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Re: Is a 0.5V loss from alt. to battery a concern? (more) Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 26 Apr 2006 13:41:54
In Reply to: Is a 0.5V loss from alt. to battery a concern? (more), MIke C, Wed, 26 Apr 2006 13:06:06 Members do not see ads below this line. - Help Keep This Site Online - Signup |
By definition, the battery is being charged if the voltage applied is greater than the unloaded battery voltage. For a lead-acid car battery, that's 12.6 volts. So any voltage above 12.6 is charging the battery. 13.3 is most certainly charging the battery.
As to the voltage difference - where are you measuring it? "Ground" is a relative term, sorry to say.
First, pick a nice spot of bare metal on the engine block. Next, find a nice spot of bare metal on the chassis in the engine compartment. Measure the voltage between the engine block and the chassis. It should be less than 0.05 volts. If not, check the ground strap for the engine.
Next, measure the voltage between the body of the alternator and the chassis. It, too, should be less than 0.05 volts. If it's greater than that, check the ground wire for the alternator. Remember when looking at a connection, the current flows through the part you DON'T see - the underside of the head of the bolt, the lug where it presses up against the chassis. If you measure a voltage difference, pull the connection off, brighten up all the contact surfaces with some fine sandpaper or Scotchbrite, and sock it back down.
Next, measure the voltage between the chassis and the negative POST of the battery. If you read more than 0.05 volts, you've got an issue. Try measuring between the negative post and the negative clamp. If you see more than a few millivolts, pull the clamp off and polish up the post and the inside of the clamp. If the clamp to post was OK, but you measured a drop between the clamp and the chassis ground, then pull off and clean up the battery ground wire. Peek into the insulation at the ends. If you see a buildup of greenish or whitish powder, replace the cable - that's corrosion.
Once the grounds are OK, measure the voltage between the B+ connection and the battery CLAMP. It should be well under 0.05 volts. If not, that cable has an issue. Try the same trick between the positive clamp and the positive post.
It's possible to lose 0.5 volts between small voltage drops from the alternator to chassis, battery cable to chassis, battery cable/clamp to post (both positive and negative).
It's good to clean them up - 0.5 volts is a bit much. But again, 13 volts is fine to charge the battery.
Here's a question - how far do you drive? The purpose of the battery is to provide power for starting, and to smooth out current demand. Otherwise, it's dead weight - the alternator provides all the power for the car's needs, and to re-charge the battery power lost to starting. But that takes some time. If you start the car and drive a couple of miles, and then let the car sit, that's not going to recharge it. If the car sits around undriven for a couple of weeks at a time, and then only gets a very short (10 minute or less) drive, the battery won't gain. Just sitting around does drain a battery some.
However, if you're taking 20 minute or longer trips, the battery should be getting charged by 13 volts.
posted by 192.249....
, Wed, 26 Apr 2006 13:41:54 <-- Viewing This Message, Wed, 26 Apr 2006 07:07:20, Wed, 26 Apr 2006 10:52:49, Thu, 27 Apr 2006 05:53:47
, Tue, 25 Apr 2006 21:46:11
, Tue, 25 Apr 2006 22:23:43
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