heavy voltage drop???
Thread Starter
TECH Veteran
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Joined: Feb 2002
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From: Phoenix, AZ USA
heavy voltage drop??? For some reason I'm getting a really big voltage drop when the fans kick on. The drop is so large that the engine actually looses power/misses for a moment till the voltage kicks back up.
My dad said that sounded like either the alternator was old or was just not big enough. How would I test if its good and is there anything larger that I can bolt up without too much modding to the car?
My dad said that sounded like either the alternator was old or was just not big enough. How would I test if its good and is there anything larger that I can bolt up without too much modding to the car?
Re: heavy voltage drop??? First thing I would check is the output (amperage) of the alternator, particulairly at idle hot.
If it is ok then check the draw of the fans & a/c clutch.
I'd bet on a weak alternator.
If it is ok then check the draw of the fans & a/c clutch.
I'd bet on a weak alternator.
Re: heavy voltage drop??? Need to know "voltage relative to what". Chassis?
Block? Should be the same, but a lost, loose,
busted or crusted ground braid can make fan current
take the long way around.
Electric motor starting current can be high, and
alternator slow to react. The surge has to be taken
up by the battery. Crusty terminals or a dying batt
can give you a transient voltage sag when load is
applied abruptly. With an old-style VOM you might be
able to see the voltage dip, and if you looked at
battery posts, and at various power/ground points
you might be able to dope out where the big drop
starts (battery posts, at least, should have no
deflection).
Block? Should be the same, but a lost, loose,
busted or crusted ground braid can make fan current
take the long way around.
Electric motor starting current can be high, and
alternator slow to react. The surge has to be taken
up by the battery. Crusty terminals or a dying batt
can give you a transient voltage sag when load is
applied abruptly. With an old-style VOM you might be
able to see the voltage dip, and if you looked at
battery posts, and at various power/ground points
you might be able to dope out where the big drop
starts (battery posts, at least, should have no
deflection).
Thread Starter
TECH Veteran
iTrader: (6)
Joined: Feb 2002
Posts: 4,766
Likes: 0
From: Phoenix, AZ USA
Re: heavy voltage drop??? thanks guys......I'll take a look at all of that this weekend....
when you say "check the output of the alternator", I'm looking for any voltage drop when the fans hit right?
when you say "check the output of the alternator", I'm looking for any voltage drop when the fans hit right?
Re: heavy voltage drop??? A voltage drop is normal..., when more amperage is demanded of the alternator the voltage will fall.
This is normal, but if the alternator is weak or is always charging a weak battery it will drop off voltage even worse.
The output amperage of the alt. is what needs to be checked,along with the battery.
This is normal, but if the alternator is weak or is always charging a weak battery it will drop off voltage even worse.
The output amperage of the alt. is what needs to be checked,along with the battery.
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Re: heavy voltage drop??? The only way to do this properly is to have a carbon pile load device with a inductive amp pick -up, or a battery/ alt system tester.
Maybe you know an auto shop you can have test these item's for you?
You have to have this type of equipment to check
the full output of alternator & see if it's OK.
It's just to expensive to buy one for personal use.
Maybe you know an auto shop you can have test these item's for you?
You have to have this type of equipment to check
the full output of alternator & see if it's OK.
It's just to expensive to buy one for personal use.
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