Battery overcharging (Ford Focus)

15 volts is very unindicative.

What is it really? 14.4 ???

You need to have the data, accurate data, to look at these things.

If there is an overcharge, where do you think the problem is most likely coming from???

Put a voltmeter on the battery while the motor is running. Set it to DC volts and see what it's charging at. If it is overcharging the alternater is your problem since it has an internal regulator.

One other thing you can check is your ground cables to make sure they are nice & tight. I know on motorbikes if the ground isn't good I get an overcharge and I blow bulbs.. Not sure if it applies to automobiles but it can't hurt to check.

15 volts sounds about right. i think the voltage requirement might vary slightly depending on the type of battery, but 15 volts sounds good. What is wrong is it boiling the water out of the battery or?

I will second checking and cleaning all the main battery cable connections! Don't forget the cables have two ends. A dirty connection sure can make a volt gauge read high on my vehicles, so can a polished up fan belt.

When the fan belt gets polished up, it will no longer grab the alternator pulley under load which again makes my volt gauge get really swingy and stay too high. I test for that by taking a cold off engine and seeing if I can hand slip the alternator pulley. If I can and the belt is properly tight, it have become polished up and needs replacing. The alternator takes a few HP to spin up under load and if it will hand slip it will load slip too.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

An additional note A normal lead acid auto battery should charge a 14.2 volts and read 12.8 volts after surface charge os gone 1-3 hours. Heat is what does the dammage in most cases of over charging. As a rule of thumb if the temputare is above 85f, it should not be charged at more than 14.2

- 14.3 volts, if temputare is 32F, 14.2 - 14.5, at no time should the battery be charged at more than 14.5 volts, it will warp the plates quickly and the battery will never recover.

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LOL. When a fan belt slips, it over charges!!! LOL That's a good one Mike!

That is a question I asked way back in the thread.. How does he know it is overcharging? No response.

No, its not right. 15.0 volts sustained for an extended period is too high. The charging threshold for a lead-acid battery is around 13.8 to

14.4 volts depending on temperature. Holding one at 15 volts for an extended period will just boil the electrolyte.

But trusting the dash gauge is also a mistake- the voltage should be measured with a quality voltmeter at the battery terminals. Tenths of a volt are very important in this case.

It slips under the original starter load, then when it finally grabs a bit, the volt gauge shows high as it tries to charge the battery back up. It is still slipping so the amps aren't transferring well so the volt gauge stays high.

Same for a bad connection, it makes the volt gauge go high, but be really swingy under load.

When mine is reading high, cleaning the battery connections and/or fixing the fan belt gets it back more rock solid near 14.2V.

Mike

When voltage regulators were adjustable I would set them for about 13.5 volts when hot to 14 volts when cold. That is high enough to charge a battery in good condition and will never overcharge. It has been a long time since I have seen a voltage regulator that is adjustable, and the specs for some alternators call for voltage as high as 15 volts. It is unfortunate that an alternator and voltage regulator operating within specs will overcharge a battery.

I fully agree with you, Steve.. He posted "15 volts" but that does not give me any confidence that it is really 15.00 volts. Could be anything

The quick way to see what it is actually doing is to toss a meter on the battery and a scan tool as well. The scan tool will tell you what voltage the computer is seeing and the meter on the battery will give you that voltage. In many vehicles 15 volts on the dash could be OK, When you look at the voltage drop due to the circuit resistance the battery may only be charging at 14 volts or so.

Also keep in mind that on most newer vehicles the computer is controlling the charge rate, regardless of the internal regulator. It varies the voltage on the sense line to the regulator to compensate for the load and temperature the vehicle is in.

when hot to 14 volts when cold. That is high enough to charge a battery in good condition and will never overcharge. It has been a long time since I have seen a voltage regulator that is adjustable, and the specs for some alternators call for voltage as high as 15 volts. It is unfortunate that an alternator and voltage regulator operating within specs will overcharge a battery.

GM has been notorious for running their electrical systems at a significan over-voltage for a number of years now. It plays hell with light bulb life, too.