Alternator: Post ("after") installation. . . . .

[LieutenantCracker]

'99 Crown vic, 4.6, V8--Just installed new "alternator" ("Generator", according to the FSM) & I now, obviously, need to test it to make sure she's putting-out the ammount o' the proverbial "juice" that she's supposed to (and YES, it is "quotation marks day", for those who've noticed my overuseage, there-of!). Problem is, Everywhere I look online calls for a "high rate discharge tester" and an ammeter... The ammeter, I have but, not the latter. Is there any way to test the new alt, w/ ONLY an autommotive multimeter?

--Thanks, in advance!

Louis Tennant Racker
Atl, Ga

A little side-note question: I bought the car used but, only about a year old at the time (not a police car) and about 3-4 years ago I noticed that the "u-bracket" that's supposed to secure the alt from the top, is missing. Looks like it WAS there at one time b/c the tops of the posts where the bolts would go are silver (everything surrounding is painted black.) I asked a mechanic about it and he said it seemed secure enough being held by the two bolts at the bottom so, no need to bother w/ finding an other one. I haven't had any problems b/c of it, that I know of but... any thoughts on the matter, anyway?
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[way2old]

The High rate discharge tester is a carbon pile rheostat. If your ammeter does not read at least 100 amps, do not try to test the alternator. Easiest thing to do is to go to your local parts house and ask them to test your charging system. Most of them will do it for free. Make sure they give you maximum amperage and voltage readings. The bracket should be replaced to stabilize the alternator due to the load placed on it by the belt tension under a high load condition. The top brackets stabilize it so it will not flex forward.

[ctwright]

Yes, using a multimeter you can check at your battery terminals. Have your multimeter set for dc voltage above 20 volts.

You should have anywhere from around 14.1 to 14.7 volts with the engine running. If that checks good your alternator is good but if it does not check okay it doesn't necessarily mean your alternator is bad could be somewhere else in the charging system.

I've never used a special ammeter to check current flow from alternator to the battery and have never had a problem diagnosing a problem with a charging system using a regular multimeter and checking voltage at the battery.

[way2old]

The multimeter used to check voltage is an OK test to check to see if the regulator is working properly. However, if there are no amperes for the voltage to push, the alternator is not of much use.All electrical componets run on amperes, the voltage is what is used to get it there. If you have an alternator that is rated for 130 Amps, and it is only outputting 20 amps, before long the battery will fail as the current required for vehicle to run will exceed the amps being generated by the alternator. Then it starts pulling from the battery. Good luck.

[ctwright]

Originally Posted by way2old

The multimeter used to check voltage is an OK test to check to see if the regulator is working properly. However, if there are no amperes for the voltage to push, the alternator is not of much use.All electrical componets run on amperes, the voltage is what is used to get it there. If you have an alternator that is rated for 130 Amps, and it is only outputting 20 amps, before long the battery will fail as the current required for vehicle to run will exceed the amps being generated by the alternator. Then it starts pulling from the battery. Good luck.

Also too if there is no current flow from the alt to the bat there will be no increase in voltage in that range at the battery. The voltage regulator does not produce a voltage, it keeps the voltage at the alternator from rising too much to keep from overcharging, funny how they would use a voltage regulator for that purpose and not an amp regulator.


And I know already all about volts and amps, voltage is the rating of the force of electricity. Amps is the rating for current flow. The battery draws the current from the alternator. The alternator does not output current. Current is dependent on the load(resistance) of a circuit, whatever that may be. The battery would be considered the load(resistance) in this circuit. The alternator would be your voltage source.

All of these different aspects of electricity are related in that if you change one of them it will effect the other. Voltage is equal to current times resistance. If you increase resistance in a circuit the current will drop. If you decrease resistance in a circuit the current will rise.

As long as the voltage is within specs the alternator is doing its job, the battery being the resistive load is what determines current flow from the alternator and if the current it is pulling is lower than should be then the voltage would not be within specs.

[ctwright]

You will probably have to call around some junkyards for the bracket you need.