Low voltage (13.5) at battery
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.
Just curious, but why would you expect more than 12 volts on
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.
Jeff in MN
87 535is 245k Recent top end re-work
88 528e 290k
90 535i 115k
98 740i 115k New Magnaflow Cats, No More Codes
Grand Master
think you got problems? my battery is reading 6V right now!!!
Alusil, Dinan DME | ITG Air Filter | Eibach/Bilstein HD | 26/20 Swaybars | Iridium plugs | Depo/ProLumen HID | Optima batt. | no AC | Stoptech brake lines, Frozen rotors, brass bushings, Superblue
Grand Master
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.
Alusil, Dinan DME | ITG Air Filter | Eibach/Bilstein HD | 26/20 Swaybars | Iridium plugs | Depo/ProLumen HID | Optima batt. | no AC | Stoptech brake lines, Frozen rotors, brass bushings, Superblue
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.
Super Moderator
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.
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.
Big, Big Time Poster
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.Originally Posted by 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.
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
Are there any test points which I can go from?
Big, Big Time Poster
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
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