Tricky one: do I have alternator, battery problems or is it entirely something else?

[1JZGTE]

My car gets used once a week for a round trip of around 20 miles, rest of the time it is garaged. The issue is that every 5 - 7 days or so, the car will kill the battery. I'm at a stage where I fork out on a new battery annually, because there's only so much a CTEK charger can do in restoring a battery that has been drained to 10v or so, about a 12 - 15 times a year.

 

There is a stereo with two amps in the car, but I don't really blast it much. In any case, I have 0 gauge going to the amps, 2 x 4 gauge earth and a 2 x gauge cable from alt to batt, in addition to whatever the standard cable is. All cable connector rings have been sanded down, as have the earthing points, so all good there.

 

I know it is not the battery at fault, as I get the biggest I can fit into the tray and it's usually a 70 - 70Ah battery with 650 - 700CCA. I am thinking maybe it is the alt or the wiring?

 

I am not very technical, but I have done some testing and here are my results. All testing done with a 100% full battery, floating at 12.6v before testing began.

 

TEST 1

Check circled fuses in box under bonnet, all fine according to my multimeter.

 

 

TEST 2

I unplugged the plug pictured below, out from the alt, then switched ignition on, only (engine not running). I used the multimeter to check each of the 3 pins shown with one lead to each pin and the other to a ground connection. Results as pictured. Don't know if it is significant, but the 1st pin from the left reads 12.14v with ignition on but 12.39v with ignition off?

 

 

TEST 3

With engine on, alternator stud / bolt reads 14.3v

 

TEST 4

Engine on, battery to alt casing = 14.3v (+ terminal) and 11.3v (- terminal)

 

TEST 5

Engine on, battery to alt stud / bolt = 25.6v (+ terminal) and 14.3v (- terminal)

 

TEST 6

Engine on, light on, air con on full, music on 75% of volume, voltage drops to 12.2v after about 2 minutes and doesn't go back up. I am sure that if I left the car to idle, the voltage would slowly continue to drop

 

So those are the bits that I have done. Would be grateful for any advice or what other things I should try with the multimeter to try and diagnose what the issue may be. I really don't want to keep buying batteries!

Edited October 8, 2013 by 1JZGTE (see edit history)

[Abz]

Something has to be draining the battery... do you have a car alarm fitted? Can you take that out of the equation?

[straightsix]

If you're only doing 20 miles once a week, I'd suspect the alarm and not the alternator.

 

Measure the amp draw on the battery when you arm the alarm.

[1JZGTE]

Hi Abz, that is what I am thinking, but I am not sure how best to test this?

 

The only thing I can think of is to take off the negative battery terminal and in between that and the negative battery post, to put in the multimeter. I did that but it shows a really small draw, but then this is with the alarm not armed (because negative is off the batt).

 

 

Measure the amp draw on the battery when you arm the alarm.

 

What is the best way for me to do this please? I am not great with electronics I'm afraid so need a bit of spoon feeding! The test I just carried out now shows a very small draw amount but doesn't take the alarm into account as car was not alarmed when I did that test.

Edited October 8, 2013 by 1JZGTE (see edit history)

[straightsix]

You can still arm the alarm - the multimeter set in 'amp' reading will complete the circuit. Don't crank the engine when connected like this though as it's too much draw on the meter leads.

 

You'll need to allow the reading to stabilise for about 5 minutes to get an accurate reading.

[Guest Roger NE]

I doubt if you have any kind of fault at all . . .

 

If you're only driving the car 20 miles, once a week, THAT is your problem. You'd barely be putting back what you're taking out just cranking the engine to start it . . . and even though your alarm won't be taking a lot of current, it will still be draining the battery.

 

Can you not leave the battery on charge when you're not using it? Or at least put it on charge for 24 hours once a week?

 

Ideally, a lead acid battery should be charged by connecting a constant 13.8 Volts across it . . . then it will take whatever current it needs. (you can also leave it on 24/7 without doing any harm)

[Supra Kong]

Start the car and whilst running remove the negative terminal on the batterie... if the car continues to run it shouldnt be the alternator!!

[Guest Roger NE]

Start the car and whilst running remove the negative terminal on the batterie

 

Don't do that for goodness sake . . . you're likely to blow up your ECU and other electronics on the car, let alone the Alternator itself !

 

Although the Alternator sends out D.C., it's not smoothed, it's a series of pulses - it relies on the battery to provide the smoothing and turn it into proper D.C.

[Kirk]

Start the car and whilst running remove the negative terminal on the batterie...

 

Lesson 1. Learn how to spell Battery.

 

Lesson 2. Don't do that.

[Andy Blyth]

You have some strange readings, especially for test 4 and test 5. Please could you measure the resistance (with the engine not running, everything turned off) between the alternator casing and the battery negative terminal? It should be significantly less than 1 Ohm. You may struggle to make a meaningful measurement with that multimeter but the reading you make could give us a clue. Make sure that you are getting a good contact to the alternator casing with your probe by scratching through any corrosion.

 

It is probably a good idea to check for the presence of the main grounding cable between the battery negative terminal and the engine block. It should connect underneath the intake runners.

[1JZGTE]

the multimeter set in 'amp' reading will complete the circuit. Don't crank the engine when connected like this though as it's too much draw on the meter leads.

 

From what I can tell, the multimeter is so weedy, that even when the circuit is 'complete', I can open the door and the door light doesn't even go on!

 

I doubt if you have any kind of fault at all . . .

If you're only driving the car 20 miles, once a week, THAT is your problem. You'd barely be putting back what you're taking out just cranking the engine to start it . . . and even though your alarm won't be taking a lot of current, it will still be draining the battery.

 

For comparison, my dad has a diesel estate, 2.5 litre. He uses it maybe once a week for a 10 mile trip if that and he has NEVER had issues and the car always starts, batt is always fine, this is why this is really getting to annoy me. Alarm manufacturer emailed me back saying the alarm should, ordinarily draw about 20 - 30mA a day.

 

Start the car and whilst running remove the negative terminal on the batterie... if the car continues to run it shouldnt be the alternator!!

 

I think the other, more knowledgeable, members already made it clear that this is probably a very BAD idea

 

You have some strange readings, especially for test 4 and test 5. Please could you measure the resistance (with the engine not running, everything turned off) between the alternator casing and the battery negative terminal?

 

Hi Andy, thanks for your reply and for picking up on the odd readings. I will try again tomorrow and will report back. FYI, I used a Dremel on the alt case today to ensure there was no corrosion on it.

Edited October 8, 2013 by 1JZGTE (see edit history)

[Guest Roger NE]

the multimeter is so weedy, that even when the circuit is 'complete', I can open the door and the door light doesn't even go on

 

That is strange . . are you sure you don't have the meter on a VOLTAGE setting, rather than a CURRENT setting? In fact, thinking about it, you may have accidentally drawn a lot of current when you first connected it, and blown the current shunt inside the meter - that would explain it.

 

Yes I would expect an alarm to take between 20 and 100 mA . . . but you need to measure what the total current drain on the battery is, in case something else is taking current . . . for example, you mention external amplifiers - are they completely disconnected from the battery, or left on "standby"? If not, they could be draining the battery.

 

So it's frustrating that you can't get a reading. (personally I hate digital multimeters . . . they're prone to all kinds of errors in the readings. You know where you are with an Analogue meter . . . plus you can see variations in readings much more easily)

 

And regarding your Dad, I'd still say he's lucky . . . I really wouldn't expect a car battery to stay charged with that little use (why do you guys bother having a car if you hardly ever drive them?!)

Edited October 8, 2013 by Roger NE (see edit history)

[Havard]

(why do you guys bother having a car if you hardly ever drive them?!)

 

Because for the three or four times year when I can offload the kids, have time to myself etc, it's epic.

 

My Supra costs about £100 a go by my recent reckonings.

[Guest Roger NE]

I still suspect there's nothing wrong with your Alternator, and it's just the current drain of your Alarm and Amplifiers that is draining your Battery, due to lack of use.

 

But I've been looking at your Voltage readings from your first post, and I'm rather confused - where are you putting the negative probe of the meter - on the Chassis of the car? (that's where you want it)

 

Questions:

 

1. With the engine running, when you put the positive probe on the Alternator output stud, is it exactly the same voltage as when you put it on the + terminal of the battery? (ie around 14V)

 

2. When you put the positive probe on the Alternator casing, does it read zero?

 

3. Where are each of the probes when you get the 25.6V reading?! (can't understand how you could get this)

Edited October 9, 2013 by Roger NE (see edit history)

[straightsix]

As already said - I'm not suspecting the alternator at all, just it's lack of use. My first thought on any car with a current drain (if you actually have one) is the alarm unless they are known to have a loom running through a weak spot on the tailgate for interior lights etc.

 

I would maybe check the battery fully before looking for anything else. Fully charge it on a mains charger and then drop test it.

 

How old is the alarm? It's possible that the alarm control unit is pulling too much from the battery when armed. Do you have a garage that you could leave the car in for a few nights with the alarm disconnected?

 

I was wondering where you got the 25.6v reading too!

 

If you're not great with electronics, I'd be careful where you stick your probes!

 

 

 

 

Dr. Roger - I concur

[Chris Wilson]

Just disconnect the alarm and see if that cures things. you need to be VERY careful with multi meters on a current measuring setting. They nearly all have internal fuses, but they are sometimes a fairly obscure type and can be hard to get and expensive. If you get the thing running and load up the alternator / battery with as much heavy draw electrical stuff on the car turned ON (things like headlights on full beam, heater blower, heated rear screen, wipers, etcetera), and measure the voltage on the battery terminals THEMSELVES (not the connectors), you should see at 13.something volts at a fast idle. If you do see 13.* to 14.low * volts the alternator and regulator are functioning OK. I suspect the alarm, they are a PITA. To check the battery for self discharge just leave it disconnected for a couple of weeks, if it won't start the car then it's faulty. If it will then something is draining it. That uA reading makes me think you have overloaded the mA current reading circuit in the meter and blown the fuse. there's very little need for mA readings on car charging circuits Use the 10 Amp setting, and even then be very careful about what's turned on. You really need a clamp type current reading device. They convert current flowing in a wire by induction and out put a VOLTAGE to the multimeter, meaning you can't blow either up.

[1JZGTE]

Hi gents, sorry for the late response, work has been keeping me busy.

 

As advised, I have redone some of the tests again. I have taken photos of each one, so you can clearly see what the meter is showing and whether I am doing it right or not! Oh and please ignore the incorrect polarity on the 2nd pic, I touched the probes wrong way round, but reading should be unaffected.

 

Please see below, conclusions / advice what to do next welcome!

 

 

 

 

 

Edited October 13, 2013 by 1JZGTE (see edit history)

[listy]

When did this problem start? By any chance, was it after the amps were installed?

I'm only asking as one of my mates installed an amp and sub combo, and for some reason, when the car was turned off, the amp still drew a current from the battery, draining said battery completely over 2 days.

 

As it's such a simple test, try disconnecting the cable from the battery to the amp, and see if you still get the same problem.

If the problem goes away, the simple solution is to fit a switch on the remote wire from the stereo to the amp, so you can manually break the circuit.

[Chris Wilson]

Tests are sound. 136mA will drain a battery over a period of time. Disconnect the noise box stuff, and see if it's that. If not start pulling fuses to isolate circuits. 99.9% of the time it's some junk fitted after the car was made that's the problem. And Jeez, people sure like adding *%$@# to Supras these days! If not the sound stuff suspect any alarm. I have started to refuse to do electrics on some Supras, such is the state of the wiring that's been added. Behind the dash can look like the snake pit in an Indiana Jones film.

[Guest Roger NE]

Yes, nothing odd about your readings now . . . nothing wrong with your Alternator

 

And as Chris said, the current draw (that presumably your Alarm is taking) is enough to flatten your Battery over a couple of weeks if your battery ISN'T fully charged (which it won't be, given your lack of use of the car)

 

As I suggested previously, is there no way of connecting a charger for 12 hours or so at least every couple of weeks? That's really what you have to do if you don't drive it much.

[1JZGTE]

Yes, nothing odd about your readings now . . . nothing wrong with your Alternator

 

And as Chris said, the current draw (that presumably your Alarm is taking) is enough to flatten your Battery over a couple of weeks if your battery ISN'T fully charged (which it won't be, given your lack of use of the car)

 

As I suggested previously, is there no way of connecting a charger for 12 hours or so at least every couple of weeks? That's really what you have to do if you don't drive it much.

 

 

Hi Roger

 

The battery will go flat in approximately 5 - 7 days, even when fully charged. The 136mA reading I took was with the car fully armed and locked, which is how it usually sits.

 

If it went flat every 2 weeks, that would be fine, but once a week is annoying.

 

I'm glad you guys think that the alt isn't an issue, so I guess I will just try to drive it a bit more often. I will also take Chris's advice and disconnect all audio related gadgets and see where that takes me

 

Thanks again to everybody for their time and help.

[Chris Wilson]

I would best guess it's one of these:

 

The alarm

 

The audio "stuff"

 

An interior light, maybe boot light or footwell light staying on.

 

.136 Amps at say 12 volts is 4.08 Watts, so if it's a bulb it's a small one, and interior light bulbs are about 5 Watts. Disconnect the power feed to the audio stuff and see if the reading drops. My Skyline will start after 3 months of total inactivity. But it hasn't any gizmos

[1JZGTE]

Hi Chris, it deffo isn't a bulb in the boot as I took it out ages ago when it blew and never put a replacement back in. I also don't think it is interior lighting as I watched the car very carefully and in the dark to see if it was one of the interior lights or maybe a footwell light.

 

Last thing to check is the stereo - will do that and report back with the results.

[Big Supes]

Isolator switch for the battery is the way to go for cars that don't get a lot of usage. Your alarm could still be powered from a permanent live.

[Guest Roger NE]

Your Alarm could easily be taking 136mA . . . . . but it could be that SOME of the current is from a big Amplifier on Standby, as others have said, so see how the current changes when you disconnect the Amplifier.