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Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418
Posted: 08:15am 18 May 2022
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Ok I've been very busy harvesting aerosharp chokes from the carcasses of my ever growing junk pile.....
According to the STICKER on the inductors, I have the following:
7 pieces of 10A 2.67mH (all unpotted)
3 pieces of 15A 4mH (2 of which are potted with silicone)
3 pieces of 20A 3mH (all 3 potted in silicone)
ALL of them have access to the centre winding, so I can halve the inductance easily. And I assume I can parallel the two sides to halve the inductance and double the current????
Now I'm building a 200V DC 3 phase inverter based on the EG8030 so I need 200uH X 3 right?
What will happen if I use all 3 of the largest 20A 3mH inductors, cut the centre link in each and re wire in parallel for 1500uH.
That's about 7x the inductance that I need. Will that be a problem?
What happens when you have too much inductance? Will it all have more of a propensity to resonate in tandem with the transformer?
poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1388
Posted: 08:55am 18 May 2022
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put inductors in series to increase total. just like resistancewronger than a phone book full of wrong phone numbers
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961
Posted: 09:39am 18 May 2022
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I have cut one of those large chokes in half (or was it quarter) and measured about 400uh not sure if that measurement is exact, but it was an el cheapo meter to test with. Have posted it somewhere, that grey potting is not too difficult to remove.Cheers Aaron Off The Grid
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418
Posted: 09:40am 18 May 2022
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Not sure if you follow or if I have missed something basic:
they are already in the milliHenries according to the stickers. Say I use half of the big chokes. That's 1500 microhenries (Too big)
I need 200 microhenries.
So what will happen if I have too much inductance?
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418
Posted: 09:45am 18 May 2022
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That's promising. What effect will having 2x the required inductance be?
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961
Posted: 10:44am 18 May 2022
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So far, twice the inductance hasn't been an issue that I am aware of, for our 48v inverter builds. Many more times the inductance (I had up to 685uH) created a bad sign wave and high idle current, enough to scare me, there was probably some saturation as well.
So twice the inductance may not be a problem for you.
Edit. Just thinking, I might have cut it in half then half again to get to 400uH, not as straight forward as we would like, but would parallel better if possible, will need to experiment. Edited 2022-05-18 21:09 by RevlacCheers Aaron Off The Grid
Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418
Posted: 12:39pm 18 May 2022
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Something dawned on me just now. The current rating stamped on the chokes I have is just based on the thickness of the copper wire. The stamped figure won't have anything to do with the magnetic saturation characteristics of the core. So despite being rated for 20A, I think it's going to saturate well before 20A if I don't increase the air gap.... Hmmmm
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