Winding a 4 gauge inductor - Page 1
Forum section: electronics / projects

author: Purduephotog
author_rank: Regular Contributor
timestamp: August 17, 2017, 02:20:19 am
content: Previously on lost:https://www.eevblog.com/forum/projects/refresh-of-'big-inductor-diy-style'/msg1134448/I've finally had time to get the pieces together and started trying to winds 4 gauge copper on the massive core. Turns out it's rather drop hammers on my toes.If I build some shims on the outside of the core to round out the center post, making it easier to send this pita copper wire, will I incur much penalty? Maybe 20% more wire will be needed.

author: Rerouter
author_rank: Super Contributor
timestamp: August 17, 2017, 02:55:27 am
content: If its a conventional E/I core, then Form the coil on a similar sized piece of timber in a vice, when done, pry it off and drop it in on the core. If you layer the timber kapton tape first, it will slide off much easier.

author: Purduephotog
author_rank: Regular Contributor
timestamp: August 17, 2017, 03:01:58 am
content: It is. I simply can not bend the 4 gauge tight enough to go around the form. Hammering it doesn't help.

author: Ian.M
author_rank: Super Contributor
timestamp: August 17, 2017, 03:22:19 am
content: The penalty for shimming a square center leg to have half-rounded end pieces is 28.5% extra wire length, increasing copper cost and resistive losses in the same proportion. However you probably don't need full half rounded end pieces. About the smallest radius corners that would be windable would be 1 wire diameter radius. I believe from your photos the E lams are 2 1/2" across the center leg, and 4AWG wire is approx 1/5" diameter. Allowing for insulation, a 1/4" radius should be acceptable, and, assuming a square center leg it will only add 5.7% to the wire length required.You certainly shouldn't be trying to wind straight onto the core. A former or mandrel is essential so you are only trying to bend the wire in one plane. If you are winding on a former the mandrel is essential to support it to withstand the crushing forces while winding . Ideally you'll want a split hardwood mandrel (with the split on the slant and both pieces waxed and highly polished) so when you move the halves in opposite directions to unwedge it, it separates from the coil or former easily. If you aren't using a former, either groove the mandrel faces or prepare the mandrel with lengths of linen cord with the excess taped down away from the winding area, so you can tightly tie (and glue) the wound coil to stop it springing apart when you remove the mandrel.I did say in your other topic, that I'd probably choose to wind such a heavy coil from thin copper sheet (or heavy foil), one turn per layer, interleaved with Kapton tape for insulation. The depth of the E looks to be about 3 1/2", so to get the same CSA as 4 AWG wire you only need 10 mil (0.25mm) foil. Assuming Kapton tape of 0.1mm total thickness, you should be able to get over 80 turns on.

author: Purduephotog
author_rank: Regular Contributor
timestamp: August 18, 2017, 01:33:22 pm
content: Thanks for reminding me about the copper sheet- I couldn't remember why I decided to not go that way until I re-priced the copper rolls. Mill finish copper, 6", would cost around 100$ and I'd have to slit it to 3". I already have the 4 gauge wire for free.I tried on a bobbin/mandrel and just keep coming up failed. I figured adding some circular reliefs to the bend radius would be better than cranking the thing constantly on 90s. If I can get that to work maybe it'll be OK.I'll put out a note on CL asking for copper remnant and head down to the local scrap yard to see if they get any flashing. If I can find a big enough partial roll then I might have a chance there.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 18, 2017, 02:09:53 pm
content: It is perfectly OK to use more strands of thinner wire in parallel. Just make sure to get the same number of turns - so usually wind them together. If the wire it to think there will be extra gaps and to much force with sharp tools can damage the isolation.