Making your own 12/25v PSU
First of all, you have to understand what you are actually doing (unlike me) as you’re dealing with mains voltage and large electrolytic capacitors. If not done properly you could seriously harm yourself or others!!
What you need:
- Multimeter with continuity testing
- 2 matching PSUs
- 4mm Banana connectors
- Decant soldering iron
- Female servo connectors.
After reading about the theory on how to make a 25v PSU out of 2 x 12V supplies for a while, I decided to make one so my charge times would decrease, allowing me to use the full 20A on the Turnigy Reaktor charger.
The idea is simple; float the ground from the negative terminal on the PSU from the case, or another way of putting it, make sure there is no connection between the negative terminal and the outside of the PSU case.
Using a multimeter set it to the continuity mode to check for shorts. If you put one end on the case and the other on the metal it will make a tone, meaning there is a direct connection between them. Now this is a bad idea if you are connecting 2 of them together.
Preparing the PSU
You have to short out the pins to enable the PSU and if you want there is another pin to put the fan on its lowest setting for a quiet PSU.
Also, it’s a good idea to solder the banana plugs and put the relevant heat shrink around the plugs for better protection against shorts. I used blue and yellow heat shrink for the negative and positive on the alternate supplies to make a visual difference when connecting them together.
Opening the PSU up
I like to disconnect the power and short the DC and AC terminals in case there is any residual power sitting in the caps before I start. The reason why you need to open the PSU up is to locate where the case and the negative DC terminals make contact, usually a screw or two that are holding the main PDB onto the case.
Easy does it
When opening the case, I managed to pull the wires for the green LED at the rear of the case for indicating power on the AC side. Not to worry though I managed to solder a 2S balance lead onto the PDB and solder the other side on to the cable and jobs a good’un.
Locating the ground points
I worked it out to be these two pads on the front of the case to be the ground, so I superglued some plastic over the pads and drilled a hole through the plastic so the screw can still secure the board to the case. I also had to grind part of the standoff on the case as this would have made contact with the inside of the pads and eventual caused a ground
Test, test and test again
Once you have replaced the batteries in your multimeter after all that testing and you now no longer have a connection between the ground pin and the case I think I must have tested over a hundred times just to make sure while putting the PSU back together.
Overall I’m really happy with the charger. It’s cutting down my charging times and I now have room to expand with another charger as I have 48A @ 25v or 96A @ 12v, that’s a lot of angry pixies. Now, would i recommend you do this yourself? In short yes, but make sure you know what you are doing before you even open the PSU up. I wanted to make sure I knew what I was doing before I even started which is the reason why it took me so long to make. if you want to find out more, check out this thread on RCGroups