Author Topic: Choke-input DC-filter  (Read 359 times)

Offline kamelryttarn

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Choke-input DC-filter
« on: June 20, 2019, 11:43:58 AM »
The other day I received an arduino shield for my motorcycle tachometer project. It will be used to convert the ~12V system to 5V and also provide a little backup power.

Since there is a fair amount of noise on the electrical system I figured it would be a good idea to add some kind of filter on top of the filtration the shield will provide for me so I bought a DC choke of 320mH rated for 600mA with a specified DC resistance of 7.8 Ohm. My goal is to remove some of the worst spikes and dips but do I NEED a capacitor as well and should I place it before or after the choke? I know a capacitor will make the filter circuit perform BETTER but what I would like to know is if I MUST place a capacitor just before or after or if it's just good practice. Can a choke WITHOUT a capacitor even make things worse and possibly break certain components?

My initial plan is to use my oscilloscope and measure before and after the choke to see what kind of difference it makes but if just a single choke can actually make things worse and damage my shield I do not want to do that before I have checked with people who has a better understanding about this than I do. All information I can find about chokes refers to using the after a rectifier bridge @ 50/60Hz

Offline johnf

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Re: Choke-input DC-filter
« Reply #1 on: June 20, 2019, 12:09:27 PM »
I prefer after the choke so as to minimise circulating current around the filter this also tends to let you use lower value caps that have higher self resonant frequencies so the filter works to higher frequencies

Offline kamelryttarn

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Re: Choke-input DC-filter
« Reply #2 on: June 20, 2019, 12:53:58 PM »
But isn't there a risk that the cap placed after the choke will try to feed current back when cranking the starter motor? Short circuit current will be close to 2A . Won't that hurt the choke?

Offline johnf

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Re: Choke-input DC-filter
« Reply #3 on: June 20, 2019, 08:58:07 PM »
the cap will try to hold up your feed to your regulator the choke will limit current flowing back
No it will n ot damage choke for a small shortime slight overload.
The worst thta can happen is the choke saturates effectively removing its core making the coke equal to it being air cored while it is in saturation
It immediately recovers after the overload to be as it should

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Re: Choke-input DC-filter
« Reply #3 on: June 20, 2019, 08:58:07 PM »

 


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