Quote:
Originally Posted by
Jaypetermen 
Great setup for the Treads power supply. I am looking for a solution like this to power my Millett Hybrid. I ordered the treads a couple years ago, but I am now getting back around to using it. I do have a some question about your Treads build.
-- Is this the case you used? http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_115052_-1
-- I am looking to provide 24VAC to the treads, do you have a part number for the transformed that would fit this case?
-- Did you solder the regulator to the board from the outside of the case, after everything is cased up?
-- How do you adjust the voltage after everything is cased up?
Jay
I actually used the vented one in the pics above, but as AMB noted - Jameco doesn't seem to be carrying that one anymore. Still, if you route the LM317 to outside the case, there's no need for venting.
The transformer was also a Jameco one - they used to sell it for $2.50 (now $5.95): http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_209015_-1
It's a dual secondary, so you have to wire the outputs in series for 24VAC at 0.8A.
The regulator (LM317) was soldered to the TREAD PCB, but I soldered some spent resistor leads on it to make the leads longer. I believe I soldered the regulator to the PCB after the PCB was mounted into the case, but there's no reason you'd have to do that, other than making a bigger hole. Heat-shrunk and insulated leads are not much smaller than the width and thickness of the entire TO-220 regulator, anyway.
If you notice in the pics, there's a small hole in the bottom that allows access to the trimmer screw. Since you're only adjusting the output anyway, it's not an issue to put your DMM probes on the DC connector (2.1mm) - there's no need to get inside the box.
The difficulties were:
- Finding nylon screws long enough and robust enough to fit through the split bobbin transformer's mounting holes (there's a threaded connector used in conjunction with two screws in the pic).
- Finding a way to allow the fast-on connectors to clear the transformer (those are right-angle connectors and are actually filed down on the tips).
- Finding a way to get the LM317 out of the case and onto the heat sink (as noted, I soldered extra lead lengths onto the regulator and made many trial fits.
- A different electrolytic power cap was used - 1000uf, I believe, that was bigger round, but much shorter than what Tangent supplied in his TREAD kit. There was also quite a bit of trial and error in bending the leads to get the cap mounted sideways. There's obviously no room to allow for a vertical PCB mounting. (There's a strip of cable tie around the cap to keep it secure.)
Edited by tomb - 9/27/10 at 8:13am
