also it seems the temperature sensing thing is a PT1000 I think? It's a little silver cylinder that connects directly to the board, no daughterboard. Chinese brand.
there is the picture that I am referring to. Look at both the blue and the red - the curves are not smooth - it's like jagged. Even the 'MCU Temperature' seems to oscillate by about 1 degree up and down (including the decimals....)
Also got this after PID tuning my bed:
Warning: heater behaviour was not consistent during tuning
Auto tuning heater 0 completed after 4 idle and 25 tuning cycles in 1536 seconds. This heater needs the following M307 command:
M307 H0 R1.369 C277.3 D5.29 S1.00 V24.2
Send M500 to save this command in config-override.g -
@Reefwarrior said in PID Tuning help needed:
Also it seems the temperature sensing thing is a PT1000 I think? It's a little silver cylinder that connects directly to the board, no daughterboard. Chinese brand.
Why do you think Pt1000? It could be a plain thermistor.
Photos?
Yeah that graph looks a bit fuzzy which would explain the warning.
The overall curve of the graph looks ok though, so I think the values it provides should be usable.
Perhaps a good time to replace the temp sensor with something better quality.
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@Phaedrux Unfortunately I am not in a position to be able to do that. I'm one of 70 pilots that got retrenched when our government decided to liquidate the national airline.
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I'm not sure that that means, but if you want to continue to roll with the equipment on hand, you can verify that the tuning results are accurate by setting a printing temp and seeing if the graph and reported temps are stable.
The fuzziness in the graph may also be a result of noise from running near other cables. You could verify that by temporarily isolating the thermistor wiring and seeing if that makes a difference.
