streetdreams Posted February 24, 2005 Report Share Posted February 24, 2005 I brought home my multimeter tonight, I started the car and checked the voltage at the battery terminals 14.89 problem is I noticed as the car ran the voltage kept slowly dropping after 10 minutes it was at 14.54 this is miniscule but just wondering why it trickled down? could my alt not be up to snuff? when I shut the car off I checked the battery again and it was at 13.51. p.s man its cold out there, -15 for an hour will do that to ya Quote Link to comment Share on other sites More sharing options...
Strecker25 Posted February 25, 2005 Report Share Posted February 25, 2005 in the cold an alternator will generally put out a higher voltage until it warms up, gm's internal regulators keep it within 13.8-14.4. You cant really check the state of your alternator as far as amperage goes unless u have one serious ammeter, any standard dmm will blow up quickly. Quote Link to comment Share on other sites More sharing options...
1990lumina Posted February 25, 2005 Report Share Posted February 25, 2005 When if the car was off as you say after an hour that is quite high since it is only a 12volt battery. Quote Link to comment Share on other sites More sharing options...
streetdreams Posted February 25, 2005 Author Report Share Posted February 25, 2005 1990lumina I dont understand what your saying, please explain because I'm trying to learn everything I can about electricity and charging systems. btw the car wasnt running for an hour only 10 minutes, I was outside at the friggin bus stop for over an hour though that I came home and did the car stuff Quote Link to comment Share on other sites More sharing options...
Canada Posted February 25, 2005 Report Share Posted February 25, 2005 Thats damn typical of any charing system to do so. The only true way to test an alternator is to load test......any shop or part store can do this. Quote Link to comment Share on other sites More sharing options...
glock19 Posted February 25, 2005 Report Share Posted February 25, 2005 Ok here it goes..... Your alternator needs to charge the battery which is actually 12.6V. In order to do this it needs to put out a higher voltage than the battery so the current will flow into the battery and charge it. This is controlled by the regulator in the alternator. No when the battery is fully charged and you do not have an excessive electrical load (i.e. headlights, stereo system), the voltage of the alternator will drop down into the 13V range. In addition, the alternator also provides the voltage and current for the entire electrical system while the car is running, and uses the battery for backup. I am guessing since you said it was at night that you probably had the headlights on and the additional drain cause the alternator to put out a higher voltage to compensate. In order to measure the current the alternator puts out there are 2 ways. The first is to put your DMM inline with the cable coming off the alternator. This will blow the fuse in your meter since most meters only measure 10A and your alternator can put out 100A. The other way is with an inductive pickup that is placed over the wire. The current induces a voltage in the pickup, which can be measured and correlate to a current. This is the correct (and easier) way to measure the output current. Glock Quote Link to comment Share on other sites More sharing options...
1990lumina Posted February 25, 2005 Report Share Posted February 25, 2005 Sorry man..didn't mean to confuse you (I think I was confused when I posted that). The above post by glock19 sums it up nicely. - Jeff L. Quote Link to comment Share on other sites More sharing options...
streetdreams Posted February 25, 2005 Author Report Share Posted February 25, 2005 cool, thanx guys weirdest shit I learnt all about charging systems at my job last year but now its not in my memory until I listen to all this and than it comes back. in high school I did welding class but havent welded in 5 years.since I started working in a shop I would say I didnt know how (everybodies so quick to point out your flaws if you dont know how to do somthing in a dealership shop), recently started playing around with it and reading up again and its all coming back. I think if your not interested in somthing when you study/learn it you brain stores it as unimportant or dosent even store some of it but if your interested it's the opposite like horse power and weight, I can recite the Kg and power for most cars, why? I dont know just happened that way Quote Link to comment Share on other sites More sharing options...
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