Ferrite Beads - Page 1
Forum section: electronics / general

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 27, 2014, 02:22:54 pm
content: I was in the "harness designers meeting" this morning at excavatoree-co, and one our other platform guys said he had a cab harness that was acting as an antenna and receiving interference that affected the computerized information display module.The problem was solved by adding two ferrite beads, but he mentioned the cost is high - 10 dollars per bead. They then proceeded to discuss alternatives like shielding, etc. Ten dollars per bead sounds high to me - should we be looking for a better supplier?

author: IanB
author_rank: Super Contributor
timestamp: February 27, 2014, 02:29:33 pm
content: They are probably "military spec" beads

author: w2aew
author_rank: Super Contributor
timestamp: February 27, 2014, 02:36:18 pm
content: You can probably find them cheaper, but of course it all depends on the size needed, and the type needed. Assuming that you're looking at the "snap-on" variety, here's an example of a supplier offering them well under $10http://www.rfparts.com/chokes-inductors/chokes-ferrite.html

author: b2theory
author_rank: Contributor
timestamp: February 27, 2014, 02:37:22 pm
content: How big is the harness and what frequency are you trying to attenuate? Is the harness all low voltage low frequency?

author: Excavatoree
author_rank: Frequent Contributor
timestamp: February 27, 2014, 02:53:43 pm
content: Quote from: b2theory on February 27, 2014, 02:37:22 pmYes, it is all low voltage (12V) and low frequency. However, he didn't have the details at hand. If he adds them to the meeting notes, I'll post them.There is no problem with the vehicle as designed, but during the EMC susceptibility test (I'm not involved with these, so I'm a bit unfamiliar with them) the operator control module (input terminal for the vehicle ECU) acted as if an operator had pressed a touch screen button. The engineer said that it is a result of the module not properly immune to such interference, and he admitted that the beads on the harness were a "band-aid."Someone suggested stainless steel braid covering, but isn't that even more expensive?

author: b2theory
author_rank: Contributor
timestamp: February 27, 2014, 04:22:03 pm
content: Quote from: Excavatoree on February 27, 2014, 02:53:43 pmThere is no way to say whether shielding (braid or foil) will be an equivalent fix. Shielding is transparent at some frequencies and it will also be dependent on your grounding network. From my experience and without knowing the region of susceptibility, ferrites will be a cheaper, more predictable, and more flexible solution.He is correct in that it doesn't sound like you have root cause, but that may be a good enough solution.

author: JackOfVA
author_rank: Unknown
timestamp: February 27, 2014, 10:10:00 pm
content: $10 for a ferrite bead is on the expensive side, but it depends on the physical size and material mix. It's not out of line for a physically large bead manufactured from the most expensive material.If cost is an object and if the installation permits, multiple turns through the bead yields more attenuation (N^2) than a single turn. However, if the wire is also carrying high DC current, then you have to watch out for DC saturation of the core, which drives down the inductance.