Flickering lighting LED's when heat bed heats
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@dc42 could you suggest an external mosfet that’d work well with my board or they all pretty much the same? Thanks
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An external mosfet won't help if the flickering issue is caused by the PSU. It will only help if the issue is the resistance of the wires between the Duet and the PSU.
I suggest you measure the voltage at the PSU terminals, and at the Duet VIN terminals. Do this both with the bed off and with it on continuously (i.e. heating up). If you tell us those 4 values then we can advise on the best way forward.
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Unable to measure at the Power adapter terminals because it uses a R7B connector but at the VIN terminals it was 24.2 volts with the heater off and 23.83 volts with the heater on continuously. One thing I did notice was that the lighting LEDs flickered and the power adapter buzzed together when the temp reached 50°C. Also, because I had the printer on it's side, I could see that there was a red LED flickering next to the VIN to Bed fuse.
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Has anyone got an idea as to what is going on please?
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@JTBrown said in Flickering lighting LED's when heat bed heats:
red LED flickering next to the VIN to Bed fuse
That is the LED showing the bed heater is turning on and off (which is normal with it set to PWM)
The voltage drop you indicated (from 24.2 to 23.8) should not be enough to make the LEDs flicker.
Can you try setting the Bed heater to "Bang Bang" for now and see they flicker as the heater turns on and off ( set B1 in the M307 command for that heater)
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@JTBrown said in Flickering lighting LED's when heat bed heats:
I've just taken it to 600 and it still buzzes. The flickering stopped though so that's a start.
Think I'll just keep the LED's turned offThe buzzing is the PSU responding to the change in load at the PWM frequency. It's probably harmless.
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@T3P3Tony Thanks that done the trick. Could you explain why? many thanks Jim
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I suspect the improvement in behavior with increasing PWM frequency has to do with stored energy in the filter capacitors. You may be very close to the limits of your power supply, ad it cannot provide 100% to the bed. At low PWM, you are fully depleting the filter capacitors, and requiring the power supply to ante up a full-power pulse during the 'on' phase. At higher frequency, the filter capacitors are supplying enough energy, and the power supply only sees the average load. It is likely to work much better with a bigger power supply.
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@mendenmh Hi, thanks for your input, it was the "setting the bed heater to Bang Bang" suggestion that worked. cheers
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@JTBrown That is moving to the other extreme, in which the power supply's feedback loop probably has time to catch up and keep the voltage constant. If the supply has enough oomph, it may be ok. The observed behavior, though, was a sign you might be near the edge. The other possibility is that the supply is badly designed, so the low-frequency behavior of the regulation doesn't cross over nicely with the filtering of the capacitance. Incidentally, I had this problem, exhibited differently, and very annoyingly. For many months, all the LED lights in my house flickered annoyingly. It took a long time to associate it with the 3d printer. Somehow, the PWM frequency for the bed, which I had at one point set to 30 Hz, had gotten trampled back to the default 10 Hz. It takes only a tiny bit of line voltage variation at 10 Hz to crate enough flicker for the eye to see. It's pretty much at the top of the frequency response. So the whole house line voltage was being microscopically modulated, resulting in a drool-inducing flicker.
