I've been putting up with my '84 Sierra's lackluster alternator performance
for a long time now. Unless driven very regularly, it would have dead
batteries. Now it doesn't even really charge them when driven or run...the
output starts out strong after starting (14.5 volts) but soon drops to 12.8
with next to no load (everything that can be turned on is turned off).
The battery connections look good at both ends, and neither battery is very
old. The drive belt is tight, so I think the alternator is sick and dying.
It is original to the truck as far as I know. I've been looking for a new
one, and the consensus at various auto parts stores is that the alternator
is rated for about ~75 amps maximum output on these trucks. This can't leave
much left over for charging both batteries when you factor in headlights,
radio, blower fan and all that stuff being turned on. It really seems like
such a "small" alternator would lead a very hard life.
However, the clerk at Advance Auto Parts showed a number of beefier choices,
going all the way up to a 140 amp rated unit. I'd tend to go for the larger
alternator...the idea being that a larger unit would be under less stress
and have more ability to take on heavy loads when they appear and while
still charging the batteries.
What I'd like to know is if I'm on the right track here--if I should spend
the extra money for the large alternator or choose something smaller (there
are a few choices between the stock unit and the higher rated ones)? Also,
would the larger unit be compatible with my truck (belt and mounting wise)?
Thanks in advance for any info, thoughts, whatever.
you looked so lonely sit'n on the board with NO ONE
Sounds like the thing does ok as long as it's being driven. (?)
Sounds like it's causing the problem after sitting for a day or so.
Sounds........like you should check for an amperage draw BEFORE
you go buying any new altenator dude.
The output should be around 14.2 or a little better on initial
with the voltage dropping back to 12.8 or so shortly after if you
have any, many, acessories running. That's normal op.
I know you well enough to realize you prob know that......
We've had a couple trucks outta the shop FLEET recently doing
the EXACT same thing....amperage draw on various circuits has
been the culprit so far.
Anywhooo..........i'd ck that first.
Could be the Alt is working.
Could be the electrolyte has accumulated on the plates.
Could be a current draw when sitting.
jest some guess's..........
Who'd you piss off...so no one wanted to talk to you??
~takes a toke......pours one fer WillyWalsh the WashRack man~
From anyone else I would guess a typo. From you, showing off your
SULFATE from electrolyte is accumulating on the plates.
like yer the FIRST one to EVER point that out to me.
~takes a toke.....exhales in Dobony's direction.........who said 2nd
smoke was bad for you~
This is backwards...
Charging voltage will be a bit low after initial start up as the
alternator works to replenish the battery after a large amperage
draw from the starter, the voltage will slowly ramp up as less
current is used to recharge the battery.
Delco alternators -do- have temperature compensating circuitry,
charging voltage will tend to be higher in cold weather
conditions and lower in hot weather conditions.
Naturally, any accessory load from the truck will raise amperage
and lower voltage.
The voltage shouldn't go under 12.8 when the alternator is being
loaded at its maximum output rating.
You need to go out tomorrow and connect the carbon pile across
the battery, amp meter to the alternator output and a volt meter
to the battery.
Take an open circuit voltage reading from the battery.
Start the engine and maintain 2000 RPM, note volt meter reading.
While maintaining 2000 RPM engine speed adjust the load across
the battery with the carbon pile until the amp meter reads near
maximum alternator output rating, does the volt meter read higher
or lower than the no load voltage?
If you adjust the carbon pile for less amperage output from the
alternator, does the voltage reading go up or down?
I suspect what you and Marsh are seeing is the effect of tapering
off the engine speed from a cold start.
I see this guy is up to old tricks and passing bad info. Battery
charge does not determine voltage of charge, only amperage rate.
Regulator will hold voltage constant within limits of output abilty of
alt. If voltage climbs when charged it is a sign of a weak alternator
or bad regulator because voltage should be contastant or tend to
decreases as underhood temps rise, not increase.
Let the Trolls desend as their egos and insecurities need to be
Yes you are. Lets remind everyone why YOU left for a few months.
(Confuses a 4T65e with a 4L65e and won't admit it.)
SBJ: Dumb brake question
(Discribes the wrong brakes and won't admit it.)
SBJ: Front wheel bearings-2000 Blazer??
(Claims torque specs are wrong when they are not.)
SBJ: Snoball Defense System v1.01
(Snoball breaks these out when he knows he's wrong
and doesn't want to admit it.)
Snoman these are things YOU wrote.
Don't like what YOU wrote?
Then YOU should stop posting.
Should we point out to it that its signature field is grammatically
flawed or should we keep laughing at it? I mean it kinda highlights the
incompetents of the troll nicely. Then again if we do point it out, it
will never be corrected... http://tinyurl.com/2okyfx
Take the batteries in and have them checked first. I suspect that one
of the batteries is not in the best condition. When you disconnect the
batteries check the resistance between the leads. There should be very
high resistance. If the needle moves very much then you have an short
somewhere. Disconnect a fuse at a time and find out which one is
shorted out. Then find the direct culprit.
I don't know. I did find out recently that if I bring them up with an
external battery charger, they will stay up.
I'll do the resistance check you suggest. I'm also going to pull the
alternator and have it tested to see what happens. It seems weird that it
drops down to 12.8 volts with nothing happening and even less when loaded.
Revving the engine up doesn't help, and I don't really know exactly where
2,000 RPM is. I'm also not sure how you'd hook a tachometer up to a Diesel
engine. The ones I have are electronic and actually hook up to an ignition
coil on a gasoline engine.
The alternator's behavior strikes me as weird. I have a number of other GM
vehicles and not a one of them ever drops much below 13.5 volts output, even
when fully loaded.
I don't have a carbon pile, so I can't make any of the tests you suggested.
Nothing weird about it, that's what dead alternators do.
2000 RPM can be guesstimated.
There are a number of ways to measure RPM, a photo tachometer,
thru the alternator or by connecting a magnetic tach pick up in
the holder above the harmonic balancer.
Nothing weird about it, 12.8 volts and dropping is a dead
alternator. And when I say dead alternator, that doesn't
automatically mean the component itself is bad, you still need to
verify the associated circuits to it.
Have you tried full fielding it?
Have you checked for battery voltage at the output stud on the
back of the alternator and at the red wire in the plastic 2 wire
Is their voltage at the brown wire with the key on?
On Jan 25, 10:52�pm, "William R. Walsh" . It seems weird that it
..........you omitted that from your original post!
Yank the Altenator and carry it in to have it checked.
Carry yer credit card with you.
Like Cuda said....symptoms of a bad altenator.
~takes a toke.......goes back up to exhale in Dobony's face~
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.