Bad Alternator?

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Lenny33

Lenny33

Joined
Nov 10, 2018
Threads
45
Messages
603
Location
Conifer, Co
So tonight, out of nowhere, my t belt light come on followed closely by filter, oil, and battery lights. Truck is running fine, but dash lights were getting dimmer by the time I got home.....
Bad alternator, right?
 
Multimeter - measure battery voltage at idle and at say 1500rpm. With battery in good nick and alternator working you should see somewhere in the 14.4V range at 1500rpm.

Best to measure than guess...

cheers,
george.
 
Budge from what voltage?

cheers,
george.
 
With the engine running.... have you checked the voltage at the charging stud on the back of the alternator?
Should read as George_TLC stated above....
If not... then its either the voltage regulator (diodes), or alternator internals or reference voltage to excite the regulator.
 
I have not, but I will when I get home (started my 48 hour shift this morning). Thanks so much for the advice!
So in my amateur mechanic mind, here is what I did: I put the tester on my wife’s car first to see how a car that works will react. On the battery connections, the voltage would drop when being started, then come back up and past baseline after startup, then return to baseline. This all made sense to me with battery draw on startup and then subsequent alternator charging.
Once I then compared on the same test with the Prado, voltage would drop ever so slightly at startup, but then would not go up again to charge the battery (and it had not been topped off by the trickle charger yet).

So, I guess I knew that the alternator was my problem, but not specifically what was wrong with it.
 
also stupid first check, make sure that you didnt blow your fusable link. Could also be a bad earth, most likely alternator though. My internal regulator went bad and caused random high voltage spikes that burned out my brake lights. It was crazy when it happened, the green lights behind the ODO cluster went super bright and pulsed every 20 or so seconds. Looked like a damn UFO flying (cruising?) down the highway. Good news is terrain tamer has a nice model that fit and worked great. Got it from Cruiser Brothers, and a spare.
 
Mine just crapped out and too and I had the same symptoms. You can check out my thread about it linked below.

I first replaced the brushes in the existing alternator ($25 fix and easy) which was worth trying but my alternator still isn't fully charging the batteries. I'm about to go with a higher output aftermarket alternator from Amazon.

forum.ih8mud.com

24V Alternator for 1PZ

I'll add to the alternator issue discussion on here (shout out Ebike toter) because mine is also having issues. Yesterday I cranked over the troopy and all the dash lights that usually go off after the truck cranks over remained on - filter, battery, timing belt. The good people of...
forum.ih8mud.com forum.ih8mud.com
 
When I get home I will do a few more checks like the fusible link. My bet is that I will be replacing an alternator, but we will see.
Kind of looks like a pain to get to.
 
Yeah, that's bad and will kill the battery.

So, either alternator is dead or fusible link from alternator to battery. Check voltage on back 'stud' output of alternator to confirm.

If alternator is bad, it's feasible that it can be 'fixed' with a new brush set.

cheers,
george.
 
george_tlc said:
Yeah, that's bad and will kill the battery.

So, either alternator is dead or fusible link from alternator to battery. Check voltage on back 'stud' output of alternator to confirm.

If alternator is bad, it's feasible that it can be 'fixed' with a new brush set.

cheers,
george.
Click to expand...

The first step in learning is admitting your ignorance, right? 😁
Just check voltage from positive on alternator to a ground in truck?
 
From negative post on starter to ground on truck is same voltage as the battery is seeing.
 
Lenny33 said:
The first step in learning is admitting your ignorance, right? 😁
Just check voltage from positive on alternator to a ground in truck?
Click to expand...

Yep, positive post on alternator to ground while engine running. If it is the same voltage as the battery then fusible link likely good. And if not near 14.3V at say 1000-1500 engine RPM, then alternator is bad (brushes/regulator and/or diodes).

Alternator gets its ground connection through its body. Starter gets its ground through its body too. This means engine block to battery negative better be in GOOD condition...

cheers,
george.
 
11.67 at the battery and 11.60 at alternator while engine running at about 1500 RPM.
So fusible link is fine and alternator is bad.
Thanks so much for guiding the newb through this - I really appreciate it!
 
Alternator out and with a lot of “phone a friend” help from Ebiker, I have a bad voltage regulator to deal with. Tomorrow morning, I am going down to Denver to see just how good this alternator repair/rebuild place is that I found!
 
Bad diodes.
1996242


Getting diodes and brushes replaced for significantly cheaper than a $1500 alternator from Megazip! 😁
 
Great you have it diagnosed. I'd have them check the bearings are good at both ends while they have it apart. Doesn't hurt to squirt a bit of lubricant into them (if sealed they can inject with a grease needle).

cheers,
george.
 
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