Hello everyone,

Last week my dad came from the grocery store and he said that, when leaving, the car was difficult to start, that it took longer than normal.

So I went out and tried to start it for my self, no dice. It cranked once and then the door locks cycled and that was it.

I threw it on the charger and got it started. I checked batter voltage and it was around 11.8 v or so. I revved the engine and it near 13.

So I decided to swap the regulator. I had one lying around that I'd modified with a diode to increase output voltage. I figured maybe his regulator was shot. I believe it came out of my other SD a few years ago.

Installed the new regulator and now its putting out around 13.2 at idle with nothing turned on. Once you load down the car with a/c, blower, and headlights the voltage will drop down to 12.2 which is not sufficient to charge the battery. Add to that the occassional turn on of the aux-fan and the battery will be dead within a few days.

So my question to you guys is does this point to a faulty alternator or a faulty battery? I charged the battery up a bit before I left for the weekend. I got back today and started it up and the car stared up no problem. So this might make me lean towards alternator, especially since the regulator has been replaced...

I think stores are closed now so I cant run it down for a test.

I'd actually like to upgrade the alternator to a higher output one, so long as its the same price or a small bit more...

Just figured I'd get some thoughts.

-Kris

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I just upgraded my alternator with one that fits a 1989 Saab 9000. Bosch AL129x. Search the forum and you will find the write up. No problems with the installation of the 115 amp.

John

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Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI

Output voltage at idle is meaningless. The alternator cannot keep up with any decent load at idle.

Run the engine at 2000 rpm and read the voltage with the headlights on. It should be close to 13.5.

Yup. 13.5 with headlights, no a/c or blower, near 2000 or so.

When I turn on headlamps + a/c + blower, it drops down to 12.8.

When I turn on headlamps + foglamps + a/c + blower down to 12.3.

Just for reference my other 300SD, whose primary purpose is to keep leaves off my driveway right now, idles (no load) at 13.8V. Headlights drop it to 13.5V. Blower+AC+Headlight drop it to 12.2V. Aux fan would drop that down even lower if I tripped it.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

That's a bit too low. I'd see if a new regulator cured it.

It should be able to maintain above 13V with the load you've indicated above.

Are you confident of the accuracy of the meter?

I agree it should be nearer 13 with that load.

The regulator was replaced. Actually it was replaced with one that I modified with a diode to raise overall output voltage.

I'm confident with the meter. It not an el cheapo meter. Its not an uber expensive Fluke either. Its a Triplett 9045.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Before any sort of charging test is done the Battery has to be fully charged.

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84 300D, 82 Volvo 244Gl Diesel

I'll throw it on the charger for a few hours over night. My dad is gonna take it to work tomorrow and after stop by the place and have it tested.

It was sitting at 12.4 V last time I checked it.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Well, either you've got a problem with the meter or a problem with the voltage regulator. There isn't much of anything else that would cause low output voltage at 2000 rpm.

If the battery was weak, the voltage would be exceptionally high...........demanding more from the alternator............not exceptionally low.