alternator overcharge

[Hippie]

How would high resistance in the field circuit yield an overcharge? Would it fool the regulator into thinking that the field voltage/magnetism is artificially low, thus cranking up the alternator output?
Colin

Perhaps. Honestly I don't know why the higher resistance would cause a high output, but he did say the field voltage was higher than normal.

[dingo]

i dismantled my spare alternator [which needs diodes and brushes replaced] and finely smoothed out the copper rings on the shaft...then made nice clean contact between the two rings and measured 4.6 ohms

Have to wait a couple of days for streetsweeper to pass and for icy offshore winds to abate...before i can remove the alt.

cant quite figure out what, if any, effect the high 11 ohm reading would cause...and whether it is the culprit?

[chitwnvw]

If you want to do a write up, I and I assume others would do readings, we can try and get a handle on 'normal'.

[dingo]

yeah a write-up is definately in order...i will gladly contribute what i have found, once i have arrived.

meanwhile...my next thing is to look at 'isolation diodes' after i read this bit from Sir Ratwell

T

he reason for testing the smaller isolation diodes properly is that when they fail the VR will be confused and not know how to control an alternator that can otherwise output full voltage/current. They provide the voltage signal used to determine the battery voltage. If the test is skipped, you may simply get back home with your alternator, reinstall it, replace the regulator on the advice of the auto parts store and still have charging problems.

Referring to the Fluke test sheet, Checking ripple voltage

"Switch your meter to AC, black lead to ground, Red lead to battery
A good alternator should measure less than 0.5 VAC with engine running. A higher reading indicates damaged alternator diodes"

"To check alt diode leakage, connect the multimeter in series with the alternator output terminal when engine is not running. Leakage current should be a couple of milliamps at the most. more often it will be in the order of 0.5 milliamps" (Meter set to DC amps)
Output terminal is the one that goes to the battery +

[dingo]

[album]81[/album]


see pic: isolated diode trio...has to be unsoldered from circuit to be tested..these from spare all tested good 500ohms one way and nothin the other way

as far as the above mentioned diode tests...1. my meter dont got no AC setting 2. i measured 0.00 DC Amps..tho the 15 Amp setting may not be sensitive enough to read 50 milliamps [.05 amps]..so im not sure how relevant that reading was.




ehhh...ok how do i get the image to appear??
(I opened the address you highlighted in another window, found the Album Tag and got a thumbnail. Then I right-clicked the image, copied and pasted the address. Hit "edit" just to see the nomenclature but don't change anything)

[Hippie]

Looks like the diodes are OK.

[dingo]

my dad suggested i try the old standby...using a lightbulb as a regulator....inserting it between DF and B+. (harness disconnected) it has worked for me before, in a pinch...this time it did nothing..still getting 16V.....which point to issue NOT being the reg

[steve74baywin]

its in the gallery/album


[album]gallery/image_page.php?album_id=14&image_id=81[/album]


my dad suggested i try the old standby...using a lightbulb as a regulator....inserting it between DF and B+. (harness disconnected) it has worked for me before, in a pinch...this time it did nothing..still getting 16V.....which point to issue NOT being the reg

A voltage that high points to regulator, or diode.
Is the voltage DC like it should be or is it AC?

[dingo]

first thing i found...large black rectangular capacitor/condensor ? rusted thru and shorting against the case

is that possible culprit?

[Hippie]

It ain't helping it.

[dingo]

leaving no stone unturned, i checked the capacitor...as best i know how. measured resistance on 20k scale..then after a few seconds it discharges followed by NO continuity...so i guess that checks out.

[Amskeptic]

first thing i found...large black rectangular capacitor/condensor ? rusted thru and shorting against the case

is that possible culprit?

IIRC, that is the radio interference capacitor. Your alternator, do you have a replacement spare alternate Known Good Alternator?
Colin

[dingo]

yes...somewhat...missing one brush and needs diodes re-soldered...nothing major.

also, question: can those two sealed bearings be somehow 're-lubricated' ?

[dingo]

put the original back,,,and fired up....for a short while holds at 14.2V.....but then goes into its wild state 15,16,17 again

so the search continues

[dingo]

removal.....opened up the back and measured the isolation diodes....they all measure about 1.5k in one-direction only..so i guess they all check out.

anything else i can measure while i have it open ?

i measure DF to D-(ground) and now i get a wildly fluctuating 29 ohms...38 ohms and everything in between...measured at the terminals on rear-deck

while i spin the pulley, i get great fluctutation in DF to D-(ground)...sometimes it settles on 11 ohms, but while spinning it can be anywhere from 11 to 50 ohms