A couple of bench top power supplies for cheap

2 posts / 0 new
Last post
Last seen: 3 years 6 months ago
Joined: 03/17/2012 - 20:10
Posts: 4122
Location: Connecticut
A couple of bench top power supplies for cheap

Last night I made 2 bench top power supplies from 2 old Ryobi NiCad chargers. One of them is Battery powered!
For the AC powered unit I started with this.

I ripped out the original charging circuit and left the AC transformer. 22V AC

I had to drill a hole for the pot for the voltage control for the replacement supply board.

This was about $5

I drilled a couple of more holes for 2 binding posts, wired it up and done!
Variable output 1.3V – 32 at 1.5A short circuit protected and current limited.

The second one I put together started with a second identical charger. I didn’t need them anymore as I have converted over to Li-ion packs. All my older 18V Ryobi tools also run on the newer Li-ion battery packs.
This time I ripped out the transformer and charging circuit, leaving only the shell AND the contacts for the battery pack.
I drilled 4 holes for 2 sets of binding posts. One set will be connected directly to the contacts of an inserted battery pack, the other set will connect to the output from one of the LM2596 boards that are popular.

It would have been better had I mounted the heat sink on the back of the board connecting to the thermal vias under the chip. This board is adjustable from 1.5V to about 34V @ 3A with the sink.The voltage is adjusted by the multi turn pot. It’s blue at the top of the board.

I originally planned on using 2 of these boards, wired in parallel for 6A. When I first hooked then up I realized that there was some cross channel leakage if the 2 boards were not exactly set equal. So for the time being I only installed 1.

Because this charger was originally meant to charge only the NiCads, I had to cut out a key that was in place to prevent other type batteries from being inserted into the slot.

I set the LM2596 board for 14.4V as that is the upper end of the charging voltage for an automobile. I did that for 2 readons, one being that auto accessories can be run off this portable charger and secondly I could use it to bring up a slightly rundown car battery. I must emphasize slightly. Could come in handy some day.

The purple and the gray binding posts output the 14.4V and the red and black binding posts are connected directly to the 18V battery. For now what I use them for is testing battery packs that I repair for myself. I get them in the recycle bin and have over 20 of them now that work very well. Here is a low ohm, high power load resistor I use to test the funtionality of the packs.
There are 2 – 2ohm resistors that I can use in series or parallel. That way I have a choice of 1,2 or 4 ohms.

WarHawk-AVG's picture
Last seen: 1 year 7 months ago
Joined: 01/04/2014 - 06:47
Posts: 5071
Location: H-Town

Oh wow, NICE! There are aare some of those boards that have built in volt and current displays for a few bucks more…

Awesome job man!

I used one of those ac transformers my HVAC buddy gave me and a full wave bridge rectifier and a 1000 uf electrolytic cap from Radio Shack (man they are getting expensive) to make a 28~vdc really uuuugly power supply and the above mentioned display modules to make a simple 2A max variable volt power supply… uglier than a mud fence but works