24V will work, technically

A project log for Monoprice Select Mini Electro-Mechanical Upgrades

Endeavoring to build upon the existing fanbase work of this $200-ish printer.

Michael O'BrienMichael O'Brien 08/05/2016 at 03:172 Comments

I've mentioned this before and before I get into other stuff right now, I'll say it again: you can drive this board from a 24 VDC power source. Just because you can though, doesn't mean you should.

There are 2 things you need to be aware of if you wish to do this:

  1. Primary filter capacitor needs an upgrade
  2. MOSFETs absolutely need a protection/freewheeling diode

See my parts list for both.

The main point of contention of if this were possible is the SMPS chip, XL1509; datasheet link. It supports a 40V input and supports up to 2 A output. This means that the inductor and output caps probably should be resized, though currently I've not felt a ton of heat from that guy so I haven't even considered swapping it with a lower resistance one for better efficiency.

If you recall my prior findings, the stock hardware configuration allows forma 37-38 V spike when the MOSFETs turn on. Kinda bad for a 30V 'FET, no? And with that being a 12V power brick, just imagine how bad that will be with a 24 V PSU. As long as you have a protection diode in place, you will be okay.

So, if you wish to switch to a 24V hotend, heated bed, and fans, this board will let you with some minor modifications.


Michael O'Brien wrote 09/09/2016 at 21:40 point

I'd advise against it initially unless the PID temp control can be sorted out and be made a bit better. That or compensate in hardware by insulating the heater block to prevent the undershooting. I too am curious if using a higher voltae on the steppers will help solve the control problems or if the control problems are a result of the knockoff drivers. I'm getting close to answer that, but I'm not there yet. There is a 3.3 V rail, but no 5 V rail on the control board, though.

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razorboy wrote 09/07/2016 at 16:05 point

I'd love to see somebody try this. I think moving to 24V has a lot of advantages. Heaters heat faster, steppers get more torque, etc. I just read that TI DRV8825 motor drivers work much better at 24V. (Not really applicable here, but interesting).

I've done the 24V conversion to a RAMPS v1.4 board. It's just SMD cap replacement. Since it's a shield, the Mega underneath can be powered independently. (My 24V heater cartridges just came in the mail!) MK2B heatbeds also come with 2 separate loops that are connected together for 12V and can be disconnected and run in parallel for 24V.

So, the hotend change is easy; just a cartridge replacement. I haven't looked at how the Mini's heated bed is laid out, but it should be straight-forward to either cut the traces and make them parallel, or to just swap the whole thing out. The steppers and drivers should work fine on 24V, although the current might need to be adjusted on the drivers. I don't know how I would handle the fans... they could easily be swapped out with 5V fans, and run from a 5V rail. If there isn't a 5V rail available, a simple 12V linear or LDO regulator would be easy to add. 

Doesn't sound too complicated! It's easy! (Famous last words.)

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