alternator problem?

We have a 94 ford explorer. The ammeter says it's charging
when we drive on the highway. But when we drive in stop and
go traffic the needle goes down. Eventually the battery goes
dead if we keep driving in the city.

Would appreciate any help with this.

THanks.

On 11 Apr 2005 08:50:13 GMT, *selah* > wrote:

>We have a 94 ford explorer. The ammeter says it's charging
>when we drive on the highway. But when we drive in stop and
>go traffic the needle goes down. Eventually the battery goes
>dead if we keep driving in the city.
>
>Would appreciate any help with this.
>
>THanks.

Have the alternator checked; it sounds likek the rectifier bridge (the
diodes) is not working right.

--
Bill Funk
Change "g" to "a"

Thanks.

I've noticed that the ammeter goes down each time the rpm goes below
around 650 and then goes up again when the rpm is above 700. Is there
a way to set the idle speed - or should it not make a difference?



In article >, Big Bill wrote:
> On 11 Apr 2005 08:50:13 GMT, *selah* > wrote:
>
>>We have a 94 ford explorer. The ammeter says it's charging
>>when we drive on the highway. But when we drive in stop and
>>go traffic the needle goes down. Eventually the battery goes
>>dead if we keep driving in the city.
>>
>>Would appreciate any help with this.
>>
>>THanks.
>
> Have the alternator checked; it sounds likek the rectifier bridge (the
> diodes) is not working right.
>

On 15 Apr 2005 08:35:52 GMT, *selah* > wrote:

>Thanks.
>
>I've noticed that the ammeter goes down each time the rpm goes below
>around 650 and then goes up again when the rpm is above 700. Is there
>a way to set the idle speed - or should it not make a difference?

Going from memory, 650 isn't very low for idle.
I'm not sure how to set the idle speed, either. Maybe Jim will help.
Have you had the alternator checked?
>
>
>
>In article >, Big Bill wrote:
>> On 11 Apr 2005 08:50:13 GMT, *selah* > wrote:
>>
>>>We have a 94 ford explorer. The ammeter says it's charging
>>>when we drive on the highway. But when we drive in stop and
>>>go traffic the needle goes down. Eventually the battery goes
>>>dead if we keep driving in the city.
>>>
>>>Would appreciate any help with this.
>>>
>>>THanks.
>>
>> Have the alternator checked; it sounds likek the rectifier bridge (the
>> diodes) is not working right.
>>

--
Bill Funk
Change "g" to "a"

"Big Bill" wrote:
> On 15 Apr 2005 08:35:52 GMT, *selah* >
> wrote:
>
> >Thanks.
> >
> >I've noticed that the ammeter goes down each time the rpm
> goes below
> >around 650 and then goes up again when the rpm is above 700.
> Is there
> >a way to set the idle speed - or should it not make a
> difference?
>
> Going from memory, 650 isn't very low for idle.
> I'm not sure how to set the idle speed, either. Maybe Jim will
> help.
> Have you had the alternator checked?
> >
> >
> >
> >In article > , Big Bill wrote:
>  >> On 11 Apr 2005 08:50:13 GMT, *selah*
> > wrote:
>  >>
>   >>>We have a 94 ford explorer. The ammeter says
> it's charging
>   >>>when we drive on the highway. But when we drive
> in stop and
>   >>>go traffic the needle goes down. Eventually the
> battery goes
>   >>>dead if we keep driving in the city.
>   >>>
>   >>>Would appreciate any help with this.
>   >>>
>   >>>THanks.
>  >>
>  >> Have the alternator checked; it sounds likek the
> rectifier bridge (the
>  >> diodes) is not working right.
>  >>
>
> --
> Bill Funk
> Change "g" to "a"

You don’t say by how much the ammeter reading goes down. But this
sounds normal to me. Every alternator made gives less output at lower
speeds. Every alternator made has a steep curve in the engine idle
speed range. So an alternator rated at 120A for example, only gives
120A at high speed, around 6000 alternator RPM (maybe 2000 engine
RPM). This same alternator might give a max of 50A at 1600 Alt RPM
and 70A at 1800RPM. The engine idle speed probably falls between
these two values. The lower alternator output at lower speeds is
completely normal, and not a quality problem. It is part of the
physics of any alternator.

So if you say 1) the alternator was checked and is OK, and 2) highway
speeds are no problem, but city driving is a problem, then I suspect
the most likely case is that you have added some aftermarket
electrical components which are drawing too much current at low speed,
and draining the battery. (Average engine speed in City driving is
much lower, more idling)

Did you add anything, like a subwoofer, new electric radiator fan,
refrigerator, etc ?

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