Interesting battery/alternator observations
01-12-2006, 11:01 AM
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I just purchased one of these 3.6A intelligent switch mode battery chagers and thought I would try it out on my car.
To my surprise it took nearly 15 hours before the charger indicated that the battery was charged.
I quizzed the BMW tech. and he said that at best the alternator just maintains what charge is in the battery already. Each time you start the car you take a bit more out and if you drive short distances the battery never recovers.
My car was not started for a month but then I drove it for a week or so. The alternator however could not catch up all the lost charge during the month of inactivity.
I tested the battery voltage using the hidden menu volt meter. Voltage while engine was running went from 13.9v before the charge to 14.3v after the charge!!
So, do your car (and your alternator) a favour and give the battery a good charge from time to time, specially in the cold months or if you are about to park your car for an extended period.
By the way these smart charges enable you to charge the car from the connection points in the engine bay without having to disconnect your battery first.
Cheers
Streak
To my surprise it took nearly 15 hours before the charger indicated that the battery was charged.
I quizzed the BMW tech. and he said that at best the alternator just maintains what charge is in the battery already. Each time you start the car you take a bit more out and if you drive short distances the battery never recovers.
My car was not started for a month but then I drove it for a week or so. The alternator however could not catch up all the lost charge during the month of inactivity.
I tested the battery voltage using the hidden menu volt meter. Voltage while engine was running went from 13.9v before the charge to 14.3v after the charge!!
So, do your car (and your alternator) a favour and give the battery a good charge from time to time, specially in the cold months or if you are about to park your car for an extended period.
By the way these smart charges enable you to charge the car from the connection points in the engine bay without having to disconnect your battery first.
Cheers
Streak
01-12-2006, 12:06 PM
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My Ride: '04 545iS 6 spd, bought new via eBay, 11/05; Blk/Gry, Cold, L7, PDC, BMW Rear seatcover for pets.
First "Bumwa" was a new 1971 2002. High performance 5s since 1987. Beamer motorcycles too, currently on an 07 BMW K1200 GT; also a Moto Guzzi 1000 SP III.
This sounds like a lot of baloney. If anything, BMW over specs their alternators. Heck, the one on the first revived R series (oil head) bikes could light up a small-sized Amercian town. Given the complexity and number of electronic gadgets on these cars, I would expect an uber-alternator, but I don't know the specs. Shouldn't be hard to check though.
Cheers,
Ray Hull
Cheers,
Ray Hull
01-12-2006, 12:11 PM
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Anyone else find that if you power up (but not start) the car and play with the audio or iDrive etc it only takes about 5 minutes before you get the low battery warning????
01-12-2006, 12:35 PM
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Originally Posted by swajames' post='223432' date='Jan 12 2006, 01:11 PM
Anyone else find that if you power up (but not start) the car and play with the audio or iDrive etc it only takes about 5 minutes before you get the low battery warning????
01-12-2006, 02:27 PM
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The battery is rated something like 80-100Ah. Your charger is only rated 3.5A. It did not have enough juice to charge this big capacity quickly.
But to drain the battery to low in 5 minutes is crazy unless the car is hooked to something like the Las Vegas neon lights.
When I measured with a volt meter, I got 16+ V without the car starting. All my previous cars gave something like 13+. Maybe the meter is out of calibration.
And, the tech is probably right. With short distance drives, the alternator does not have long enough time to charge the battery. The next time, the engine is cranked, more juice is loss than the short drive charging could recover, and the battery will just go down further. And, any electrical system will have some leak from power to ground; so over time, the battery also loses its charge.
But to drain the battery to low in 5 minutes is crazy unless the car is hooked to something like the Las Vegas neon lights.
When I measured with a volt meter, I got 16+ V without the car starting. All my previous cars gave something like 13+. Maybe the meter is out of calibration.
And, the tech is probably right. With short distance drives, the alternator does not have long enough time to charge the battery. The next time, the engine is cranked, more juice is loss than the short drive charging could recover, and the battery will just go down further. And, any electrical system will have some leak from power to ground; so over time, the battery also loses its charge.
01-12-2006, 02:58 PM
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Originally Posted by Stranger' post='223482' date='Jan 12 2006, 11:27 PM
The battery is rated something like 80-100Ah. Your charger is only rated 3.5A. It did not have enough juice to charge this big capacity quickly.
But to drain the battery to low in 5 minutes is crazy unless the car is hooked to something like the Las Vegas neon lights.
When I measured with a volt meter, I got 16+ V without the car starting. All my previous cars gave something like 13+. Maybe the meter is out of calibration.
And, the tech is probably right. With short distance drives, the alternator does not have long enough time to charge the battery. The next time, the engine is cranked, more juice is loss than the short drive charging could recover, and the battery will just go down further. And, any electrical system will have some leak from power to ground; so over time, the battery also loses its charge.
But to drain the battery to low in 5 minutes is crazy unless the car is hooked to something like the Las Vegas neon lights.
When I measured with a volt meter, I got 16+ V without the car starting. All my previous cars gave something like 13+. Maybe the meter is out of calibration.
And, the tech is probably right. With short distance drives, the alternator does not have long enough time to charge the battery. The next time, the engine is cranked, more juice is loss than the short drive charging could recover, and the battery will just go down further. And, any electrical system will have some leak from power to ground; so over time, the battery also loses its charge.
infact the very same topic came up today at service dept,and tech says the first thing they do is plug in the charger because the car is being worked on and not sleeping.
but reading voltages is innadaquate unless under load the specific gravity? reading from each cell of the battery will indacate the state of charge.but battery is sealed now so advice to trickle charge is the correct answer ibelieve.
these models are silently running a lot of sensors etc.and if you like me infrequently have short duration journeys with a return in the dark then the battery gets a bashing. imop
01-12-2006, 03:06 PM
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Originally Posted by radioham' post='223495' date='Jan 12 2006, 03:58 PM
THE TECH IS CORRECT charging on short trips will not be enough ,the shutdown mode on the car will stop all consumption so as to leave enough for a start .
01-12-2006, 08:43 PM
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I am sure the tech. is correct, I'll do some more research. He also said that they have just bought a bunch of chargers to top up the batteries of cars while they are there being serviced for this exact reason.
However my practical findings support him. Yes my charger is only 3.6A but the fact is, I thought my battery was fully charged because that's what the alternator should do, it wasn't and needed a top up of 3.6A for 15 hours.
Another interesting fact is that a battery is considered fully charged when it's resting voltage is at about 12.9v and flat at 11.4v, that's only a 1.5v difference.
Those of you getting the low battery warning may like to try and charge the battery as I have and see if the problem persists?
Streak
However my practical findings support him. Yes my charger is only 3.6A but the fact is, I thought my battery was fully charged because that's what the alternator should do, it wasn't and needed a top up of 3.6A for 15 hours.
Another interesting fact is that a battery is considered fully charged when it's resting voltage is at about 12.9v and flat at 11.4v, that's only a 1.5v difference.
Those of you getting the low battery warning may like to try and charge the battery as I have and see if the problem persists?
Streak
01-12-2006, 09:33 PM
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Originally Posted by streak' post='223589' date='Jan 12 2006, 09:43 PM
I am sure the tech. is correct, I'll do some more research. He also said that they have just bought a bunch of chargers to top up the batteries of cars while they are there being serviced for this exact reason.
However my practical findings support him. Yes my charger is only 3.6A but the fact is, I thought my battery was fully charged because that's what the alternator should do, it wasn't and needed a top up of 3.6A for 15 hours.
Another interesting fact is that a battery is considered fully charged when it's resting voltage is at about 12.9v and flat at 11.4v, that's only a 1.5v difference.
Those of you getting the low battery warning may like to try and charge the battery as I have and see if the problem persists?
Streak
However my practical findings support him. Yes my charger is only 3.6A but the fact is, I thought my battery was fully charged because that's what the alternator should do, it wasn't and needed a top up of 3.6A for 15 hours.
Another interesting fact is that a battery is considered fully charged when it's resting voltage is at about 12.9v and flat at 11.4v, that's only a 1.5v difference.
Those of you getting the low battery warning may like to try and charge the battery as I have and see if the problem persists?
Streak
Batteries in general have a large range (discharge time) during which the voltage doesn't change much, and after a point, voltage drops sharply...
I wonder what the battery voltage is when the warning appears? Could be that the warning is a bit over sensitive?