Duet3 5V power question
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I've been digging through the forums trying to better understand how the three jumpers for 5V work on my new duet 3. Specifically, I'm wondering about the safety of having the internal supply jumper (INT 5V EN) jumped while using both the USB power and 24V. I found a post from 2018 that I think is about duet 2 which says this should be safe, but I want to double check for the duet 3.
Additionally, if USB is provided and the internal source is enabled, which provides the power and what will happen if one is cut off? (ie if the USB or 24V supply shuts off, will the SBC and duet internals keep getting power?).
And finally, if the duet 3 provides the power while both are connected, is there any concern with back feeding into the USB power?
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@ddeflyer said in Duet3 5V power question:
I've been digging through the forums trying to better understand how the three jumpers for 5V work on my new duet 3. Specifically, I'm wondering about the safety of having the internal supply jumper (INT 5V EN) jumped while using both the USB power and 24V. I found a post from 2018 that I think is about duet 2 which says this should be safe, but I want to double check for the duet 3.
The INT 5V EN jumper turns on the internal Vin -> 5v buck converter. The disadvantage to the internal converter is that you can't separately control the power to the motors, heaters, etc from the board logic.
It's safe to have both the internal converter and USB providing 5V at the same time although it can get confusing.
Additionally, if USB is provided and the internal source is enabled, which provides the power and what will happen if one is cut off? (ie if the USB or 24V supply shuts off, will the SBC and duet internals keep getting power?).
Both supplies are tied together so it's not an "either or" situation. They can both be providing 5V but given that the internal converter can supply more current (about 4A based on the converter's spec sheet) it's probably going to take most of the load. If USB power drops, everything should keep chugging along. If the Vin drops and the converter shuts down, it'd be a fair bet that whatever's supplying the USB power will NOT be able to keep both the Duet AND the SBC powered.
And finally, if the duet 3 provides the power while both are connected, is there any concern with back feeding into the USB power?
No. There are protection diodes in place to prevent backfeeding to the USB port.
Personally, I don't like powering from USB. In fact, I made a suggestion to the Duet team that they should add another jumper to disconnect USB power all together. In the mean time, I gave a USB cable a vasectomy to prevent power from coming that way. I also don't use the internal 5V converter because I want to control Vin separately from the board logic. I actually power the Duet3 from the SBC. It's one source of power and with an adequately sized power supply can power both the SBC and Duet3 very nicely.
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Thank you, this was very helpful!
