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battery keeps dying while driving.


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on my 78 Lincoln mark V. car would not start, so i got a new battery. drove for about an hour. and then it died while i was driving and would not start back up. charged it then it started and died agan. I assumed it was the alternator. so i got it bench tested and they said it was fine. so what is preventing the alternator from charging the battery? voltage regulator? or something else?

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Voltage regulator would be something to check. Also be sure to check ALL connections to those items.

If that checks out then make sure your belts have the proper tension. I assume the bench testing of the alternator was done using the pulley off the car, but it it's not properly attached that could limit your current generation as well. Finally check the continuity of the cables/wires involved.

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I've never heard of a car stop running because of a bad battery. I've even removed batteries from cars while they were running to swap batteries. None ever died unless they had a generator instead of an alternator. There must be something else going on in addition to the charging problem.

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If that checks out then make sure your belts have the proper tension. I assume the bench testing of the alternator was done using the pulley off the car, but it it's not properly attached that could limit your current generation as well. Finally check the continuity of the cables/wires involved.

i took the alternator out. and brought it to o'reilly auto for the bench test

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Could be the coil heating up and crapping out. Then it will cool off and run again.....for a few miles and crap out again. I speak from experience on this one.

I wonder how long it took you to figure it out. I had that problem on a car once. At one point I decided to have the pros figure it out for me and took it to the dealer. They did not figure it out either. Eventually, about 6 months on, after one of the bouts of poking at things under hood by the side of the road I noticed wax on my fingers. Started looking really closely at places and things that might have wax in them and spotted a crack on the tower of the coil.

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I wonder how long it took you to figure it out. I had that problem on a car once. At one point I decided to have the pros figure it out for me and took it to the dealer. They did not figure it out either. Eventually, about 6 months on, after one of the bouts of poking at things under hood by the side of the road I noticed wax on my fingers. Started looking really closely at places and things that might have wax in them and spotted a crack on the tower of the coil.

what coil are you referring to?

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Just about any battery place will check your charging system while you wait. I know that a lot of the auto parts stores do thia all the time. This way, you'll find out whats going on. The regulator regulates the amount of voltage being charged back to the battery, so if the regulator is bad, your battery might not be geting any charging voltage. Also like others have said, could be a problem with your wiring.

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Just about any battery place will check your charging system while you wait. I know that a lot of the auto parts stores do thia all the time. This way, you'll find out whats going on..

As Jim said, have them check the voltage at the battery before and after starting the engine, which will show you the charging system output, if any. Or, if you can not make it to the shop, borrow a friend's device and check it out yourself.

Forgot to mention, borrowing repair advice is the best reason to join an AACA Region or Chapter. (Promotional post:D)

Wayne

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To late for this little test now but a quick way to test an alternator if you have problems on the road is with a screw driver. In the center of the rear of the alternator there is a bearing or bushing, if the alternator is charging it creates a magnet in this bearing. With the motor running, stick the end of the screw driver up to the bearing, if it's charging it will suck the screw driver to it. If you don't feel anything it's not charging.

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Is the light on the dash working? I once had a car that wouldn't charge and the "Alt" light on the dash was burned out. Replaced the bulb and that fixed the problem. Needs that small discharge to start the alternator field.

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Check to make sure there is voltage at the battery end of the wire from the regulator.

Worn brushes can cause a lack of current so the alt. can not keep up with the total battery drain.

A Motor or Chilton manual will have in car tests you can do, (1978 had two different regulators)

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Take it to a good auto electric rebuilder. I stopped trying to fix my own alternators years ago. Also, I stopped buying parts store alternators because they are junk.

Last one I dealt with was a 2000 Ford Windstar. The battery kept going dead but the alt light never came on. I changed the computer, battery, belt, finally took it to the shop and they diagnosed a faulty rotor that worked ok at idle but put out barely any charge when revved up.

My local shop charges less to rebuild an alternator or starter than they cost at the local parts store, and the quality is far better.

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Like R.W. Burgess said, have you checked the battery voltage with the engine running using a volt meter (VOM or a DVOM)? If it is 12 volts or less car not charging. Check the voltage from the housing of the alternator to the positive alternator terminal as one check, and then check the voltage at the + & - of the battery. If you have about less than 13.5-14 volts you have a bad alternator, if you have that voltages it would indicate the car is charging so you have other problems.

As for the car turning off, that is very possible. If the battery voltage on most 12 volt cars drops below about 9.6 volts, the electronics of the car starts to shut off. Not quite as critical for cars prior to electronic ignition, but is true since.

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I've never heard of a car stop running because of a bad battery. I've even removed batteries from cars while they were running to swap batteries. None ever died unless they had a generator instead of an alternator. There must be something else going on in addition to the charging problem.

I am confused by this statement. It seems to me, that the electrical system doesn't care what produces the current as long as the current is there. Maybe at a low idle speed a generator will not put out enough power to run the engine.

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I had a bad ground cable once that did strange things and drove me nuts until I figured it out. I checked and cleaned the battery terminals a dozen times and it looked good. Turned out the cable corroded between the wire and the ground lug on the bolted end. Rare, but it can happen and you can't see the problem if the end is well covered.

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I am confused by this statement. It seems to me, that the electrical system doesn't care what produces the current as long as the current is there. Maybe at a low idle speed a generator will not put out enough power to run the engine.

Got your answer in your question.

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No, on some cars with generators, the battery is necessary to complete the electrical circuit. If the battery is removed, the circuit is opened and the engine will stop running.

A car at low idle will still run but the generator warning light will flash.

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I just dealt with this yesterday on the Benz. My alternator light came on but, contrary to what you might expect, the light would dim at idle but stay bright under load. That told me the belt was likely loose as the lower RPM of the alternator spinning allowed it to grip the belt, but once speed built up it lost friction and would not charge. I tightened the belt, but also noticed that my positive battery terminal had slight surface oxidation, which can also interfere with charging cycles, so cleaned that with a wire post brush. I also found a wire with it's sheath splitting so I fixed that with heat shrink. After these fixes my battery was again receiving proper charge.

This is my check list:

* Check V-belt for proper tension.

* Test battery at rest with multimeter, DCV using 20v+ setting.

* Test battery after starting and running.

* Check and clean battery terminals.

* Check connectors at back of alternator, clean and apply dielectric grease.

* Check an clean ground cables (any and all you can find).

If none of these make a difference you can check the brushes on your voltage regulator if it's the removable, internal kind, just pop it out from the back by swinging it out after removing the two screws, but if it's built in to the alternator or a separate unit you may have to have it tested by pros. You can buy the voltage regulator by itself, buy a rebuilt alternator or buy a new alternator.

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  • 2 weeks later...

One thing no one mentioned. The wire that goes between the alternator and the Solenoid, The biggest one. I have found them to have bad spots internally. If the vehicle has had an alternator that has failed in the past and shorted in the failure, it can cause "hot spots" in the wiring. This will reduce the ability for the electric to flow. Also, over time, the wire can corrode and turn green inside. To find the bad spots you can tug on the wire. If you feel it springing, you have a bad spot. It will pull apart fairly easily. Dandy Dave!

Edited by Dandy Dave (see edit history)
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Basic tools for any owner of any older car: a VOM or DVOM. And NOT the one the guy behind the counter at your local AutoZone, AdvanceAuto, or other cheapo 'rebuilt' parts retailer.

Take a VOM, check the voltages as suggested by Larry Schramm.

When and if the car quits, immediately open the hood and check the battery voltage, then check the voltage at the fuse box, etc etc..

Touch the ignition coil,, is it HOT or just warm?

I can't count the number of times a 'customer' tried to do their own 'repairs' after a telephone call to check on our price for a new alternator.

A few days later, the car shows up, 'nice' shiny new alternator, and it still won't charge..

Sometimes it's a fuse in the fuse block under the dash.

Often it's a bad wire, hidden corrosion.

And often the 'new' shiny, 'rebuilt' alternator is faulty..

OR my favorite is the alternator that is putting out AC current.. I ask, did you hook up the battery terminals backwards?

Answer: only for a split second.

I ask: are your reactions faster than the speed of light?

Answer: no, of course not.

I say, well electricity travels at speeds way, way faster than anyones reflexes.. so even a split second of wrong voltage blows the diodes.

Anyway.. buy a few tools, and do some diagnosis before throwing a handfull of new 'rebuilds' at your car.. you never find out what part was

causing the problem, and you don't learn anything about your cars.

GLong

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Yup, Nothing like having a Multi Meter and Load tester, and knowing how to use them, to sort out an electrical problem quickly. Dandy Dave!

I have heard the term 'load test' in reference to a starter motor. What kind of meter would do this?

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BTW pulling a battery with an engine running is a really, really, REALLY bad idea. I have seen surges over 200v from a 10SI and anything electronic that is turned on (and that includes some tube radios) may let its smoke out.

Also checking for a hot spot is always a good indicator whether a component or a connection. A $29 IR temp gun is an excellent investment & prevents burned fingers. I have also used to identify a misfire (the exhaust head pipe will be cooler on the cyl that is not firing) and tell if an ac is operating properly. Many uses.

BTW most 12v cars use a 6v coil and a ballast resistor when running. That way the ignition will be hot even if a cold crank pulls the battery voltage way down so is wired direct for cranking and through the resistor when running. Wiring with the coil direct is like winding a stock XKE to 7,000 rpm. It will do it once.

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Dave, is that tester made exclusively to test the voltage drawn off the battery when the starter is engaged ? I have a Fluke multi-meter model 86, that may perform that function. If not $39 is a good investment.

My multi-meter is a lot more tool than I am electrical technician.

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Your multimeter will not do a load test. The load tester has a heavy piece of Nichrome wire inside. These type of testers have a switch that you hit to do a load test on a battery. It is like giving the battery a shock like the draw of the starter will. If it stays up in the green range the battery should be good. If it drops below in a few seconds, either the battery needs a charge, or the plates are Sulfated and the battery is junk. You can also test the starter load by having someone try to start the car while you have the meter hooked up. Even your multi meter will do this test. If it Drops below 10 Volts on a 12 volt system, and your battery is good, the starter may be on its way out. Dandy Dave!

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If you hit the starter and have a drop of 5 volts or less, you need to look at the cables and also at rebuilding the starter. Windings that have been heated to the point that the insulation is gone will be a dead short and kill even a good battery quickly. You will be surprised at how a good starter, cables, and clean grounding surfaces will make a difference in how fast the starter will spin. Dandy Dave!

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