View Full Version : PSU ramblings

09-09-2008, 11:06 PM
Ok, i've spent a good amount of time over the past few days trying to figure out a PSU design.

The primary (mains) side is mostly sorted. I know what components I'm planning on using, and how I'm going to initially wire it (there may be a slight change with how the e-stop control turns the toroidal on/off, but I'm happy with the current plan for now).

However, on the secondary side, things are a bit more complicated.
Because I'll be running the Geckos at near max voltage (55V secondary x root 2 = 77vdc, geckos max is 80v), I need to incorporate some method to limit voltage.
Also I'd quite like to limit the start-up surge, and have some way of dumping the charge on e-stop.

For voltage limiting / reverse load dumping, there are a couple options on
the Gecko site.

http://www.geckodrive.com/upload/servo%20e-stop%20dump1.pdf is a circuit that dumps the charge on e-stop, and provides over voltage protection.
Would it still work if I was to put some form of current limiter between the main bridge and capacitor?

It would be something along the line of what Irvine008 suggested in the last thread, but I'd be more inclined to use a relay to elminate any volt drop once the current limiter is bypassed.

Other option is a similar current limiter set-up, but with a relay that closes and connects a resistor across the main capacitor to dump the load, then the simpler Returned Energy Dump in line to each drive (http://www.geckodrive.com/upload/servo%20e-stop%20dump1.pdf).

I quite like the idea of the combined circuit, as it means everything is kept in one place, but then the other option, although more spread out, would be far simpler to build/wire.

10-09-2008, 12:16 AM
There are two forms of over-voltage.. that due to the power supply output rising due to rising mains voltages and that due to the back-emf of the motor(s). The circuit you identify deals with the first form. Its far to slow to deal with back EMF transients although this could be incorporated as all the elements are essentially there.

10-09-2008, 06:48 PM
The thought of a big battery to power everything is crossing my mind at the moment!

Ok, think I'll go back to the simpler approach.
Relay with a 240ac coil that's connected to the primary side of the TX, which disconnects a load dump resistor across the main capacitor when powered (ie resistor connected through the NC contacts).
Then a Returned Energy Dump connected up to each drive. At least I'm assuming having one on each drive is the better option?