Alternator
Deceased
Joined: 03-22-2012
Posts: 1,012
From: Rogers City, Michigan
Very sensible post. 
There was a time when and if you touched a battery cable to the battery post and it showed a spark - it meant you had a short - unless you had the key or etc on.
Now with all the electronics a spark doesn't mean any thing unless -as you say - its drawing more than .035 milliamps.
The amp meters in the old cars usually showed 10-15 amps when car is running. When you turned on the headlights it would show a momentary discharge (milliseconds) until the alt or gen stabilized.
Boydie
There was a time when and if you touched a battery cable to the battery post and it showed a spark - it meant you had a short - unless you had the key or etc on.
Now with all the electronics a spark doesn't mean any thing unless -as you say - its drawing more than .035 milliamps.
The amp meters in the old cars usually showed 10-15 amps when car is running. When you turned on the headlights it would show a momentary discharge (milliseconds) until the alt or gen stabilized.
Boydie
Amp meter will only show + or - when there is a load either way...volts on the other hand will show no matter what the alt is doing, unless its defective..its possible to produce low voltage and not show any problems except for a battery that doesnt seem to want to stay charged (discharges during normal operation. Most newer cars will not run anymore under a certain voltage, self protection, therefore a batt has to be present for the car to stay running. As far as amps..14,5 is nothing when you have lights drawing up to 10amps PLUS the eng electronics, fuel pump, injectors, ignition pulses,,stereo blasting and so forth..so at full tilt an alt may be producing well over 75 amps. I believe these output around 125 amps stock , at least replacements do. The battery serves 2 functions..buffer for spike alt loads and to start the car ( and accessories). After that all load is on the alt. The old cars at idle will barley show any amp draw. These newer ones..well, I couldnt find a hard number but its probably up there especially if the fan is turning. Also, found that key off, at the batt, you should not be over .035 milliamp draw, anything more and you have a battery drain going on somewhere....
Senior Member
Joined: 04-14-2010
Posts: 432
From: Wisconsin
Manufacturers haven't put an ammeter in a car since the 60s. An alternator that only puts out 15 amps wouldn't keep up with the electrical requirements of modern vehicles. Most alternators these days are capable of at least 60 amps output. The meter on the dash of an HHR is a voltmeter. A voltmeter tells you much more than an ammeter. Turn the key switch on without starting the engine. The voltmeter will read about 12.4 volts. When you start the vehicle it should go up to at least 13.6 volts or it won't charge the battery. If it goes up over 14 volts, it can overcharge the battery and boil the water out of it. The regulator in the alternator reads system voltage and adjusts output accordingly. With an ammeter, the driver would need to keep track of how long it was charging and make sure the meter goes back to 0 once the battery is charged.
If the voltage stays up while the engine is running, the alternator is working. If the vehicle will restart several times after the engine is shut off, the battery is ok. If the battery goes dead after the vehicle sits for a while, it is most likely something drawing current from the battery.
Common draws are things left plugged into 12volt outlets, like cell phone chargers or GPS units. Lights are the next common draw, glove box, interior lights. Next are accessories like dvd players. A defect in the alternator can cause it to draw current.
If the voltage stays up while the engine is running, the alternator is working. If the vehicle will restart several times after the engine is shut off, the battery is ok. If the battery goes dead after the vehicle sits for a while, it is most likely something drawing current from the battery.
Common draws are things left plugged into 12volt outlets, like cell phone chargers or GPS units. Lights are the next common draw, glove box, interior lights. Next are accessories like dvd players. A defect in the alternator can cause it to draw current.
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