Alternator question

[JoeNoble]

Ok so looking at this pic basically I have both the yellow and grey wires going to the big post on the back of the alt but I've left the green wire alone. The truck runs better than it ever has and my battery light is not on. However I tested my battery and alt, the battery tested bad but hasn't given me any issues but the alt failed the diode test but was otherwise fine. My question is did I bypass he diode somehow? If so where does the diode need to go?

 

[adsm08]

Do a real diode test. Look for AC voltage at the batter with the engine running.

 

[RonD]

How did your battery test bad?
12.6vDC after sitting overnight is marginal, 12.4vDC is replace PDQ, it will only crank a few times if its cold out, maybe not at all if its really cold out.
Batteries have 2.2vDC per cell, 6 cells = 13.2vDC when new
As they age they get shorts between the plates, this drains them.

 

[JoeNoble]

Do a real diode test. Look for AC voltage at the batter with the engine running.

I'll check that out tomorrow morning.

How did your battery test bad?
12.6vDC after sitting overnight is marginal, 12.4vDC is replace PDQ, it will only crank a few times if its cold out, maybe not at all if its really cold out.
Batteries have 2.2vDC per cell, 6 cells = 13.2vDC when new
As they age they get shorts between the plates, this drains them.

At work (autozone) we have a machine that basically says good or bad. The battery is an optima that was in a car I bought about 3 years ago but I'm not sure how long the previous owner had it.

 

[shane96ranger]

I've come to find that Autozone's testing equipment isn't that reliable.

 

[JoeNoble]

I believe it

 

[JoeNoble]

Do a real diode test. Look for AC voltage at the batter with the engine running.

Yep I've got a/c voltage. So where should I put the diode?

 

[RonD]

The diodes are in the alternator, an alternator has 3 phases of AC power, this is converted to DC by the 6 diodes, 2 per phase, and usually another diode on the DC output.

How much AC voltage did you see?
.05vAC or less would be normal, so millivolts are OK

 

[JoeNoble]

Ok so assuming I'm doing it right I have 20-22 volts.

 

[RonD]

replace alternator
Shouldn't have 22volts AC OR DC

And yes battery is most likely bad now, but disconnect cables and test it again.

Late model used are usually fine, lots of Fords used the same alternator.
Rebuilt is more but less than new

http://www.therangerstation.com/tech_library/alternator.htm

 

[JoeNoble]

replace alternator
Shouldn't have 22volts AC OR DC

And yes battery is most likely bad now, but disconnect cables and test it again.

Late model used are usually fine, lots of Fords used the same alternator.
Rebuilt is more but less than new

http://www.therangerstation.com/tech_library/alternator.htm

The alternater is new, the problem is the pin where the "S" wire plugs in snapped off so I wired it straight to the main post of the alt which made my battery light go off but the truck still ran like crap so I routed the yellow wire to the main post as well and the MAF problem that I have been having off and on since I bought the truck is now gone.

 

[JoeNoble]

Idk maybe if I replace the alt and put the "S" wire back where it belongs and keep the yellow wire on the main post?

 

[JoeNoble]

I was thinking about stepping up to a 130amp anyways now that I have an electric fan.

 

[adsm08]

You can't be genuinely getting 22V AC. The computer would be fried and the engine wouldn't run at all. One of the big reasons modern cars use DC voltage is that the computers can't handle AC.

It also kinda makes ignition coil operation an issue.

 

[JoeNoble]

Did I have my meter on the wrong setting?