Battery not recharging, update, details, QUESTIONS!

PorscheDV · 09-27-2001, 11:34 PM

again, thanks everyone, all the advise has been great help so far, ive already searched for topics relating to this but can't seem to find my particular situation (im not just being lazy!)

first some details/update...
what i know is my battery is good (had it tested at pep boys) its not being charged or at least holding it...ive jumped and push-started the car, driven for an hour and a half, stopped, and immediately restarted...nothing...not even turning over

ive charged the battery, AND jumped it(seperated occasions) (allowing the car doing the jumping to recharge my p-car's batt) and the battery holds THAT power! (=batterys good)

Now, i borrowed my brothers $500 digital industry super delux voltmeter...this is what i got...the battery (after i charged it) was putting out 12.7 (normal), i started the car and got 14.4 (normal right?) revved to 3,000 RPM...steady at 14.4, with lights on and a few other accesories i got 13.7...it stayed within 13.3-5 or so and 14.4 no matter what i threw at her... (=alternators good, right?!)

?!?!? so doesnt this mean my alternators putting out what its supposed to?!

now get this?! with the car running, i pull the positive lead...(a bad alternator will cut immediately, a good one will allow the car to run) what's it do? stumbbles, hesitates, recovers, hesitates...dies! man! if thats not right down the middle?!

does that give any insight to anyone on what the next thing to check is? otherwise, my only other option is to check each ciruit right?! im hoping these details narrow it down towards a certain direction...

Thanks everyone for all the help!

Zendalar · 09-27-2001, 11:52 PM

Er..I remember reading somewhere that removing the positive lead from the battery while engine is running can cause a failure in alternator/regulator

//Zen

rstoll · 09-28-2001, 03:41 AM

Go get you a new battery.

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Robert Stoll
83 SC
83 944

Joeaksa · 09-28-2001, 04:15 AM

You are making progress.

Next step is to hook the VOM up inside the car. Find a hot lead and clip the red wire to it, and ground the black lead to the frame of the car. This way you can see what your voltage is while you are driving and if it changes after a bit of driving.

If the voltage stays the same all the time while you are driving, fine. If the voltage changes (usually lower but can be higher) while you are driving, then something is breaking down, usually due to heat.

If the voltage changes after the alternator/regulator/diodes get warm, then you know that the charging system is breaking down and needs attention. Usually a diode or winding in the alternator breaks down with heat and the voltage drops down after a while. It could also be a wire or lead that is loose and moving as you drive...

If the voltage does not change while you are driving, then it should be simple. You would have either a bad battery (re Rstoll's suggestion) or a short in the car that is draining the battery when you are not driving. Even if the battery is good now, a short that would drain it this fast will kill the battery anyway. Batteries like to stay topped up and taking any battery all the way down then back up is not good.

Try these checks and get back to us. As mentioned above, its not a good idea to pull the battery lead while the motor is running and can result in damage to the alternator/regulator/diodes.

JoeA

john70t · 09-28-2001, 05:45 AM

It probably doesn't apply in your case since your taking reading right off the battery, but you can get voltage potential with little current flow, like a thick wire that's shredded down to one strand.
It'll show 14 volts but it will flow 1 amp, not 100.
Mabye you can double check all your electrical connections (ground, alt...) they can corrode internally and get loose.
You can do a voltage drop test too-put the voltmeter on each side of a wire. The meter should show .1 volts or lower. Anything higher and voltage is being dropped (used)across that connection.

Rot 911 · 09-28-2001, 05:49 AM

Here's what I think the problem could be, not necessarily in any particular order:

Bad connection to the starter.
Bad ground strap at transmission or battery
Bad starter
Bad battery

Actually from what you describe it sounds like your alternator and battery are just fine. It sounds like more of a problem getting juice to the starter than a charging problem.

Kurt V
72 911E

Early_S_Man · 09-28-2001, 06:23 AM

Just one bit of info to add to the pile ...

It is perfectly normal for alternator output Voltage, and hence, system Voltage, to be higher when first started up with a cold engine ... typically 14.2 - 14.5 Volts. After the engine is fully warmed up and alternator is warm, too, system Voltage falls to 13.5 - 13.8 Volts. The reason is directly due to higher Voltage drops accross the silicon rectifier diodes at higher temperatures ... and there is really nothing that can be done by the Voltage regulator to compensate for those higher 'losses' inside the alternator. It is quite normal, and happens in any electrical system ... whether made in Detroit, Nagasaki, or Stuttgart!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

john walker's workshop · 09-28-2001, 07:49 AM

you don't say what year the car is, but any time you disconnect the battery from the system, the electric fuel pumps die and the ignition shuts off. DUH! you can pop diodes in the alt too. so what's the voltage in the battery when it won't start? did you load test it? 150A for 15 seconds. what does it draw down to after the test? 10.5V is the lowest it should go, if the battery was charged well before the test (gravity readings in the middle of the good range)

[This message has been edited by john walker's workshop (edited 09-28-2001).]

Harold_89_911 · 09-28-2001, 09:08 AM

I would like to add something similar to the other posts. Check also the connections to your battery. When the connections are slightly corroded, you would get similar symptoms. You do all the measurements and all looks fine when the car is running. Then you try to start it and the big amperage draw makes the voltage drop over the corroded connection and it behaves like your battery is empty. It is very easy to verify this condition. Measure the voltage of the battery at the battery poles while somebody else is trying to start the car and do the same by measuring at the connectors of the battery. If the voltage doesn't really drop the first measurement but does with the second, you have a corroded connection. Also, I would agree with the others that I would not disconnect my battery with the engine running. Maybe OK very long time ago but the electronic circuits in cars have been getting too sophisticated (and expensive) for this kind of abuse.

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Harold
89 911 Targa
89&91 Saab 900

PorscheDV · 09-28-2001, 09:43 AM

woa! you guys are awesome! thanks for the advise AGAIN!!

yeah, i knew about the potential probs with pulling the lead, but i had a few friends there that are kinda gear heads (ok, one of them is into bugs..dont flame!) and that was all their 'tried and true' methods...and i WAS DEPSERATE! ok, i'll get new friends...

ill try driving with the meter hooked up next (warm), then check for voltage drops and corroded connections..from there i'll check the connections you guys have suggested and update..i have to work now and wont be back till sat or sunday, so it'll be a few days...

oh and the cars' actually a 76 912E..(do i belong?!) i'm asking here because of the increased traffic...thanks again guys, i really appreciate this, i'll keep you posted!

PorscheDV · 09-28-2001, 12:31 PM

ok, another little update...

i tested what the car was drawing from the battery when the car was off (to see if i had a short) i put a voltmeter between the pos. lead and pos. post on the battery (as per stephans suggestion) i was pulling 10.8 with no radio or alarm..just clock (i think) normal? i pulled all fuses in the trunk one at a time (but replacing them before going onto the next fuse) and i never got a drop (i stopped at only those fuses because i had no way of knowing what i was pulling, should i have kept going?) (dont have a key telling me what fuse is what)

now i got the car started and drove it around for about 20 minutes on a hot day (from your suggestions) at idle i then got 14.2...(down from 14.4 on cold start) now with the lights on (each time the batterys gone dead so far has been after night driving) i got 13.2...(down from 13.7 cold)is that too low? is it possible my alternator cant handle recharge only when the lights on? or is my lights just pulling too much? or normal?

also, if it was a short, it would go dead from sitting, say, overnight...mine goes dead immediately after ive driven an hour or so at night (thus far at night, possibly by coinicidence)

also, im thinking about replacing the diode...where is that? how can i find/pull it?

thanks again!

911pcars · 09-28-2001, 02:42 PM

You mentioned testing alt. output during the day yet you're having battery problems at night. How about testing the alt. output at night? You might find that your headlights/accessories may be overloading the alternator and/or your alternator isn't putting out enough current to support what you have. An alt. output of 13.2 volts is on the borderline as general charging specs are around 14.4-14.6 V or so. Just to make sure you have the correct voltage-reading connections, the red VM lead is on the + battery post and the black VM lead is on the - post (or known good ground).

Try switching on ALL electrical accessories (high beams, radio, fan, AC compressor, rear window defroster, etc.) and see if the alternator can keep up. I suspect it won't and you'll have to look at the alternator as your main culprit.

Placing a voltmeter in series, between the pos. post and the pos. cable measures the voltage drop of the entire elec. system (how much source voltage is used up in a circuit) and not current draw. Total voltage drop should be the same as the source voltage. In this case, I don't think you need this information. If alternator output is to specs, you want to find out if excessive current draw is draining the battery. This is called "parasitic load"; current is leaking out of a circuit and draining the battery but short of drawing enough current to blow a fuse or overheat a wire harness.

To measure parasitic load, switch your DM over to measure current (amperage) and connect the meter in series with the neg. post and neg. cable (a little safer connection than the + side, but measures the same current draw). Typically, you should not draw more than 30 mA with a system at rest save for the intermittent clock, security system and radio preset memory. Pull the fuses and/or disconnect major harness connectors and see if you can isolate the circuit at fault.

A good automotive electrical shop should be able to verify whether it's a faulty charging system or a parasitic load.

Sherwood Lee
http://members.rennlist.org/911pcars

Roland Kunz · 09-29-2001, 04:28 AM

hello

now get this?! with the car running, i pull the positive lead...(a bad alternator will cut immediately, a good one will allow the car to run) what's it do? stumbbles, hesitates, recovers, hesitates...dies! man! if thats not right down the middle?!

I´m sorry this testmethode proves nothing except your luck. The alternators will survive a short time runing without battery.

As you have a expensive Voltmeter you surly can messure the actuall drawn currency via a vice reader or hooking it inline ( normaly fused to 10 amps ).

Then messure how much amperage is drawn while the ignition is off and remove fuses to find the user. Sometimes your alternator has a shoot diode ( by runing without battery ) and will drain the battery.

You also can see it if your alternator control light is slightly dimming with ignition off.

Grüsse,
Roland

Joeaksa · 10-03-2001, 06:03 PM

PDV,

What happened? Did you find your problem?

Pls let us know for the next time it happens!

Thx,

JoeA

davis911s · davis911s's Garage

I don't know why I didn't post this earlier. I think it is the battery, I had the same type thing before. The battery had the Volts but not the amps required. A good shop can test that easy for free. But if not, Try replacing it with a battery that you know is good, drive around with it and see what happens, if the same happens you know it's not that, then move on.

Shawn

PorscheDV · 10-03-2001, 09:27 PM

hey joe! thanks for asking...

well, i havent fixed the problem yet...my battery holds a charge fine (no short) it seems to be recharging...keeps a consistant 12.6-7...

i know better than to pull the pos. lead now...(stupid VW friends!)

new clues made me pretty much believe it was my starter...so i bought a new rebuilt one, but at $180 i wanted to be sure before i installed it (once installed at all, you cant return)

so...i find the wire on my starter that comes from the starter switch...(that way, when i duplicate the problem, i check to see if this wire gets hot at start up..if it does, i know my starter isnt turning over, if it doesnt, the problems elsewhere.)

drive the car around to duplicate the problem (oh, also, ive tried simulating night driving, alt. seems to be fine, it was coincidence my problems happened at night, oh yeah, i also had the problems come during the day!) get this...no matter how far i drive, or how long, the car starts right up! (i stop the car practically every 10 minutes after full operating temp...) GEEZ!! figures!

so after a couple of hours, i call it a day, and plan to try again tomorrow...i have all afternoon to duplicate the problem (bet you it wont happen! till i decide its ok, and manage to drive an hour away, then it wont star!)

anyway, as soon as something comes up, you guys will be the first to know!

911pcars · 10-03-2001, 10:35 PM

I'd suggest keepng an eye on your battery. A fully charged battery should be around 13.2 Volts (2.2 volts x 6 cells). Ask your electric shop to load test it and see how it does. With a borderline battery, any parasitic load on the battery when the car's sitting for awhile will discharge it to a point where it won't crank the engine.

Keep us informed. Mystery electron stories and their ultimate solutions are something we can all learn from.

Sherwood Lee

Joeaksa · 10-04-2001, 05:31 AM

PDV,

Agree with Sherwood that the battery is looking more and more suspect, especially if the alternator is consistently putting out good jolts. Do you have anyone you can switch batteries with and see if the problem stops or follows the battery?

Stay in touch so everyone knows the next time!

Joe

adrian jaye · 10-04-2001, 06:34 AM

Quote:

Originally posted by PorscheDV:
Now, i borrowed my brothers $500 digital industry super delux voltmeter...this is what i got...?!?!? so doesnt this mean my alternators putting out what its supposed to?!

Not a good test a meter will only pick up the surface voltage, you need to load test it with a proper load tester.

A meter is good as a guide for voltage drop.

with the car running, i pull the positive lead...

Oppps, "bad idea", you should never ever do that, you've probably knackered your alternator and/or voltage regulator.

does sound like the battery is "not" holding a charge, simplest thing to replace.

Mind you if you've now blown the alernator and assoc. electrics. You might not be able to tell