oldgringo

Replaced alternator in May 10. Had tree fall on car (minor damage) but noticed that only had 11.8 volts showing. Replaced alternator (warranty) but still have same reading. Looking for other answers. Would loose ground cause this type of reading?

Keystring

Yes.

Check the grounds on the bellhousing, drivers side.

Also check the bracket and braces for the alternator at the 'block' side. Could have corrosion keeping the alternator from grounding well.'

hooked073

check to see if you have 12 volts on the wires going into the side of the alt. if you have voltage on one side and not the other jumper across them while still hooked up and see what happens

c4cruiser

What is the voltage at the battery terminals? Use a voltmeter at the terminals instead of the volt gauge. If the car is not running and you see less than 12v at the terminals, then the battery is discharged. A fully-charged battery should read somewhere around 12.4 to 12.6v. Have a load test done on the battery. I'll bet it's shot.

You can attach a jumper wire from one of the bolts that hold the alternator to the frame to use as a ground and then check voltage at the alternator post where the large red wire attaches. With the engine running and a good alternator, the voltage can be from 14.3 down to as low 13.6 or so if the battery is fully charged.

oldgringo

Will check when I get back home. Much thanks for the info.

jfb

First, charge your battery up with a battery charger. Batteries are considered discharged when their terminal voltage is 12.0 volts or lower. Don't let batteries sit discharged, it ruins them. Normal alternator voltage is 14.7 volts cold and this voltage drops to 13.7 volts when the alternator gets to its operating temperature. Don't run the engine thinking the alternator will charge up your dead battery, this shortens the life of the alternator. You can tell the state of charge of your battery by measuring its no load voltage at its terminals. 12.0 volts and lower, discharged, charge your battery up with a battery charger. 12.9 volts and higher, fully charged and linear in between. Engine idling, you should measure the same voltage on the alternator output terminal that is on the battery terminal. If the alternator output is 14.7 volts and the battery is much lower, you have a blown fusible link in the alternator output wire. Replace it.

hooked073

JFB you have to have 12 volts on the large term on the back of the alt plus 12 volts on the #2 term of the alt key on for it to have the ability to charge. I said to use a jumper wire across them if one had 12 volts because it is hard to see the term numbers. and putting 12 volts on both of them will not hurt a thing. Also on average we have to jump start 2 or 3 vehicles a day in the fleet for all sorts of reasons but mostly driver leaving lights on. I have never seen or have had any problems letting an alt charge the battery, In fact that is what they are for. Now I have seen where the alt were underrated for the applacation and have premature failure. 12 volts on the batt term tell you very little about the battery condition. I have seen 1000's of batteries read 12 volts with a volt meter be total junk. You need a load tester I prefer a carbon pile to put the proper amount of load on the battery to see if it is good and or has enough charge to start the vehicle. There are some good electronic load testers out there I have a couple that seem to work good.

jfb

Nope, you are dead wrong about alternators being on cars to charge dead batteries. Alternators are on cars to replace the charge lost while cranking the engine and they supply all the current to the car's electric loads. Dead batteries draw very large current and for a long time, this is what heats up alternators and shortens their life. You may not destroy the alternator immediately, but you sure don't do it any good. Furthermore, car batteries take many hours to fully charge and it is extremely uneconomical to idle a car engine for 8 hours to fully charge a battery. Use a battery charger! Measuring the no load voltage on the battery terminals is a good test for determing the state of charge, but it is not a complete test and I did not state that it was. I stated to measure if there was 14.7 v on the alternator output and much less on the battery post only to determine if the fusible link was blown.

hooked073

I did not mean for it to come out that it is there to charge dead batteries. But like said it is not a problem and I have never seen where it has shorten the life of an alt. And you do not let it idle you jump and down the road you go. What do you do when you go out leave the lights on and come out and the battery is dead? You dont go home get your charger plug it in ang let it sit for hours no you jump it go down the road and forget it at least I do. Most comercial chargers put out a max of 50 amps. most are 30 amps. Average alt is 84 amps not full filded whitch you will never see unless you mechanicly do it. The alt will charge a battery much faster then a charger. Im not trying to be a bad *** hope it does not come out that way. But the way you said dont think the alt will charge a dead battey and stuff I felt was scaring the op or anyone form doing something that will not harm a thing and has been done probley from the time they started putting batteries in cars. I don't know of anyone who does not have a set of jumper cables or a jump box around.

jfb

I'm not taking your reply as insulting, and you are right, if you are stuck somewhere, you get a jump and drive home or wherever you were going, but you still heat the heck out of your alternator. Also modern no water batteries state the charging current shouldn't exceed 10 amps for long periods. I own jumper cables.

hooked073

alls cool