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EMI Suppression Cores

Old 12-29-2003, 08:43 AM
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Default EMI Suppression Cores

I am starting to see these on rc cars in Japanese magazines. What do they do and how is it helping? I see them use it on the wires going to the batteries and some also use it from the ESC to the motor.
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Old 12-29-2003, 10:44 AM
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They are there to help suppress glitching from motor/radio interference.
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Old 12-29-2003, 12:33 PM
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I have a set on my cars...haven't really notice any difference with or with out them... if there is....it's very negligable...
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Old 12-29-2003, 12:43 PM
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Default Re: EMI Suppression Cores

Originally posted by Suradaj
I am starting to see these on rc cars in Japanese magazines. What do they do and how is it helping? I see them use it on the wires going to the batteries and some also use it from the ESC to the motor.
You can also twist you motor wires together which will help eliminate motor noise.
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Old 12-29-2003, 01:44 PM
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i belive that they are nothing more than a ferrite magnet. they are used frequently in the rf telemetry industry. i've mostly seen signal wires run through them, though. i dunno how much they help us out, but if you're underweight, that's a good way to start.

how important is the convention of how the wires are run through them? i've always seen the wires wrapped vs. zig-zagged in high end installations. that way the current flows in one direction through the core of the magnet. does that matter??
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Old 12-29-2003, 01:50 PM
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Originally posted by seaball
i belive that they are nothing more than a ferrite magnet. they are used frequently in the rf telemetry industry. i've mostly seen signal wires run through them, though. i dunno how much they help us out, but if you're underweight, that's a good way to start.

how important is the convention of how the wires are run through them? i've always seen the wires wrapped vs. zig-zagged in high end installations. that way the current flows in one direction through the core of the magnet. does that matter??

I've always seen them mounted on the positive wires going into the motor and battery pack.
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Old 01-07-2004, 12:34 PM
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I don't think I will notice the difference but doesn't hurt to try.

Thanks for the info guys~!
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Old 01-07-2004, 12:47 PM
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I'd propably use them if I was having a glitching problem that I couldnt fix, but dont know that they will help much even with that...
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Old 01-07-2004, 10:32 PM
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i encountered some glitching gremlins at a certain track, after installing this ferrite core does indeed help to suppress the glitching somewhat.
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Old 01-08-2004, 07:59 AM
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do you guys know if these EMI supression cores come in different types/values (like capacitors, diodes, etc.)? what is commonly used for RC applications? im going to the electronics shop tom and i hope to find one but i want to be sure if what im getting is ok for RC use
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Old 01-08-2004, 08:12 AM
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Originally posted by marvi
do you guys know if these EMI supression cores come in different types/values (like capacitors, diodes, etc.)? what is commonly used for RC applications? im going to the electronics shop tom and i hope to find one but i want to be sure if what im getting is ok for RC use
There are different vallues... I just grab one that has the right diameter for the wires. .20in..works great for 12ga - 14ga wires.
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Old 01-08-2004, 01:32 PM
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Just thinking, wouldnt' it be more beneficial to put these things on the signal wires (3 conductor wire) from speedo to receiver, and receiver to servo??
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Old 01-08-2004, 01:52 PM
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The art of using ferrite is complex. I'm not an RF guy, but I have put them in a few products, so I'll see if I can distill this a little.

Ferrite is a special form of elemental iron, which exists in a cubic lattice, like a salt crystal. It has a weak magnetic quality, but nowhere near that of other ferrous metals, There ain't no such thing as a ferrite magnet, at least in the "refrigerator magnet" sense. It's used as a core material in transformers and chokes to increast inductance without increasing the length of wire required, and also increasing the current handling before saturation.

In RC stuff, they'd be most effective on the positive wire from the ESC to the motor. The motor has a ton of inductance itself and will filter the current returning in the negative wire quite well. The wire from the battery to the ESC is pretty clean, and it really doesn't need any filtering. The best way to do it would be one tor two turns of wire around a small ferrite donut between the motor and ESC.

There are numerous types of ferrite belnds for different applications, current levels, frequencies, etc. Picking the right one really is an art in some senses, and is an art I'm not entirely qualified to practice.

At the frequencies present in RC stuff, caps make more of a difference than ferrite will. Ferrite has very little effectiveness at the low (<100kHz) frequencies used for ESC modulation, whereas capacitors are happy smoothing things down to DC. Adding inductance to a wire increases the resistance to fast changes in current. Adding capacitance makes a circuit more resistant to fast changes in voltage. In the case of modern ESCs, we need both, but having more capacitance is better than more inductance.

-dave

Last edited by dpaton; 01-08-2004 at 09:49 PM.
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Old 01-08-2004, 01:57 PM
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Originally posted by PitCrew
Just thinking, wouldnt' it be more beneficial to put these things on the signal wires (3 conductor wire) from speedo to receiver, and receiver to servo??
No. The pulses that the receiver sends to the servo are very fast (~200 times faster than an ESC switches), and ferrite will round over their edges, making glitching more likely, since the pulses will be harder to read. Ferrite will be most effective on the positive motor line, and then only minimally so. You're better off making sure your antenna never folds back on itself and you aren't using a graphite antenna mast first.

-dave

Last edited by dpaton; 01-10-2004 at 08:11 PM.
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Old 01-08-2004, 03:00 PM
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...wow Dave. Thanks for the info
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