Brand New Alternator not making over 12.3v at 2k RPM is it bad?

[cobrajocky]

I have a 97 Mazda B-4000 SE 4.0L Xtr Cab (same as a Ranger XLT), with 98.4k miles. The original Motorcraft Alternator finally gave up the ghost, fortunately the battery still got me home. I bought a new, no doubt Wuhan CN made, Alternator (aren't they all these days) #AFD0012 through Amazon distributed by DB Electical rated at 95A like the original Motorcraft, same in physical size. Their site and the chart on the Amazon lists it as compatible to my B-4000 and the equiv Ford 4.0L V6 XLT Ranger too. Installed smoothly in <45 minutes (not my first rodeo), but I immediately noticed that the voltage at the battery terminals was barely over 12.4 V. I then measured it with a DVM at the + voltage terminal on the Alternator to an engine ground at 2k RPM =2.3V and 2.5k RPM = 12.2V! When I turn on the headlights, there is a very noticeable drag on the running, but doesn't kill the motor.

Oh, I did test the Amperage output of the Alternator with my ancient Craftsman Engine Analyzer system and it showed a 10AMP output at 2k RPM.

So my question is, is it obvious the Chop Suey Alternator is bad (probably 1 or more diodes open in the rectifier), or could something else be limiting the voltage output? All the connectors are fine as far as I can tell, no corrosion, fit well to the Alt. What else ??

The original Alternator was occasionally "spiking " in voltage output, first 5 to 15 minutes of running (on initial cold start up) shooting up to a "pulsing" 14.8 to 15.2V for a couple of months before it died. The Dash Battery warning light was intermittently flashing and then would turn off when voltage dropped below 13.8- 14.0 V. (I have a cigarette lighter port Digital Volt Meter.)

Appreciate any and all thoughts, except the crazy ones.

 

[Dirtman]

Amazon chinese alternator? Of course its bad...

But for fun, what are your battery voltage readings with the truck off. The old alternator spiking over 15 volts could have easily damaged the battery.

 

[RonD]

First Test the Trucks wiring

Key OFF
Read battery volts first, lets say its 12.4volts
Use alternator's metal case for the ground on all wire tests

test voltage on B+ terminal, the stud and nut terminal on back of alternator, with wire still connected
Should read 12.4volts, battery volts, if not then Fusible link is blown

Now unplug the 3 wire connector on alternator, test the Yellow wire, should be 12.4 volts, if not then 15 amp fuse in Engine Fuse box is blown, Fuse 6 in 1997

Now test Light Green wire on 3 wire connector, should be 0 volts
Turn key ON
Re-test Light Green wire, should now be 12.4volts or close to it, if not 7.5amp fuse in CAB fuse box is blown, #15
This wire is the ON/OFF switch for alternator and also the Battery Light circuit, just FYI


If all wires test OK, then plug 3 wire connector in and start engine
Test battery voltage, should be above 14v but below 15v
If not alternator is bad


Yes, alternator will run up close to 15v just after start up to do a Fast Charge for battery
After 5-10min it should drop down to 13.5-13.8volts, under 14v, about 1.1 volt above battery voltage engine off

 

[cobrajocky]

Amazon chinese alternator? Of course its bad...

But for fun, what are your battery voltage readings with the truck off. The old alternator spiking over 15 volts could have easily damaged the battery.

Battery sitting cold (So Calif cold is 60 degrees at night, 76 days) for a few days after charging with a 2A charger for 4 hours was 12.5v, plenty of amps to spin the motor fast to start it. I have doubts the battery is bad, ..... kicked in the knees a bit, maybe.

 

[cobrajocky]

First Test the Trucks wiring

Key OFF
Read battery volts first, lets say its 12.4volts
Use alternator's metal case for the ground on all wire tests

test voltage on B+ terminal, the stud and nut terminal on back of alternator, with wire still connected
Should read 12.4volts, battery volts, if not then Fusible link is blown

Now unplug the 3 wire connector on alternator, test the Yellow wire, should be 12.4 volts, if not then 15 amp fuse in Engine Fuse box is blown, Fuse 6 in 1997

Now test Light Green wire on 3 wire connector, should be 0 volts
Turn key ON
Re-test Light Green wire, should now be 12.4volts or close to it, if not 7.5amp fuse in CAB fuse box is blown, #15
This wire is the ON/OFF switch for alternator and also the Battery Light circuit, just FYI


If all wires test OK, then plug 3 wire connector in and start engine
Test battery voltage, should be above 14v but below 15v
If not alternator is bad


Yes, alternator will run up close to 15v just after start up to do a Fast Charge for battery
After 5-10min it should drop down to 13.5-13.8volts, under 14v, about 1.1 volt above battery voltage engine off

RonD ... you've given me advice before, thanks for jumping in.

Testing this morning before posting this thread"

Battery cold for a few days after charging at 2amps for 4 hours (3 days previous) was 12.4 to 12.5v at the terminals.

I also tested at the Alt B+ terminal (red to battery cable) while idling at 1250 RPM was 12.3V (I used a ground at the engine block though). I'll check this again in the morning grounding on the Alt body, but I think I did "just poking around" for a some alternative readings and I still got 12.25 to 12.3. Actually the highest output reading I got was 12.48V grounded to the radiator housing!

Where is the Fusible Link on the 97-98 Ranger / B-4000 4.0L V6? What does it look like?

I will test the 3-wire alternator connector also tomorrow morning. Get back to you then

Thanks again very much!

 

[RonD]

If B+ had "Battery Volts" engine on or off then fusible link is fine

But one end of fusible link(should be a grey wire) will be connected with Battery positive cable on a stud/nut setup like a starter relay on inner fender
Then the other end is in the wiring harness connected to the Black/orange stripe wire that goes to B+

Battery positive-------stud-----(fusible link)--------(black/orange wire)-----------------------------B+ alternator


A fusible link is a 6" to 8" wire that "acts" like a slow blow fuse, it can tolerate amp/voltage spikes that would blow a regular fuse
Fusible link is one or two gauges smaller than the wire its protecting and it uses a non-flammable insulation and softer wire, when it "blows" insulation evaporates and metal separates, so no fire, and no smoke for the most part, lol

Some look like this: https://www.onallcylinders.com/wp-content/uploads/2017/11/09/Pico-Fusable-Link.jpg

Or this: https://media.napaonline.com/is/image/GenuinePartsCompany/NWMDC?$Product=GenuinePartsCompany/44845

Or this: https://static.summitracing.com/global/images/prod/xlarge/RNB-85621_DE_xl.jpg


In 1997 wiring is shows it as a 12gauge dark Grey wire

 

[cobrajocky]

OK I checked the following:
Battery is a Heavy Duty, 48 months rating and is 28 months old. When I charge it with an external charger 13.5V at 2Amps for 4 to 6 hours it holds a 12.8v charge for 48 hours.


Tested the 3-wire cable to the Alternator, with the ignition OFF - Yellow wire shows ~12.5V, the associated 15A fuse is good, the green wire is showing 0 volts (as it should) until you turn on the ignition (not start) then ~12.5V, and the associated 7.5 A fuse is also good.

Also checked the single ground wire (white w/black stripe) to the Alternator with a connector and shows 0 voltage and continuity to ground.

As I wrote before, the B+ power wire to the Alternator shows 12.5V that the battery is holding this morning.

The "Fused Link" from the Neg Battery post to chassis gnd is also good.
-------------------
Is there any other possibilities to check, or is this pretty conclusive that the new "tofu" Alternator is bad (perhaps a faulty rectifier module)?

The original Alternator is a Motorcraft, I can't find a part number anywhere on the body, just a cast in raise number "2" on the upper mount ear and a cast number "17" next to the rectifier. The Motorcraft rectifier has two part numbers: F5DU-10316-AA and 6H08AA by the connector port.

Should I just rebuild this OEM Alt, or just replace the rectifier part?
The bearings feel pretty good, spins freely and I never heard any noise before the Alternator died. If I remember by diode electronics, would the spiking intermittent voltage from the Alternator (+15.5volts) mean failing diodes in the rectifier?

Where do I find a good but inexpensive rebuilding kit or just a replacement Rectifier at a great price? (I'm on Social Security, tight budget )

Thanks for your input, very very appreciated from everyone!

 

[RonD]

If those 3 wires, B+, Yellow, and light Green all check as OK but battery volts with engine started doesn't go above 14volts, then alternator is BAD, 100%

Charging system are very simple to test

I didn't mention the White wire because it pretty obvious if its unplugged, lol, but it does need to be plugged in to alternator and not frayed at the 3 wire connector


Wrecking yard OEM is a good choice

Yes, you can put in a new voltage regulator, not hard to do
But B+ circuit can fail as well which requires a full rebuild which should be with new bearings since its apart

 

[Dirtman]

Its amazon. Return that hunk of poop and do what ron said, go get a junkyard unit. An OEM junkyard alternator is more likely to work than a brand new chinese alternator from amazon or ebay. Most yards will even give you an exchange warranty too.

 

[cobrajocky]

Well figure this out. Without any prayers, I got in the truck to run over to AutoZone to have the old Motorcraft Alt tested (they do it free), so immediately upon starting the Dash battery light was off (it has been on all this time indicating a fault) and the Tofu Alternator also immediately was charging and charging at a very consistant rate too. The Digital Voltage meter adapter for the "accessory port" (cig lighter type) was showing a constant 14v, after the running for a while (5 miles) it dropped to 13.8V, turning the AC on jumped back up to 14V. I stopped at a few places along the way and back home and still running, no battery fault indicator and the voltage stayed the same (about 2 hours of driving around).

So, .... WTF? What could it be? (again no prayers involved and hammer strike repairs). Before I unplugged and replugged all the connectors several times, thinking I might have a bad connection after the initial install .... now all of a sudden it works?!

Now here's the kicker .... Autozone tested the old intermittently voltage spiking (+15.5v) Motorcraft Alternator on their in-store test machine (their tester even spins up the Alternator on the bench for the testing) and the damn thing "Passed"!! Note that their tester is a pass/no pass, does not show voltage output or Regulator condition. The Alternator was dead as a doornail before I took it out of the truck - 0 Voltage output. At least this new one WAS showing 12.5V output, just nothing higher.

Obviously something else is going on with the trucks charging / electrical system. But what?

 

[RonD]

Nothing weird or magical, lol.

One of the 3 wires has a bad connection, thats all there is to a charging system, that and the alternator

Usually not the B+, because its an OUT, but can be, so yellow or light green wires are the only 2 choices really