Today I load test the alternator by an instruction in an aftermarket repair manual. The instructions says to turn on headlights, defoggers, fan, radios, cigarrete lighter, etc and measure the voltages. It reads 13.6V at 2000 rpm or 11.2V at 750 rpm. It's within normal range according to the book. But the headlight seems a bit weak unless rpm is above 1300 rpm or sometimes it just too weak for the starter. We hardly drive in the highway. It has an alarm system. Is the alternator fine? TIA Tibur
It looks like the alternator is OK, but the battery itself may be on its way to failure.
You may want to try AutoZone or Sears for a quick check of your charging system and the battery itself.
First make sure that all of the battery connections are squeaky clean and tight. If the cable posts are loose inside the battery might as well head to the battery store.
You can load check the battery itself with similar test as above.
With nothing connected, the battery should read 12.4 volts. If below that, it isn't charged fully or is defective. If you have a battery charger, try it.... but replace any battery that can't hold 12.4 volts or higher with no cables connected.
Then make sure the battery isn't just taking a surface charge by giving it a load, then check the open circuit [no cables] voltage again. Turn on your headlights [with battery connected] for 15 minutes, then turn them off and wait 5 minutes. The battery should still show at least 12.4 volts. If it can't, it is getting old and is only taking a surface charge.
With no-load and the headlight 15 minute load test, rough battery voltages for charge are: 12.0 volts = 25% charge 12.2 volts = 50% charge 12.4 volts = 75% charge 12.6 volts or more = 100% charge
If the battery is 5 years old, swap it anyway if it is a premium model. If not a premium model, derate that to 4, 3, 2 years.
The 3-year old low-price, drained-several-times, weak-battery described above is now replaced with a new 7-years warrantee battery. Let's see how long this one will go. I have another similar alternator question for a second car, if I may.
Recently my wife's '97 BMW 318ti's alternator was replaced and it shows
13.7V at any rpm with no loads. With loads it's 13.6V at 2000 rpm or 9-10V at idle. Engine off it reads 12.6V. Alternator is Valeo, made in France. Battery is two years-old. Is the alternator fine? Attn: Battery experts! Thank you. Tibur
I don't see anything suggesting the battery was bad. However the volt meter makes testing a battery so simple. Find a problem before trying to fix it - which is why that voltmeter is a so important tool.
Run car even at idle without electrical loads. Battery voltage should be above 13 volts. Turn car off. Battery voltage should be somewhere in the neighborhood of 12.5 to 13 volts. Turn on high beams. Battery voltage should maintain over 12 volts and over many minutes, never drop below 12 volts. That is a good battery.
Described previously is what I would expect from an alternator problem. Alternators really are three separate electrical generators. If one fails, then output voltage will appear low during low RPMs. This is why smarter mechanics have an oscilloscope). Alternator will charge battery under most conditions but will slowly discharge battery during a full load of electrical peripherals (headlights, read window defogger, heater fan).
That idiot light can be a problem. An alternator that outputs power will still discharge battery. Idiot light properly reports that alternator is outputting electricity (even if that is not enough electricity). Same problem can also occur if fan belt to alternator is slipping. Great profit to the local repair shop. They sell a new battery since - as demonstrated here - knowledge of how alternators can fail is so little understood.
A car battery that does not last at least seven years (never even garaged) suggests a car problem - either > Attn: Everyone,
Wow, that's the biggest load of crap I've heard in quite some time. I doubt if even 5% of batteries sold make it to seven years and I'm pretty damn sure that doesn't mean that the other 95% all have car problems. Bob
In over twenty years, never had a single car go less than seven years on a battery. BTW, the lead acid batteries used for battery backup (in serious systems) are expected to last on the order of 20 years. But then they sit inside controlled environments.
Back > Wow, that's the biggest load of crap I've heard in quite some time.
And you live in an area where batterys should live a long life due to temperatures that don't get extremly high or low. On my own vehicles I load test the battery every fall but pass or fail it's outta there after 5 years. Batterys are cheaper than tow trucks. Bob
I've heard bigger loads of crap, but that was pretty good. People's personal experience always comes out in these posts. We don't know who the experts are in most cases. Take everything with a grain of salt. I went to jump start a lady's car two weeks ago who walked home because it was dead. It was parked in a grocery store lot with cars next to it. The battery read 8.69V on my digital meter and yet it started. Go figure. The battery actually was serviceable while the voltage regulation was gone. Weird things happen. A battery can last
15 years, barely. I've never kept one more than four years myself.
And more importantly, are of an entirely different construction and design, since they have an entirely different set of design requirements than an auto battery, so this is pretty much meaningless as far as an auto battery is concerned.
In addition to their design, UPS batteries are rarely subjected to prolonged vibration, even in California.
As for batteries lasting 7 years, perhaps yours do, but careful folks change them out much sooner, 4-5 years even for the premium units.
Older lead acid batteries used brute force with lotsa lead available. Current ones have considerably less lead and rather different internal construction. At least in the 50's and 60's you would usually get a warning as the battery begins failing more gradually compared to todays life cycle that looks pretty much like Niagara Falls.
The trouble is that most people are ignorant of how the battery works and abuse them... and the auto mfrs keep adding features which encourage the abuse. E.g. how many people with auto-off headlamps use it as a feature rather than as a safety against forgetfulness?
Rgds, George Macdonald
"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??
Therein lies 'battery stress' that can lead to premature failure. If one completely discharges a battery, then premature failure is probable. Just another reason why that inexpensive 'headlights left on' warning device should be standard equipment.
As car battery life expectancy increased, so did life expectancy of lead acid batteries in controlled environments such as communication buildings. Both increases due to better battery construction and superior recharging methods. Engineers note life expectancy in communication facilities has increased substantially to something just under 20 years - which is consistent with increased battery life expectancy in cars. To be consistent, car batteries that once got 3 or 5 years in the 1970s are getting something less than 10 years today.
For those who are suffer> The trouble is that most people are ignorant of how the battery
Expected average life is a confidence index; not a statistical average. It means a majority of batteries must exceed those numbers. For example, 99.9% of antimonial lead alloy batteries will exceed the 26 to 29 month life expectancy. It does not mean that 99.9% of batteries will fail in the 26 to 29 month period. It means that battery can be warrantied for 26 to 29 months, and manufacturer should have very few premature failures (and pro-rated warranty claims).
If batteries lasted 26 to 29 months, then something approaching 50% of the batteries would fail prematurely while still under warranty.
I have a 2 liter bottle of coke. Does that mean the coke contains 2 liters? No. Maybe 99.999% of those two liter bottles contain 2 liters or greater. Again, 2 liters is not the expected average quantity. Two liters is also a confidence level. Battery is rated same way. Battery is expected to last longer than 26 to 29 months - a confidence level.
My 1976 GM Freedom battery (that 'no add water' battery, an early calcium lead type?, became the 1970s standard) was still work> In my former life, I managed a battery specialist distributorship. >
Just thought I'd throw in another alternator question in this thread. I've been getting intermittent voltage fluctuations in my electrical system. The fluctuations can be seen the in lighting system and by the in-dash volt meter. An oscilloscope on the battery terminals with the car at idle shows +/- 0.2 volts at approximately 6Hz (higher Hz at higher RPMs). I had my charging system tested at an auto parts store and it turned up ok, with the battery being a little weak. About 8 months ago I had a voltage regulator go out and was over-charging the battery for a little while. Since then the alternator was replaced.
My question are:
- What is the acceptable +/- voltage that a properly functioning alternator supposed to output, if any?
- Will the voltage fluctuations cause damage to other systems in my car?
- Is it possible that my slightly weak (and possibly damaged) battery isn't "filtering" the voltage fluctuations?
I plan on pulling the alternator and having it bench tested, but I'm waiting until the weather clears.
Thanks,
- Dave
Tibur Walts> Today I load test the alternator by an instruction in an aftermarket repair
No manufacturer rates a product's quantity or life expectancy with a statistical average. Its not complicated. When they say a battery is expected to last 48 months, they don't mean half the batteries will last less than 48 months and the other half will last more than 48 months. That would be an 'arithmetic mean' of 48 months.
Instead, something like 99.99% of those batteries must last
48 months ... or longer. They provide a minimally acceptable life expectancy number. It is called a Confidence level. What's so difficult about this? It's a standard concept in any first level statistics course. Why are you now getting so emotional over a mathematical concept that is so trivially simple? Why do you insult because you did not know this?
Expected average life is a Confidence level. They don't publish a number that 50% of the batteries will not meet. They publish a number that most every battery is expected to meet. That is called a Confidence level.
You do remember the 1970s. If that 24 month battery failed in 14 months, and if you still had a receipt, then the pro-rated warranty was automatically honored - no questions asked. All batteries either exceeded their rating, or would be replaced by that warranty. So where does this nonsense about batteries lasting too long have any relevance? Or is that just another silly insult.
There is no lecture here. Just simple business math. Its called a Confidence level.
A lead acid battery's performance is directly traceable to temperature - which is why they are rated with a cold cranking amperage. However performance and battery failure are two completely different things. Temperature is completely irrelevant when a battery will not even hold a charge. Temperature makes no difference when one cell short circuits from a pile of debris shorting electrode plates. Another failure condition estimated by the Confidence level.
Please read carefully before jumping to conclusions. I never said a battery not starting at -20 degree failed. I noted that a battery that had frozen when new still managed to well exceed its confidence level. Completely different meaning from what you assumed. Frozen batteries (like over discharged batteries) don't always last much longer. This one did. It was still working five years later.
Your lecture about battery performance is noted as accurate, but is simply preaching the the choir about something completely irrelevant. A battery that should have failed before its confidence level predicted (because it was frozen), instead went on to long exceed its life expectancy. Now that it is posted a second time, do you understand - and notice how my tone has changed because you insult with arrogance rather than learn what a confidence level is.
I guess you never took any introductory statistic lessons in school. Shame. In Japan, simple statistics is required of every Jr High School student - even future battery salesman. Just another insult you earned.
Now, maybe you would like to st> Apparently "w_tom" likes to make something
The "difficulty" with this is that you made up the 99.99% number.
The duration of the warranty is not the expected life. The life expectancy of a car in the US is around 17 years, the warranty is significantly shorter. On the other end of the scale, my tire pressure gauge has a lifetime warranty even on the battery. I do not expect the battery to last another 50 years, but I sure hope I will.
And maybe you should stop trying to blow smoke up everyone's ass. You bring to mind the old saying that if you can't dazzle 'em with brilliance baffle 'em with bullshit.
If you have an automotive alternator driving a resistive load (no battery in the circuit, negligible capacitance and inductance) the ripple voltage would be about 1.4V (peak to peak) or about 0.5V (RMS). This is assuming a three-phase alternator with the output DC voltage regulated to 14.5 V RMS.
The ripple voltage changes very little with load current.
When it comes to judging the health of the alternator, the magnitude of the ripple is not as important as the shape. Normally it will look something like: _ _ _ _ _ _ _ _ / \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_
If you have a failed diode (open) in the rectifier you will have something like: _ _ _ _ _ / \_____/ \_/ \_____/ \_/ \_____
If you have a failed diode (short) in the rectifier you will have something like: _ _ _ _ _ / \__ __/ \_/ \__ __/ \_/ \__ __ V V V
Some ripple is inherent in the system and does not cause damage. It can sometimes cause noise in poorly designed audio equipment.
Voltage fluctuations CAN cause damage. If the alternator is full-fielded under moderate load the output voltage can get very high. The service manual for my '94 Civic warns against letting the voltage rise above 18V during fullfield testing of the alternator. A common failure mode for voltage regulators is that the alternator is fullfielded.
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