Well, the #s are for the new battery I had put on Friday. So I’m getting 12.6V. However, with the engine running, I’m only getting about 13.5V. Could this be a sign my alternator is going bad? Alternator is only 10 months old. My understanding is you should be getting about 14.2 to 14.7V on the battery with the engine running. I have two cheap small dash cams plugged in all the time. I don’t think these two small dash cams would lower the charging voltage that much but I could be mistaken, and plus I’m using analog multimeter so reading can be a bit inaccurate as you have to look at the needle instead of the number on the LCD screen. And today, the car stalled with the check battery light on. I immediately restarted the car, and it seems to have been ok after that. Not sure if my new battery is faulty or if my alternator is going bad 10 month after getting replaced.
Stop driving yourself crazy checking voltage. Have the battery and alternator checked by a professional and you will have a real answer or just drive on.
Alternator voltage output can be 13.8-14.3 volts, depending on the engine RPM’s and the electrical load.
Tester
Today, a mechanic A did a free alternator test, and said I have a alternator voltage regulator failure so it’s not fully charging the battery, and is charging the battery about 85%. Since the alternator is still under warranty, I went to a mechanic B who replaced my alternator, and he didn’t accept voltage regulator failure because battery voltage with the engine running is 13.4 volt which he said is normal (which seems a bit low to me), and said it’s normal for a new battery to be charged about 85%. He also did alternator output voltage test with his multimeter, and it was 13.54 volt. The mechanic B volunteered the next door mechanic C to bring out one of those dolley type of Snap On tester. The next door mechanic C at first said the output voltage seems a little low (and the 1st mechanic said if I get throttle body cleaned, the voltage will go up at least 1 volt), and then did an amp test with the gas pedal pressed, and the amp went over 100 amp so concluded I have nothing to worry about my alternator. And added if I went to a part store like Advanced Auto Parts to get my alternator tested, their tests are often wrong. What do you think? Do alternator output voltage 13.54, battery voltage 13.4 with engine running, amp over 100 with gas pedal pressed, new battery charged 85% sound in the right ball park? If I run into problem with alternator, it seems like mechanic B will say to get throttle body cleaned.
Further thinking about this, it doesn’t seem like mechanic B will provide warranty on the alternator. In that case, should I just monitor my alternator and battery by getting it tested about at least once a month, and start thinking about buying the alternator on eBay, and hiring someone to install it? If it’s difficult to get warranty on the parts, why go to a brick and mortar shop, and pay more? Perhaps, I’ll just hire someone who can do it on craiglist or thumbtack…
It sounds like you are looking for a problem that doesn’t exist. Why did you feel the need to test the new battery and alternator? Is there a problem with the car?
This is the charging system test information from the service manual;
Check the charging circuit.
(1) Keep the engine speed at 2,000 rpm, check the
reading on the ammeter and voltmeter.
Standard amperage: 10 A or less
Standard voltage: 13.2 to 14.8 V
Well, the alternator isn’t exactly new. It’s 10 months old. Battery is new. The car once stalled yesterday with check engine light on, and it seemed to have been ok after that, and today, I got all these tests done on the alternator with the #s I posted in this thread. So I changed the battery to avoid a problem, and it seems like another problem that can affect the new battery has been discovered if I really have the voltage regulator failure on the alternator. This is a bummer. If I indeed have a voltage regulator failure, how do you advise I monitor it, or if I ignore it, can the alternator and battery last at least one year?
You can’t diagnose a bad alternator or regulator with a few voltage measurement. If you still have problems, take it to a place that can do a real load test on the alternator.
If the car stalled out, and then restarted OK, it is not an alternator or regulator problem. Or battery problem. And when a car stalls, the check engine light will always come on.
Which service manual? (I missed what this vehicle is.)
After replacing the battery the Engine control module will take some time to adjust the idle speed just right to compensate for the 11 year old dirty throttle body, that is why your mechanic offered to clean it for you.
Toyota, in a different thread the vehicle was a 2006 Camry.
A little off the point, the mechanic did NOT offer to clean my 11 year old throttle body. He said the alternator charging voltage will go up by at least 1 volt if I get throttle body cleaned which in this case wasn’t convincing thing to do based on what another mechanic tested. Based on my experience with him, if the voltage doesn’t go up, he will again say it’s something else so there’s no point in paying him again to clean the throttle body. I might as well go to another mechanic or do it myself.
Your battery is OK. Your alternator is OK. Drive on happily. Never heard of cleaning the throttle body would increase alternator output by 1 volt. I think they are taking advantage of you. Listen to Tester and Nevada. Over and out.
That’s what I’m hoping for. I don’t think there’s much I can do if the mechanic doesn’t honor the warranty. He keeps saying it’s something else. If I were to get it load tested at a more equipped place at a cost based on test cost, then me thinks it may be better to just get the alternator replaced.
Battery voltage/alternator voltage is only an indirect indication of battery or alternator status.
The voltage also depends on RPM, and the existing battery charge as well as other things.
Batt/alt voltage is often also temperature compensated.
The hotter the battery the lower the voltage.
13.5V is OK on a hot battery.
your stalling issue is not related to your charging system.
and few mechanics will replace a good part under warranty. He will have to turn that alternator in to get his money back, at which case it will test fine and they will tell him he is out of luck, and out his money.
@eddo: Thanks for your opinion, but how do you know the alternator is good when its output voltage is below the normal range of 13.8 to 14.8 volt? Plus another mechanic tested its voltage regulator to have failed which he said is the reason for low voltage output, and the responsible mechanic refuses to accept all private mechanic and part store’s test result except Toyota Dealership’s. The responsible mechanic also blamed my throttle body for low alternator output voltage without even inspecting my throttle body. The responsible mechanic also claimed since the alternator manufacturer is a sister company of Toyota, it’s impossible for their alternator to fail. Does it take much to see what he’s trying to do?
Off the point, why should I care about the mechanic’s money when he doesn’t care about my safety and my money? My safety could affect your safety if you happen to be driving near me. The only solution would be to go to another mechanic (not the one who found voltage regulator failure) for a 2nd opinion so the responsible mechanic not honoring the warranty costs me money if money matters.
If the engine cranks robustly as a matter of course day after day every morning — that rr rr r rr sound with the key in “start” — the battery is ok, and the alternator is charging it ok. Cranking is a much tougher chore for the battery than just keeping the engine running. A battery voltage measured at 13.5 v with the engine running doesn’t indicate a problem, at least not one that would cause the engine to stall. It might be a little on the low side of the acceptable band, but it is still ok. The charging voltage is a complicated function of the charge state of the battery and the ambient temperature inside the engine compartment. Add to that the engine rpm, and the total electrical load. All that varies all the time. The more fully charged the battery is, the lower the charging voltage will be. As I recall you have a new battery and new alternator, so the battery is probably almost fully charged, so a lower than normal charging voltage isn’t unexpected.
One thing that can cause the idle charging voltage to be on the low-side is if the engine rpm at idle is lower than specified. The way an alternator works, imprecisely speaking of course, the electrons in the coil of wire on the rotating part of the alternator don’t like to be rotated through a magnetic field, and so they run to the ends of the wires to get away, which produces a voltage in the wire. The faster the rotating part rotates, the more the electrons don’t like it, and the higher the voltage. So if it isn’t rotating fast enough, the electrons aren’t as grumpy & slack off their trek to the end of the wires, and the voltage goes down.
Lower than normal engine rpms can happen with a dirty throttle body. Or when the battery is disconnected and the computer forgets how to compensate for the throttle body and has to re-learn it. I forget what year car you have, but cleaning the throttle body is a pretty common thing on older cars. I had to clean the throttle body on my Corolla a couple of years ago as part of solving a higher than normal idle rpm problem. The backside of the throttle body gets pretty grimy from the egr and pcv gunk, and that can cause the throttle butterfly valve to not move freely, which can adversely affect engine idle rpm.
Lower than normal engine rpms is a common cause of stalling, and I expect that’s contributing to your stalling too. When you say it the cel turns on and it stalls, what is probably happening is that it stalls, then the check engine light comes on. That is supposed to happen. If the engine isn’t rotating and the key is in “on” the check engine light automatically comes on. That doesn’t indicate a problem beyond that the engine stalled. Best of luck there OP. It sort of sounds like you almost got the problems solved.
Just in case it has not been said, recharging a battery does not improve the battery, it may bring it up to it’s full potential, but will do nothing for prolonging life.