HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 13, 2011, 12:51 PM
KB3VOJ
cherokee180c's Avatar
USA
Joined Sep 2007
2,591 Posts
Question
LC Filter Location?

I have been looking through a ton of LC filter posts, but can't seem to find a difinitive answer to this question, even though I am sure it must have been covered somewhere...

If you have a system running a 5V camera and VTx, and you are designing to run everything off the single main 3S battery to a separate BEC for 5V supply, should the LC filter go after the step down to 5V or before the BEC? I am leaning toward after the BEC, but want to be sure. I will have other torroids on the lines near the camera, VTx and GPS.

I also thought about using the standard ESC BEC to power the rc control system only (Reciever and servos) so the BEC is even more isolated on just the VTx, and camera.

Any thoughts?
cherokee180c is offline Find More Posts by cherokee180c
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 13, 2011, 01:06 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
Honestly, it will not matter much (assuming you keep the choke on the BEC). The LC filter is a linear filter.

If you are going to use a separate BEC to power the plane then what I would recommend is to use a diode (1N4002 should do) on the 12V supply right before filter then the BEC. so you have 12V - Diode - Filter - BEC. The reason is that the a diode will knock out a considerable amount of interference from the ESC (but not from the camera or VTX coming back in). The filter then elminates the rest. Since switching BECs are noisy, they have their own choke which I recommend you leave in. In fact, I'd add a few more turns to it. Also, you could opt to leave the capacitor out of your LC filter (making it simply a coil of wire only) in this configuration as your switching BEC already has one.

If you are going to run everything off of one BEC, then I would recommend leaving the diode out (it would just be useless) and placing the LC filter after the BEC.

-Alex
IBCrazy is offline Find More Posts by IBCrazy
Reply With Quote
Old Jan 13, 2011, 01:13 PM
KB3VOJ
cherokee180c's Avatar
USA
Joined Sep 2007
2,591 Posts
Thanks Alex. One last quick question.. One of the biggest problems I have with the normal ferrite rings is to get enough wraps around them. I noticed that the dpcav LC filter uses a fairly thin wire and gets a ton of wraps around it to help pull out the interference. Would you consider that to be a upgrade over just using a normal ferrite choke where I might only be able to get 5 wraps around it?

I am thinking of 12V-BEC-dpcav LC filter - VTX/Cam. I will use the diode if I use the ESC BEC as you suggest.
cherokee180c is offline Find More Posts by cherokee180c
Reply With Quote
Old Jan 13, 2011, 01:25 PM
Blu-Core is my friend
Gundy's Avatar
La Crosse, WI
Joined Apr 2006
818 Posts
Just a thought...
If the only place I am concerned about noise, is in my video, then I could just "filter" the power line into the Vtx and the video-in line to the Vtx......??

Later,
Gundy
Gundy is offline Find More Posts by Gundy
Reply With Quote
Old Jan 13, 2011, 03:41 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
I use 22 or 24AWG magnet wire and can get upwards of 50 turns in there. However in a pinch you can use a 1/4" bolt about 2" long and wrap the wires around it a bunch of times. I'd get magnet wire though. It's cheap. I can send you some free if you local Radio shack doesn't carry it.

-Alex
IBCrazy is offline Find More Posts by IBCrazy
Reply With Quote
Old Jan 13, 2011, 03:50 PM
NDw
Registered User
Ireland, Limerick, Kilmallock
Joined Aug 2010
2,123 Posts
Just wondering does the wire to be wrapped around the ferrite ring have to be insulated? I imagine so but just double checking.
NDw is offline Find More Posts by NDw
Reply With Quote
Old Jan 13, 2011, 08:00 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
Yes, it needs to be insulated. Magnet wire has a nice thin enamel coating for an insulator.

-Alex
IBCrazy is offline Find More Posts by IBCrazy
Reply With Quote
Old Jan 13, 2011, 09:49 PM
Registered User
Bolingbrook, IL
Joined Jan 2009
139 Posts
Alex,

Do you wrap a single magnet wire for Vcc line, or triple of them for Vcc, Gnd and signal lines?
Wise_Man is offline Find More Posts by Wise_Man
Reply With Quote
Old Jan 13, 2011, 11:21 PM
KB3VOJ
cherokee180c's Avatar
USA
Joined Sep 2007
2,591 Posts
I think my problem is that for the LC filter I made on my EZ* I was just using a small RF choke (looks like a resistor) (not a wrapped ferrite ring) for the L part of the LC circuit.
cherokee180c is offline Find More Posts by cherokee180c
Reply With Quote
Old Jan 14, 2011, 07:56 AM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
Quote:
Originally Posted by Wise_Man View Post
Alex,

Do you wrap a single magnet wire for Vcc line, or triple of them for Vcc, Gnd and signal lines?
Either works, but typically I wrap both power and ground wires around the choke. 15-20 turns is plenty.

-Alex
IBCrazy is offline Find More Posts by IBCrazy
Reply With Quote
Old Feb 01, 2011, 06:57 PM
Navigator
volto's Avatar
USA, CO, Durango
Joined Sep 2010
670 Posts
I am planning on using a ferrite choke from an old dead PC power supply, the wire is already wrapped around it, just have to solder onto the ends.
volto is offline Find More Posts by volto
Reply With Quote
Old Feb 01, 2011, 08:26 PM
KB3VOJ
cherokee180c's Avatar
USA
Joined Sep 2007
2,591 Posts
Just be careful, as not all are ferrite. I used one that didn't work and it turned out the core was steel.
cherokee180c is offline Find More Posts by cherokee180c
Reply With Quote
Old Feb 01, 2011, 08:41 PM
Navigator
volto's Avatar
USA, CO, Durango
Joined Sep 2010
670 Posts
Uh oh, hopefully it works cause I have already soldered it all together, with shrink tube and all
volto is offline Find More Posts by volto
Reply With Quote
Old Feb 01, 2011, 08:44 PM
KB3VOJ
cherokee180c's Avatar
USA
Joined Sep 2007
2,591 Posts
Mine was a steel with a green paint on the outside. Came right off a motherboard.
cherokee180c is offline Find More Posts by cherokee180c
Reply With Quote
Old Feb 01, 2011, 08:47 PM
Praying for better weather
Coyote64's Avatar
Joined Dec 2007
4,211 Posts
Heres where i get mine from, good price and two sizes 20 of each :

http://cgi.ebay.co.uk/Two-Sizes-Wire...item1c0c1d7bd1
Coyote64 is offline Find More Posts by Coyote64
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Sander Style LC Filter Blue Chip FPV Talk 162 Nov 20, 2014 12:33 PM
Discussion Whats an LC filter? EyeFlyPlanes FPV Talk 24 Nov 12, 2014 09:53 AM
Discussion LC filter, reduced my range?... Kev.au FPV Talk 57 Nov 12, 2010 03:33 PM
Question Building an LC Filter? spagoziak FPV Talk 11 Aug 31, 2010 09:51 PM