Duet 3 Mini 5+ - 12V Rail Total Current Draw Above 800mA?

RogerPodacter

I am slightly above 800mA with 4 devices connected to my OUT3-OUT6 on a Duet 3 Mini 5+. I am interested to know which model/part number chip regulates the 12 volt rail, and if it has any safety margin designed in? I would like to run slightly above at approximately 1 amp. I want to run the following components but i dont want to stress or burn out the regulator.

Water Pump 0.475 amps @ 12 volt
Radiator Fan 0.290 amps @ 12 volt
120mm Noctua fan 0.96 amps @ 12 volt
Small fan 0.035 amps @ 12 volt

Total Current 0.9 amps (896 mA)

I have directly measured each device while in operation with a power supply to obtain the above power draw. Could the Mini 5+ handle up to 1 amp current draw on 12 volt or is that pushing it too far?

On the 5 volt rail i have a PanelDue 5, one Endstop, and a thermocouple daughterboard running 2 TC's.

infiniteloop

@RogerPodacter said in Duet 3 Mini 5+ - 12V Rail Total Current Draw Above 800mA?:

I am slightly above 800mA with 4 devices connected to my OUT3-OUT6 on a Duet 3 Mini 5+.

Nice calculation, but you have to consider the initial currents as well (rule of thumb: twice as much). Water pumps are especially tricky, they take some more current until the water flow is established. So, I would add an external P-MOSFET for the pump and feed it separately.

RogerPodacter

@infiniteloop yea it looks like the pump pulls almost double current when first turned on. but i was hoping the regulator can handle such a short blip of power since it would not be supplying continuously. i already have an external 12v power supply, but i am trying to save that for another device so i want to max out the Mini 5+ as much as feasible.

infiniteloop

@RogerPodacter

so i want to max out the Mini 5+ as much as feasible.

I've tried that, at the expense of the MOSFET on the respective OUT port.

On another thread, you linked to the pump in question: that is specified with 0.7A at 7V. Driving it with 12V from the Duet is completely out of spec. Both other versions ("colours") tolerate 13.5V. Maybe the 7V are wrong data, but I would use an external MOSFET anyway, except of… if you are a soldering addict

RogerPodacter

@infiniteloop ok so its a bad idea. thanks for the input!

dc42

@RogerPodacter can you use a 24V water pump instead?

RogerPodacter

@dc42 well i have a 12 volt Noctua fan connected to the other 4 wire PWM, so not really. and i already purchased the 12v pump. but i guess i could ultimately change both devices to a 24v version which would solve my issue in the longterm.

thanks all for the help.

RogerPodacter

amendment to my question, what if i put the 0.475 amp pump on the Duet 3 Mini 5+, and put the other 3 devices on my 3HC expansion board? i assume the Mini 5+ could easily handle that load safely?

dc42

@RogerPodacter if the 0.475A pump uses a brushed DC motor then the starting current could temporarily overload the 12V regulator; however that should not matter because the 12V rail on the Mini5+ isn't used for anything other than the OUT ports, so a temporary drop in voltage shouldn't matter. Whereas the 12V regulator on the 3HC also feeds the stepper drivers, so if the voltage dips even for a short while then the drivers will lose their settings.

RogerPodacter

@dc42 thats useful info, many thanks.

this pump is not a brushed motor its a modern consumer electronics PC cooling pump. to be confident this morning i used an Oscilloscope and external power supply to monitor startup current of this pump, and it has a slow linear increase from zero to 0.475 amps over about 0.5 seconds. I'm ok with this and willing to take that risk running it on the Duet 3 Mini 5+.

i would like to add the large fan, and it has about a 140% startup power draw to 0.355 amps, and stablizes at 0.295 amps. both devices together pump and fan i think i am safe to use them on 12 volt.