Given many of us won't be driving much for the moment, did wonder just how
hard an alternator charges a battery after a cold start. In amps - given
virtually no car has an ammeter these days. I know you can buy clamp
meters, but they're not accurate at low current on DC, so when I've needed
to measure things on the car, just use a DVM, as 10 amps is enough for
most. And don't want to buy one just for this. ;-)

So assuming a good battery with enough charge to start the car. Voltage on
charge 14.4v No other load than engine electrics.

Obviously the charge current will taper down as the battery charges.

--
*I believe five out of four people have trouble with fractions. *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman wrote:

wonder just how hard an alternator charges a battery after a cold
start. In amps - given virtually no car has an ammeter these days.

They may not have an ammeter on the dashboard, but they do have one on
the CAN bus.

http://lh5.ggpht.com/_lF5XJ5xAktU/TOSPHKoUU4I/AAAAAAAAABg/mRTCnyRQk8E/s800/vcds_battery.jpg

On 02/05/2020 12:31, Andy Burns wrote:

Dave Plowman wrote:

wonder just how hard an alternator charges a battery after a cold
start. In amps - given virtually no car has an ammeter these days.

They may not have an ammeter on the dashboard, but they do have one on
the CAN bus.

http://lh5.ggpht.com/_lF5XJ5xAktU/TOSPHKoUU4I/AAAAAAAAABg/mRTCnyRQk8E/s800/vcds_battery.jpg

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

The Natural Philosopher wrote:

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that

yep, mine is rated 140A

In article ,
Andy Burns wrote:
The Natural Philosopher wrote:

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that

yep, mine is rated 140A

So you are guessing it charges a low battery at 140 amps? ;-)

--
*If God dropped acid, would he see people?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) formulated on Saturday :
So you are guessing it charges a low battery at 140 amps? ;-)

No, there would need to be a rather large difference in voltage between
the alternator and battery, to achieve that and as the battery attains
a charge, its voltage rises quite rapidly.

I would suggest nearer an initial 20amps, which would rapidly fall to
maybe 3 to 6 amps. A flat to full charge time when being driven, can
require 6 to 10 hours of being driven. Which is why it is always best
to put such a battery on a mains charger for 24 hours, if at all
possible.

On 02/05/2020 16:52:58, Dave Plowman (News) wrote:
In article ,
Andy Burns wrote:
The Natural Philosopher wrote:

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that

yep, mine is rated 140A

So you are guessing it charges a low battery at 140 amps? ;-)

For the few seconds to a minutes of a flat batter I can well believe
that may be the case. As soon as the terminal voltage goes to 14.5V or
the regulated charge current will naturally tail to a more modest value.

There is very little literature on battery charging, of when a charging
device might switch from constant current to constant voltage at
different initial charging currents.

Dave Plowman wrote:

So you are guessing it charges a low battery at 140 amps? ;-)

Yuasa recommended rate is only 5A

On Saturday, 2 May 2020 15:38:46 UTC+1, Andy Burns wrote:
The Natural Philosopher wrote:

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that

yep, mine is rated 140A

But only for a short time.

On 03/05/2020 06:47:18, harry wrote:
On Saturday, 2 May 2020 15:38:46 UTC+1, Andy Burns wrote:
The Natural Philosopher wrote:

Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that

yep, mine is rated 140A

But only for a short time.

That's not my experience for a Chinese sourced Bosch replica on a boat
application, where the alternator will happily kick out 150A over a
prolonger period.

One of the reasons why high amperage alternators is specced is all the
electrical power needed when all the car appliances are used, rather
than just topping up the battery between starts.

The Natural Philosopher explained :
Alternators are good for at least 15A. I wouldn't be surprised if they can't
mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

But not charge current into the battery.

On 02/05/2020 15:44, Harry Bloomfield wrote:
The Natural Philosopher explained :
Alternators are good for at least 15A. I wouldn't be surprised if they
can't mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

But not charge current into the battery.
Yes, charge current into the battery if its flat enough


--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."

Jonathan Swift.

On 02/05/2020 15:55, The Natural Philosopher wrote:
On 02/05/2020 15:44, Harry Bloomfield wrote:
The Natural Philosopher explained :
Alternators are good for at least 15A. I wouldn't be surprised if
they can't mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

But not charge current into the battery.
Yes, charge current into the battery if its flat enough


A quick look at a few battery specs suggests that a charge rate above
50A can damage a lead acid battery if maintained for more than a few
minutes.

Bill

In article ,
Harry Bloomfield wrote:
The Natural Philosopher explained :
Alternators are good for at least 15A. I wouldn't be surprised if they can't
mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

But not charge current into the battery.

Remember it is Turnip. Never reads or understands a question.

--
*Change is inevitable, except from a vending machine.

Dave Plowman London SW
To e-mail, change noise into sound.

On 02/05/2020 16:53, Dave Plowman (News) wrote:
In article ,
Harry Bloomfield wrote:
The Natural Philosopher explained :
Alternators are good for at least 15A. I wouldn't be surprised if they can't
mostly manage over 50A if needs be

Oh.. treble that - apparently 45A - 200A is the range...

https://www.powerstream.com/car-battery-faq.htm

But not charge current into the battery.

Remember it is Turnip. Never reads or understands a question.

But he's got a degree in this!

On Saturday, 2 May 2020 11:29:48 UTC+1, Dave Plowman (News) wrote:
Given many of us won't be driving much for the moment, did wonder just how
hard an alternator charges a battery after a cold start. In amps - given
virtually no car has an ammeter these days. I know you can buy clamp
meters, but they're not accurate at low current on DC, so when I've needed
to measure things on the car, just use a DVM, as 10 amps is enough for
most. And don't want to buy one just for this. ;-)

So assuming a good battery with enough charge to start the car. Voltage on
charge 14.4v No other load than engine electrics.

Obviously the charge current will taper down as the battery charges.

Depends on the state of charge of the battery.