Interference.

I am using a Mosfet unit to control the bed heating, but it is causing interference with the TV, is there any way I can stop this, maybe some sort of filter.
moving the printer or TV is not an option.

Does the interference start:

1. as soon as you turn the bed heater on, or:
2. when the bed heater temperature approaches the set point.

If #1 then it is the PSU generating the interference, not the bed heater and mosfet.

If #2 then the mosfet is probably turning off too fast and the back emf caused by the inductance of the heater and the wiring is causing the mosfet to avalanche. Run the 2 bed heater wires next to each other to minimise inductance. You can add a Schottky flyback diode or RC snubber network in parallel with the bed heater to catch the back emf spike, or a capacitor between mosfet gate and source terminals to slow down the mosfet turn off to around a microsecond.

Edited 1 time(s). Last edit at 02/11/2019 02:39AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

thanks for taking the time to reply.
As soon as the the Mosfet clicks in it halts the picture and sound, once the heat reaches it's temp it starts, as the temp drops and the Mosfet clicks in so it interferes with the TV.

One thing I didn't mention here, is that it only interferes on certain channels not all. This sounds as if it a frequency thing,

Quote
erniehatt
thanks for taking the time to reply.
As soon as the the Mosfet clicks in it halts the picture and sound, once the heat reaches it's temp it starts, as the temp drops and the Mosfet clicks in so it interferes with the TV.

Sounds like the PSU is generating the interference when it is heavily loaded. What sort of PSU is it?

The other possibility is that the bed heater MOSFET is oscillating. Unlikely, but not impossible if the layout of your controller electronics wasn't designed to prevent it.

Edited 1 time(s). Last edit at 02/14/2019 05:22PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks, Here's a link to the PSU
[www.ebay.com.au]

Sadly that is a generic china power supply, the insides are often quite different from one to the next.

I would get a second supply, from a different source, as a spare is never a bad thing

Then swap them and see if anything changes.

Thanks to both of you for your feedback, much appreciated'
Yes, a spare will not go astray, I may just do that.