Help with Modifying Prusa i3
June 15, 2018 03:55AM

Hopefully I've posted this in the right place....
I would like some help / advice with modifying my 3D printer which I've had a bit of trouble with since owning it.

It's a Prusa i3 (wooden laser cut frame) with the standard PCB heat bed and stock hot end from eBay and I've owned it for about a year and a half.
It took months to configure it and get it printing how I wanted and then the first time I came to actually do more than a test print, the control board burned out!
The board that was supplied with the printer was a GT2560 (clone?) and it burned out at the fuse / fuse holder.

Up to that point, I had gone through an entire roll of PLA just setting it up, calibrating it and getting it to print just right and the first time I try to use it for more than calibration prints to do a long duration print (8 hours) it burned out about 2 hours in.... Needless to say I wasn't impressed and the manufacturers didn't want to know.

So, I decided to move to Ramps and upgrade the printer with a MK3 Aluminum heatbed along with some non electrical mods like brackets to firm up the frame and fix the printer to the bench and the anti-Z wobble mods.

I spent a day changing everything over, re-installing stuff and then finally I powered it up for a test print so I could start calibrating it all over again and guess what... Yup, the Ramps board started smoking after about 10 minutes of warming up and printing!

I verified the MK3 heatbed was wired correctly and the wires were soldered correctly to the heatbed and I metered the heatbed's resistance which read at 1.6 Ohms which I believe is within spec.

This was about 6 months ago and I've not touched the printer since.

Now I'm looking to rebuild it and get it back working so what I'm hoping to do is to split the printer's power demands between two power supplies.
I'm going to use the original 12V supply to power everything on the printer except the heated bed.

For the heated bed, I'm looking to purchase a 24V supply and a separate external MOSFET control board to take the heatbed load away from the Ramps board and hopefully that will stop all these burn outs.

This is the MOSFET control board I've ordered:

What I'm not sure of is what amperage 24V supply to get. I want something with some "headroom" just in case.

If I can get it all working again, I'm tempted to go back to using the GT2560 because it worked well prior to the burn out and all my saved settings and calibrations are for the GT2560. I only went with Ramps as a last resort - not that there's anything wrong with Ramps.

Also if there are any improvements that might help in the future, I'd like to hear them please while I'm in the process of rebuilding / improving.

Many thanks,

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