Battery Draining

Is it draining while you're running the car, or when it's parked up?

Only happens when its parked up. Hve checked the alternator etc and all seems fine there it is charging ok with 13+ volts when engine is in idle but if left parked up for 12hrs + it struggles to start

Can you hook an ammeter in the hot lead from the battery? If so, you should be able to pull fuses to locate the drain. May get enough indication by just monitoring battery volts while pulling fuses.

If it's not going through a fuse, start disconnecting stuff. Do you have/can you get hold of a wiring diagram?

[Edit: don't try to start it with an ammeter in circuit!!!]

ya will try the ammeter over the weekend thanks

Depending on the vintage of the car you may have a number of parasitic loads that are always on. Engine computer, radio memory and dial lights, not to mention any accesories you have added. Dumb things like electric locks and wiindows can stick and draw current. So when you find a fuse circuit that does draw current double check to see if maybe it is supposed to draw some current even with car turned off.

Despite the above comments, odds are still, its a diode in the alternator. Statistically this is the most ffrequent cause of leaking battery problem.

Hello John Mull

If the above fail, alternator troubles would be likely.

Sometimes the alternator has a faulty diode or diodes which do not switch "off" correctly.

The best way is a bit involved:

1. Disconnect the battery.
2. Dismantle the alternator.
3. Remove the diode plate.
4. Using a transformer with a secondary voltage of around 15 Volts at 10 Amps, run a set of car lamps (bulbs) around 150 Watts total, in series with each diode in turn, and an oscilloscope across the diode you are testing.
5. The diode as it is being tested will halfwave rectify the AC from the transformer, the lamp current will warm then heat the diode, and there should be sharp switch-off each half cycle of that AC as shown by the Oscilloscope waveform trace.

Poor diode switching is easily seen, as a shaky and variable trace, with no sharp switching trace curve on the Oscilloscope.

This above method I thought of myself, some 40 years ago, when Automotive Electrical workshops were unable to locate a similar problem to yours.

Most alternator makers use 50 volts PIV Diodes, (they save some 60 cents per alternator by so doing), and a small jump start, or voltage surge can easily damage a diode.

I found the best idea was to replace all diodes myself, soldering them in - remember half are reverse polarity to the case/heatsink, ensure correct installation please, and 800 PIV diodes were only a few cents dearer, then I never had any further bother.

Trust that assists you.

Kind Regards....

I replaced the battery, suspecting it had gone "South". I put the old battery on the charger in the shop and rode around with the new battery until today. When I went to start the car "Click" and nothing else.

After recharging, I put a steady 50 amp load across the old battery while measuring voltage drop. Never went below 10.VDC. That battery was fine so the problem is elsewhere.

I've a charger on the car now at a low 2amp setting overnight. Tomorrow I'll put a digital ammeter in series with one of the battery terminals and see if there is a draw from some consumer.

Once apon a time, when these blasted machines were simpler, you could disconnect the cable from the battery in the dark and if you saw a small arc, you knew something was eating electrons without a permit.

Not any more! Now you must have a post graduate degree in electrical engineering just so you can change spark plugs. . . . . assumng you can find them!

L.J.

usually is the under hood light, globe compartment light or a charger

Do you have Air Ride Schocks the air pimp will run the battery down also the electric door locks if you have a key pad.

My bother changed the computer in his after months of trying to find the problem. Dealer could not find problem either.

Dear Sir/Madam: Have you checked your Alternator Output Voltage? Some alternators have 3ph with 6 diodes to rectify back to the 12vdc. If the one or two of these diodes go shorted (conduct in both dirrections) you will get (a) Higher partially rectified out put voltage. (b) This will boil the battery water down quickly. The simple test, with engine running slide your hand slowly down the side of the battery, if it is much warmer than ussual, or if it is warmer near the bottom than near the top, the Battery is already sulphated at the base( the platelets on the battery plates have settled to the bottom and are shunting out a percentage of the plates.) Either one of these possabilities will cause the battery to drain through the failed diodes in the Alternator while shut down. When a Battery goes low on water quickly, always test the Alternator. Your Old Retired Troubleshooter. Carl.

Most of the newer cars have one or more sets of relays in them. You might want to mark them and then pull them out and see if the load on the battery goes down. It is not uncommon for one of the them to stick. These relays may not always be fused. As mentioned above the alternator may also be bad. With the engine off disconnect the large red wire off of the alternator. DO NOT LET THIS WIRE OR THE WRENCH TOUCH GROUND OR YOU WILL GET A BIG SPARK. If there is any kind of spark when touching the red wire at the alternator terminal the alternator is bad.

I've had similar things happen due to faulty: trunk (boot) lamp, under-hood (bonnet) lamp, cigarette lighter, glove box lamp, passenger-side courtesy lamp (hard to notice when only the driver is present), none of which were apparent to a check as was described by others here, so I presume they were not fused accessories (much to my surprise).

Check you are charging your battery. 13+ volts is not accurate enough. With a digital meter you should see 14 or 14.2 volts at the battery with the engine running and after a fair run (sy 1/2 hour) without headlights. you may need to get someone to rev the engine to about 1200Rpm to get this figure. If you cannot get that then you have either have a faulty alternator, probably the diodes which you can buy as entire plates, i.e sets of 3, or a high resistance in the charge circuit. this is most easily checked by measuring the alternator output and the battery voltage (engine running). if they are more than 200mV different then you probably have a corroded connection or something similar.

best of luck

Chas

Here is another thing you may try for clues. After the car engine is cooled off and the battery is still charged. open the hood and feel of everything you can get your hands on. If any thing is warm under the hood and everything else is cool than something is not turning off. What ever it is that is warm is bad or the control circuit to it is bad. You can do the same thing under the dash.

I did like you said. The radiator and exhaust manifolds were hot. Does that mean that there is a short in my radiator and exhaust manifolds? Come on you knew that some AH was going to say it.

Hello bob c

I hope you didn't burn yourself.

Kind Regards....

Hello Whyme,

I tried to feel under dash but it is closed off by a housing cover. Access is through the front after remove the dash panels.

John there's general agreement that if the battery is capable of holding a charge, then it's for certain that the problem falls into a very limited range of possibilities:

1. a modest consumer (as opposed to main headlights or starter) is draining the battery when still.

2. There are no drains on the battery beyond normal demands but it simply is not being replenished by the alternator after starting the car.

My experience in these matters is pretty extensive but not recent as I long ago abandoned working on cars when I left the auto industry.

However, the fundamentals have not changed much.

"Back in the old days" we viewed the charging system as a 3 legged stool. If any one leg failed, the system failed. The battery, the generator and the voltage regulator functioned as a team or not at all.

The generator has been replaced by much more efficient alternator and the mechanical relays of the voltage regulator have been replaced by solid state circuit boards buried within the bowels of the alternator. So what was once a trio is now a pair.

You have to establish if the alternator is putting out current. An inductive ammeter is by the simplest way of testing this as it can detect current flow without having to disconnect the battery cables. As a rule inductive ammeters are not as precise as those wired in series but we are not looking for precision here but a simple yes or no answer. Does the alternator work?

Based on raw current, the starter is by far the heaviest consumer in the system. If after draining juice from the battery to start the car, there isn't an obvious and deliberate evidence of the alternator replacing the energy used, then its probably safe to say that the alternator has failed in some way and must be replaced with a rebuilt unit.

If however, the ammeter shows a healthy output for a few minutes of engine running before tapering off to a lower rate, then it appears probable that the alternator functions as it should.

If you wish to double check this, turn on an assortment of consumers, headlights, A/C, etc. With each new consumer, the current flow from the alternator should increase to match the demands of the added consumer plus some extra to recharge the battery.

When the battery is fully charged, any output from the alternator is likely to be only to handle current consumers (no pun intended)

If, after establishing that the charging circuit is functioning as it should, then all what remains is the often time consuming process of illumination. One by one, you must track down the load that is slowly draining the battery while at rest.

I've no counsel for you as it's a trial and error process of elimination that some have already covered in previous posts.

However, one obvious place to start is to disconnect one battery cable, hook up a good digital multimeter with a micro-amp range in series and look to see if any current is flowing when the car should be dormant. I doubt the culprit is the clock or radio station memory.

These efforts some times take awhile before an answer is found; more than you might have to invest on any given day. If that's the case, my suggestion is that you disconnect one of the battery terminals after using the car and only connect it again when testing or the car must be driven. Hopefully, you'll find the time to work your diagnostic investigation a few circuits at a time until you find the culprit.

Good luck

L. J.

We need to back up a bit because you've stated nothing that verifies that the battery has actually been drained, only that the car will not start (presumably will not crank); and while failure to crank could indicate low battery charge state, there could be numerous other reasons for failure to crank. You will need to measure nominal 12V (-2V) across across battery terminals before attempting to crank the engine. If battery voltage reads normal, then it is safe to assume the battery has not drained and that crank failure stems from other cause. The fact of charging voltage with engine running also tends to point elsewhere than a battery fault. So come back with that info so that we know its draining of battery we are trying to fix and not something else. Also, you have not in fact checked all the obvious lights. When an engine will not crank, it is expedient to turn on headlights. If they remain out or very dim, then the battery is discharged; if bright then, again, you will need to look for other no-start failure mode.

Perhaps I am mistaken but I thought it had been already established that the engine would start

As for my own dead battery issue, today I confirmed my suspicions: the alternator is not putting out current.

An inductive ammeter placed over one of the battery cables shows a steady discharge condition after starting and gets worse as consumers are turned on. Racing the engine has no effect.

Mercifully, the alternator is not terribly difficult to get at but given my experience with Murphy and his %$#&$#! Law, that view might change.

I am disappointed at the cost of "remanufactured" alternators however.

L.J.

Patience. You have done worse things than this.

Have you checked for voltage at the large post of the alternator? Most vehicles are now equipped with some form of circuit protection for the charging current. Look in the wiring diagram at the large wire coming out of the alternator. Try to identify where the protection is in that wire. If that wire has no connection, no alternator will charge. try that before you remove that alternator. Good luck. If I can help in any way let me know.

"Most vehicles are now equipped with some form of circuit protection for the charging current. Look in the wiring diagram at the large wire coming out of the alternator."

Thanks Bob, I'd not thought of that. Like I wrote earlier. . . . . it's been a long time. I do have a wiring diagram for this year, make and model which I acquired about a month ago, in my attempt to repair turn signals that won't work. I've tested, changed and swapped every fuse and relay without success. But that's another story!

L. J.

What is the make-model of your affection?

Hello Laughing Jaguar

<"....I am disappointed at the cost of "remanufactured" alternators however.....">

Having sent in alternators to official autoelectrical workshops for testing, I found that they never seemed to understand about diodes which switched improperly.

One workshop even reverse connected the battery in our LandRover, thus destroying the new car stereo, a CB transceiver, and set fire to the wiring.

Unbelievably, they said it "was my fault' for installing an alternator to replace the original generator.

Thus I decided to do my own alternator testing, per: http://cr4.globalspec.com/comment/269892/Re-Battery-Draining

Since that time, some 30+ years ago, I have tested brand-new alternators, from both car and truck, and some of those new alternators have faulty diodes.

All that this means, is the Quality Assurance is sadly lacking, either in the diode factories, or later.

But with the alternator makers mostly using 50 PIV diodes, it is easy for a small surge to damage a diode.

Kind Regards....

For what it's worth...

Whatever "would not start" means, exactly, I looked for evidence that battery charge level had been checked previous to failed start attempt (whatever that might mean), but did not see any. So I was wondering if it could be the case that OP was jumping to a conclusion about battery drainage. In effect (said another way), every possible no-crank condition could be attributed to unwanted battery drain, provided you did not know (had not verified by other than start attempt) that the battery was in fact drained.

I generally make it a practice to try to eliminate what might have been overlooked . . . because oversights (the kick myself syndrome) are not at all uncommon with troubleshooting.

The car is a 2000 Mitsubishi 4 door Mirage with a 1.8L, 16 valve engine and 5 speed manual gearbox. The problem with the directions ceased when the fuse for that circuit was pushed forcibly into the socket. They work fine now. Just a loose fuse.

The alternator is functioning well too. The battery was fully charged during the inductive ammeter test. When the car was allowed to sit still with the head lights on for 20 minutes, the alternator responded with a high charge rate.

Still not sure if the cause of the dead battery has been found or not. We'll see.

Thanks

L. J.

I was terrified that you were going to tell us it was a Jaguar. I owned two Plymouth Crickets ( English made Hillman Avengers, I think.) Plus a few assorted English made cars to work on. I have no confidence in English electrical systems as used in automobiles. Apologies to all that I have offended. Lucas was the god of darkness.

John, it appears you and I are from the same era and share similar experiences.

The situation with Lucas became so wide spread that a cartoon showed up in a national magazine.

It showed a rocket preparing for a space launch with two British astronauts aboard. The captain said:"The most frightening situation in the world"

On closer inspection I saw a placard on the wall of the space capsule that read: "Electronics by Lucas"

What made the cartoon especially painful was that it appeared, not in an automotive magazine, but in the New Yorker!

I worked for Porsche and Audi in those days and after setting up our display at the New York Coliseum for the NY Auto Show, brought the magazine to a few Lucas reps who were sitting innocently in their show booth.

They looked at it, got red faced and quite upset. The show opened but the men were never seen again and the booth remained unmanned for all three days.

Friends that worked for Jaguar in later years alleged that among the very first thing that Ford did upon acquisition of Jaguar was to invite the management of Lucas to a meeting, a very brief meeting, in which they were presented with a deadline and a long list of quality and design improvements. . . or else.

I never heard anything further but Jaguar's reputation in the American market improved dramatically under Ford's guidance. Whether or not Lucas was still a part of that mix or not, I don't know.

L. J.

I have no confidence in English electrical systems as used in automobiles. Apologies to all that I have offended.

That struct a chord

So what is this? What are you trying to say? After all the potential test pilots were interviewed no one would fly in a plane with Lucas electronics, so they went to an unmanned version?

Personnel issues created the demand for higher tech