Tips on rewiding an inductor? - Page 1
Forum section: electronics / repair

author: vmallet
author_rank: Regular Contributor
timestamp: October 23, 2019, 06:06:17 am
content: On the continuing saga of attempting to resurrect an audio amp that burnt up (in the thread "can this amp be salvaged") I'm looking at rewinding an inductor which insulation melted.My goal is to get the inductor within 20% of its original spec to see if it's worth going any further with the rest of the amp.My plan is to:- unwind the inductor- coat the wire with Plasti Dip- re-wind the inductor the best I can.Does that sound reasonable? Any advice or tips about what to do and what to look for?(bonus question: where could I find an inductor that looks the same with a similar 30mH inductance?)A couple of pictures:The inductor I'm trying to resurrect:Its sibling that got a bit of heat but still measures within specs:The dead inductor after unwinding it. The insulation is pretty much all gone.

author: spiette
author_rank: Newbie
timestamp: October 23, 2019, 06:59:35 am
content: Assuming the core is ok, I'd try measuring the wire's diameter and length. Get some new wire that matches and rewind the core.

author: andy3055
author_rank: Super Contributor
timestamp: October 23, 2019, 04:41:03 pm
content: Quote from: vmallet on October 23, 2019, 06:06:17 amspiette is correct. Do not use the old wire. Trying to insulate with plastidip is no good. The enamel coating is very thin in these wires. You should get new wire. It should not cost so much for such a small quantity. Once you have the wire gauge, you can easily find it in eBay. Rewind both inductors to balance the two channels. By the way, do not scrape the wire. If necessary, burn off the remaining gunk with a lighter and let it cool down. Do not pull or stretch while it is hot.Mouser has a range of them if you know the value from the diagram:https://www.mouser.com/Search/Refine?N=1525859

author: vmallet
author_rank: Regular Contributor
timestamp: October 23, 2019, 05:32:29 pm
content: Thanks. It appears to be 17 AWG (I measure ~ 0.044") and I just ordered the cheapest spool I could find to try it out for the sake of the learning exerciseQuote from: andy3055 on October 23, 2019, 04:41:03 pmGood to know. What can go wrong when scraping the wire?Quote from: andy3055 on October 23, 2019, 04:41:03 pmThat's the thing, I can't seem to find anything remotely similar on Mouser (or DigiKey). The value is supposed to be 30uH according to the schematic and the few 30uH inductors I see definitely don't look like that.

author: andy3055
author_rank: Super Contributor
timestamp: October 23, 2019, 07:28:27 pm
content: Quote from: vmallet on October 23, 2019, 05:32:29 pmIf you scrape the wire, you will effectively reduce the wire diameter and will read a lower diameter and the result is your gauge will be wrong. You will end up with a thinner wire.30 uH seems a big number for an inductor. Can you confirm that? I saw 3.3 uH inductors that looks like having the same psychical dimensions as yours.

author: vmallet
author_rank: Regular Contributor
timestamp: October 23, 2019, 09:45:15 pm
content: Quote from: andy3055 on October 23, 2019, 07:28:27 pmThe schematic and the measured value (of the other inductor) say 30uH from how I'm looking at things.Here's the relevant section of the schematic; the inductors I'm looking at are L10 (and L9, not pictured). With its 3.3uF capacitor it gives an LC filter with a 15kHz cut-off frequency (it's a one-channel sub-woofer amp).

author: andy3055
author_rank: Super Contributor
timestamp: October 23, 2019, 10:37:34 pm
content: I see.Somewhat different in construction but these might work:https://www.digikey.com/products/en/inductors-coils-chokes/fixed-inductors/71?k=inductor&k=&pkeyword=inductor&sv=0&pv2087=u30%C2%B5H&sf=0&FV=183%7C421681%2C-8%7C71%2C1221%7C346647&quantity=&ColumnSort=0&page=1&pageSize=25