I've recently installed a cheap car radio (removed the OEM radio) and experienced a lot of alternator whine, at all RPMs. I did not expect this since the very old and dated OEM radio on max volume produced no whine whatsoever. I also thought that in most modern cars the alternator would be fully regulated and that alternator whine would not even be heard since the voltage stays very stable at 14.4 V, no matter what RPMs. Maximum ripple is about 150mV, which I would consider to be very good since this would only happen when turning on headlamps. All other loads will not cause ripple above about 100mV. This was measured at the radio terminals without the radio connected. Turning on or off the headlamps did not produce any clicking or popping sound, but the alternator did and it is quite annoying.
Anyways, to eliminate the alternator whine I built an LC circuit. That is a series inductor with a parallel capacitor. That helped a little, but the whine was still there. So I decided to change the circuit to a CLC circuit. This worked better, but the whine was still there. I then opened the OEM radio and discovered they used a CL filter, first the parallel capacitor of 3300uF and then the inductor. Mine was basically the same, but I had it the other way around as mine was a LC filter and not a CL filter. Also, they had a crapload of capacitors in parallel before the inductor. It was something like 0.1uF, 1uF, 10uF 100uF and 3300uF, all in parallel and then the inductor.
As sure as hell, when I replicated their circuit it worked and the whine was gone., completely gone. I'm just curious if there is a logical explanation why it would make such a big difference in building a CL filter rather than an LC filter. What would be a logical explanation? Almost all filter boxes I found in most cars had it the other way around and while it did suppress the noise, this one worked even better.
Can anyone explain this? I'm confused. I assume that they did this to eliminate reflections or do some sort of source transformation since inductors act as capacitors at very high frequencies and capacitors will act as inductors at very high frequencies. But this is only at very high frequencies, and cannot be heard, but in this case it worked.
Although I'm sorted now, I'm just trying to better understand this and was hoping someone with better knowledge than me can tell me what topics I can maybe Google since I don't exactly understand what is the real difference between parallel capacitors and one big single cap. I know that adding capacitors in parallel is NOT the same as just having one bigger cap.
Anyways, to eliminate the alternator whine I built an LC circuit. That is a series inductor with a parallel capacitor. That helped a little, but the whine was still there. So I decided to change the circuit to a CLC circuit. This worked better, but the whine was still there. I then opened the OEM radio and discovered they used a CL filter, first the parallel capacitor of 3300uF and then the inductor. Mine was basically the same, but I had it the other way around as mine was a LC filter and not a CL filter. Also, they had a crapload of capacitors in parallel before the inductor. It was something like 0.1uF, 1uF, 10uF 100uF and 3300uF, all in parallel and then the inductor.
As sure as hell, when I replicated their circuit it worked and the whine was gone., completely gone. I'm just curious if there is a logical explanation why it would make such a big difference in building a CL filter rather than an LC filter. What would be a logical explanation? Almost all filter boxes I found in most cars had it the other way around and while it did suppress the noise, this one worked even better.
Can anyone explain this? I'm confused. I assume that they did this to eliminate reflections or do some sort of source transformation since inductors act as capacitors at very high frequencies and capacitors will act as inductors at very high frequencies. But this is only at very high frequencies, and cannot be heard, but in this case it worked.
Although I'm sorted now, I'm just trying to better understand this and was hoping someone with better knowledge than me can tell me what topics I can maybe Google since I don't exactly understand what is the real difference between parallel capacitors and one big single cap. I know that adding capacitors in parallel is NOT the same as just having one bigger cap.
If you stop the noise at the source that would be best. Connect a 1uF suppressor capacitor from the output terminal on the alternator and the adjacent ground. The other cause could be two earthing points are being used. Don't earth the aerial and chassis. Earth the chassis. You can prove this by disconnecting all external inputs and aerial wire. If it stops reconnect each in turn to find out where it is coming from.
You'll have better luck with LCL "tee" filters than with CLC "pi" filters. You want to create a high (AC) impedance node, and then shunt the AC to ground with a capacitor. LCL does this better than CLC.
Have you tried the ones they sell in stores and on Amazon? Two of these in series, with caps on the inside and chokes on the outside, would make a truly fine LCCL filter.
Have you tried the ones they sell in stores and on Amazon? Two of these in series, with caps on the inside and chokes on the outside, would make a truly fine LCCL filter.
Keep in mind, no to make ground loops, for example, run the speakers and antenna ground only at the radio terminals. Grounding at both sides the shield of the coaxial wire of the antenna, or the return of the speakers make ground loops, and then a closed noise circuit.
Are you sure that nothing else changed when you made the last change? A simple filter shouldn't make that much of a difference.
Yes Sir, you're absolutely right. I saw the same thing, the LC filter only works when trying to remove very high frequencies, but frequencies in the audible range CL or like you said, LCL filters certainly work better.
I've never really bought a filter like this, I feel they're way over priced. It's just a too big of a schlep for me to buy one. I don't always like buying stuff, especially when I can build one. It's way more fun to build one plus it will make me learn something new. Laziness was never my strong point, I believe in hand-on experience.
But thanks for the pointer, I agree. LCL filters work better to remove the alternator noise. Using the right inductors, you can almost remove the noise completely.
um, what radio did you install? what vehicle? most all aftermarket head units are internally, or externally filtered fairly well. if you happen to pick up "alternator whine", it's indicative of an install issue, and having to over-filter might be a band-aide to mask the real problem.
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