24volt power


  • administrators

    @deckingman:

    Actually you can still get PWM to work with 12v fans on a 24v system. I'm using a CPT CT241205 24v to 12vdc converter to run two tiny 30mm 12v blower fans which I can't source in 24v. The trick is to set the PWM frequency to a low value in the M106 command. e.g. M106 P0 S0.0 I0 F10 H-1. This is what I have for my print cooling fans and sets the PWM frequency to 10 Hz (I think the default is 500Hz). The 10Hz is an arbitrary value that I've found works. I guess the data sheet would tell me what the switching frequency of the converter is actually capable of.
    HTH
    Ian

    I wouldn't advise this. A 12V fan might contain an electrolytic capacitor rated at 16V.



  • @dc42:

    @deckingman:

    Actually you can still get PWM to work with 12v fans on a 24v system. I'm using a CPT CT241205 24v to 12vdc converter to run two tiny 30mm 12v blower fans which I can't source in 24v. The trick is to set the PWM frequency to a low value in the M106 command. e.g. M106 P0 S0.0 I0 F10 H-1. This is what I have for my print cooling fans and sets the PWM frequency to 10 Hz (I think the default is 500Hz). The 10Hz is an arbitrary value that I've found works. I guess the data sheet would tell me what the switching frequency of the converter is actually capable of.
    HTH
    Ian

    I wouldn't advise this. A 12V fan might contain an electrolytic capacitor rated at 16V.

    Don't understand. Fan is connected to the 12v output of the DC to DC converter. The 24v input of the converter is connected to fan 0 connector of the Duet. So using F10 in my M106 command, I'm feeding 24v at 10Hz to the 24V input of the DC converter rather than 24V at the default 500Hz. Why would this hurt a 16v electrolytic capacitor on the 12V side of the conveter?


  • administrators

    Sorry Ian, ignore what I wrote, at first glance I thought you were running a 12V fan from 24V with 50% PWM.

    However, a better way of using PWM with a 24V to 12V converter that is kinder to the Duet fan mosfet would be to use the converter to generate a 12V rail from the 24V supply, then connect the positive fan terminal to the 12V output instead of to the pin on the Duet. Or, if you want all the fans to be 12V, you can feed the 12V output of the converter to the centre pin of the fan voltage select jumper on the Duet WiFi.



  • David. No probs.

    Also, thanks for the tip on wiring the converter and just using the Duet mosfet to switch the 0V gnd on the fans. It's only the print cooling fans that need to be 12V but a 12V rail might be useful for some LED lighting or some such in the future. I've got 60 Watts to play with and the fans only take about 1 Watt.



  • LEDs wire in series pretty easily too.



  • @DjDemonD:

    LEDs wire in series pretty easily too.

    Yes I knew that. You can dim them using PWM too - now there's a thought for using a spare fan connector…..............



  • Yeah I'm doing that, have macros for 100%, 50% and off.



  • @dc42:

    @LeonMF:

    @Adamfilip
    What I can't speak to is what, if any, real world system improvements you'll get as I converted from 12V when I upgraded to the Duet. I can say it works great and, theoretically, should have more torque for a given current but I just don't know what that means to system operation, heat and noise.

    The benefit of 24V over 12V is that motor torque is maintained to higher speeds before it drops off. It's possible to calculate the back emf due to rotation and due to inductance, to work out at least approximately what voltage you need to maintain torque up to a target speed.

    I know that but it is still worth the clarification for those that don't!

    What I really meant was that I can't speak to the real world benefits of using 24V for a given system. I've never had a 12V system that had my speeds limited by the motor torque instead of the mechanics. For example, I converted to 24V when I upgraded to DuetWiFi but I have no tangible performance benefit and I really didn't expect one. What I hoped for (and please correct me if I'm wrong) was that I could run the motors at a lower current for the same performance and quieter operation. It turns out I didn't need this since the Duet is quieter anyway. 🙂

    To put it another way, are there many people who actually get real world machine performance benefits from going 24V? Perhaps those that have much heavier moving build plates?



  • Surely it depends on how fast you want the printer to move. I am always impressed when I send a move command to my new delta to move at 250mm/s, and it does. No, I'm not yet printing at anywhere near that speed, but its impressive nonetheless. Perhaps with enough trial and error printing at speeds closer to this rather than 30-50mm/s will be possible.

    Its a bit like performance car tyres - they're a waste of money on a car never driven on the limits of grip, might as well buy budget. But then if you do decide to drive and corner fast you can't.

    I've opened my eyes to better ways of doing things in the process of building my latest printer with some of these enhancements 32 bit electronics, 24v power which until I used them I didn't think I needed.



  • Another thing to consider besides just the motors is the heated build platform. Going from a 12v to a 24v heated bed requires significantly smaller wiring and is less stressful on the power supply, interconnects, PCB traces, and MOSFETs.

    I went with a 24-volt setup on my 3rd printer build and I can tell you, from now on all of my future builds will be 24-volts as well.


  • administrators

    See https://duet3d.com/wiki/Choosing_stepper_motors#How_to_work_out_the_power_supply_voltage_you_need to work out what power supply voltage you need to maintain motor torque at your desired travel speed.



  • @dc42:

    …However, a better way of using PWM with a 24V to 12V converter that is kinder to the Duet fan mosfet would be to use the converter to generate a 12V rail from the 24V supply, then connect the positive fan terminal to the 12V output instead of to the pin on the Duet. Or, if you want all the fans to be 12V, you can feed the 12V output of the converter to the centre pin of the fan voltage select jumper on the Duet WiFi.

    David, this sounds great. I am converting to 24V, but I would love to keep all my fans 12V.
    Just to make sure I understand it right, I would connect the converter to the 24V power supply, then remove the jumper "V_Fan" and connect the central pin to the 12V output of the converter. I assume that fans have common ground with "Power In" and that the converter carries the common ground from input to output, and I do not have to connect the output ground. What is the best way to connect 12V to the "V_Fan" pin, solder or use an unpolarized 3-pin connector?
    Thanks,
    TJ.



  • @W3DRK:

    Another thing to consider besides just the motors is the heated build platform. Going from a 12v to a 24v heated bed requires significantly smaller wiring and is less stressful on the power supply, interconnects, PCB traces, and MOSFETs.

    I went with a 24-volt setup on my 3rd printer build and I can tell you, from now on all of my future builds will be 24-volts as well.

    Wait till you switch over to a silicon AC heated bed with a SSR. You will throw away your 24V setup in no time. Some heated beds have 800 watts of pure heating power!!



  • @ShadowX:

    Wait till you switch over to a silicon AC heated bed with a SSR. You will throw away your 24V setup in no time. Some heated beds have 800 watts of pure heating power!!

    Er…...I have AC heated bed but no intention of throwing away my 24V setup - why would I want too? Also, bed heater should be carefully matched to the bed size and to some extent the thickness of the plate and whether it is insulated or not. Too big a heater will be difficult to control if not downright dangerous.



  • @deckingman:

    @ShadowX:

    Wait till you switch over to a silicon AC heated bed with a SSR. You will throw away your 24V setup in no time. Some heated beds have 800 watts of pure heating power!!

    Er…...I have AC heated bed but no intention of throwing away my 24V setup - why would I want too? Also, bed heater should be carefully matched to the bed size and to some extent the thickness of the plate and whether it is insulated or not. Too big a heater will be difficult to control if not downright dangerous.

    Very much agree here I use the 0.5W/cm3 rule of thumb hence to 620mm diam one I have just ordered is 1500W at 240V

    this is going on a 650mm diam bed of 8mm Ecocast (Not sure that 6mm wouldn't sag in the middle under heat) If someone could convince me it will stay stable then I would rather use 6mm.

    Doug



  • Hi Doug,

    That's a big bed! I can't say that 6mm x 650mm dia won't sag but if you can possibly use it instead of 8mm I'd strongly advise it. Maybe you could fit a brace under the bed to support it? I went for 10mm on my 400 square bed - big mistake. When you first start to heat it, there is a huge difference in temperature between the underside and the top. If the temperature sensor is fitted between the heat pad and the aluminium, it'll control the temperature at that junction which bears little resemblance to the temperature at the top of the plate until the heat actually "percolates" through. I drilled a 3mm hole, about 40mm deep into the edge of the plate and put the sensor there which helped but it's not ideal. The other thing is that it takes forever to cool down - not an issue if you have a removable surface such as glass but otherwise it's like 45 minutes or more to drop from 50 deg C to just above ambient.

    On the other hand, the extra mass does help to keep the printer stable and damp out any vibrations (but a paving slab on the base would probably work better).

    Ian



  • Ian

    I Know what you mean my current bed is 400x400 (Or was till I chopped the corners of for the Delta and that is 6mm which is fine.

    If you remember we spoke about the temp issue and I pointed out that I drilled my plate to put the thermister closer to the top surface tho out on the periphery of the bed the heater I have ordered I have asked for there to be a 20mm diam hole at the centre of iut to allow me to get the Thermister as close to the top of the center of the bed as I can (I have some that are mounted in a M3 Brass carrier so I will drill and tap the center of the bed to take one of them.

    Dont think it would be easy or even possible to brace the center without beefing up the whole bottom section especially taking into account the silicon pad?

    Doug


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