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Alternator Woes

gavin

Explorer Addict
Joined
September 27, 2002
Messages
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City, State
Anchorage, Alaska
Year, Model & Trim Level
'97 Explorer XLT AWD 5.0L
Ok.. so I recently replaced my alternator in my 97 V8 Sploder, cuz I was having some problems that I assumed was the alt.
So I replaced it, and the first thing I noticed, was that my ammeter moves unlike it used to.
It used to be, all accessories on, in drive but idling, the ammeter wouldn't move. Now, with the new alt, the ammeter drops about 3/4 of the way down.
And just the other day I noticed this.. I have a digital read-out capacitor hooked up to my amp.. it shows a fluctuating voltage of 14.92-15.00 volts at idle, in park.
Now isn't that just a little high?
If it's the voltage regulator, isn't it internal, meaning I'd have to replace the alt again?
Anything else to look at?
 



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it does seem a bit high..... 14 is about normal...... it is internal... dont know what to say
 






Let me guess

Your monster amp cap is connected directly to the battery. There can be a wide difference between the battery voltage and what the rest of the car system sees. I would be checking the cables and connections from the battery POS to the main fuse in the distribution box. If there is resistance, a load will drop the voltage. It is at that point that the voltage regulator sees a lower voltage and tells the alternator to put out more. That means the battery will be at 15V and near the fuse will be only 13.5 volts. These high draw systems can also cause damage on the NEG to body connection.
 






Yes, both caps are bridged together, and connected directly to the battery.
But here's the kicker... before I replaced the alternator, it showed 13.5-14.2 or so on the cap.
Only after I replaced the alt did it start showing a higher voltage.
Also, what would cause the ammeter to drop so drastically, when nothing has changed except for the alternator? Other than it being a weaker alternator, of course, which it shouldn't be cause it was a rebuilt oe part.
 






acceptable voltage readout from your charging system is 13.6-15.2 volts.

I don't understand your "ammeter" question. Ammeters read amps, not volts. amps would vary depending on if you were at idle or 2000+ RPMs and what load you are presenting on the vehicle. your Internal Voltage Regulator (IVR) on a properlly operating alternator will increase the output of the alternator depending on the load present. if you turn on your head lights, then it will boost output of the alternator to produce enough voltage and amps to accomodate what you are asking for.

so it will vary depending on the load you present to it. some alternators can be stronger than others just by manufacturer tolerances.

you need to do a charging system test on your vehicle to truely determine the condition of the alternator. most shops have Vat 40s or 60s to test this. takes a few minutes.

adding all the additional amps, lights, etc to a stock rated alternator 95 amps on alot of them is gonna wear it out faster than no additional load put on the charging system
 






Starters, O2 sensors, and alternators are replaced for a lot of bad reasons. Just the act of moving the wires on an alternator and starter can often make the problem go away. I would spray the connector at the alternator along with a couple insertions to clean the contacts. Do the same with the 40A and 15A alternator fuse. Buy a cheap $5 digital voltmeter so you can find the real problem. It just might leave you stranded. If you really have 15V on the battery, that will shorten the life.
 






Originally posted by MattPersman
acceptable voltage readout from your charging system is 13.6-15.2 volts.

I don't understand your "ammeter" question. Ammeters read amps, not volts. amps would vary depending on if you were at idle or 2000+ RPMs and what load you are presenting on the vehicle. your Internal Voltage Regulator (IVR) on a properlly operating alternator will increase the output of the alternator depending on the load present. if you turn on your head lights, then it will boost output of the alternator to produce enough voltage and amps to accomodate what you are asking for.

so it will vary depending on the load you present to it. some alternators can be stronger than others just by manufacturer tolerances.

you need to do a charging system test on your vehicle to truely determine the condition of the alternator. most shops have Vat 40s or 60s to test this. takes a few minutes.

adding all the additional amps, lights, etc to a stock rated alternator 95 amps on alot of them is gonna wear it out faster than no additional load put on the charging system

not to sound rude, but how do you not understand my ammeter question?
Old alternator, at idle, all accessories on, did not move.
New/Replacement alternator, at idle, all accessories on, drops about 3/4 of the way down.
Other than a different amperage alternator, what would cause this?
 






Originally posted by gavin
not to sound rude, but how do you not understand my ammeter question?
Old alternator, at idle, all accessories on, did not move.
New/Replacement alternator, at idle, all accessories on, drops about 3/4 of the way down.
Other than a different amperage alternator, what would cause this?
An ammeter would go up with more accessories and down with less.
Engine RPM would only affect it if the alternator was incapable of producing the required current at that RPM.

A voltmeter, what is on the dash, however should stay rather steady, only fluctuating with high loads turning on/off and RPMs changing quickly.


To anyone in general.
Alternators do not produce voltage, they only generate current.
You turn on a bunch of lights and the overal system resistance goes up.
Higher resistance with the same current and voltage goes down.
Regulator sees that, up the current output to mach the load and voltage returns.
Turn off the lights and you have excess current making the voltage go up.
Regulator cuts current, voltage drops.
 






Ask yourself this question. How does the internal regulator know what the voltage is? The regulator monitors the voltage after the 40A fuse in the distribution box on the line with the 15A regulator fuse. This voltage is with respect to the engine block.

The voltmeter on the other hand measures voltage with respect to the car body.

A resistance in the main 12V wire can cause the voltage to raise at the battery and still be lower at the dash voltmeter.

Resistance from the engine block to the car body produces lower voltage at the dash voltmeter and normal voltage at the battery.

Above 15V, the battery can draw enormous currents from the alternator. When the draw is more than the alternator can produce, the voltage doesn't raise anymore at the battery. At idle alternators can't produce that much current.
 






How would you explain voltages dropping to 12.8 or worse while driving.. but at idle, a smooth 14.0+?? (but a lot of the time just 13v, with random fluxuations to 14v) This problem is getting annoying, I replaced my alt, and battery.. and whenever I'm driving voltage drops a lot.. can this be a corrosion issue? There is a little bit, I cleaned as much as possible but I don't know if it's In the cable. Any ideas? Explanations? I can't even use my HIDs anymore, they won't fire without flickering... not enough power... and slow crank... Something is wrong here... I'm lost.
 






>5.5 year thread revival. Good one. :thumbsup:

I wonder if they'll respond to your questions. :D
 






Just figured it was better than making a whole new thread.
 






Clean your battery cable connectors really well. Clean your battery terminals. Spray permatex anti-corrosion spray, not the cleaner, on everything. Wear safety glasses when disconnecting or reconnecting as batteries can explode. Don't disconnect or reconnect right after charging as hydrogen builds up in them.
 






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