Duet 3 Firmware configuration issues
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You can drive a relay with low side switching, but you're right mechanical relays isn't the best choice, even with low PWM frequencies they'll be switching under load which isn't ideal. Solid state relays, or using the heater outputs as is would likely last longer. (Ouputs 1 through 9 have diodes to protect against back emf from driving relays and other inductive loads directly).
Not sure if the limitation of using PT100 daughterboard on expansion is one of the web configurator (its made to give you a starting poing and support the most common setups, not every possible setup) or if the limitation of needing to have the sensor on the same board as the output is still not resolved (thought it was, but not sure)
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@deckingman I wrote relay but I meant SSR. They worked on the previous configuration.
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@Pierrelito That should be fine but remember to set the PWM frequency to something like 10Hz. I'm not sure what the default frequency is. It used to be 10Hz for bed heaters using the bed output and (I think) 500Hz for everything else.
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in RRF3 the default is
500Hz for all outputscurrently 250hz for all heaters, 500hz for all fans, and 50hz for all sevos. so still a good idea to specify Q10 for the SSRs (which was the default for bed output in RRF2), and use zero cross detection SSRs for minimal EMI. -
@bearer said in Duet 3 Firmware configuration issues:
in RRF3 the default is 500Hz for all outputs, .......................
Are you 100% sure about that? My memory is crap these days but I thought I remember reading somewhere that when creating a bed heater (H0), the frequency would be set to 10Hz by default, for backwards compatibility. Could be wrong - most likely am. But this prompted me to check my config and I haven't specified a "Q" value for my bed heater which is mains via an SSR and it's been working fine since I converted to gen 3 last July(ish).
I'll add a Q10 to my M950 H0 in any case.
Edit. But if there is a 10Hz default, it might be applied to out.0 rather than to H0.
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@deckingman said in Duet 3 Firmware configuration issues:
Are you 100% sure about that?
i thought i was; but its 250hz for heaters and 500hz for fans and 50hz for servos. An any case no ouputs defaults to 10z after RRF3, not even !bedheat on a duet2 as H0.
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@bearer Ah, OK (but it's a little surprising). I'll see if I can get one of the moderators to highlight those defaults in the documentation.
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Also back on topic, the OP should be aware of the limitations regarding heaters, sensors and combinations thereof, with regard to expansion boards as documented here https://duet3d.dozuki.com/Wiki/Duet_3_firmware_configuration_limitations
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@deckingman Thank you very much for this document. Never saw it before, it will come in handy.
