Battery output

Well since no one bothered to answer this question in my previous thread, and then started spouting nonsense about bow waves, I'm gonna ask again.

What sort of voltage should the battery be showing with the engine running and alternator charging properly?

Reply to
Carl Gibbs
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Depends on the car and what is else is on but between 13V-14.4V. Older cars might need to be at ~2k revs.

John

Reply to
John Greystrong

On an old car or a modern truck between 13.8 and 14 volts at any rpm with the lights etc off.

On anything remotely modern from 14v up to 14.7v is normal due to alternators having changed to properly charge new fangle maintainance freew and and AGM and recombinant batteries.

If its not doing that, or it drops much below 13.8v with lights etc on then you have a problem

Reply to
Burgerman

That's what i thought. So when the recovery dude reckoned everything was ok when it was just about chraging at 13v with the lights on he was talking rubbish!

Thanks for the info!

Reply to
Carl Gibbs

Yep he was like most people! Talking Bollocks!

A fully charged battery even an old type one will be at about 12.8v - AFTER STANDING for 24 hours. Directly after or during charge it can be at 14.7 or above.

A recently charged one (engine stopped) can be at 14.4volts plus. Its called surface charge. It means that you charged up some of the impurities! It means v little. The thing is that a car battery has hundreds of amps pulled from it every time you start car. It is always a bit discharged. So rather than the alternator give 12.7 or 8 volts (fully charged voltage) which would - eventually - charge it sort of(like weeks) it charges at the batteries "top" float voltage including the impurities, plus a bit! The bit is to equalise cells. Not all are at the same state of charge. It drags the low ones up. Its called equalisation.

Trust me the blokes a dummy.

Burgerman.

Reply to
Burgerman

Assuming the battery to be in a reasonable state of charge somewhere between 13.8 and 14.4V.

Reply to
Dave Plowman (News)

14.0-14.4

Any thing less than 14v lights off and car running for say 20 mins I would be concerned. Anything above 14.4 and I would again begin to be concerned.

Ed

Reply to
Ed

Around 13.8.

Fraser

Reply to
Fraser Johnston

That's actually too high for a 'maintenance free' battery as most are these days. The max when it is charged should be 13.8 or even slightly less. That's the same figure as the constant voltage charge for a SLA type.

Reply to
Dave Plowman (News)

Ah but because the average journey is pretty short the actual charge and equalization voltage needs to be higher to keep the battery topped up. Many bikes are charging at almost 15volts for this reason. Trucks (long engine runs on average) charge at 13.8 up to 14v normally so that this short overcharge doesent bugger the battery. In a car that gets started (big discharge) and goes two mins tyo the shop/school this results in a permevant slightly discharged battery as the charging current is too low.

A decent maintainance charger will charge them to 14.5 or 6 volts, to equalize and bring up all the "lower" cells to make sure this battery has ALL its cells fully charged and then drop back to 13.8 or 14v for the rest of the time its connected.

The short term slight overcharge voltage is needed to keep all cells in ballance. If you only charge to and at float level then some cells can be overcharged and some undercharged. The ballance gets worse over time and eventually you dry out somer (charged) cels while sulphating the low ones.

Reply to
Burgerman

Please excuse the crap spelling and other errors I am typing this while watching tv on a crap remote keyboard.

Reply to
Burgerman

I do lots of pretty short journeys in my BMW but every time I've looked at the voltage it is 13.8. It has a massive alternator, though.

The SD1 is the same, but with only a 75 amp alternator. I have a very accurate LCD meter (4 digit, 0.05% +/- 1 digit) installed direct across the battery and that soon drops down to < 13.8 after an average cold start in daylight if the battery is in a good state of charge. Never goes over

14.4.
Reply to
Dave Plowman (News)

Older alternators were matched to old style acid topping up batteries before the calcium etc got added. These typically were 13.8v (controlled by a simple 13.8 zenner. Modern maintainance free use other non lead additional components (typically calcium) in the batteries to reduce the amount of gassing so they can be nominally sealed and not need topping up. But their fully charged finishing voltage is a bit higher. So more modern alternators are slightly higher output in voltage.

Calcium maintainance free batteries are crap by the way and do not last as long as pure lead grid batteries! They just dont need topping up.

It is possible to still buy real pure lead batteries like optimas that do things differently. They chemically recombine the oxygen and hydrogen released and allow it back into the electrolyte. So they are still sealed but still lead! And they do produce gasses when charging but it is converted back to water...

However THESE batteries use modified acid of a diff strength to make them compatible with modern cars (calcium batter) low maintainance batteries... So even though they use old style lead plates, they have a 13.9to 14.1 float and a 14.75 equalisation charge.

Reply to
Burgerman

My values are limits and measured on the output of the alternator in that case...

Reply to
Ed

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