Heating the Hotend and the Bed
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No need to install the MOSFETs. It's still worth measuring the voltage on the bed terminals - take great care not to short the multimeter probes together while doing this. Then compare that voltage with the voltage on the PSU output terminals.
If there is a difference of more than about 0.2V between the two voltages, consider using thicker wires, and check that the terminal block screws on the Duet are tight. Otherwise, turn up the voltage on your 12V PSU, then retune the heaters.
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I am indeed running an ATX.
I know you can adjust psu voltage, but from my research you can't adjust atx voltage without modifying it.
Isn't this correct?Maybe the atx is the problem for ALL my heating problems and I should just replace it with a psu.
Or maybe a bigger atx? I thought 450w of which 360w is dedicated to the rail running to the board would be plenty. -
You may find that your ATX PSU is providing somewhat less than 12V on its 12V output. The less expensive ATX PSUs use a single feedback loop that averages the error on the 12V and 5V outputs. So if you have a low load on the 5V output and a much bigger load on the 12V output, the 5V rail ends up being high and the 12V rail ends up being low. The better branded PSUs don't have this problem.
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Thank you, David.
Is there an ATX that you'd recommend that would power everything adequately?
I thought I had bought a decent one, but apparently not. -
What brand of PSU did you buy?
I only have experience of two ATX PSUs powering a 3D printer. The Alpine PSU (550W AFAIR) one that came with my Ormerod kit had the problem I referred to above. I then purchased a Corsair CX430M, and that one was much better - the 12V rail remained close to 12V under varying loads and the bed heating time was less. But after that I bought a cheap 300W fanless Chinese LED/CCTV PSU and enclosed the business end of it like this https://www.thingiverse.com/thing:441081. It's been powering that printer for about 3 years.
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APEVIA Venus 450W from Amazon.
It had good reviews and I never thought the power drop would be that much despite the higher wattage.The only reason I wanted an ATX was for the remote power on option, the ability to navigate DWC without powering up the whole printer, and the 5v rail to power my Pi Cam, all in one box and having one power cord for everything.
I am of the mind now to just get good PSU and turn it on the old fashioned way, while separately powering the RPI.
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I suggest you measure the 12V output of the PSU, with the bed heater both off and on, to see how good that PSU is.
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ATX PSUs aren't just 12V. A 450W PSU will be the 3.3V, 5V, and 12V rails added together. On the Apevia Web page the current on the 12V rail is 32A, i.e. 384W. Therefore the Anet and CoreXY should be similar on the paper. If the ATX supplies several 12V rails, the current on one f the rails might be even lower.
Have you tried to perform a PID tuning (M303) wit the P parameter? The P parameter is the PWM fraction to use.
I have recently migrated my PSU to 24V with a 50W heater and I noticed that with standard PID calibration the M303 without the optional P parameter produced a temperature overshoot. The temperature it raised very quickly to the desired temperature, but the risk of fire in the case of an issue is high. I returned the temperature adding the P parameter with a final value of 0.3 that does not produce the temperature overshoot warning but on the downside it takes longer to reach the printing temperature. It is not a big problem for me, because the print has to wait for the bed anyways.As I understand from the Wiki, the default value for the P parameter is 0.5. Try re-tuning the PID with a specific P parameter on higher values and check the results.
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This is the specification for you PSU on the Apevia Web page: http://www.apevia.com/ProductsInfo.asp?KEY=Venus%20Power%20450W%20(ATX-VS450W)
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As I understand from the Wiki, the default value for the P parameter is 0.5. Try re-tuning the PID with a specific P parameter on higher values and check the results.
That's only true for old versions of firmware. On recent versions (1.18 and later AFAIR) the tuning algorithm is different and P1.0 is the default.
If you are using a 12V heater cartridge with 24V power, I strongly advise you to buy a 24V cartridge and use that instead.
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Thanks for the clarification. I just re-read the Wiki and for V1.18 it mentions the default value of P=1.0 (my bad)
My cartridge is from Aliexpres and specifies 24V/50W. However I have measured a resistance of 8.1 ohms, which would mean 20W if powered with 12V and 71W if powered with 24V. That got me thinking of the quality…...
