I was going to do a big writeup of what I had found was needed etc, only to find its been done very nicely here
So I've gone for a Taurino power as it takes a 24v supply, including from a ramps.
The caps on my ramps are all 35v rated, so that's a good start.
The 11Amp fuse is as expected only rated to 16v, so that has to go.
I have a 24volt Kapton heater, rated at 8.5amp, so I needed to find a replacement fuse in that range.
I found this at a local auto part shop. 10-32volts 10amps, and auto resetting.
Its about 2mm taller that the original fuse. Seems ideal.
This is designed to fit into a socket, that that would have made it much taller.
So I just drilled some 2mm holes in the tabs and soldered in the thickest solid copper I could find. (off of a coil in a dead power supply) The centre of each of the fuses tabs lines up very nicely with the original fuse wire spacing, which was a plus.
The fuse looks a little odd, I'm so used to them being yellow squares. But fits nicely.
So I setup my test workbench (kitchen table!)
Using a 24volt 16.5 amp power supply, I tested a bare ramps on the Taurino power
It didn’t go bang, that is a good start!. Then I plugged in a thermistor into the extruder thermistor port to stop marlin complaining, that read fine also. Next I added in one Pololu driver and tested that. Worked as expected so I populated and tested the rest of the Pololu drivers. All worked.
Next the big one, I plugged in the 24 volt Heated bead and its thermistor.
I turned it on, and it all worked! I can now get my HBP to 115C in 15 minutes, that’s with very poor insulation.
I did replace my HBP FET with a IRLB8743. I know that the FETs that came with the this board aren’t up to the normal 12volt 11amp load, let alone 24volt. Better safe than sorry.
NB all plugging in was done with everything off!
Now all I have left is the hot end (which is a 12v makergear) and 12v fans to work out.
I'm tempted to try this, to create a 12 supply.
Then I can just use the hotend and fans as normal, using 12v as their supply and GND threw the appropriate FETS.
I can just set an upper limit to the PWM for the hotend and run it directly, but what happens if the controller crashes with it on?, instant melt down that's what.
I might also just runs the fans from a 7812, as they are low power...