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Two PSU's In One Printer?

Posted by Plecc 
Two PSU's In One Printer?
June 03, 2018 07:34AM
Hi all,

I would like to swap out the mighty board in my CTC Dual for a ramps board with DRV8825 drivers.

The CTC is a 24v printer, so all the heaters and the stepper drivers will be connected to the 24v supply.
But the arduino, LCD and a few ancillary bits need 12v.
I have a spare 12v PSU, is there any reason I shouldn't run both 12v and 24v power supplies in the same printer from the same mains supply?
Re: Two PSU's In One Printer?
June 03, 2018 03:03PM
There should be no problem at all. If something doesn't work connect the ground of the outputs of both PSU.


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Re: Two PSU's In One Printer?
June 03, 2018 05:53PM
DRV8825 drivers have issues with accurate microstepping when using 24V power with low inductance motors. So they may not be a good choice, depending on the motors in your printer.

In what way do you expect RAMPS to be better than the Mightyboard? RAMPS has several design issues that most other boards do not.

Edited 1 time(s). Last edit at 06/03/2018 05:56PM by dc42.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
Re: Two PSU's In One Printer?
June 04, 2018 08:04AM
Thanks for the feedback,

Srek - Do you mean, tie both the negatives together on the D/C side? (sorry just have to be sure)

dc42 - That's good to know, thanks. So is this only a problem when running the drivers on 1/32 ? can it be avoided if i set the drivers to 1/16?
My steppers are made by Bohong
- 42HB34F04ASG-09 for the Z axis.
- 42HB34F1AB-01 for the X and Y axis.

I could only find this generic data sheet for the X and Y motors - [www.goodluckbuy.com]
It states that the inductance is 9.3 mH/Phase, so are these low or high inductance motors?

I also have a full set of A4988 drivers if they would be more suitable? If not can you recommend a suitable plug in driver?

Its not really that I think the ramps board is any better, quite the opposite actually. My decision is based on everything else associated with the boards.

MightyBoard
I rly dont like the Makerware software and replicatorG is versatile but quite outdated and slices tragically slow. (I've had more complex models take well over an hour to slice!!!)
.x3g files add additional incompatibility problems.
To add a part cooling fan appears to be very tricky, i'm struggling to generate the commands within the code for variable fan control and not just on/off.
The board uses thermocouples for the hot ends which is nice but there is still a running debate on the type of these thermocouples, I thought they were type K but some are convinced they are type T its very hard to find a straight answer.
Oh and the thermocouple bead is crimped into an INSULATED ring tab and then connected to the heat block so any gains in precision from using thermocouples are negated by the poor installation.
User interface of the mightyboard and the CTC sucks, the buttons are horrible to work with and get stuck in the plywood cut-outs.
I'm not very experienced with this board or firmware and i'm a bit reluctant to start learning all about it as it all appears very outdated and unsupported these days.

RAMPS
I can use Repetier Host and choose between Slic3r and Cura.
Firmware tweaks are super easy and I understand marlin's settings so much better.
Fitting a part cooling fan is also very straight forward.
The online support for Marlin and ramps is amazing.
The ramps UI (the micro switch pot) is nice to use in comparison to the buttons of the mightyboard.
The ramps board is extremely versatile when it comes to strange mod's and add-on's
It uses thermistors, so at least the bead can be fitted directly into the heat block.

All my other printers run on marlin and G-code, so I typically don't use the CTC because the setup and slicing are so slow and limited in comparison to marlin.
Thats why!

Supposedly i can update the firmware of the mightyboard to a recent version of sailfish, lots of people appear to have done this but none actually say why and what the benefits are.

Edited 1 time(s). Last edit at 06/04/2018 08:05AM by Plecc.
Re: Two PSU's In One Printer?
June 04, 2018 08:44AM
Quote
Plecc
Srek - Do you mean, tie both the negatives together on the D/C side? (sorry just have to be sure)
Yes


[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]
Re: Two PSU's In One Printer?
June 04, 2018 10:42AM
Thanks Srek,

Is it best to do it anyway just to play it safe?
Re: Two PSU's In One Printer?
June 04, 2018 05:06PM
Idealy there should be only one connection, if the board already does it you shouldn’t.


[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]
Re: Two PSU's In One Printer?
June 05, 2018 03:12AM
Quote
Plecc
dc42 - That's good to know, thanks. So is this only a problem when running the drivers on 1/32 ? can it be avoided if i set the drivers to 1/16?
My steppers are made by Bohong
- 42HB34F04ASG-09 for the Z axis.
- 42HB34F1AB-01 for the X and Y axis.

I could only find this generic data sheet for the X and Y motors - [www.goodluckbuy.com]
It states that the inductance is 9.3 mH/Phase, so are these low or high inductance motors?

I also have a full set of A4988 drivers if they would be more suitable? If not can you recommend a suitable plug in driver?

The problem occurs at x16 microstepping too. There is a good article on the problem at [cabristor.blogspot.com]. The arrangement of diodes to work around the problem is commercially available as the "TL-smoother". 9.3mH is quite high inductance, OTOH the motor current rating is low which doesn't help. However, the low current rating (0.84A) makes TMC2208 drivers suitable, and they provide up to x256 microstepping and microstep interpolation.

I found the specification for the Z motor at [f01.s.alicdn.com]. These are very low current motors (0.4A) so my guess is that your printer uses two of them connected in parallel. Again, the TMC2208 would be suitable.

Quote
Plecc
Its not really that I think the ramps board is any better, quite the opposite actually. My decision is based on everything else associated with the boards.

I was assuming that you were already running Marlin or Repetier firmware on the Mightyboard. If you are stuck with the original firmware, then I understand your reasons for wanting to change the board. But I still think Arduino/RAMPS is a poor choice for a system that will benefit from using 24V power.

Edited 1 time(s). Last edit at 06/05/2018 03:13AM by dc42.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
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