Powering 12V_EXT on Duet3 1.01

[DocTrucker]

Morning All.

The advice for the 12V rail on the Duet3 is 800mA and "small fans". The fans on the Raise3D Pro2 dual head seem to be fine for that. Two small part cooling fans and a larger fan (all axial) for the heat break coolers.

The issue is I also have an LED strip for part bed illumination and a larger (rated 400mA, main case diameter ~70mm and ~20mm wide) radial blower that I'm repurposing to blow air under the main board. I think I may be pushing my luck on the 800mA guide.

I had thought about feeding 12V to the permanent fan connector but not sure how current draw would be ballanced between the onboard and external regulator. The former is diode protected against reverse current but if supplying marginally higher voltage it could end up supplying all the current anyway.

Plan b is just to feed the posative legs of the fans from the external source and sink through the board. The MOSFETs on the curcuit diagram are labelled Q25A/Q25B. I couldn't find a spec sheet on these. What is their safe continuous - rather than peak - current draw?

[droftarts]

@DocTrucker said in Powering 12V_EXT on Duet3 1.01:

@droftarts cheers. Missunderstood your first message as 2A limit when using 12V derived from VIN, rather than 2A limit per output when the jumpers are set to feed V_IN to the outs.

That said I'm surprised the selector-jumpers itself doesn't limit the current more than it aparrently does.

Hmm... actually, I think you are correct, as the selector pins are Molex KK too. Molex KK has a current limit of 2.5A (see the 'product specification' links on this page), and that applies to the voltage selector as well as the actual fan pins. Jumpers are rated at around the same https://www.farnell.com/datasheets/2706775.pdf. So the limit per bank is 2A (to be on the safe side), though if you are supplying power separately, and just using the MOSFET on the GND side, 2A is fine for the header. Also, the MOSFET DMT6018LDR appears to be rated for 8.8A: https://www.diodes.com/part/view/DMT6018LDR

I'll check with the others, and will likely update the documentation.

Edit: we use Wurth pin headers, which are rated at 3A, as are the jumpers, so maximum total current for each group of fans fed from a voltage selector is 3A.

Ian

[droftarts]

@DocTrucker when powered from VIN, the current limit is usually 2A on the fan connectors, on a Mini 5+ at least (I can’t remember which Duet 3 you have). I’d expect the same limit on the GND side (ie the MOSFET) if you are supplying it from an external supply. See the pin description here: https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Mini_5+_Hardware_Overview#description-of-connections

Ian

[DocTrucker]

@droftarts it's the full fat main Duet3 board with the steppers on board. Revision 1.01. The docs say 800mA draw when using the onboard 12V supply, but it doesn't say what the individual MOSFETs are rated too if I feed the 12V side of the devices being switched from an external source. I can't see the part codes for the MOSFETs. I think the Q references are simple the components ID on the board rather than it's manufacturer part code.

[droftarts]

@DocTrucker it’s in the same place in the 6HC docs: https://docs.duet3d.com/Duet3D_hardware/Duet_3_family/Duet_3_Mainboard_6HC_Hardware_Overview#description-of-connections

OUT 7, OUT 8, OUT 9 These are intended for fans. Maximum recommended current 2A each when supplied by VIN.

Often these are limited by the current capacity of the connector, rather than the MOSFET, though I don’t have a part number for that to check.

EDIT: If you look at the ibom https://github.com/Duet3D/Duet3-Mainboard-6HC/tree/master/Duet3_Mainboard_6HC_v1.01 I think the MOSFET part number is DMT6018LDR.

Ian

[DocTrucker]

@droftarts cheers. Missunderstood your first message as 2A limit when using 12V derived from VIN, rather than 2A limit per output when the jumpers are set to feed V_IN to the outs.

That said I'm surprised the selector-jumpers itself doesn't limit the current more than it aparrently does.

[droftarts]

@DocTrucker said in Powering 12V_EXT on Duet3 1.01:

@droftarts cheers. Missunderstood your first message as 2A limit when using 12V derived from VIN, rather than 2A limit per output when the jumpers are set to feed V_IN to the outs.

That said I'm surprised the selector-jumpers itself doesn't limit the current more than it aparrently does.

Hmm... actually, I think you are correct, as the selector pins are Molex KK too. Molex KK has a current limit of 2.5A (see the 'product specification' links on this page), and that applies to the voltage selector as well as the actual fan pins. Jumpers are rated at around the same https://www.farnell.com/datasheets/2706775.pdf. So the limit per bank is 2A (to be on the safe side), though if you are supplying power separately, and just using the MOSFET on the GND side, 2A is fine for the header. Also, the MOSFET DMT6018LDR appears to be rated for 8.8A: https://www.diodes.com/part/view/DMT6018LDR

I'll check with the others, and will likely update the documentation.

Edit: we use Wurth pin headers, which are rated at 3A, as are the jumpers, so maximum total current for each group of fans fed from a voltage selector is 3A.

Ian