can somebody confirm this? bad alt

[Alxsmt]

picked this up today due to a charging issue. worked great! for about 3 min.. then had worse issues than before I replaced it. checked over everything. had the alt tested, came out good. tore half my wiring harness apart.. found nothing but everything being correct.

with me testing it, with the car running and no charging cable attached, I was getting zero volts at the post. thinking maybe it the computer wasnt telling it to turn on I checked over the 2 small wires connecting to the alt, according to the diagrams they both have power, and they do. one goes to the starter with the charger wire and the other goes to the gauge cluster.

then a friend told me to check the charge post to the alt case for ohms.. this is what I got. meaning its grounding out and its bad IMO. can anybody confirm this?

[robertisaar]

looks like 103,200 ohms(since in the 200K setting and seeing 103.2) from post to case? i wouldn't call that bad, but i don't know what "normal" is. 103,200 ohms to a 14 volt source is 135.6 microamps... it's probably not even measurable.

[Alxsmt]

I tested one on a subaru and it came up as open. to me it seems like any connection is bad. but im not an expert. you told me a lot more than I knew lol. If this isnt my issue im 100% clueless.

I have not gone over my grounds, well they are tight but I didnt check for corosion under them. could this possible be a ground issue?

[robertisaar]

it's possible that it's a ground... you do need both positives and grounds to be functioning well to keep everything happy.

you could force the alt to charge by manipulating the L circuit. if you connect it to +12V through a 35-500 ohm load when the alt is spinning(at a normal idling speed or higher), that will tell the regulator to start regulating voltage. 35-500 ohms at 14 volts is 400mA to 28mA... so if you have anything that will draw something along those lines(the instrument panel battery/volts bulb is normally used in earlier applications, or in the case of later stuff, it's internal to the PCM), that will do it. if you connect directly to 12 volts, you'll kill the regulator.

another way to test...... that isn't necessarily the safest way to go about testing, but should show issues..... is to use another vehicle's +12V and ground system. instead of jumping, when the engine is running on the car with the "bad" alt, connect the +12V(and only 12V) between the two vehicles, see if it clears up issues, if it does, you have something to deal with on the positive side. take that off, now connect the grounds together, preferably near the alt on the "bad" one to rule out a missing engine-frame or engine-battery ground strap. clears it up, ground issue.

[Alxsmt]

well I didnt 100% follow the first part, but the 2nd one I can do! maybe Ill try that tomorrow before I check the grounds.

thanks!

[Syndicated]

You can't measure resistance while a circuit is powered, not only is it a great way to fry your meter, you'll never get a correct reading, since the battery in the meter is applying power to the circuit at the same time 12v is coming from the car.
If you have a measurable reading from stator to ground (post to case) I'm thinking you have a bad alternator.

Have your battery tested when you take that alternator back!

[Alxsmt]

resistance was checked with the ign off, and again with the alt off the car. volts was tested with the car running, and turned off.

I hooked another cars charging system directly to the berettas alt, it worked great! meaning the wiring is good.

so..
charge output - 12v constant
2 wire connector - one wire 12v constant, other wire 12v with the ign on.

I also had it tested at another parts store, came out good.

[geoffinbc]

Put the meter on the battery with everything off. Keep it there and have someone start the car. Tell us what happens before during and after the engine starts.

[Alxsmt]

well I would have, but they let me swap it out today. guess what? this one works! I have no faith in alt testers now. so much for tearing my wiring harness apart lol

[robertisaar]

it really depends on how they're tested... most are just low-load and test voltage, but what's needed is high load voltage and current.

[geoffinbc]

Agreed. And depending on the type of machine it could be up to the operator to interpret the test results. Most parts store employees are idiots.

[Alxsmt]

makes sense I guess but seems weird they would turn away business due to not having a high load tester! the guy that swapped it out for me Ive knows for years due to going there all the time. he said there was a slight ripple in the testing but it still checked out good.