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Ways to suppress voltage spikes and noise in tight quadcopter builds
#1
It‘s common practice to add a capacitor to our builds in an effort to suppress transients that are unavoidable with fast rise/fall times and large currents in low ohm high henry inductors. I've tried this approach and it seems to work well at soaking up the spike. 

Problem I find is that as our builds inevitably get smaller and our input voltages get higher the larger the capacitor gets. I've been using 1000uF as a ball park, and @ 25v its a large component to fit into a tight build. 

My question, is 1000uF capacitor for mini quad an over kill? And is there another way to subdue this spike using a different layout or component? I read up on the TVS recently (transient voltage suppressor) and I wondered if it could be useful, its form size is generally a lot smaller than the capacitors I'm using. Or perhaps a correctly rated zener? Just wondering if anyone out there has tried a different approach?
#2
Well, a TVS is really good at eliminating high voltage spikes (i.e. as a flyback diode for a relay) but I believe the capacitors benificial in that it can help prevent a brown out (punch the throttle really hard and the voltage sags too much) AND in the case of you cutting the throttle rapidly ( surely you have read that the collapse of voltage in an inductor produces large spikes)

All in all a single capacitor is probably the best thing for the job and a TVS would be best for a reverse polarity situation on solely eliminating a spike.

Now you also need to understand the duty cycle of a TVS because if you hit *most* TVS diodes with a large inrush of current they're likely to go poof
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#3
(25-Dec-2016, 04:33 PM)cche Wrote: Well, a TVS is really good at eliminating high voltage spikes (i.e. as a flyback diode for a relay) but I believe the capacitors benificial in that it can help prevent a brown out (punch the throttle really hard and the voltage sags too much) AND in the case of you cutting the throttle rapidly ( surely you have read that the collapse of voltage in an inductor produces large spikes)

All in all a single capacitor is probably the best thing for the job and a TVS would be best for a reverse polarity situation on solely eliminating a spike.

Now you also need to understand the duty cycle of a TVS because if you hit *most* TVS diodes with a large inrush of current they're likely to go poof

Thanks for your response. One of my concerns with the tvs is that it may not handle the current. However it was my understanding that we were dealing with high voltage, not high current. I believe most mosfets have a similar component integrated for this purpose. Yes Im aware of the conditions that generate spikes (di/dt) I hand not considered response time however.
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#4
I've gone with a 100uH inductor inline of my fpv 12v regs. When that's coupled with a 1F 25v cap on the battery, it completely cuts out any noise (so a basic lc filter). There have been instances where my cap was disconnected in a crash. The inductor suppressed all noise from reaching the video. Now that's great and all but I'm also running a pololu reg (switching reg) so it already has some small amount of filtering. I suggest trying out a small inductor + low capacitance cap as an alternative to a single large capacitor. They are both energy storage devices. Look for smd inductors because size is key here
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#5
I've been meaning to try a TVS, used them loads in other applications but none as harsh. I have one waiting to go on. After an LC filter it should have no problem, it's across the power rails that I'm nervous about but I figured if I put a small (surface mount so it weighs nothing) fuse in line then if things get really bad or the TVS fails short circuit from the abuse then at least the fuse will just pop. Will be interesting to see how warm the TVS is when I land (the one I have can take a fair bit). I'd still use a capacitor, just not one as huge.
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#6
My quads are fine with 2x 35V 470uf, they are pretty small (don't look at my latest build, those are same specs but bigger, kind of bought the wrong ones there).

Friend of mine had serious electrical noise problems with a naze r6, even only 1 of those caps fixed it completely.
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#7
Hello can you post a pic of where are placed the caps?
I have lots of noise when punching out throttle and i have no caps on pdb batt pads
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#8
A 470uf 25v rubycon low esr cap on each esc is how I normally do my builds. It's often plenty of room on the arms if you're doing a tight build in my experience.
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#9
I was jut thinking about adding a cap to my build. My FC is going to b powered directly from the BATT. And I would like to add a little extra protection. Can someone recommend a small size cap for the main BATT please.

Oh - PS: Just incase your wondering, I'll be using the new Spektrum F400 FC. Minimum input V is 3S.

Thanks
Randy
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