Alternator question

[siteunseen]

This is for my '87 Hardbody Pickup so I apologize in advance.

I am having tremendous battery drain every night, completely dead in the mornings and I can smell what smells like burnt wiring.  The alternator is putting out 15.6 volts while at idle, measured at the battery terminals.  After it sits for more than 30 minutes I have to roll start it or jump it off.  After reading around a online I think the voltage regulator is shot.  I haven't done the meter in line and start pulling fuses yet, maybe this afternoon I'll do that.

Any advice would be appreciated.  I like that old truck as much as my Zs, well almost. 

300,001 back in November 2013.  Now it has 350,000 without any major work, clutches spark plugs and oil.

Edited February 6, 2018 by siteunseen

[dutchzcarguy]

Load battery , then pull all fuses.. put an amp meter there in place of a fuse... where the meter measures a big current.. there is a problem.. small current is your dashclock or so..

[dutchzcarguy]

While loading the batt, you could be seeing the fuses spark when you pull them! the drain amperage must be in the 10-'s to 25 amps to drain a big battery like from your pickup truck!   (80 -100 Ah?)

[SteveJ]

If the voltage regulator is shot, test by unplugging the alternator from the electrical system. If the battery doesn't fall flat, you found the culprit. If the battery still goes down, get a load test on the battery. 

From the high voltage at the battery, I would suspect the voltage regulator, too.

Are there any modifications (think alarm system, aftermarket electric door locks, high power stereo) or failed switches/relays that would make you think you have a drain on the battery?

[siteunseen]

Thanks Steve!  Could I just take belt off the alternator instead of unhooking those old brittle connections?  After disabling the alternator how long will it run until the battery falls flat?

No vampires except the radio clock.  I've got that fuse in the ashtray and singing some classic rock, the only thing I know the words to.

Thanks again @SteveJ

 

[SteveJ]

Don't disconnect the alternator with the engine running. You need to electrically isolate the alternator from the battery to see if it stops the drain. Heck, you would have to disconnect the alternator if were replacing it anyway. 

Keep in mind that running the battery down frequently can affect its ability to be charged and to hold charge. (Look up battery sulfation.)

[Zed Head]

I think that Steve might have meant that the VR is shorted, partially/high resistance, drawing the battery down with the engine not running.  He meant disconnecting the alternator electrically, to stop the draw.  You would probably see a change in voltage with a good meter.  Connect the meter, measure voltage, remove the alternator plug with the meter still connected, see if voltage pops upward.  Might even see or hear a small spark when you remove the plug.

Edit - Oops.  thought you were gone SteveJ...

Edited February 6, 2018 by Zed Head

[SteveJ]

No problem. I welcome your input.

[Zed Head]

I should have added - disconnect the alternator electrically with the engine not running.  Should be a quick easy check.

I thought my Nissan with 260,000 miles on a VG30E and no major work was a big deal.  Which engine does the 87 use?

[siteunseen]

3 minutes ago, Zed Head said:

 Which engine does the 87 use?

Z24, 4 cylinder with 8 spark plugs.  I've pulled boats and Exmark commercial mowers without any stumble.  Just overheats the clutch and turns the flywheel blue backing up driveways. 

So disconnect the alternator and leave the truck alone overnight. If the battery has the 12 plus volts in the morning I know the alternator is bad.  Simple enough, thank you guys. 8^)

Cliff

[siteunseen]

Problem found, easy fix for some $$$.

Thank you all for the help.  I charged the battery to 12.33 V.  Disconnected the alternator wires and checked the battery 24 hours later and it read 12.35!  I need to pull the bottom radiator hose to get the  alternator out from the topside.  Probably needs fresh coolant anyhow.

Thanks again,

Cliff

[Zed Head]

Hope you get a good replacement on the first try.

Apparently, maybe, the internal regulator can be replaced.  Might be worthwhile to just have yours rebuilt.  I bought a rebuild kit for a 2003 Ford alternator.  Just for fun.  Bearings, brushes, and regulator.  Haven't done it yet, it's a future project.  $30.

Here's the Rockauto VR for yours - http://www.rockauto.com/en/catalog/nissan,1987,d21+pickup,2.4l+l4,1210857,electrical,voltage+regulator,4884