Car Repair & Diagnostics : How to Test a Car’s Alternator

Comments

1. stankwho says:

   January 17, 2010 at 5:19 pm

   the last part..were did you plug the multimeter after you did the light test on the alternator?
2. STFUNOWlol says:

   January 17, 2010 at 5:56 pm

   If you’re talking about 400 watts total, and assuming you have a standard 12 V battery, you’d be talking about a 33 amp draw on your battery. Considering that the cranking amps of a battery are in the hundreds, and the operating amp of a battery are much lower, I would imagine that it would be fine.
3. zillsbury says:

   January 17, 2010 at 6:26 pm

   thanks govna!
4. youdragon says:

   January 17, 2010 at 6:41 pm

   i have a stock gmc truck think my alt can handle 4 100watt off road lights?
5. angelvoicedee says:

   January 17, 2010 at 6:49 pm

   There has been no mention of the exciter feed from the dash light i.e. a blown bulb/ interrupted power supply . Or voltage drop test between the neg battery terminal and the alternator chassis.
   Some diesel engines use one of the alternator terminals for the engine rev counter .
   This can be a factor to be aware of .
6. roarpony says:

   January 17, 2010 at 7:35 pm

   A ****** with an ASE badge on my shirt then. lol I’m not trying to be rude but if you want others to do the right procedures I would recomend you to know the facts. Back in the days you could do that I admit but now it’s all about electrical parts. The deadline for an ASE test is on Sept 30th. I have to redue mine on EP.
7. roarpony says:

   January 17, 2010 at 7:55 pm

   The battery acts as a buffer and stabilizes any voltage spikes that may cause damage to the vehicles electronics so disconnecting the batt is not a good choice. Do a voltage output and curren output test, a voltage drop test, a full field test if the output test fails. Make sure the batt is fully charged.
8. TBWdracula2003 says:

   January 17, 2010 at 8:42 pm

   do you think any mechanic has an ASE patch on EVERY SINGLE PIECE OF CLOTHING they wear? no. your retarded
9. albrainya says:

   January 17, 2010 at 8:43 pm

   JeRkOfF
10. tonytiger75 says:

    January 17, 2010 at 9:41 pm

    An Alternator will not motorize and spin with voltage applied to it, only DC generators do that. A car might continue to run with the battery disconnected but if anything upsets the electrical balance, like turning on the headlights, it will shut off, the alternator needs a small amount of battery power to excite and magnetize the windings or it can’t do a thing whereas a generator uses residual magnetism to generate power.
11. thenightwolf80 says:

    January 17, 2010 at 9:55 pm

    This guy speaks the truth whether you believe it or not. When connecting your DVOM from the battery to the Alt. it doesn’t matter which one is connected where color test lead wise so long its from the batter Neg. terminal to the Alt. Hot lead ( not the connector ). You should get 13.5-14.8V (DCV) anything under or over that the Alt. is defective.
12. hkssupra86 says:

    January 17, 2010 at 10:23 pm

    i’m automotive wireman..i special list repair truck ,forklift,car,excavators..eletrical system….
    u work like ****~~~
13. roarpony says:

    January 17, 2010 at 10:37 pm

    If I don’t see a patch that says ASE on his shirt that means it’s BS. lol I wouldn’t recommend performing this procedure if you’re not an expert. He did the volts but I’m wondering what “is here”? An alt… has volts and amps. Don’t play with amps if you don’t know any about current. Gamzmasta I wouldn’t recommend your procedure either. Never, never disconnect a battery while it’s running.
14. woodterm says:

    January 17, 2010 at 11:21 pm

    gamzmasta, you almost got me with this one… lol
15. bluegap81 says:

    January 18, 2010 at 12:19 am

    GOT NAP?
16. gamzmasta says:

    January 18, 2010 at 12:47 am

    theyres a easier way, its my way!, lol.
    on a serious note, just disconnect the battery terminals while the car is running, if it turns off the alternator maybe dead, if it still runs your ok, check fuses and wires before buying a new 1, final test when you have taken it out the car, conect it direct to a battery and it will spin like a fan if it is working be carefull when trying this, e.g make sure you use jump leads or something, and that you wont injure ur self
17. crackboompow says:

    January 18, 2010 at 1:42 am

    He kind of “shotguns” the alternator. he didnt check for amp output, good effort though, I hope all the fuses were checked before alt. replacement……
18. jerseyRJ says:

    January 18, 2010 at 2:42 am

    so do u touch negative battery terminal and alternator terminal for the reading?
19. Zorritototote2000 says:

    January 18, 2010 at 3:18 am

    this guy is drunk or what