Alternator Charging Issue

[ledzilla]

So, yes, looks like I have yet another alternator issue. I've had a few issues where I'd come out to my Bronco, but there wasn't enough juice in the battery for it to start. I ended up swapping batteries a couple times in the last month or so from the local junkyard (one battery wouldn't hold a charge at all). I was thinking that I had some sort of weird parasitic draw even though the only pull on the battery when not running was the radio's memory circuit (verified to be 0.3A draw when the battery connects and then reduces to below what my meter could read after several seconds, so less than 0.01A). So that wasn't the case. Then I noticed the last two times this occurred, I had driven some distance from home. I headed out in segmented runs, making stops and getting further. But it was just one straight shot home each time. No issues encountered while out and about, only after getting home and trying to start the Bronco again later on. The return journeys were all more than 30 minutes of driving with highway driving or travel on roads near highway speeds. On one of these drives, getting near home, I noticed the instrument cluster looked relatively dim and I tried fiddling with the dimmer switch, but it didn't help. Makes me think it was all running on reduced alternator output.

So, I'm of the mind that the alternator is the problem, but as with most things I don't think it has more than a one year length on the warranty. But assuming that it's not a quality issue with the alternator itself, could there be something else going on under the hood that could cause such an issue on longer drives like this? Maybe too much heat, something pulling an unexpectedly high draw on the alternator? Just want some things to look at before I try looking into replacing the alternator. I don't want to replace it only to have the same issue come back again.

 

[L\Bronco]

So, yes, looks like I have yet another alternator issue. I've had a few issues where I'd come out to my Bronco, but there wasn't enough juice in the battery for it to start. I ended up swapping batteries a couple times in the last month or so from the local junkyard (one battery wouldn't hold a charge at all). I was thinking that I had some sort of weird parasitic draw even though the only pull on the battery when not running was the radio's memory circuit (verified to be 0.3A draw when the battery connects and then reduces to below what my meter could read after several seconds, so less than 0.01A). So that wasn't the case. Then I noticed the last two times this occurred, I had driven some distance from home. I headed out in segmented runs, making stops and getting further. But it was just one straight shot home each time. No issues encountered while out and about, only after getting home and trying to start the Bronco again later on. The return journeys were all more than 30 minutes of driving with highway driving or travel on roads near highway speeds. On one of these drives, getting near home, I noticed the instrument cluster looked relatively dim and I tried fiddling with the dimmer switch, but it didn't help. Makes me think it was all running on reduced alternator output.

So, I'm of the mind that the alternator is the problem, but as with most things I don't think it has more than a one year length on the warranty. But assuming that it's not a quality issue with the alternator itself, could there be something else going on under the hood that could cause such an issue on longer drives like this? Maybe too much heat, something pulling an unexpectedly high draw on the alternator? Just want some things to look at before I try looking into replacing the alternator. I don't want to replace it only to have the same issue come back again.

Hey Led
do you know the battery voltage engine running?
It should be between 13.4 and 15.2 (depending on temp)
I'd measure DCV across the battery at 2000rpm.Then make the same measurement between the alternator B terminal and the housing. (also at 2000 rpm)
They should be pretty close to 2VDC higher than the battery, (engine off), and within .5V of each other.
If there is no charge, (Batt voltage doesn't rise), touch the rear bearing area of the alt (at idle) with a prybar or other metal tool and see if its magnetic.
No magnet means a brush or voltage regulator issue (Or primary power supply)
Magnet and no charge is a stator winding, diode, or output harness issue.

If it is charging, turn the headlights on, run at 2000rpm and measure A/C voltage between the alt B terminal and the housing. (This will test your diodes and stator windings)
It should be below .5V a/c at 2000rpm medium load (headlights)
Sorry for the blast of info.
Hope it helps.
Cheers

 

[Tiha]

Yep, check for over 13 volts when running, voltage should increase and not decrease if you rev the engine.

That era had a bad wire harness, for the longest time new alternators were coming with new harnesses so check that for burnt wires as well.

 

[ledzilla]

Well, I've already tested it to kick out approximately 14.5V at either fast or regular idle and only 0.10-0.15 volt drop with the lights on, and not running the voltage tested at something like 12.67V when I knew the battery was properly charged. The wiring is good. I upgraded the battery cable from the alternator to something like a 4ga battery cable last year. And that's the thing, that the charging is just fine when it isn't running for very long. I can go to the store, grab some food, or whatever when it seems like the engine won't be running for more than maybe 20 minutes.

I'm thinking maybe I should take one of these USB power ports I have sitting around and hook it up. They have a voltage display in the middle. Get it wired up and sit it on top of the dash, keep an eye on that actual voltage, see if I can identify when it drops or something.

Hey Led
do you know the battery voltage engine running?
It should be between 13.4 and 15.2 (depending on temp)
I'd measure DCV across the battery at 2000rpm.Then make the same measurement between the alternator B terminal and the housing. (also at 2000 rpm)
They should be pretty close to 2VDC higher than the battery, (engine off), and within .5V of each other.
If there is no charge, (Batt voltage doesn't rise), touch the rear bearing area of the alt (at idle) with a prybar or other metal tool and see if its magnetic.
No magnet means a brush or voltage regulator issue (Or primary power supply)
Magnet and no charge is a stator winding, diode, or output harness issue.

If it is charging, turn the headlights on, run at 2000rpm and measure A/C voltage between the alt B terminal and the housing. (This will test your diodes and stator windings)
It should be below .5V a/c at 2000rpm medium load (headlights)
Sorry for the blast of info.
Hope it helps.
Cheers

So, the back of the alternator looks like the attached photo. Would the "B" terminal be the big red terminal?

 

[L\Bronco]

Well, I've already tested it to kick out approximately 14.5V at either fast or regular idle and only 0.10-0.15 volt drop with the lights on, and not running the voltage tested at something like 12.67V when I knew the battery was properly charged. The wiring is good. I upgraded the battery cable from the alternator to something like a 4ga battery cable last year. And that's the thing, that the charging is just fine when it isn't running for very long. I can go to the store, grab some food, or whatever when it seems like the engine won't be running for more than maybe 20 minutes.

I'm thinking maybe I should take one of these USB power ports I have sitting around and hook it up. They have a voltage display in the middle. Get it wired up and sit it on top of the dash, keep an eye on that actual voltage, see if I can identify when it drops or something.



So, the back of the alternator looks like the attached photo. Would the "B" terminal be the big red terminal?

You bet!
Let me know what you find.
Cheers

 

[ledzilla]

OK, so it's actually quite difficult to reach that terminal with the alternator installed, and I started getting a little panicky trying to reach it with the engine running, thinking I was going to mash my hand against the headers. So instead I touched the multimeter probe to the other end of the cable where it connects to a 350A bus bar (as seen on TV-- I mean in the attached photo). It gave me a reading of ~14V. I then tested against the battery terminals and got the same voltage reading.

 

[L\Bronco]

Ok cool, its charging and the cables look ok.
Do the A/C voltange check. Go from your bus bar and the alt housing (in A/C voltage mode) with the headlights on. Bring the rpm up a bit too.
You should see well under .5V a/c
A diode or stator winding could be bad, in which case it will appear to charge normally. The symptom you get sounds a lot like your issue.
Lets knock that one off the list, then move on
Cheers

 

[ledzilla]

Well, I took it for it's first drive around since repairing the exhaust the other day. I actually noticed several times that everything dimmed here and there. These instances weren't long, no more than a few seconds each time, but it's telling. I'm willing to bet that had I connected a multimeter or a voltmeter and watched the readouts each time the lights dimmed, there would have been a voltage drop from charge voltage to battery voltage.

Guess it's time to see whether or not the warranty has expired on that alternator.

 

[ledzilla]

So, yeah, the warranty expired a few months ago. I'm tempted to order a voltage regulator from somewhere like RockAuto and swap it out, just to rule out the alternator itself completely failing, since regulators are much cheaper than entire alternators, but I don't trust the quality of aftermarket regulators. I've had a lot of trouble with them on my '78 LTD.