Alternator Capacitor

When a rectifier diode shorts out it will allow AC to pass causing very high ripple current in the remaining DC output which is what most often kills the regulator and capacitor.

The capacitor is typically just working as a simple noise and spike suppression device but is still very necessary.

Thank you for the information that you supply. I really appreciate it.

Come to the topic. If there are any problem on the regulator or alternator life if the capacitor is broken? Where can I get this field of information? Any recomment website or references?

Thanks

If the capacitor is bad your regulator life could be a few seconds to many years. It all depends on its design and working conditions.

I see. That sound interesting.

Can I said that it is not necessary to replace broken capacitor?

If there are any websites, references or solid information state that "effect of capacitor on regulator" which I can refer to? Just like what you said "If the capacitor is bad your regulator life could be a few seconds to many years". Thanks

It would be helpful to tell us what type of vehicle you are working on, as well as the manufacturer of the alternator.

More details result in quicker and better answers.

I am involving in workshop repairing. Models like Mit, Hit, Denso, and so on. Too many that I cant list all out. From 50A until 140A. So I am struggling in this problem. Comment pls. Thanks

Well, a capacitor (to use an analogy) is like a storage tank in a hydraulic system. "Stores" changes (not exactly an correct explanation, but it's adequate for this discussion).

I assume you have the workshop manuals or service information for ALL the various types of vehicles and alternators you are working on. If not, you need to get them. There is no practical or safe way to service your vehicles/parts without them.

You need detailed information to execute your job. You may be dealing with "A" circuit alternators or "B" circuit alternators; internal regulators or external regulators, different wiring setups, etc.

Without this detailed information, and the proper diagnostic equipment, this will be extremely hard to perform successfully.

Thank for giving respone. I appreciate it.

I deal with both integral and external regulators.

The capacitor is necessary for Electro Mechanical Interference (EMI) shielding. If you have a sensitive receiver (0.5 uV for full quieting) and the capacitor is not functional, there will be a whine that will vary (increase/decrease) in frequency as the engine speed varies. This electrical noise is transmitted to other adjacent receivers in the vicinity. The FCC requires all devices, capable of transmitting, to meet stringent criteria.

The reference for this information is FCC Interference Handbook (1980 edition). Information can also be found in NAVSEA 0967-LP-000-010 (INSTALLATION AND MAINTENANCE BOOK [ELECTRONICS]) (Bonding/Grounding [EMI]).

Good Luck in the contest

Capacitors are used in a cct for so many reasons aprt from the primary things we know.

The configuration of the cct has made it to act the way u described.the capacitor and regulator are networked and u only need someone who understand and can interprete the functionality of that part of the cct,then u may or may not do with the capacitor.

Certain components in a system could still be ignored or bypassed while u still have yr normal output result.But first understudy the importance of such a component.Find out why yr regulator or rectifier get damaged and correct or fix this problem first.

Check yr manual and consult experienced people on that machine or the manufacturer.

Patrick Whowha

Most capacitors in alternators are used to reduce noise on the line. This is definitely the case on generators where they reduce the noise from brushes on commutators. Not removing the noise on lines being fed to diodes increases the likelihood of damage because of higher voltage peaks being fed to them. This means that " if the cap aint there the diodes probably won't be there fer long either" .Still, it would be nice to see a print to be sure what its purpose really is.

10s for comments.

But where can I get these all information. I mean websites or references that I can refer to. Actually I had a tested machine use to test the regulator purposely. The regulator tested well with the setting I set. But after I assembly whole set alternator, I found that the regulator fail when I test it finally with DV tester. The set point of voltage is run away.

Comments pls

thanks for comments.

You mean diode in the rectifier? or inside the regulator? FYI, the current pass through the '+' and '-' diodes (rectifier)and then the capacitor. Comments. 10s

OK, An alternator that has a regulator mounted inside it feeds a current to the slip rings to create a magnetic field in the rotor. The spinning rotor causes the outer windings to feed 3 phase ac to the rectifiers that provide the output voltage and current. These rectifiers are the large stud mount devices that are mounted on the large heat sink. Are these the rectifiers you are talking about?

The regulator and its attached circuits control this current to keep the output voltage at the correct amount. That is usually about 14 to 15 volts. If your voltage is going above that, the problem is in the regulator circuit. Most regulators have a small diode pack that is used to provide voltage to supply the regulator with its operating voltage that allows it to feed the rotor. If there is a capacitor at this point it is to provide smoothing to provide a level voltage for the regulator. Is that what you're talking about?

Does this help any?

Yes, you are right.

That what I am talking about. You mean that the capacitor smoothing the current came out from the diode to the regulator?

So from you experience, what may happen if the capacitor broken? Regulator life degrade? Any significant references can I refer to? Comments.

If the capacitor is faulty, it will cause the regulator to be unstable and can cause intermittent problems in the vehicle that are extremely hard to trace. If it is broke fix it.

After many years, (27) in the automotive business and many "rebuilt" alternators, I can tell you for a fact that the manufacturer will not put something like an electrolytic capacitor in an alternator unless it is needed. The cost is simply to high. Many re-builders try to get by cheaply and not replace ALL bad components. This has led me to R&R of the same component multiple times more than I care to remember. The unit may work on the bench, but what about when it is installed in a vehicle that will not tolerate ripple.

I had an alternator that had ripple from a voltage regulator that exposed itself when the headlights were turned on at idle. The fuel injection system saw the ripple as engine RPM and began injecting mass amounts of fuel. Need I say more.

Unless you are an engineer with full schematics and a complete understanding of the device, don't re-engineer it. If it is for your own use play with it at your hearts content. It it is for sale to the public, then do your company and the consumer a favor and fix it right.

The only other thing I forgot to mention is to check for a short to ground on the rotor. That will give you all kinds of serious problems too.