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49 votes
Accepted

Car battery at 10v, then shows 14,5v while car running after boost, then when car turns off, drops to 10v again within a minute

Nope. That pretty much sounds like a dead battery. It sounds as though one of the cells has a short in it, which is causing your rapid voltage decrease. There's no way to fix this other than battery ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
27 votes
Accepted

Car won't start after sitting for 2 years even with a jump. Is it a starter or alternator issue?

If the battery is completely dead, especially after sitting for two years, it most likely won't take a charge. Without the battery getting charged, you most likely don't have enough juice coming ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
22 votes

Alternator dying so junk car?

A rounded bolt is not a reason to junk a car. The numbers you're quoting sound fine for an alternator; if it was below 12V, I'd be worried. If you're still concerned, take the car to a spares store ...
PeteCon's user avatar
  • 8,712
21 votes
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Why do cars die after removing jumper cables?

It's because of a couple things: The battery is very dead and the alternator cannot put out enough power at idle RPMs to run the whole system and charge a battery. This leads to a lack of power which ...
Cc Dd's user avatar
  • 2,879
19 votes

Can a weak battery destroy an alternator?

Your question is difficult to answer without you knowing the inner workings of an alternator. The basics. If you move a magnetic field near a coil of wire the electrons in the wire get excited and ...
vini_i's user avatar
  • 16k
19 votes
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Why can't alternators provide full current at idle?

Cost is the main reason. An alternator that can provide full charging current would be far larger requiring bigger rotor and stator windings. This would make it more expensive and heavier. The ...
vini_i's user avatar
  • 16k
18 votes
Accepted

Can a car AC unit be run on just the car battery?

I can't give you numbers or calculations without some work, but I can tell you than energy is never free. Cars have an A/C compressor that is mechanically driven by the engine because this is the ...
JPhi1618's user avatar
  • 13.2k
17 votes

Will fitting a physically bigger battery reduce the working life of the alternator?

Great question! Taking a few minutes to think through this logically should come up with something. First of all, realise that a larger battery with a higher amperage (CCA) will not cause any ...
anonymous2's user avatar
  • 5,235
13 votes

Can a car AC unit be run on just the car battery?

Well, Teslas (and presumably other all-electric cars) have A/C so it's not impossible, but A/C takes a fair amount of power. On the other hand, Teslas store a lot of energy. The A/C is something ...
Spehro Pefhany's user avatar
13 votes

Car won't start after sitting for 2 years even with a jump. Is it a starter or alternator issue?

It's the battery Starting an engine takes a much larger energy impulse than jumper cables can deliver directly through their typically-thin wires and the small surface area of their alligator clamps. ...
Harper - Reinstate Monica's user avatar
12 votes

Will fitting a physically bigger battery reduce the working life of the alternator?

For most of the time, the battery doesn't provide any electrical power to the car. All the power is coming from the alternator. Think about it this way: the alternator probably has a maximum current ...
alephzero's user avatar
  • 2,954
12 votes

Trying to use a car alternator for a power source (not for car)

Several features. Firstly, alternators have a magnetic field that is adjustable by adjusting the amount of current at the field. This causes the output voltage of the alternator to be adjusted. The ...
juhist's user avatar
  • 14.6k
11 votes

Can a weak battery destroy an alternator?

Absolutely yes. I sell alternators all day every day - and a poor battery is often the root cause of alternator failure. A battery with a short in it will cause the alternator to run at full output ...
Bevan's user avatar
  • 561
11 votes

Technique to test an alternator - fact or fiction?

To directly answer this question, no it won't work and you run the risk of damaging your alternator if it is good while doing so. The test you are asking about was used quite successfully with ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
10 votes

Car won't start after sitting for 2 years even with a jump. Is it a starter or alternator issue?

Others have already told you the battery is a goner, I'll go into why: When a battery discharges lead sulfate builds up on the plates. It is deposited in very tiny crystals that will covert back to ...
Loren Pechtel's user avatar
10 votes

Car battery at 10v, then shows 14,5v while car running after boost, then when car turns off, drops to 10v again within a minute

The answer from Paulster2 explains what happened. This answer deals with what will happen next: A battery with a dead cell can explode while being charged (while the car is run). In some cases, it ...
fraxinus's user avatar
  • 2,102
10 votes
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Best way to recharge battery using alternator?

Of the two, running it at higher RPMs will result in a faster/better charge for the battery. That said, It should be of note, the alternator really isn't made to be used this way, yet people do it all ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
9 votes

Can a car AC unit be run on just the car battery?

The short answer to your question is no. As @JPhi1618 noted, the compressor is mechanically driven. Without the compressor you don't have any cooling. The AC runs by changing the state and pressure of ...
cdunn's user avatar
  • 9,296
9 votes
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I shorted the alternator for a second with a multimeter set to measure current

No, you most likely didn't mess anything on the car up, though you might have fried your multimeter. If the vehicle still runs and nothing seems messed up, more than likely nothing is. Something you ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
9 votes
Accepted

Have I fried my alternator through frequent use of an external charger?

It's very unlikely your charger had anything to do with your alternator failure, unless you were running the charger and your engine at the same time, even then I'd expect a charger to cut out as it ...
GdD's user avatar
  • 17k
8 votes

Can a weak battery destroy an alternator?

A battery that has an internal electrical short, usually one of the plates has come loose and is touching its neighboring plate will cause the alternator to work much harder than normal. This can ...
Fred Wilson's user avatar
  • 11.6k
8 votes

Can a car AC unit be run on just the car battery?

Yes, this is possible. Several companies (VAG, BMW) have switched to AC units that are driven by electric motors. For BMW, this is part of their Efficient Dynamics strategy, where they'll switch the ...
Hobbes's user avatar
  • 4,412
8 votes
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Why won't my car even crank?

That wire will have been the main power connection from the alternator to the battery it is used for powering the car and charging the battery while the engine is running. By forcing this onto the ...
HandyHowie's user avatar
  • 25.4k
8 votes

Car battery dead for a while... now it won't charge?

I'm not going to tell you to try and utilize a battery charger to fix the issue as @MoveMoreCommentsLinkToTop has suggested in the comments, but it has been my experience when a battery has sat for an ...
Pᴀᴜʟsᴛᴇʀ2's user avatar
8 votes

Will fitting a physically bigger battery reduce the working life of the alternator?

In fact the larger capacity battery may, under certain circumstances, increase your alternator's life. Many vehicles with enhanced sound systems install a larger battery to smooth out the load spikes ...
dotancohen's user avatar
  • 1,723
7 votes
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Connecting to the Battery During Emissions Testing to Measure RPMs?

The voltage being a little low (13.75 is not low enough to be considered a problem in any case) is not going to affect their RPM reading - as it's the frequency of voltage variations that is measured ...
Rory Alsop's user avatar
  • 18.6k
7 votes

one wire alternator

The one tool you will need to purchase / borrow is a Volt Ohm Meter (sometimes called a Multimeter). Then you need to use it to read voltage AT THE BATTERY, before the car is started and after the ...
zipzit's user avatar
  • 6,569
7 votes
Accepted

Car won't start...alternator or starter?

To differentiate between the starter and the alternator you can check the battery voltage – should be about 12.6 with the engine off and 13.5-14.2 with the engine running if the alternator is doing ...
dlu's user avatar
  • 14.5k
7 votes

Does increased load of electronic devices from your car reduce fuel economy?

The alternator's drag on the engine varies with the electrical load on the alternator. So, yes, as you increase the electrical load, the alternator consumes more power from the engine, and the fuel ...
dlu's user avatar
  • 14.5k
7 votes

Alternator dying so junk car?

I have seen somebody spot-weld a short bolt to the rounded nut they are having trouble removing. It's cheap and quick if the equipment is on hand.
Les Ferguson's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible