Dual PSU 12/24v

phantomix

@fizban
24V has many advantages for heaters (less current for the same power) and for the TMC stepper drivers (more headroom for their operation. I think Alex Kenis did a video on that, which I currently cannot find [1]).

The fans are controlled by TR1 / TR5 / TR9? which only connect the minus side of the fan to ground. [2]

If you need to stay with 12V fans you can, as I understand it, I would try it as follows (see wiring [3]):

connecting both grounds of the supplies together
connecting "POWER IN" to the 24V supply
remove the "V FAN A" / "V FAN B" jumpers. Imagine "VIN" and "5V" as outputs on these pin headers and "V_FAN_A" / "V_FAN_B" as inputs
connecting the 12V supply to the middle pins ("V_FAN_A" / "V_FAN_B")

Note that I haven't seen the schematic of the board yet and am NOT fully sure about not damaging anything with this setup.
Especially, you should have a look at fuses, but as I suspect from [2], there aren't any...

phantomix

[1] https://www.youtube.com/channel/UCSi3noC0JkukKm1rl-tt9YA/featured
[2] https://ffls1.s3.amazonaws.com/campaign_overview/P6BwDwxw3QzIecw6g7SCtaSpzqVAJyKLlWrTLzpw.png
[3] https://duet3d.dozuki.com/Wiki/Duet_2_Maestro_Wiring_Diagram

Duckle

I am running my fans on 12v with an otherwise 24v powered board.

Just connect the fans + to +12v, and then the fan GND to the

Like this

Jacotheron

I used a buck converter set to 12V to power my fans and LED strips (they get their 12V from the buck, and then the Ground is through the fan pins, since the PWM is switched on via the GND pins). It works easier (for me) than a separate power supply. These buck converters come in various shapes and sizes, but are usually quite cheap and usually offers around 90% efficiency (compared to a 50% for a standard 12V regulator IC, when converting from 24V to 12V). They are also smaller than most power supplies that can supply more than 2A.

I have previously read that sometimes connecting 2 power supplies' GND together can cause issues (their GND not being at the same potential, but if using good quality power supplies this should not be an issue).

Fizban

@duckle
I didn't think of that tbh. So both pu's on main.
24v psu to board and heatbed (guess the mosfet is still a good option)
GND from fan to pin (the 24v supply)

is pulled from the 12v psu along with the LEDs I guess this makes sense yeah

Side note, I tickled down the PSU to 20v as it's current function is only to supply the heatbed. I guess I can turn it back up to 24 even ? Or does this have little to no effect?

SupraGuy

Personally, I believe that connecting V_FAN_A/V_FAN_B to the 12V supply is a superior approach. Since V_FAN_A and V_FAN_B can connect to either 5V or V_IN using the jumpers as supplied, it's pretty sure that it does not cross-connect anywhere other than at the jumper, and if you have that covered with the connector to the 12V supply, you aren't going to accidentally jumper it and (for example) connect 12V to your 5V rail, which is almost certain to do bad things. You can then also use the extra fan outputs as envisioned without having to make up any crazy wiring harnesses.

I have a buck-boost step-down converter which I plan to have provide 12V, and it will be connected to the V_FAN_x input on mine. I'll probably use a 3 pin Dupont connector just to keep the other 2 pins covered. I have a couple of other things that I'll want powered with a constant 12V which I'll wire separate from the Duet, since it doesn't need to be switched.

Fizban

@supraguy
I'll need to see that setup eventually

My fix for now will be running it all via 12v and heatbed on 24v via mosfet. I found out that it's not just my fans, but my heater cartridge is 12v as well.

I planned on getting a volcano so I'll run some 24v cartridges along with it. I'll find a work around on the fans with converters.

dc42

@jacotheron said in Dual PSU 12/24v:

I used a buck converter set to 12V to power my fans and LED strips (they get their 12V from the buck, and then the Ground is through the fan pins, since the PWM is switched on via the GND pins). It works easier (for me) than a separate power supply.

Please do not connect the input of a buck converter to a controlled fan output. Applying PWM to the input of a buck converter may overload the fan mosfet, because of the high input capacitance of the buck converter.

The input of the buck converter should be connected to either the VIN terminals or to an always-on fan connector. Then you can connect the output of the buck converter either to the centre pin of the fan voltage selector jumper block after removing the jumper (if all fans are 12V), or to the positive wires of the 12V fans (with the negative wires connected to the FAN- terminals of the fan outputs).

SupraGuy

@fizban That works, and isn't a bad solution if 12V supplies your motors adequately. My MBot printer runs the opposite way right now, with a 12V heat bed operated via MOSFET from an otherwise 24V printer. (My 24V supply wasn't adequate to run the bed, which was added on, and I had the 12V PSU, bed and MOSFET.) It's better than not having a heated bed, but the 24V bed that I have on the other printer -- exact same type -- heats so much faster. I'll probably upgrade the heat bed (and PSU) on the MBot printer at some point, but for now, it works.

In that case, a couple of full-time fans are running on the 12V supply.

On my new printer, I haven't got a part cooling fan installed yet, I still need to get the design put together for it. I have a few fans in both 12V and 24V versions. The 12V versions are less expensive, and much easier to replace. Currently I'm using a 24V 30mm fan to cool the hotend heat sink, but that's the only one of those that I have, and I have several 12V ones, as well as 40mm ones. As such, I could currently run all of the fans at 24V, but I think that as a long-term solution, 12V fans are so much easier to replace. Plus, I already have the 12V/2A converter, so I don't even have to buy anything.

Jacotheron

@dc42 said in Dual PSU 12/24v:

Please do not connect the input of a buck converter to a controlled fan output. Applying PWM to the input of a buck converter may overload the fan mosfet, because of the high input capacitance of the buck converter.

I figured as much, and ensured that the input is directly from the power supply, providing constant voltage on the Fan select. Also I decided it may not be effective to switch a buck converter on and off at PWM speeds.

When I started I also had a 24V fan, but since it was the E3D heatsink fan, I simply powered it directly from the power supply. It was since replaced for a 12V fan to be more quiet (though it was not more quiet).

Fizban

Ok so I've got it all connected.
Board runs 24v powering system/bed/steppers
hotend runs 12v via the old mosfet.

Blowers runs on the 5v and the heatsink fan is directly powered by the 12v psu.

Now to make another post, cause I cant connect to the damn thing

Thanks for the help regarding this!