Alternators keep going bad

Tiny
REGNAR71
  • MEMBER
  • 1997 HONDA ACCORD
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 260,000 MILES
Two alternators went bad within a couple days and will not charge battery but tested good on bench test before putting in vehicle. What is causing alternators to go bad?
Sunday, April 3rd, 2022 AT 8:34 AM

1 Reply

Tiny
AL514
  • MECHANIC
  • 4,692 POSTS
Hello, what's happening with the charging system? Are you getting a battery light on each time or are you just reading a low voltage with your multimeter?

If you are actually getting a battery light on and the alternators are failing, first make sure all your ground connections are good. Doing a voltage drop measurement is the best way of testing circuits while the car is running.

For a voltage drop test, you would take one multimeter lead from the positive terminal of the alternator and the other lead to battery positive. You're looking for a reading very close to 0 volts. What you are doing is testing to see how much voltage is being lost between the alternator and the battery on the positive side. You can also do this with the negative side.
Don't bother doing a resistance test, which won't show a problem because the circuit isn't loaded. Test with the head lights on and maybe the defrost is loading the charging system.

A battery with a shorted cell or multiple shorted cells will damage an alternator. Try swapping the battery out. Also know that Honda's will sometimes show a charging voltage low (12.8volts, around there). The ECM does this when it can to save on gas mileage.
Also check the underside of the fuse box in the engine compartment for corrosion.
Do not unhook the battery while the car is running, I know this used to be a test a lot of technicians would do, but it's not a good test any longer.
One other thing, I'm not sure where you are getting your parts from, but you may be getting bad parts. Alternators are just remanufactured now, and sometimes the diode sets are not always replaced or the voltage regulator. Sometimes these used parts are cleaned up, spray painted and resold. I've seen that personally.
But check the battery first, see what its reading for voltage before you start the car. This is 1996, the system is not too complicated. Make sure all the wiring is solid. If there are connections that are corroded and heat is building up, causing the alternator to be overworked it will fail.
Another thing is if there is a sound system in this vehicle, an amp and box in back with subwoofers. Those types of setups require an alternator that can supply more current.

https://www.2carpros.com/articles/how-to-check-a-car-alternator
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Sunday, April 3rd, 2022 AT 9:27 AM

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