Low voltage (13.5) at battery

[bmw540]

Hello I am trying to find out what is causing my battery not to fully charge. I have taken the alternator to a guy who has said the alternator is generating 14.2 volts and I have also replaced the battery.:( Not sure how to fix this issue. Has anyone had this problem or ideas where to start trouble shooting.

[Jeff in MN]

a 12 volt battery. I just check my Chrysler T&C and it is reading 12.1 and my e38 is reading 11.70. Both cars have been sitting for several ours and both systems are in perfect order and starting fine. The Chrylser battery is 2 years old and the e38 is at least 5 years old.

[BillionPa]

think you got problems? my battery is reading 6V right now!!!

[BillionPa]

anyway... as far as the battery putting out a certain voltage, if the car is OFF expect 12, unless you have a 7 cell batt then expect 14.

the alternator will generate 14.2V, but as current is used by the ignition system, and an assload of other electronic gadgets, you will drop about half a volt before the battery.

13.5 is only about a quarter of a volt lower than "norm", so dont sweat it.

[bmw540]

not sure what you mean... it is a 12 volt battery.

Manual states should have 12.4-12.6 volts (fully charged) at the battery with engine off and around 14 volts when the engine is on. I have also done a load test at the battery with the engine off and there is no current draw so I can only guess that there is an extra load when the engine is running to cause the voltage to drop or the regulator in the alternator has had it, but the electrical guy said the alternator is outputing 14.2 volts so need ideas about where to test where the voltage can be dropping...i.e. from the alternator back to the battery.

[shogun]

Search archives. Before you start checking battery voltage you have to wait more than 15 minutes to get all small gimmicks to a rest.
Then start checking the battery. But if you just open a door or something else, all is on stand by again and you have to wait again.

Do not know how you check your battery. At the battery poles? Or in engine room somewhere?
Is your DMM a cheap unit? I do not trust a 6 $ multimeter. Anything beyond 0.1 is wrong.
Have tested that with 3 different cheap multimeters and a FLUKE.
World's in between.
Are the batteries on your multimeter 100% o.k.? Check that, also that males a difference.

[bmw540]

cheers shogun, yeah I am using a fluke multimeter. I get 12.2-12.3 and 13.3-13.5 at the battery terminals with off and on. I have not checked in the engine bay. I guess you are suggesting at the jump start pole in the engine bay?

I did not wait 15 min so prob will get a lower voltage. I just got my carsoft 6.5 cables from the internet today so intend to have a play tonight if the wife decides to give me a break.

[bsell]

Hello I am trying to find out what is causing my battery not to fully charge. I have taken the alternator to a guy who has said the alternator is generating 14.2 volts and I have also replaced the battery.:( Not sure how to fix this issue. Has anyone had this problem or ideas where to start trouble shooting.

Lead acid batteries are in a good state of charge if they produce 2.1v/cell. If your battery has six cells, the good charge voltage should be 12.6v.

That being said, a better indication of state of charge for a lead acid battery requires a battery hydrometer. It measures the specific gravity of the acid by floating a different number of balls depending on the specific gravity of the acid. These are pretty cheap and a useful tool to find out your actual state of charge.

Since your alternator tested at 14.2v but you only have 13.5v at the battery, you are losing voltage (voltage drop) somewhere between the two. To find this drop (resistance), measure the voltage across each connection between the battery and alternator on both the positive and negative sides. Of course the engine must be running to get some current flowing around while doing these tests so take care of the moving and hot parts.:)

If your multi-meter (MM) registers a voltage write it down as you need to find 14.2-13.5=.7v of drop. With our cars being so old, there may be voltage drops at several locations or the whole wire may be corroded and resisty.

Brian

[bmw540]

cheers Brian,

Are there any test points which I can go from?

[bsell]

not sure what you mean... it is a 12 volt battery.

Manual states should have 12.4-12.6 volts (fully charged) at the battery with engine off and around 14 volts when the engine is on. I have also done a load test at the battery with the engine off and there is no current draw so I can only guess that there is an extra load when the engine is running to cause the voltage to drop or the regulator in the alternator has had it, but the electrical guy said the alternator is outputing 14.2 volts so need ideas about where to test where the voltage can be dropping...i.e. from the alternator back to the battery.

I take it you measured at the battery posts and not on the wires themselves? If the post-to-clamp connection is dirty or skined over you can loose charging ability so scrub that clean.

I have cured similar voltage drops by cleaning every connection between the alternator and battery. There is nothing like some medium-grit sandpaper and elbow grease to break the 'skin' between connections.

As I said below, your cars are getting older and the wires in them can get corroded causing voltage loss. The fastest check is between the positive post on the back of the alternator and the positive post of the battery. Do the same test from the alternator attachment to the engine block and the negative post of the battery.

If you find some voltage in one system (negative or positive), you have halved the number of connections requiring testing.

Repeat the process, connection by connection until you find your problem.

Brian

[632 Regal]

first of all check the fusible links by the battery, thats usually a major area.

[bmw540]

ok will do. I assume there is a fuse on the positive side of teh battery to test for a voltage drop. I really hope this is the cause of the issue as I just want to get back to driving and having fun again.

[shogun]

I just have got a nice exampe of a broken fusible link

[bsell]

first of all check the fusible links by the battery, thats usually a major area.

Are you saying the links get corroded easily?

I figure if he had a burned link, something major wouldn't work giving him other symptoms than a weak battery.

Help educate a new E34 owner,

Brian

[shogun]

Does that look like corrosion in the pics?
That is a crack!
Thousands of times it has been found.

[bsell]

Does that look like corrosion in the pics?
That is a crack!
Thousands of times it has been found.

Oh 3 times Grand Master, I did not mean to rile you up.:D

What this BMW newbie is not getting is how an open circuit will cause a voltage drop at the battery and not a complete lack of charging. If the link carried the juice back from the alternator to the battery, then he should have battery voltage at the posts whether the engine is running or not.

Help me see the light, Grand Master;)

[bmw540]

I get the car back tonight from the mechanic who I have little faith - he who is not even a mechanic...

I will have a look at the link you have been talking about and mesure the voltage and current draw. The only issue they could find was to replace a bearing in the alternator so they really have no idea.

Fingers crossed will provide feedback tomorrow.

[bmw540]

just got my alternator back again after being tested. now getting 13.7 - 13.9 so assume there is no problem. What you you think?

[BillionPa]

doesnt sound too bad, although our cars seem to like it on the high end.

i just got my car working again after my dead batt fiasco, and im getting 14.28V at the battery during idle (500rpms) and 12.4ish when the car is off.

the VR in the alternator is a 14V unit, so if you are getting output within 2.2% of that you should be fine. the voltage drop to the battery shouldnt be too high though, there is some pretty hefty copper wire, and to cause a 0.2 to 0.4V drop means there is extremely high resistance somewhere (actually its quite low, but high when compared to what it should be)

check the junction box under the engine bay remote battery terminal for corrosion.

[bmw540]

I have not looked there. Is this located just underneath the remote battery terminal. Do you have a picture. I will have a look tonight if not tomorrow. I agree that I was hoping for alittle higher voltage. The mechanic said there was some corrosion and a heap of leaves and dirt on the back of the alternater.

Did you do any repairs to your alternater or was if just the battery.

[BillionPa]

a relay fused shut in the engine bay that was drawing current directly from that junction box, killed the battery and wouldnt let my charger charge (as the draw was 2.6A and the charger was 1.25). when i installed the wire in the junction box originally, the screw that held the three or so hot wires together was really loose.

[bmw540]

how did you measure the current draw?

out of interest what current draw should I be expecting on the charge system with the engine running and all accessories off.

woundering if I can run my ammeter on the junction box with the engine running, but think i might damage something.

so you get just over 14v @ idle, what do you get with the fan on "1" position?

[BillionPa]

i measured the current draw with the engine off by sticking the ammeter between the battery post and the main ground wire.

if you try to measure the current from the alternator or at the battery during startup you will fry the ammeter instantly, and the car will not run.

i will measure the batt voltage in the morning for the fan in all positions, and at night with the HIDs and fog lights on.

[mzarifkar]

not the most accurate way, but you can press the 1000 and 10 button on your OBC at the same time, then enter test 9 and hit s/r: it will give you battery voltage. while running, mine is usually at 14.25-14.05. also try going to position I (radio) and see the volts drop to about .2

I am not sure exactly where it measures this voltage across

[bmw540]

does anyone know what the current draw should be at the battery with the ignition off and also with it on.

[BillionPa]

i got a voltage reading at the battery, while running the radio, HID low beams, halogen fog lights, exterior accessory lights (given with low beams) and the heater fan on pos 1, of 14.26V

current draw for my car with the ignition off was posted in my "massive current draw" thread.

[BillionPa]

oh by the way i just verified that the battery is connected to the alternator through that junction box under the jump start terminal.

[BillionPa]

the other wire that goes in there is supposedly pin 14 of the data link connector.

[bmw540]

Think I have found the problem...

The OBC display back light has blown and the voltage is now around 14v. I noticed that the display was always bright but never "clicked" that this might have been the issue.

I will check the voltage at the lamp connections and also the ratings of the lamps to see what is causing the problem.