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RFI Suppression for 12 Volt Motor

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New Member
I did a search and came up with nothing. Can someone tell me, what I should do for RFi suppression on a 12 Volt, Revolving Light? I have such a lamp on my tractor, and it creates RFI on my "Work Tunes" Hearing Protection, with built in Radio.

Thanks in advance.


New Member
It would be nice to get some capacitor values. Not particularly interested in spending $50.00 on a module and shipping from some outfit on the Internet, when there are all of twelve cents of capacitors contained within! lol

I've never used Ferrite cores. What do they do? Suck up the RF? Are they value or frequency specific? How does one use them on DC or AC lines?


Most Helpful Member
I have used around .01 - .1 uf capacitors for typical RF bypass applications.
On occasion smaller ones may work as well it sort of depends on what size of motor you have.
One across the motor leads and one from each lead to the motor case typically cleans up the noise. Also most anything that uses a commutator or slip rings would benefit from one or more on each side or the slip ring or commutator as well.
Dirty sliding contacts can also make a fair amount of odd RF pops and static interference at times.

Most electronics circuit boards have many similar sizes on them that are used just for RF and odd noise bypassing. If you have junk board off some home electronics device you likely have a good source of small capacitors that would work well enough.
They are typically the tan or green ones that are rather flat from side to side similar to whats in the picture above.
Most often they have a three digit number on them. a '472' would mean its a 4700 pF capacitor. A '473' would be a 47000 pF capacitor. And a 104 would be a 100000 pF or .1 uF capacitor.
The last digit represents the number of zeros behind the first two digits.


Well-Known Member
The motor in your revolving light probably already has a cap on its terminals. What type of light bulb does it use? If it is a gas discharge type it's probably the inverter in the light causing the RFI.
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