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2.9 Alternator


Mhfco6

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My 88 Bronco keeps dying even after charging the battery. I’ve tried 3 different batteries. The last one was recently tested good. When charging the battery the alternator is warm to the touch. Truck will start after a good charge. Once the truck is shut off, it will not start back up shortly afterwards after sitting.

My question is, if the alternator tests bad is a 65a sufficient. There are way more 80+ amp options for some reason. Truck does have factor A/C. Thanks!
 
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franklin2

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65 is plenty big enough for a stock truck. But you can put a different size on it if it will fit. Sometimes the larger alternators are physically larger also.

If your alternator has a shorted diode, it can put a constant drain on the battery. You can use a testlight hooked up a certain way to test for a drain.
 

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A 12 volt test light connected in series between a disconnected battery cable and the battery terminal will test for a draw on the system. If test light illuminates... there is a drain. Works on positive or negative side.
 

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A "good" battery will test with 12.3volts to 12.8volts after sitting unused for 3 or 4 hours
A battery has false higher voltage after being charged, so has to sit for a bit to get a true voltage reading
End of life for car/truck battery is when it starts to self drain, an internal short
Generally speaking car/truck batteries last 5 to 7 years, before the chemicals and plates can no longer hold a charge

After engine is started, connected Battery voltage should show 13.5volts to 14.8volts, thats the acceptable alternator voltage range
Under 13.5volts means alternator is not working

The Battery is ONLY USED to start an engine, the Alternator provides ALL the electrical voltage/amps after engine starts

Yes, 65amp alternator in a pre-1995 stock vehicle, is fine, as said

80 to 200amp alternator is fine to use, if it fits, as said
Amps are the "available" power not the output of the alternator
If the vehicle uses 45amps with all electrics on then that's what the alternator provides, whether its a 65amp model or 200amp model, just the 45amps comes out

Amp rating is "available" power/amps in case you needed/wanted to add more electrical devices, like big ass stereo, or multiple driving lights, or a winch, or a snow plow, ect........

Like your home may have a 200amp(110/220vAC ) panel/breaker box
You don't use 200amps all the time, but they are "available" to run lights, oven, drier, refrigerator, Heat/AC, ect..................when needed
 
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Dustin_89BII

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So let’s say the 12v test light — between batt terminal and disconnected batt cable— illuminates showing a parasitic draw.

After starting the car with a fully charged battery, would the voltage go up to 13.5-14.8 v, or could the parasitic draw make it look like the alternator isn’t working?
 

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No, parasitic draw wouldn't effect alternator voltage in any year

And if you have a computer there is ALWAYS a parasitic draw, just not enough to kill the battery within 6 to 10 months

Computer and digital radios with clocks are always drawing voltage from battery with key off, they have Keep Alive Memory chips, to hold past "learned" fuel trims, and correct time for clock and pre-set stations

Computer memory draws, 0.02amps(20mA) so might kill a battery after 10month of sitting
Radio, 0.01amp(10mA)

You would need an amp meter to test actual draw, with key off, 0.03amp is acceptable
The test light method only worked on non-computer vehicles with push button radios, no clock

After driving vehicle, shut it off and try to restart it, if it cranks fast and starts then shut it off and unhook your battery's Negative cable
Then hook it back up the next day, if engine can't crank or is slow cranking then battery is self draining, not a parasitic draw issue
 

franklin2

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The testlight method will still work on computerized vehicles IF you use the old style testlight with the old time little incandescent bulb, not a LED bulb and not a digital readout type of testlight. Even with all the memories and computers, they still will not draw enough to light the old time testlight bulb. On the worst vehicles you might get a very dim hard to see glow. But any type of bad draw on the system will light the testlight very bright.
 

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I purchased the 65a alternator from Napa with a lifetime warranty. Voltage while running would be 13.9 one day and 12.2 the next. Truck also died if the negative battery cable was removed.

New alternator, power cable from battery to solenoid and ground cable from battery to frame. While running reading is now 14.20.

Thanks to all!
 
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Shran

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Truck also died if the negative battery cable was removed.
This is really not good for new vehicles, old stuff with carburetors was not a big deal but you should not be doing this test on anything fuel injected.
 

franklin2

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This is really not good for new vehicles, old stuff with carburetors was not a big deal but you should not be doing this test on anything fuel injected.
I did this once on a old 66 pickup I had. It did have a 1979 v8 in it with a HEI ignition. The battery was smoking. I took the battery cable off while it was running, it ran a few more seconds never to run again until I put a new ignition module in it. Turns out something was wrong with the alternator. With the battery on it, the battery was smoking but holding the voltage at idle to about 16 volts. When I took the battery cable off the voltage shot up to who knows what and blew the ignition module out. Hate to think what would have smoked if it was a more modern vehicle. Glad I didn't have the radio on.
 

Mhfco6

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Well the alternator didn’t fix the issue. Still having to jump the Bronco to start it. Something is killing the battery. Immediate restart after shut off works, if I wait 10 seconds an try to start I got nothing.
 

franklin2

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Well the alternator didn’t fix the issue. Still having to jump the Bronco to start it. Something is killing the battery. Immediate restart after shut off works, if I wait 10 seconds an try to start I got nothing.
Do the testlight test for a drain and see if you have one. Pull the negative battery cable off and set it on a rag. Clip the testlight to the battery negative battery post, and stick the probe into the cable end sitting on the rag. If the testlight lights bright, you have a drain. You can then pull fuses and any added on wires till the testlight goes out.
 

Mhfco6

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Do the testlight test for a drain and see if you have one. Pull the negative battery cable off and set it on a rag. Clip the testlight to the battery negative battery post, and stick the probe into the cable end sitting on the rag. If the testlight lights bright, you have a drain. You can then pull fuses and any added on wires till the testlight goes out.
AWESOME. Will try this today and let you know what I find out. Thanks Franklin
 

Mhfco6

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No draw seen and battery tests at 12.48 after sitting for 19 hours. Guess I’ll start looking for voltage drop in all the cables. The starter solenoid is buzzing when trying to start so I swapped it out but no luck there either.
 
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