Posted on Monday, 14th May 2012 by Auw Jimmy
It’s been a while since this idea came to my head few months back. Now it’s time to make it happens. As you might also know that Lundahl is one of the good transformer maker. They use their own C-Core most of the time for their production, included this Choke.
Though I believe they don’t have issue with their “open” design, some people prefer to have it potted to minimize any vibration possibility (included me). So here I come, a potted choke project with this Lundahl.
First problem came to me few weeks back was how to find appropriate enclosure to house this choke. Definitely not easy. Doing custom made housing would be my last resort. After spending few weeks searching, I found a chassis from Hammond which was quite OK for my purpose. I tried to contact nearest Lundahl agent which located on Malaysia (Octave) but they didn’t have it. I also planned to give a visit to Martin Electronics located in Singapore as they carried quite a lot of Hammond stuff, but unfortunately, I was so busy in other thing and have no schedule to fly to Singapore. And last resort, I gave an email to Chris (Partconnexion) and his assistant as usual quoted me with best pricing. Well, I hated to spend almost the same with my goods price for shipping, but got no choice this time. Canadian post is always too expensive for me
After the Hammond came few days ago, it’s time to start drilling…
I put the choke outside to heat it and reduce the moisture. According to my infrared thermometer, the surface temperature was around 44 degrees Celcius. Not bad huh? The best actually to heat the choke inside an oven – which I didn’t have any. So this free heat from the sun was definitely better than nothing.
Okay, back to drilling part and now we have 4 holes to lock the Lundahl inside.
The Lundahl screwed to the Hammond chassis. Tight and secure!
I needed to solder 4 lead-out from the Lundahl to the outside of the chassis. For this purpose, I have ordered 6N-OCC solid copper wire (14 AWG). This wire was actually shielded with a Teflon transparent sleeve. But for this project, I experimented with some extra sleeve after the Teflon one.
This was how I did it. The green bar was a LED torch to light the choke inside the chassis and I soldered them directly. Note the OCC wire was no longer on Teflon transparent sleeve, but covered with extra “white” sleeve.
Some extra tools and ingredients collected for the potting project (should be on Part 2 later). I was gonna play some fire and alcohol (duh!) – but definitely not at the same time. Aluminum glass and bowl, 96% alcohol, candles, and weight scaler… Any idea about the game that’s gonna be played? I thought I needed to borrow some small stove later.
All 4 pins were connected to the 6N OCC wire with WBT Silver Solder. Don’t ask me why I chose WBT while on the other entry, I prefered Mundorf Supreme Solder. This was part of the recipe.
The 6N OCC wire on the bottom side of the chassis. Ready to be connected to the power supply circuit.
Another experiment with Copper Tape and some special “white” sleeve tape. Will see if this will bring some interesting result.
So, the internal construction has been done. The next step is to pour the compound or potting material to seal the choke for good. Unfortunately, I still need some time as the potting recipe has not been finalized yet. Hope can finalized in a week or two.