How much voltage@idle loaded?

97catintenn · 10-02-2009

2005 Honda Civic EX

Still factory/new battery.

idle unloaded=14.4volts
idle loaded (a/c, hi beams)=12.97v

Autozone said it's a bad alternator, but as you soon as you give it some throttle, it jumps up in voltage. Looks to me like it is charging.

What am I suppose to have at idle loaded?

To remove this ad, register today for free or log in if already registered!

gearbox · 10-02-2009

it varies from 12-14v. the ELD determines when to increase voltage when accessories are used and it will always change. what you posted seems normal to me. if the alternator is failing, the battery light will flicker or stay on in the gauge cluster. if battery is bad, it will not hold charge and eventually car wont start if it falls below 11v. i doubt the people at autozone have any clue what theyre doing. did they measure the amp output at 3k rpm and was it around 70 amps?? if so they alternator is just fine.

97catintenn · 10-03-2009

I doubted them, too. They just used a small testing device that checks starters, alternator, and battery. The end result was all I saw, low voltage loaded at idle 12.97v.

And the clerk probably 20yrs old, said, "yep, you have a bad alternator!" and I said, okay! and drove off to buy my own voltage meter and saw how quickly the voltage rose with just a little throttle.

But, I just wanted to check with the site here to see if I was okay! Thanks

gearbox · 10-03-2009

you really need a good charging system tester not the handheld multimeters. advance auto has a good machine that does load tests and gives you amp output. thats really the only way to know for sure is checking the output under load (3k rpms). no alternator works that well at idle anyways.

97catintenn · 10-04-2009

Earlier you said that the ELD controlled the voltage. What is that? I'm used to the old alternators that had separate or built in regulators.

gearbox · 10-04-2009

ELD = electronic load detector. basically it senses electrical "load" like turning on the fan or wipers, and increases alternator output to match. then a while later when it sees the extra power is not needed, it backs off the output. i had a voltmeter at one time, and i always saw it move around from 12-14v depending on a variety of conditions, even pressing the gas.

CraigW · 10-05-2009

^Exactly, and the alternator still has a built-in regulator.

Canada models do not use an ELD.

97catintenn · 10-15-2009

I just checked my truck with a full load at idle and the voltage increased. 14.8 at idle unloaded and 15.5 loaded. Probably too much, but that's what it is.

gearbox · 10-15-2009

i think thats too high. maybe its a truck so its a different setup, but i still think there may be a problem. if it stays at 15.5v for a while, you could overcharge the battery and boil out electrolyte.

97catintenn · 10-17-2009

I've done that a few times. Batteries only last 2-3yrs in the truck. I was just amazed at how much voltage it was able to produce at idle. <hence my post above>

To fix the truck, I would need to install another battery tray and run two batteries. Being a Cummins diesel engine, they are difficult to start compared to the gas engines. And change out the regulator, which I did once and didn't see a difference.

97catintenn · 2 Weeks Ago

That regulator failed on me last week. I was driving with a charge of 18v!

Now it's down to 14.5v. So, you are correct in the above post.