i don't know if i have a bad alternator or not. i have a 91 tercel. i started the car and measured the battery voltage with all the loads off, and i got 14.10volts. then after that, i turn all the loads (wiper, a/c, headlights, stereo) and took the reading. what i got is only 12.01 volts. i let it sit for a while but the reading is still the same. the car is feels like it's hard to crank. i tested my altima and my g20 with all the loads on and it gave me 14.20. is it time to change the alternator?
Do i have a bad alternator?
If the reading was 12.01 V over the battery terminals then it sounds as though something is wrong - however 14.10 v off load sounds about right - and means that the alternator has a working rectifier / regualtor / field coil / rotor coils. This starts to narrow things down a bit.
My first thought would be to check for grim conections on the battery - poor connections might well result in this sort of thing - though if so, you would find the voltage HIGHER if you put the meter on the battery terminals than the battery posts (if a poor connection between the two)
I would start the car again, ignore stereo, just use wipers and lights - that's enough. Measure the voltage on the battery POSTS and then on the CLAMPS. Are they the same. If different, clean and tighten them.
If they are the same AND the voltage is below about 13.5, then see if you can take a measurement between chassis and the alternator output itself. Is this higher?
If this is higher voltage, then you may have a damaged / broken / corroded wire from the alternator to the battery. OR you may have an external regualtor (unusual) which is dying (also unusual). If the voltage here is also low, then you might need a new one - though probably just need new brushes if you can fit them.
Mark
Do i have a bad alternator?
clean the battery connections
yes
it does sound like your alt is going but you need to check the alt under load and load test your battery.also check for corrosion at all conections between the bat and alt.with the voltage going down like that it probably is the alt
goodluck
Try remeasuring at a slightly higher RPM than idle. If you have a good battery, and it is charged to 12.5 volts or more after sitting over night, then the alternator seems to be doing its job.
Sounds like the alternator isn't charging like it should but you should charge up the battery to be sure it's not the problem. The battery could be low enough that when the load is applied the alternator can't keep up with it all%26gt;
Do this test for your alternator..... with the car running..... remove the positive battery terminal..... if the car dies the alternator is bad, if the car keeps running it is good...... thats it. :)
Alternator itself may be OK, check the voltage regulator and the brushes. Cast the eye over things looking for a bad connection too.
Voltage regulator bad.
Do what the skunk says but make sure not to allow the cable to touch ground or you will need a new alternator.
yout a alternator will send more voltage to your battary wen your using auxillery iiems like light heater etc etc so your battery doesnt go dead while powering these things
