Quote:

Bigger is not always better for filtering hash. Caps can exhibit what is known as "series inductance" and if the bothersome hash is high enough frequency, what might be more effective is LOWER value disc ceramic caps, with short leads.

Yeah, I agree... if we were talking about high frequency noise. But there was no problem before adding an alternator; it's probably ripple from rectifying (sp?) the 3 phase alternator output to DC. If the alternator is running 2X crank speed, and there's a 'bump' in the votage at the top and bottoms of the sine waves (I'm trying to envision whether the diode rectifier pack is wired as a delta or wye; and what that'd make for noise artifacts on the output), that means the 'hash' would be 12X crank speed (a ripple that has six 'bumps' superimposed on the 12V outputs, which is running twice crank speed).

9000 RPM on the crank equates to 150 cycles/sec. A frequency 12X that would be 1800HZ. Well down into the audio zone.

I'm guessing that MSD, Crane, and others did some empirical research into picking a cap value that'd work fairly well for the average installation.
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Since I'm just a hacker who f***s around with guitar amps and pedals occasionally... I'm too lazy to try and second guess these guys (who probably had some trial-and-error in picking the value). But, I expect 38000 uF is pretty generous.

Quote:

This noise can be difficult if it's superinposed on a high-current conductor--like the main output lead. In that case one "help" is to hold the alternator--to battery lead fairly short and use the battery itself as a filter. Something amiss in the alternator can also cause excessive noise/ hash/ ripple---like open or shorted diodes, or open or shorted--or partly shorted--windings

Sometimes a "split ferrite" around the power lead to the tach can help

Welcome to the modern world of electronics--and a high rf noise floor.



Again, I'll agree with you; I shoulda' gone straight for the obvious answer: is the alternator/rectifier any good?

Since this is a drag car, the batteries are probably in the trunk; so much for keeping that charge lead short.

BTW, how do these ferrite gizmos that you see around power wires really work? I've always guessed that they had something to do with dampening/disrupting the magnetic field around a wire... never really understood how they worked.

</hijack thread>

Bringing this all back to a useable discussion for the purposes of this thread... Yeah Max, did you try a different alternator? Or have that one tested? I missed an obvious step...

-bill

Seduce the attractive, and charm the rest. ****** 489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?