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

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.

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.

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.

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.

Fredxx posted
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.


My car battery charger, bought second-hand forty years ago for £5, has
just packed up. Can anyone recommend a suitable replacement? Doesn't
have to be portable, just plug into the mains and recharge a flat car or
lawnmower battery. Preferably for the same sort of price I paid for the
last one ...


--
Algernon

Dave Plowman wrote:

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

Yuasa recommended rate is only 5A

On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltage to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do THAT

--
To ban Christmas, simply give turkeys the vote.

On 02/05/2020 17:52, Algernon Goss-Custard wrote:
Fredxx posted
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.


My car battery charger, bought second-hand forty years ago for £5, has
just packed up. Can anyone recommend a suitable replacement? Doesn't
have to be portable, just plug into the mains and recharge a flat car or
lawnmower battery. Preferably for the same sort of price I paid for the
last one ...


Halfords cheapest.


--
To ban Christmas, simply give turkeys the vote.

On 02/05/2020 18:15, Andy Burns wrote:
Dave Plowman wrote:

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

Yuasa recommended rate is only 5A


Oh dear. Yuasa batteries are a couple of ampere hours



--
To ban Christmas, simply give turkeys the vote.

On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltageÂ* to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do THAT

"Not long ago, an 80 amp alternator was considered a high output unit.
Most late model alternators produce 120 to 155 amps or more. Current
output increases with engine speed, from around 20 to 50 amps at idle up
to the unit's maximum output at 2,500 RPM or higher (refer to a service
manual for the exact charging output specifications for your vehicle)."

https://www.aa1car.com/library/charging_checks.htm


--
Renewable energy: Expensive solutions that don't work to a problem that
doesn't exist instituted by self legalising protection rackets that
don't protect, masquerading as public servants who don't serve the public.

In article ,
The Natural Philosopher wrote:
On 02/05/2020 18:15, Andy Burns wrote:
Dave Plowman wrote:

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

Yuasa recommended rate is only 5A


Oh dear. Yuasa batteries are a couple of ampere hours

yes, Oh Dear - a very quick google shows them up to 100Ah.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

The Natural Philosopher wrote:

Andy Burns wrote:

Yuasa recommended rate is only 5A

Oh dear. Yuasa batteries are a couple of ampere hours

95 Ah in this case and 850 CCA

larger battery for a 2.0 petrol than the previous 3.0 diesel, as it's a
start/stop car.

On Sat, 02 May 2020 19:06:23 +0100, The Natural Philosopher wrote:

On 02/05/2020 18:15, Andy Burns wrote:
Dave Plowman wrote:

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

Yuasa recommended rate is only 5A


Oh dear. Yuasa batteries are a couple of ampere hours

Are you saying they're useless? Always found them pretty good.



--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

Yes that's all correct. I have digital ammeters on my motorhome and
that's what they tell me.

Bill

On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltageÂ* to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do THAT

You are forgetting the internal resistance of the battery. The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Bill

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

On 02/05/2020 21:54, williamwright wrote:
On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltageÂ* to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do
THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject, I am not forgetting it.
You simply have no idea of its value.

The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Bill


--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.

Mark Twain

On 02/05/2020 22:03, williamwright wrote:
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
I see you just make that statement with no link to back it up.




--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.

Mark Twain

The Natural Philosopher wrote:

On 02/05/2020 21:54, williamwright wrote:
On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltage to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do
THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject, I am not forgetting it.
You simply have no idea of its value.

The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Bill
The charging rate must be deliberately limited to avoid damage to the
battery. The acceptable charge rate is much higher when fairly flat
than when nearly fully charged. Probably improved electronics is why
we can have much higher output alternators nowadays without risking
battery damage. The old system of just regulating the voltage could not
reliably avoid overcharging unless the maximum charge rate was
artificially limited.



--

Roger Hayter

On 03/05/2020 00:12, Roger Hayter wrote:
The Natural Philosopher wrote:

On 02/05/2020 21:54, williamwright wrote:
On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltage to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do
THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject, I am not forgetting it.
You simply have no idea of its value.

The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Bill
The charging rate must be deliberately limited to avoid damage to the
battery. The acceptable charge rate is much higher when fairly flat
than when nearly fully charged. Probably improved electronics is why
we can have much higher output alternators nowadays without risking
battery damage. The old system of just regulating the voltage could not
reliably avoid overcharging unless the maximum charge rate was
artificially limited.



BINGO.

Imagine what happens when you jump start - seen the size of the spark?

Long term charge rates are obviously low, but just after a hard cold
start the battery will soak up a lot of amps very quickly.

Because if it doesn't and its doing stop-start, the battery will be flat
PDQ .


--
"The most difficult subjects can be explained to the most slow witted
man if he has not formed any idea of them already; but the simplest
thing cannot be made clear to the most intelligent man if he is firmly
persuaded that he knows already, without a shadow of doubt, what is laid
before him."

- Leo Tolstoy

On Saturday, 2 May 2020 17:52:41 UTC+1, Algernon Goss-Custard wrote:
Fredxx posted
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.


My car battery charger, bought second-hand forty years ago for �5, has
just packed up. Can anyone recommend a suitable replacement? Doesn't
have to be portable, just plug into the mains and recharge a flat car or
lawnmower battery. Preferably for the same sort of price I paid for the
last one ...

Yes. Any modern car battery charger will work. All there is to choose is cheapos versus high MTTF ones, £12 versus £40+.

I might fix the old one.


NT

On 02/05/2020 23:49, The Natural Philosopher wrote:

Total crap. There is no pint in having a 150A capable alternator to
do THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject,

What, your a Bachelor of Batteries?

I am not forgetting it.
You simply have no idea of its value.

I fit ammeters in all my vehicles, ever the tractor. Even after a bump
start because of a flat battery the charge settles to below 30A within
seconds.

As a matter of fact, I initially fitted 60A meters in the motorhome but
soon changed them for 30A ones. (Later I re-did the control panel and
fitted digital ones.)

I've just done a search for vehicle and marine ammeters. The vast
majority are 30-0-30. A few are 60-0-60. According to you they should
all be 150-0-150.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Yes but the alternator keeps the charge to a sensible level, to prolong
battery life. Extremely rapid charging is bad for lead-acid cells.
That's why milk floats are on charge all all the time they are in the
depot. It's why disability scooters are charged at 8A or 4A depending on
the battery, which can be inconvenient in summer if the user wants to go
shopping in the day and out for a meal in the evening.

There's no doubt you can push 100A into a big lead-acid battery if the
supply is of high enough voltage, but do it routinely and the battery
won't last as long as it should.

The other factor concerns the alternator voltage. Once a flat battery
has received a bit of charge, its terminal voltage rises to the point
where to maintain a 100A (say) charge the alternator voltage would have
to be so high as to over-run filament bulbs and other equipment.

So if you spent three years getting that Bachelor of Batteries degree it
looks like you wasted your time, because you know nowt.

Bill

On 02/05/2020 23:50, The Natural Philosopher wrote:

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
I see you just make that statement with no link to back it up.


Look it up yourself then.

Bill

On Sunday, May 3, 2020 at 9:12:35 AM UTC+10, Roger Hayter wrote:
The Natural Philosopher wrote:

On 02/05/2020 21:54, williamwright wrote:
On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
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.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltage to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

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.


Total crap. There is no pint in having a 150A capable alternator to do
THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject, I am not forgetting it.
You simply have no idea of its value.

The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Bill
The charging rate must be deliberately limited to avoid damage to the
battery. The acceptable charge rate is much higher when fairly flat
than when nearly fully charged. Probably improved electronics is why
we can have much higher output alternators nowadays without risking
battery damage. The old system of just regulating the voltage could not
reliably avoid overcharging unless the maximum charge rate was
artificially limited.



--

Roger Hayter

Quite agree with the charging rate limitation. If one observes the meter on a battery charger, the starting currents through the charger would be around 4 amps in the worst case, coming down slowly to 0.5 amps in about 12/16 hours; if this is any guidance the alternator charging load would be about the same, not of the order multiples of ten amps!!

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 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.

posted
On Saturday, 2 May 2020 17:52:41 UTC+1, Algernon Goss-Custard wrote:
Fredxx posted
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.


My car battery charger, bought second-hand forty years ago for 0 just packed up. Can anyone recommend a suitable replacement? Doesn't
have to be portable, just plug into the mains and recharge a flat car or
lawnmower battery. Preferably for the same sort of price I paid for the
last one ...

Yes. Any modern car battery charger will work. All there is to choose
is cheapos versus high MTTF ones, £12 versus £40+.

I might fix the old one.

The metal enclosure is riveted together so I can't open it up. Anyway
IMLE the failure mode for devices based on a transformer is nearly
always shorting or burning out of the windings which can't be fixed.

--
Algernon

The Natural Philosopher wrote:

There is no pint in having a 150A capable alternator to do THAT

Aren't such heavy duty alternators there for heated windscreens, bum
warmers, memory seats etc?

"Algernon Goss-Custard" wrote in message
...
posted
On Saturday, 2 May 2020 17:52:41 UTC+1, Algernon Goss-Custard wrote:
Fredxx posted
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.


My car battery charger, bought second-hand forty years ago for 0 just
packed up. Can anyone recommend a suitable replacement? Doesn't
have to be portable, just plug into the mains and recharge a flat car or
lawnmower battery. Preferably for the same sort of price I paid for the
last one ...

Yes. Any modern car battery charger will work. All there is to choose is
cheapos versus high MTTF ones, £12 versus £40+.

I might fix the old one.

The metal enclosure is riveted together so I can't open it up.

Corse you can open it by drilling out the rivets or using an
angle grinder to get the head off.

Anyway IMLE

Very limited indeed.

the failure mode for devices based on a transformer is nearly always
shorting or burning out of the windings

That's bull****. Its far more often the rectifier.;

which can't be fixed.

The rectifier can be, trivially.

The Natural Philosopher was thinking very hard :
The alternator will deliver whatever voltage it meeds to but of course there
would not need to be a particularly large voltage to charge a battery that
is capable of delivering over 700 A to starter motors without crapping out

That is a rather odd statement. Some alternators output a maximum fixed
voltage, more modern ones vary the voltage slightly depending on
demand. Because a battery can deliver 700amps does not mean they are
capable of accepting 700amps as a charge current. The 700amps is for a
very short period of time.




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.


Total crap. There is no pint in having a 150A capable alternator to do THAT

The point of having such a large potential current output available, is
nothing to do with putting that current into the battery - it is there
to cope with the massive current demand of lights, cabin fans, cooling
fans, screen heaters and etc.. My cooling fan at maximum demands
50amps.

I tell you again - you need a much larger voltage difference between
the battery and the charging supply, to get an effective, high current
rapid charge into a battery. Such a high voltage would burn lamps out
and electronics.

williamwright was thinking very hard :
You are forgetting the internal resistance of the battery. The fact is that
the most charge a car will give a flat battery is around 30A, it it drops off
very rapidly. The high alternator output is to support accessories.

Correct! I have taken the trouble to actually measure it and have seen
20 to maybe 30amps delivered by a 130amp alternator, into a near flat
battery. That level of charge current rapidly declines as the flat
battery gains in voltage.

On 03/05/2020 08:52, Harry Bloomfield wrote:
williamwright was thinking very hard :
You are forgetting the internal resistance of the battery. The fact is
that the most charge a car will give a flat battery is around 30A, it
it drops off very rapidly. The high alternator output is to support
accessories.

Correct! I have taken the trouble to actually measure it and have seen
20 to maybe 30amps delivered by a 130amp alternator, into a near flat
battery. That level of charge current rapidly declines as the flat
battery gains in voltage.

I have battery chargers that will dump full permitted current into a
battery until it is =99% full.


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

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

There is no pint in having a 150A capable alternator to do THAT

Aren't such heavy duty alternators there for heated windscreens, bum
warmers, memory seats etc?

heated seats?

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On Sun, 3 May 2020 17:29:07 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile cretin's latest troll**** unread

--
Richard addressing senile Rodent Speed:
"**** you're thick/pathetic excuse for a troll."
MID: