can a capacitor be used for ac voltage ripple?

[Master ACiD]

anyone knowledgable when it comes to capacitors?

ive got an alternating current project that has some voltage ripple. i was wondering if a capacitor could be used to smooth out the voltage ripple a bit? i know they can be used for this on dc systems, but would one wired in parallel work for ac as well?

 

[Quest]

doode!

in AC projects, ripple is part of the "deal"(fundamentally speaking). So, I don't know why you want to smooth out ripple (can you be more specific plse?) with capacitor.

Also: AC rated capacitor, when used in series in the same circuit, acting as a "filter" for DC blocker and also the amount of AC passing by is determined by the capacitor formulation (see below). This is known commonly as "high-pass filter" with 6dB/octave rolloff.

If the capacitor on the AC circuit is connecing from signal to ground, same deal (DC "shorts" to ground) and the frequency governed by the capacitor will shunt to the ground also (high frequency portion, lower freq. pass through). This is also commonly known as low-pass filter, again with 6dB/octave rolloff.


Formula as follows:

X = 1 / 2(pi)FC , where F is frequency in Hz and C is capitence in Ferads (0.01 uF = 0.00000001 F).

Later,

Q.

 

[Master ACiD]

i realise that all ac is basically a ripple, but please bare with me.
ok, ive got an atv with a crude lighting system. the electrical system is very basic. just a generator and a 1 wire voltage regulator that shunts excess power to the ground. the lighting system runs off of the ac generator and there is no battery. (no electric start either). this is a good way to reduce weight and excess wiring. the downside to having no battery means the lights flicker at idle to medium rpm's when the generator isnt spinning very quick.
ive seen other people solve the problem by using a rectifier to convert the lighting system to dc and then install a very small 12v battery to get rid of the low rpm flicker. the battery acts like a biffer smoothing out the pulses of power from the generator. id rather not use a rectifier and battery if i can avoid it because of the weight and complexity penalty, so i thought that maybe just maybe i could add a motor run or some other kind of capacitor in parallel with the lights that would simulate the buffering effect o a battery and recude the flickering of the lights.

 

[brianl703]

Yes, you could use a capacitor for that purpose. I'm thinking you may need as much as 3300uF or more for that purpose.

 

[rpn453]

I don't think a capacitor will do it for you. A capacitor in an AC circuit is used to cut off frequencies or reduce reactive power. I don't think those are your problems; your problem is that the frequency is simply too low. You could consider using a rectifier to convert to DC and use a capacitor instead of a battery to smooth that out.

 

[Master ACiD]

if i did convert to dc, any idea what size cap i would need to smooth out the flickering? the headlights are 35 watts a piece.

thanks.

 

[Gary Allan]

You are running off of DC now. You just don't have enough windings to produce enough humps at low rpm. A cap could manage that, but should just dim the lights as the rpms decline. It will, somewhat, clip the top of the hump and elongate it enough to do the same on the next hump.

It should act like an electrical Accusump.

 

[Papa Bear]

Headlights running on A.C. ??? Is there no battery ????
Please explain a little more about what you are doing so we aren't shooting in the dark.

The light bulbs in your home run on 60 cycle A.C. and they don't flicker (that we can notice), that's why we changed from 25 cycle to 60 cycle here in Ontario in the '40's

 

[Papa Bear]

How do you know you have voltage ripple on an A.C. circuit ??? Did you scope it ?? Do you have a spectrum analyser ??

 

[oilyriser]

It's probably making a/c using an extra coil near the flywheel magnet. Low RPM = low output.

 

[chas3]

your a/c ripple is coming from your generator (more likely its an alternator). it probably only has half-wave rectification (1 diode is cheaper than 4). you are correct that the battery is typically used to buffer this half-wave signal. this is why one should never run their vehicle without a battery! since your generator must be self-exciting, there is no reason you couldnt use a capacitor. the size you need depends on the frequency of the signal and the load. the half-wave rectifier will charge the cap and power the load during half the cycle and during the other half of the cycle, the cap will power the load. you need a cap big enough to power the load during this off portion of the cycle. what is the hz of the signal during the low rpm (is it 1:1 with the engine rpm?) and what is the load. i think the minimum value you need will be given by f = 1/rc where r is the load and f is the signal in hz.

the smallest audio "booster" cap you can find would probably be just the ticket. there are easy to find and should be able to tolerate your operating environment.

 

[va3ux]

Quote:

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How do you know you have voltage ripple on an A.C. circuit ??? Did you scope it ?? Do you have a spectrum analyser ??

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You wouldn't use a $15K spectrum analyzer for this application. A scope would do it. But so would any decent quality multimeter : just set it for the low range on AC volts and apply the test leads to terminals. It will read AC floating on a DC voltage.

 

[Papa Bear]

He's talking about AC on AC, read the original post. Try reading AC on AC with a multimeter ??!!
I don't know about you guys but I'm not wasting any more time on this until there is more info.

 

[tom slick]

look into dual sport conversion parts. guys deal with that problem all the time when converting dirt bikes into a dual sport. it takes a pretty big cap.

here is a link to one
http://www.fourstrokesonly.com/Batteryelim.html