On Tue, 04 Nov 2003 15:50:45 -0600, "Clifton T. Sharp Jr."
wrote:

Bruce W...1 wrote:
The car is in a garage in a good neighborhood but the owner of the
garage is on and extended vacation. The theives I'm worried about are
neighborhood children. Actually it's the homeowner's car, I'm just
doing them a favor, and saving myself from having to go there to start
the car once a week.

Keeping the battery charged is not the only reason to start the car once
a week.

Suppose it means that a car battery won't last long if you keep it
steady at top charge level, instead of decharge it down towards 50%,
sense the voltage level and charge it up to 14.4V (for this cold
area), and switch off the charger until it is down to 50% again....

I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
better economy to buy a leisure type battery

73
Jan-Martin, LA8AK
http://home.online.no/~la8ak/
--
remove ,xnd to reply (Spam precaution!)

In article ,
J M Noeding wrote:

Keeping the battery charged is not the only reason to start the car once
a week.

Suppose it means that a car battery won't last long if you keep it
steady at top charge level, instead of decharge it down towards 50%,
sense the voltage level and charge it up to 14.4V (for this cold
area), and switch off the charger until it is down to 50% again....

As I understand it, that's exactly the opposite sort of regime that a
car battery prefers.

Car batteries are designed to provide large amounts of current for
engine cranking, even when cold. One of the tradeoffs in this design,
unfortunately, is that they do not tolerate deep (or even heavy)
discharge at all well. Discharging a car battery down to 50% and then
recharging it, repeatedly, is likely to greatly shorten its life. The
plates will quite literally fall apart.

Batteries having a different internal construction can handle deep
discharge quite a bit better. The older sort of "marine
deep-cycle" battery (designed for electric trolling motors) were
quite good - but I'm told that modern "marine deep-cycle" batteries
are more like car batteries in their design and no longer have a big
advantage in terms of deep-discharge life.

The best ones for deep discharge, today, seem to be the
starved-electrolyte (glass mat), and spiral-cell types. These are
often used for telecom backup applications, large UPS systems,
wheelchair motor, and electric-tractor/golfcart applications.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In normal operation a car battery doesn't get discharged to 50% and
then recharged. The starter draws a large amount of current for a very
short time and then the alternator keeps the battery charged and
supplys the current for the vehicle. It seems to me like this would be
very close to keeping the battery on a trickle charge.

In article ,
J M Noeding wrote:

Keeping the battery charged is not the only reason to start the car once
a week.

Suppose it means that a car battery won't last long if you keep it
steady at top charge level, instead of decharge it down towards 50%,
sense the voltage level and charge it up to 14.4V (for this cold
area), and switch off the charger until it is down to 50% again....

As I understand it, that's exactly the opposite sort of regime that a
car battery prefers.

Car batteries are designed to provide large amounts of current for
engine cranking, even when cold. One of the tradeoffs in this design,
unfortunately, is that they do not tolerate deep (or even heavy)
discharge at all well. Discharging a car battery down to 50% and then
recharging it, repeatedly, is likely to greatly shorten its life. The
plates will quite literally fall apart.

Batteries having a different internal construction can handle deep
discharge quite a bit better. The older sort of "marine
deep-cycle" battery (designed for electric trolling motors) were
quite good - but I'm told that modern "marine deep-cycle" batteries
are more like car batteries in their design and no longer have a big
advantage in terms of deep-discharge life.

The best ones for deep discharge, today, seem to be the
starved-electrolyte (glass mat), and spiral-cell types. These are
often used for telecom backup applications, large UPS systems,
wheelchair motor, and electric-tractor/golfcart applications.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In normal operation a car battery doesn't get discharged to 50% and
then recharged. The starter draws a large amount of current for a very
short time and then the alternator keeps the battery charged and
supplys the current for the vehicle. It seems to me like this would be
very close to keeping the battery on a trickle charge.

I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
better economy to buy a leisure type battery
====
A leisure type (deep cycle) battery is fine for a moderate load for a
relatively long time ,since the plates are relatively thick.
However they are not suitable for engine starting purposes ,since brief
demands for a high starting current cannot be met reliably over time.
That's why car batteries have relatively thin plates with a large area
capable of supplying the high starting current.

If a car is kept outdoors it is worthwhile employing a small solar panel
positioned near the south face of the car with its lead plugged into the
cigarette lighter socket. This will keep the battery in a healthy condition.
I have seen these solar panels advertised by the car accessories trade.

Frank GM0CSZ / KN6WH

Frank Dinger wrote:

I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
better economy to buy a leisure type battery
====
A leisure type (deep cycle) battery is fine for a moderate load for a
relatively long time ,since the plates are relatively thick.
However they are not suitable for engine starting purposes ,since brief
demands for a high starting current cannot be met reliably over time.
That's why car batteries have relatively thin plates with a large area
capable of supplying the high starting current.

If a car is kept outdoors it is worthwhile employing a small solar panel
positioned near the south face of the car with its lead plugged into the
cigarette lighter socket. This will keep the battery in a healthy condition.
I have seen these solar panels advertised by the car accessories trade.

Frank GM0CSZ / KN6WH

================================================== ===========

In the past I've maintained car batteries for many months using a small
(2" x 8") solar panel made for this purpose.

How much current could this put out? I don't know but I'm sure it's not
much. Nowhere near one ampere. It contained a diode and no voltage
regulator. This is the same effect I want to achieve with a small wall
wart.

If it's safe to float charge the battery at .01 C indefinitely, say 700
mA for a 70 AH car battery, then anything under 700 mA is also safe. My
200 mA wall wart is safe.

The question then is what is the self discharge rate, less things like
an alarm and clock?

Frank Dinger wrote:

I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
better economy to buy a leisure type battery
====
A leisure type (deep cycle) battery is fine for a moderate load for a
relatively long time ,since the plates are relatively thick.
However they are not suitable for engine starting purposes ,since brief
demands for a high starting current cannot be met reliably over time.
That's why car batteries have relatively thin plates with a large area
capable of supplying the high starting current.

If a car is kept outdoors it is worthwhile employing a small solar panel
positioned near the south face of the car with its lead plugged into the
cigarette lighter socket. This will keep the battery in a healthy condition.
I have seen these solar panels advertised by the car accessories trade.

Frank GM0CSZ / KN6WH

================================================== ===========

In the past I've maintained car batteries for many months using a small
(2" x 8") solar panel made for this purpose.

How much current could this put out? I don't know but I'm sure it's not
much. Nowhere near one ampere. It contained a diode and no voltage
regulator. This is the same effect I want to achieve with a small wall
wart.

If it's safe to float charge the battery at .01 C indefinitely, say 700
mA for a 70 AH car battery, then anything under 700 mA is also safe. My
200 mA wall wart is safe.

The question then is what is the self discharge rate, less things like
an alarm and clock?

I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
better economy to buy a leisure type battery
====
A leisure type (deep cycle) battery is fine for a moderate load for a
relatively long time ,since the plates are relatively thick.
However they are not suitable for engine starting purposes ,since brief
demands for a high starting current cannot be met reliably over time.
That's why car batteries have relatively thin plates with a large area
capable of supplying the high starting current.

If a car is kept outdoors it is worthwhile employing a small solar panel
positioned near the south face of the car with its lead plugged into the
cigarette lighter socket. This will keep the battery in a healthy condition.
I have seen these solar panels advertised by the car accessories trade.

Frank GM0CSZ / KN6WH

Keeping the battery charged is not the only reason to start the car once
a week.

Suppose it means that a car battery won't last long if you keep it
steady at top charge level, instead of decharge it down towards 50%,
....[snip]....
I was told that a car battery wouldn't last long anyway for this
application, so even when my car battery is 6-7 years old, it
wouldnt't last more than a year when trickle charged, while it is far
....[snip]....

I understand that battery electrolyte becomes stratified if the batteries
don't receive the shaking they would normally get through vehicle motion
OR by charging hard enough that the electrolyte "boils" enough to mix
itself up.

I do know that the batteries I've used to power all of my 'shack radios
for the last 25 years do NOT last any longer (as I thought they would)
in a quiet/protective environment than the same batteries I put in my
vehicles!

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)