inductor saturation current - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: June 01, 2019, 08:36:19 pm
content: i am looking at inductors to use in a power filter. i found what seemed to be too good to be true, a 33µH inductor with 30A constant current. But mwa, mwa, mwaaaaaaar it has a saturation current of less than 3A! surely this is wrong? what use will the inductor be after it saturates at 3Ahttps://www.mouser.co.uk/ProductDetail/Bourns/PQ2614BLA-330K?qs=sGAEpiMZZMv126LJFLh8y0s%252BS7zpDfrQRB236tWoNWQ%3D

author: Marco
author_rank: Super Contributor
timestamp: June 01, 2019, 08:40:28 pm
content: Saturable reactor?

author: ogden
author_rank: Super Contributor
timestamp: June 01, 2019, 08:45:09 pm
content: Everything is OK. RMS current is "DC rated" current handling capability of wire alone. Obviously you pick inductor by it's saturation current.https://www.vishay.com/docs/34053/definit.pdf

author: dmills
author_rank: Super Contributor
timestamp: June 01, 2019, 08:47:49 pm
content: More that you can run em HOT, and that the losses stay small due to the over sized winding (Also, you should be using the -BHA variant for high saturation).I have used such when I was trying to minimise temperature rise.Regards, Dan.

author: langwadt
author_rank: Super Contributor
timestamp: June 01, 2019, 08:48:20 pm
content: a 3A inductor that doesn't turn into a fuse until 30A ..

author: Simon
author_rank: Unknown
timestamp: June 01, 2019, 08:49:03 pm
content: Yea, but if you look at the datasteet they go from 100a saturation to 3A with the DC current always being 30A. So I take it that if I am pulsing 25A through this 33µH one it won't have much inductance?is it the case that I can have 27A of DC current with 3A oy pulsing?

author: ogden
author_rank: Super Contributor
timestamp: June 01, 2019, 08:57:02 pm
content: Quote from: Simon on June 01, 2019, 08:49:03 pmExactly.QuoteYou simply do not use inductor that saturates at 3A in circuit capable of 27A. Well.. there may be some very specific application that saturates inductor on purpose, but I bet it is not yours. Just checkedthis one(WE, 74437429203330). They do not even specify DC RMS current, just DC resistance. Saturation current is around 16.3A and rated current 13A

author: xavier60
author_rank: Super Contributor
timestamp: June 01, 2019, 09:54:14 pm
content: The Bourns data sheet shows two 33µH parts, one with almost double the Isat of the other.PQ2614BHA-330K 33 ± 10 8 1.62 1.90 30 5.1 5.9PQ2614BLA-330K 33 ± 10 7 1.29 1.60 30 2.6 3.3

author: Simon
author_rank: Unknown
timestamp: June 01, 2019, 09:57:00 pm
content: Yes bu still 30A versus either is a big difference.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 01, 2019, 10:00:13 pm
content: Bahaha, it's the same core and winding (wire, turns) and they're only varying the gap.The best inductor in that series is the value where Irms = Isat, which stores the most energy at thermal ratings. Give or take if you need more or less saturation for a given application.What are you actually filtering? Do youreallyneed that much inductance?Tim

author: dmills
author_rank: Super Contributor
timestamp: June 01, 2019, 10:05:33 pm
content: As always with any component you read the datasheet and remember always that the headlines have marketing department drool all over them.Regards, Dan.

author: Simon
author_rank: Unknown
timestamp: June 01, 2019, 10:15:17 pm
content: Quote from: T3sl4co1l on June 01, 2019, 10:00:13 pmI'm looking at PWMing a brushed motor so wanted something to take the edges aff the transitions. i was going to do a pi filter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 01, 2019, 10:39:07 pm
content: Oh, that still, just use a few uH. Not even that. Put a few dozens nF either side of it and you're fine.How much PWM was that going to be? Just on and off? Or at a modest frequency to get some buck action?Tim

author: coppercone2
author_rank: Super Contributor
timestamp: June 02, 2019, 02:36:46 am
content: Rated Current ..........Inductance drops 20 % at Isat1Inductance drops 30 % at Isat2Waht they should do, is have a separate data sheet or a separate table on the data sheet because it just looks bad.it's probably made that way so they can use the same tooling to make a bunch of inductors and possibly get more value from the machine setup. Add-on.So the part is rated for high surges which just basically ignore it, but will function as a inductor at lower currents.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 02, 2019, 06:00:43 am
content: Quote from: Simon on June 01, 2019, 10:15:17 pmYou are doing it wrong. A motor controller doesn't need an inductor - the motor is the inductor, and a massive one.There are special cases such as air-core micromotors which have so little inductance that you add external L to allow not-over-the-top PWM frequency while maintaining low ripple current, but I bet this is not the case.Your motor likely is a 10 or 100 times larger inductor (often measured in millihenries), so adding a 33uH in series is meaningless for ripple current. If your concern is EMI from brush noise and/or PWM edge rates, it's way too big.If you are looking for EMI suppression (from brush noise), you do it with small ceramic capacitors (two in series, from line to line, center tap to the motor case), and if this is not enough, by adding a common mode choke, after which you can add another capacitor. Note that this is really high frequency noise, so it's dealt with small magnetics and small capacitors, it doesn't need to store a lot of energy, the motor inductance does that for you.

author: Simon
author_rank: Unknown
timestamp: June 02, 2019, 07:28:42 am
content: Quote from: T3sl4co1l on June 01, 2019, 10:39:07 pmYea that is what I am starting to think. Been doing some simulation and I can make a nice oscilator if i am not careful. I'm using 1µH at the moment.

author: xavier60
author_rank: Super Contributor
timestamp: June 02, 2019, 08:40:58 am
content: if the current isn't continuous, load regulation can be poor.

author: Simon
author_rank: Unknown
timestamp: June 02, 2019, 08:47:02 am
content: It's a PWM drive of a brushed fan. i am using a BTS50010. I can move the parts around. i was thinking of putting onu capacitor in the switch input and then a low pass LC filter on it's output so that the switch is in the middle of the filter but this seems to produce oscilations.