'98 EB Alternator Probs & Replacement

[J_C]

The battery is in parallel but it is constantly being used as a buffer, because the output from the alternator is extremely dirty pulses with no capacitor in parallel, except upstream at electronic modules. If you were to disconnect the battery it might run, but stress everything that is not a resistive load. Do not run the engine without the battery.

As others stated, you can tell if alternator works based on being around 14V running, but this based on a battery with all cells viable, if you measure battery with engine off and it's about 2.1V low, this is typical of a battery with a cell shorted, which will also strain the alternator. You can have the electrical system below 14V with a good alternator trying to riase the battery to 12.6V which would never happen if a cell in it is shorted, but besides cooking the battery (boiling off the electrolyte) dumping all that current into it trying to get the voltage higher, the vehicle would keep running.

Based on the description of failure mode, which is pretty similar to what happened to mine, brushes and bearings alone won't cut it, will need the regulator too.

Back when I got my Advance Auto alternator they had a $40 off $100 coupon. Their coupons are not as good now but with some searching you can probably find one for 20%-25% off still.

 

[imp]

The battery is in parallel but it is constantly being used as a buffer, because the output from the alternator is extremely dirty pulses with no capacitor in parallel, except upstream at electronic modules. If you were to disconnect the battery it might run, but stress everything that is not a resistive load. Do not run the engine without the battery.

As others stated, you can tell if alternator works based on being around 14V running, but this based on a battery with all cells viable, if you measure battery with engine off and it's about 2.1V low, this is typical of a battery with a cell shorted, which will also strain the alternator. You can have the electrical system below 14V with a good alternator trying to riase the battery to 12.6V which would never happen if a cell in it is shorted, but besides cooking the battery (boiling off the electrolyte) dumping all that current into it trying to get the voltage higher, the vehicle would keep running.

Based on the description of failure mode, which is pretty similar to what happened to mine, brushes and bearings alone won't cut it, will need the regulator too.

Back when I got my Advance Auto alternator they had a $40 off $100 coupon. Their coupons are not as good now but with some searching you can probably find one for 20%-25% off still.

 

[imp]

The battery is in parallel but it is constantly being used as a buffer, because the output from the alternator is extremely dirty pulses with no capacitor in parallel, except upstream at electronic modules. If you were to disconnect the battery it might run, but stress everything that is not a resistive load. Do not run the engine without the battery.

As others stated, you can tell if alternator works based on being around 14V running, but this based on a battery with all cells viable, if you measure battery with engine off and it's about 2.1V low, this is typical of a battery with a cell shorted, which will also strain the alternator. You can have the electrical system below 14V with a good alternator trying to riase the battery to 12.6V which would never happen if a cell in it is shorted, but besides cooking the battery (boiling off the electrolyte) dumping all that current into it trying to get the voltage higher, the vehicle would keep running.

Based on the description of failure mode, which is pretty similar to what happened to mine, brushes and bearings alone won't cut it, will need the regulator too.

Back when I got my Advance Auto alternator they had a $40 off $100 coupon. Their coupons are not as good now but with some searching you can probably find one for 20%-25% off still.

Here are a few 'scope pictures of alternator output voltage for several operating conditions: The variation is termed "ripple".

These voltage waveforms are what the battery "sees". Note that if the battery is fully charged, it will have minimal effect on the ripple, which is inherent in load applied to the alternator. The peak ripple with a 62Amp load applied at 1800 rpm is only about 0.1 volt, very small. Any well-designed electronic circuitry for automotive use will have shunting capacitance wired in to prevent damage from "dirty" alternator output.

See: Alternator Ripple Effect | MOTOR

 

[J_C]

^ That can be used to verify alternator operation, but it is not the entirety of the situation, the problem being state change voltage spikes. It only shows constant RPM or load, not the lag of the regulator to respond to changing load and RPM, but especially in the case of wondering if the alternator is bad, the battery may have to take up even more of the slack in reducing ripple if it is.