This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.
But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Thanks for your help.

You really don't want to trickle-charge the battery with high current..
that will cause the electrolyte to boil out and will kill the battery for
good. You want to use one of your wall warts to power a voltage regulator
such as a LM117 or LM217, so that you can adjust it to exactly the float
level of a lead-acid battery, that is, 13.6 - 13.8 volts.
Look up the data sheet for one of those regulators and build it to output
the float voltage. The battery will only demand the current that it needs
to stay fully charged. The LM117/217 can pass up to 1 amp, but more likely
will be limited by the capability of your wall-wart. Again, this is OK,
since the battery, once fully charged, will need only a few milliamps.
I recommend the LM117 or LM217 because of the low temperature extremes that
it may encounter in the midwest winter. The LM317 is rated for operation
down to 0degC, or 32F. I'll bet your winter will get down significantly
below that, so be safe and use a component that's rated to handle the
temperature extreme.
If you still need help after getting the data sheet for the regulator, come
back here with your questions.
Cheers!!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"Bruce W...1" wrote in message
...
This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.
But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Thanks for your help.

You really don't want to trickle-charge the battery with high current..
that will cause the electrolyte to boil out and will kill the battery for
good. You want to use one of your wall warts to power a voltage regulator
such as a LM117 or LM217, so that you can adjust it to exactly the float
level of a lead-acid battery, that is, 13.6 - 13.8 volts.
Look up the data sheet for one of those regulators and build it to output
the float voltage. The battery will only demand the current that it needs
to stay fully charged. The LM117/217 can pass up to 1 amp, but more likely
will be limited by the capability of your wall-wart. Again, this is OK,
since the battery, once fully charged, will need only a few milliamps.
I recommend the LM117 or LM217 because of the low temperature extremes that
it may encounter in the midwest winter. The LM317 is rated for operation
down to 0degC, or 32F. I'll bet your winter will get down significantly
below that, so be safe and use a component that's rated to handle the
temperature extreme.
If you still need help after getting the data sheet for the regulator, come
back here with your questions.
Cheers!!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"Bruce W...1" wrote in message
...
This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.
But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Thanks for your help.

In article ,
Bruce W...1 wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

I would guess that 100 milliamperes would be more than sufficient to
overcome any self-discharge of the battery, as long as the vehicle
doesn't have any electronics onboard which are drawing current.

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.

You really don't want to do that.

The reason is this: in order for a car battery to be drawing 1 amp of
charge current on a continuous basis, you're going to have to boost
the voltage up fairly high. You'd probably exceed the electrolysis
voltage, and much of the current would end up breaking down the water
in the electrolyte into oxygen and hydrogen. If your battery's design
and chemistry don't allow the gasses to be recombined into water fast
enough, you'd be at risk of "boiling" the battery dry.

But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Lead-acid batteries are happiest if you feed them a well-regulated
charge/float voltage, with suitable current limiting. Using an
unregulated or weakly-regulated 12-volt wall-wart is probably not a
good idea - these wall warts tend to deliver a rather high voltage
(often 16-18 volts) under conditions of little or no load. Depending
on the specific wall-wart you choose, and the condition and type of
your battery, you might end up electrolyzing away the water faster
than the battery can recombine the hydrogen and oxygen. Losing a
wall-wart would be annoying; losing the battery would be worse ;-)

The best thing to do is get (or build) yourself some sort of
well-regulated trickle charger. 100-200 mA is probably more than
plenty for this application, as long as it's provided at a
well-regulated voltage. Most battery companies seem to recommend
between 13.6 and 13.8 volts for a "float charging" application - at
this voltage, the battery will self-regulate the amount of current it
takes and will not overcharge or electrolyze itself. One
knowledgeable amateur I know, recommends sticking to a lower 13.5
volts to ensure safe float-charging under a wide range of charge
conditions and temperatures.

About a year ago I put together a simple float charger to keep the
65-amp-hour glassmat battery in our city's RACES ham-shack properly
charged. It's a simple design, based on the jellybean LM317
three-terminal regulator IC and on the schematics in National
Semiconductor's data sheet for this IC. My version includes reverse
polarity and short-circuit protection, a charge float voltage which is
adjustable over a span of a volt or so, and built-in current limiting
to protect the wall wart (a 200 mA 16-volt unit, if I recall
correctly). It's not a bad one-afternoon project and the components
are the sort of thing most homebrewers are likely to have in their
junk-box.

Schematic is at http://www.radagast.org/~dplatt/hamradio/charger.pdf

--
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 article ,
Bruce W...1 wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

I would guess that 100 milliamperes would be more than sufficient to
overcome any self-discharge of the battery, as long as the vehicle
doesn't have any electronics onboard which are drawing current.

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.

You really don't want to do that.

The reason is this: in order for a car battery to be drawing 1 amp of
charge current on a continuous basis, you're going to have to boost
the voltage up fairly high. You'd probably exceed the electrolysis
voltage, and much of the current would end up breaking down the water
in the electrolyte into oxygen and hydrogen. If your battery's design
and chemistry don't allow the gasses to be recombined into water fast
enough, you'd be at risk of "boiling" the battery dry.

But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Lead-acid batteries are happiest if you feed them a well-regulated
charge/float voltage, with suitable current limiting. Using an
unregulated or weakly-regulated 12-volt wall-wart is probably not a
good idea - these wall warts tend to deliver a rather high voltage
(often 16-18 volts) under conditions of little or no load. Depending
on the specific wall-wart you choose, and the condition and type of
your battery, you might end up electrolyzing away the water faster
than the battery can recombine the hydrogen and oxygen. Losing a
wall-wart would be annoying; losing the battery would be worse ;-)

The best thing to do is get (or build) yourself some sort of
well-regulated trickle charger. 100-200 mA is probably more than
plenty for this application, as long as it's provided at a
well-regulated voltage. Most battery companies seem to recommend
between 13.6 and 13.8 volts for a "float charging" application - at
this voltage, the battery will self-regulate the amount of current it
takes and will not overcharge or electrolyze itself. One
knowledgeable amateur I know, recommends sticking to a lower 13.5
volts to ensure safe float-charging under a wide range of charge
conditions and temperatures.

About a year ago I put together a simple float charger to keep the
65-amp-hour glassmat battery in our city's RACES ham-shack properly
charged. It's a simple design, based on the jellybean LM317
three-terminal regulator IC and on the schematics in National
Semiconductor's data sheet for this IC. My version includes reverse
polarity and short-circuit protection, a charge float voltage which is
adjustable over a span of a volt or so, and built-in current limiting
to protect the wall wart (a 200 mA 16-volt unit, if I recall
correctly). It's not a bad one-afternoon project and the components
are the sort of thing most homebrewers are likely to have in their
junk-box.

Schematic is at http://www.radagast.org/~dplatt/hamradio/charger.pdf

--
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!

Bruce:

As others have indicated, you really want to use a regulated charging
voltage to keep the battery up... The voltage is important, however, more
important to getting the design right is knowing how much of a drain the
automobile puts on the battery when "nothing" is going on... Many cars will
drain a good battery in about a month, just from the residual drain that is
the result of such things as clocks and memories in radios and such. Add
anything else and you've got a good chance of needing significantly more
charging current than you might at first think.

You mention that you are worried about using a fancy trickle charger because
it may get stolen, which implies that the car is outside in the elements,
and not in a protected or secured environment. I'd be willing to bet that
if you have to worry about someone stealing a trickle charger, you should
probably be concerned about just about everything else too, once someone
notices the car isn't moving and has a power cord going to it....

In addition, being concerned about a 1-amp wall wart, which are nearly a
dime a dozen, may be false economy, considering the value of the car and
items built or installed in it. Why wouldn't the tires and wheels
disappear, or the battery itself? Same for radio and/or other
accessories... or even perhaps the car itself.

If you do go and build something to keep the battery up, bear in mind that
you are probably going to need something with a voltage around 16 volts or
so, given that most regulators require a couple of volts of headroom over
the regulated voltage. This may take you into a range of supplies or wall
warts that is higher than you may have on hand anyway.

--Rick

"Bruce W...1" wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.
But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Thanks for your help.

Bruce:

As others have indicated, you really want to use a regulated charging
voltage to keep the battery up... The voltage is important, however, more
important to getting the design right is knowing how much of a drain the
automobile puts on the battery when "nothing" is going on... Many cars will
drain a good battery in about a month, just from the residual drain that is
the result of such things as clocks and memories in radios and such. Add
anything else and you've got a good chance of needing significantly more
charging current than you might at first think.

You mention that you are worried about using a fancy trickle charger because
it may get stolen, which implies that the car is outside in the elements,
and not in a protected or secured environment. I'd be willing to bet that
if you have to worry about someone stealing a trickle charger, you should
probably be concerned about just about everything else too, once someone
notices the car isn't moving and has a power cord going to it....

In addition, being concerned about a 1-amp wall wart, which are nearly a
dime a dozen, may be false economy, considering the value of the car and
items built or installed in it. Why wouldn't the tires and wheels
disappear, or the battery itself? Same for radio and/or other
accessories... or even perhaps the car itself.

If you do go and build something to keep the battery up, bear in mind that
you are probably going to need something with a voltage around 16 volts or
so, given that most regulators require a couple of volts of headroom over
the regulated voltage. This may take you into a range of supplies or wall
warts that is higher than you may have on hand anyway.

--Rick

"Bruce W...1" wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.
But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Thanks for your help.

Get the least expensive battery charger you find and put a one of
those cheap little mechanical timers on it. And set the time to
charge the battery for one hour each day. It will be like driving
your car one hour per day.

(Dave Platt) wrote in message ...
In article ,
Bruce W...1 wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

I would guess that 100 milliamperes would be more than sufficient to
overcome any self-discharge of the battery, as long as the vehicle
doesn't have any electronics onboard which are drawing current.

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.

You really don't want to do that.

The reason is this: in order for a car battery to be drawing 1 amp of
charge current on a continuous basis, you're going to have to boost
the voltage up fairly high. You'd probably exceed the electrolysis
voltage, and much of the current would end up breaking down the water
in the electrolyte into oxygen and hydrogen. If your battery's design
and chemistry don't allow the gasses to be recombined into water fast
enough, you'd be at risk of "boiling" the battery dry.

But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Lead-acid batteries are happiest if you feed them a well-regulated
charge/float voltage, with suitable current limiting. Using an
unregulated or weakly-regulated 12-volt wall-wart is probably not a
good idea - these wall warts tend to deliver a rather high voltage
(often 16-18 volts) under conditions of little or no load. Depending
on the specific wall-wart you choose, and the condition and type of
your battery, you might end up electrolyzing away the water faster
than the battery can recombine the hydrogen and oxygen. Losing a
wall-wart would be annoying; losing the battery would be worse ;-)

The best thing to do is get (or build) yourself some sort of
well-regulated trickle charger. 100-200 mA is probably more than
plenty for this application, as long as it's provided at a
well-regulated voltage. Most battery companies seem to recommend
between 13.6 and 13.8 volts for a "float charging" application - at
this voltage, the battery will self-regulate the amount of current it
takes and will not overcharge or electrolyze itself. One
knowledgeable amateur I know, recommends sticking to a lower 13.5
volts to ensure safe float-charging under a wide range of charge
conditions and temperatures.

About a year ago I put together a simple float charger to keep the
65-amp-hour glassmat battery in our city's RACES ham-shack properly
charged. It's a simple design, based on the jellybean LM317
three-terminal regulator IC and on the schematics in National
Semiconductor's data sheet for this IC. My version includes reverse
polarity and short-circuit protection, a charge float voltage which is
adjustable over a span of a volt or so, and built-in current limiting
to protect the wall wart (a 200 mA 16-volt unit, if I recall
correctly). It's not a bad one-afternoon project and the components
are the sort of thing most homebrewers are likely to have in their
junk-box.

Schematic is at http://www.radagast.org/~dplatt/hamradio/charger.pdf

Get the least expensive battery charger you find and put a one of
those cheap little mechanical timers on it. And set the time to
charge the battery for one hour each day. It will be like driving
your car one hour per day.

(Dave Platt) wrote in message ...
In article ,
Bruce W...1 wrote:

This is not ham radio related but I know you guys have the answer.

I need to store a car unattended for a winter in the midwest. And I
want to put a tricke charge on the battery.

I'd rather not buy a fancy trickle charger because it would probably get
stolen. On the other hand I have a vast array of wall wart
transformers.

If I connected one of these transformers how many milliamps should it
put out at 12V? Or rather what's the least current that would do the
job?

I would guess that 100 milliamperes would be more than sufficient to
overcome any self-discharge of the battery, as long as the vehicle
doesn't have any electronics onboard which are drawing current.

It seems that lead acid batteries can dissipate too much current as
heat. In other words I could probably feed it one amp continuously.

You really don't want to do that.

The reason is this: in order for a car battery to be drawing 1 amp of
charge current on a continuous basis, you're going to have to boost
the voltage up fairly high. You'd probably exceed the electrolysis
voltage, and much of the current would end up breaking down the water
in the electrolyte into oxygen and hydrogen. If your battery's design
and chemistry don't allow the gasses to be recombined into water fast
enough, you'd be at risk of "boiling" the battery dry.

But would 100 mA at 12V do the job? I'd hate to lose a 1-Amp wall wart.

Lead-acid batteries are happiest if you feed them a well-regulated
charge/float voltage, with suitable current limiting. Using an
unregulated or weakly-regulated 12-volt wall-wart is probably not a
good idea - these wall warts tend to deliver a rather high voltage
(often 16-18 volts) under conditions of little or no load. Depending
on the specific wall-wart you choose, and the condition and type of
your battery, you might end up electrolyzing away the water faster
than the battery can recombine the hydrogen and oxygen. Losing a
wall-wart would be annoying; losing the battery would be worse ;-)

The best thing to do is get (or build) yourself some sort of
well-regulated trickle charger. 100-200 mA is probably more than
plenty for this application, as long as it's provided at a
well-regulated voltage. Most battery companies seem to recommend
between 13.6 and 13.8 volts for a "float charging" application - at
this voltage, the battery will self-regulate the amount of current it
takes and will not overcharge or electrolyze itself. One
knowledgeable amateur I know, recommends sticking to a lower 13.5
volts to ensure safe float-charging under a wide range of charge
conditions and temperatures.

About a year ago I put together a simple float charger to keep the
65-amp-hour glassmat battery in our city's RACES ham-shack properly
charged. It's a simple design, based on the jellybean LM317
three-terminal regulator IC and on the schematics in National
Semiconductor's data sheet for this IC. My version includes reverse
polarity and short-circuit protection, a charge float voltage which is
adjustable over a span of a volt or so, and built-in current limiting
to protect the wall wart (a 200 mA 16-volt unit, if I recall
correctly). It's not a bad one-afternoon project and the components
are the sort of thing most homebrewers are likely to have in their
junk-box.

Schematic is at http://www.radagast.org/~dplatt/hamradio/charger.pdf

Dave Platt wrote:
It's not a bad one-afternoon project and the components
are the sort of thing most homebrewers are likely to have in their
junk-box.

Schematic is at http://www.radagast.org/~dplatt/hamradio/charger.pdf

Interesting circuit.

I have to beg a fair amount of ignorance about battery behavior. I've
got a couple of the smaller sealed lead-acid batteries - the one on the
desk right now is 4Ah.

Judging from what (little) I know about these batteries, I presume it
would be safe to use your circuit as-is - that the maximum 200mA
charging current, while intended to protect the unregulated source,
would also be low enough to not overheat the battery.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com