| Author | Message | ||
| Verell Boaen (Verell)
Member Username: Verell Post Number: 723 Registered: 5-2001 |
Radio Shack, other places have a nice little digital voltmeter that plugs into the cigarette lighter outlet. Kind of a handy place. Some non-smokers just leave it there while the car is in daily use. | ||
| James Selevan (Jselevan)
Member Username: Jselevan Post Number: 533 Registered: 6-2002 |
Adam - The physical location of the voltmeter is your aesthetic preference. One lead (negative) goes to ground. The positive from the voltmeter goes to a switched (ignition switch) hot line (through a fuse). You do not want the voltmeter measuring system voltage when the ignition is off, as there is a small but significant leakage through the voltmeter that, if left on for a long period of time, might lead to a discharged battery. | ||
| TomD (Tifosi)
Advanced Member Username: Tifosi Post Number: 3575 Registered: 9-2001 |
check my other thread but I checked the old battery about 13-14 off, and at idle. replaced it, cleaned all connections and everthing works great now!!! thanks | ||
| Adam Goldman '86 TR (Icnsltmfg)
Member Username: Icnsltmfg Post Number: 573 Registered: 8-2001 |
If I want to add a volt meter to the car, where should I connect it for a perm hook-up | ||
| TomD (Tifosi)
Advanced Member Username: Tifosi Post Number: 3571 Registered: 9-2001 |
it does, thanks, how do I measure the field voltage at the alt? wire to ground? | ||
| James Selevan (Jselevan)
Member Username: Jselevan Post Number: 532 Registered: 6-2002 |
Tom - there is some information that can be gained from the battery terminal voltage and field voltage at the alternator or voltage regulator.. First, if at 2,000 RPM the battery terminal voltage is above 13 volts, and the regulator field voltage does vary with RPM, then it is likely that the problem is the battery. If the field voltage does vary, but the battery terminal voltage does not, then the problem is likely with the alternator. These are simplistic diagnostics that can be done with a voltmeter, but it may get you started. The field voltage can be measured at the alternator (small wire tab-connected to alternator), or at the voltage regulator (green wire, I believe). Basically what is happening is that the voltage regulator, with only 3 wires, is monitoring system voltage. When the + regulator connection senses low system voltage, it increases alternator field voltage to generate more current output from the alternator. When the increased current flows into the battery, the battery voltage rises, and the voltage regulator feedback loop senses the rise in voltage, and lowers the field voltage. Thus, the field voltage and the battery voltage should move in opposite directions. High (13.5 volts) battery voltage should result in low (7 volt) regulator voltage. Low battery voltage (12 volts) should result in high regulator field voltage (11 volts). Hope this helps. Jim S. | ||
| TomD (Tifosi)
Advanced Member Username: Tifosi Post Number: 3570 Registered: 9-2001 |
mike, thanks I did find those threads, just wanted to see if any level would indicate a battery issue as opposed to an alt prob | ||
| Mike Procopio (Pupz308)
Member Username: Pupz308 Post Number: 355 Registered: 10-2002 |
If the car is running and your over, say 15 volts, or under 12 volts (assuming most accessories are off), you may have a alternator or voltage regulator problem... Check the archives. Solution is to rebuild the alternator. | ||
| TomD (Tifosi)
Advanced Member Username: Tifosi Post Number: 3568 Registered: 9-2001 |
thanks, I am electrically challenged  . what does being above those numbers indicate and what does below those indicate - generally | ||
| Lawrence Coppari (Lawrence)
Member Username: Lawrence Post Number: 599 Registered: 4-2002 |
You say current. Current is amperes. If you switch over your voltmeter to read amps (mulitmeter), you will melt its internals if you place it across the battery terminals. If indeed you want to check volts, you can put it across the terminals or from positive to ground (which really is the negative terminal). With engine off you should read about 12.5 V. With engine running, you should read 13.5-14.5v. When started, it'll charge at the higher rate until battery is fully charged. After a while, it should drop to 13.5 v. Should not change much at all with rpm. | ||
| TomD (Tifosi)
Advanced Member Username: Tifosi Post Number: 3567 Registered: 9-2001 |
further to my other thread, what is the proper way to test current at the battery with a voltmeter? post to post or post to ground? what should my readings be with car off, idle and 3k rpm? and what does low and high readings mean respectively? thanks |