what can cause high voltage output on an alternator

[jacobrjett]

righto ive tried google, didnt get very far.

a few days ago I installed an amp, subs, components and a new headunit into my car, so this may be of interest.

My alternator output is far too high, I just noticed today. The car still runs but all of the lights on on the dash start flashing and the amp turns off.

The voltage is mint at idle, but when I rev it goes up to around 17 volts.

What can cause this? a bad alternator? when I bought the car it was described as having a rebuilt alternator. a badly rebuilt alternator?

is there a chance I have a short circuit in my wiring somewhere which is causing this?

[Grrrrrrr!]

Regulator is kaput.. Most are internal to the alternator, but some mostly older cars use external regulators.

the load from the boom sounds may have overloaded it and caused it to die.

[jacobrjett]

thanks... sounds fair enough...

any idea how long I have before toasting my battery? I only just bought a new one, dont want it to die as well

I get a bit of voltage drop from the amp being turned up so I guess ill drive around with my lights, A/C on and the amp turned up...

also any idea on how much it would cost to get an alternator rebuilt?

[Grrrrrrr!]

At 17volts? Not long.

[Monsterbishi]

^^^ First reply has nailed it, the regulator is toast.

STOP driving it immediately!

It will be loading up the battery something fierce, which can cause some rather unpleasant effects, the least of which being it boiling the fluid into a toxic gas (Turns back into acid when it re-condenses - including if you breath it in) and a very real chance of the battery exploding.

Plus you'll be pushing excessive voltage into everything, including the ecu, etc which don't have the luxury of over-current protection.

[Lloyd]

And when they explode, you'll know about it. Battery acid on everything and probably a dent in the bonnet. Good times.

[jacobrjett]

yikes.

ok, car is now parked waiting for a new alternator in that case!

i was hoping if i was to keep the voltage low (stereo and headlights on) i might be sweet to drive it until pay day, but youve sufficiently scared me

[Lloyd]

Do a Google images search for "exploded car battery"

[phoenix]

Do a Google images search for "exploded car battery"

Mmmm Katie Holmes

[Mr Revhead]

Had a battery explode on me last year. $&#$% loud.
Luckliy was at a mates hopuse who had baking soda so doused the engine bay in lots.


viewtopic.php?t=88141&highlight=battery

[Malcolm]

There's another possibility which is that your voltage sense wire has broken, possibly due to a blown fuse. This happened on my mr2, the alternator voltage signal becomes 0v, even though system is actually at 16v, so regulator allows it to keep charging. Check your fuses and also the voltage on the sense wire to the alternator.

[matt dunn]

There's another possibility which is that your voltage sense wire has broken, possibly due to a blown fuse. This happened on my mr2, the alternator voltage signal becomes 0v, even though system is actually at 16v, so regulator allows it to keep charging. Check your fuses and also the voltage on the sense wire to the alternator.

with a broken sense wire you may get high 15's in the voltage,
but a toyota one has an internal batt supply to the reg also,
so will never get to 17v without something inside the alternator going faulty,
usually the reg or the rotor can do it also.

What engine is it, 4age alt or 4AGZE alt? or something else?

[Leon]

Stuffed regulator in 4age's is incredibly common, been there bought the t-shirt.

[jacobrjett]

engine is a 4age, smallport.

ok, my new battery is toast well, its dead already. maybe I can charge it up and it will be ok...

what does one generally do in this situation? rebuild alternator, buy a rebuilt alternator, or buy a brand new alternator?

[Leon]

Get alternator repaired.

Oh yeah, the other side effect of the alternator pooping it's pants, is that when you have the car off, it will drain the battery with an open circuit.

So unplug the battery.

If it has killed your battery I actually have a working battery in my garage that I removed from another car (it was the wrong size for the bracket, so somebody had it tied in with rope) that you can have for $25. It seemed to be working fine when removed from the car.

[Grrrrrrr!]

And buy new battery, yours is done. It doesn't need charging, it's been overcharged to buggery already.

[matt dunn]

engine is a 4age, smallport.

ok, my new battery is toast well, its dead already. maybe I can charge it up and it will be ok...

what does one generally do in this situation? rebuild alternator, buy a rebuilt alternator, or buy a brand new alternator?

Depends on how quickly you need it to go again.

but probably not option C.

[Lloyd]

Or 4th option, throw a second hand one on.

Get it off and get your sparky to price it. If it's just brushes/bearings and a reg then it shouldn't be too much more than getting a second hand one. Much more wrong and you'll be venturing into new aftermarket prices (depends where you go).

Options in increasing price order would be get a second hand one, rebuild yours or get a new one. New should have a better warranty, rebuilt will come with a reasonably warranty, and a second hand one will have bugger all of anything.

[rollaholic]

if your battery is really new, take it back for warranty claim.

just dont tell them about the alternator

[Alex B]

If you sit there with your sound system going hard with the car off you are likely to kill a battery also, as I found out the hard way.