Trickle Charge Battery

[west]

I know this question has probably been beaten to death, nevertheless I hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is 12v
and not 13.8v, I think that the gear will still work OK (hopefully).

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.
For the life of me, I can't remember the name of those type batteries so I
can't do a google to find a supplier. I hope this is making some sense.

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

Thank you very much.

Cordially,
west

 

[Anthony Fremont]

I know this question has probably been beaten to death, nevertheless I hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is 12v
and not 13.8v, I think that the gear will still work OK (hopefully).

The voltage of a fully charged battery will be over 12V, somewhere
around 13ish.

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.
For the life of me, I can't remember the name of those type batteries so I
can't do a google to find a supplier. I hope this is making some

sense.

You are talking about a "deep cycle" or marine battery.

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

Google

 

[[email protected]]

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

solar array.... diode.... battery

NT

 

[Phil Allison]

"Robert Scott"

Even if such batteries exist, they won't have a cost-effectiveness
advantage over car batteries. You are thinking that by trading in
peak current you are going to gain in overall amp-hours. It just
isn't true. You won't find a cheaper way to store X amp-hours than a
car battery.

** Nor a cheaper way to obtain a trickle charger to use with the solar
panel than to buy one from the same store that sells the panels. That panel
is going to be the big expense.



......... Phil

 

[Robert Scott]

I know this question has probably been beaten to death, nevertheless I hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is 12v
and not 13.8v, I think that the gear will still work OK (hopefully).

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.

Even if such batteries exist, they won't have a cost-effectiveness
advantage over car batteries. You are thinking that by trading in
peak current you are going to gain in overall amp-hours. It just
isn't true. You won't find a cheaper way to store X amp-hours than a
car battery.


-Robert Scott
Ypsilanti, Michigan

 

[Pooh Bear]

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

It's probably best to get one from a specialist rather than try to roll your
own.

Eg...http://cgi.ebay.com/Compact-18w-SOL...013232727QQcategoryZ41981QQrdZ1QQcmdZViewItem

Graham

 

[Mac]

I know this question has probably been beaten to death, nevertheless I hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is 12v
and not 13.8v, I think that the gear will still work OK (hopefully).

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.
For the life of me, I can't remember the name of those type batteries so I
can't do a google to find a supplier. I hope this is making some sense.

Deep cycle batteries are more expensive than starting batteries. The
advantage to them is that they are designed to endure many
charge/discharge cycles, where the level of discharge is high, compared to
what a starting battery endures.

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

If you size the solar cell correctly, you can just hook it up to the
battery with no other circuitry. The way this would work is that when you
have power, you keep the battery charged with a charger, and leave the
solar cell circuit open.

When the power goes out, open the charger circuit, and close the solar
cell circuit. There may be some danger of overcharging the batteries
with the solar cell if it is very sunny and/or you don't use the equipment.

If you are only trying to keep the batteries topped off, and not trying to
run indefinitely, then you can just use a very small solar cell, and there
will be no danger of over-charging under any circumstances.

Thank you very much.

Cordially,
west

Good luck.

--Mac

 

[Ian Stirling]

I know this question has probably been beaten to death, nevertheless I hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is 12v
and not 13.8v, I think that the gear will still work OK (hopefully).

Nominal voltage is 13.8 fully charged. "12V" is just the sticker value.

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.
For the life of me, I can't remember the name of those type batteries so I
can't do a google to find a supplier. I hope this is making some sense.

Deep cycle.

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

Generally from who you buy the solar cell.

 

[James T. White]

On Sat, 19 Nov 2005 01:01:20 +0000, west wrote:

If you size the solar cell correctly, you can just hook it up to the
battery with no other circuitry.

You will need a blocking diode to prevent the solar panel from becoming a load
at night.

 

[Mac]

You will need a blocking diode to prevent the solar panel from becoming a load
at night.

AIUI, the diode consumes more power than the solar cell. I don't think you
need the diode.

I lived on a boat with solar cells for 2 years, and I had no diodes. It
didn't seem to be a problem.

--Mac

 

[Jim Thompson]

AIUI, the diode consumes more power than the solar cell. I don't think you
need the diode.

I lived on a boat with solar cells for 2 years, and I had no diodes. It
didn't seem to be a problem.

--Mac

See...

"PerfectDiodeForChargerIsolation.pdf"

on the S.E.D/Schematics page of my website.

...Jim Thompson

 

[[email protected]]

AIUI, the diode consumes more power than the solar cell. I don't think you
need the diode.

I lived on a boat with solar cells for 2 years, and I had no diodes. It
didn't seem to be a problem.

--Mac

Some panels will eat when unilluminated, some dont.

NT

 

[[email protected]]

"Robert Scott"


** Nor a cheaper way to obtain a trickle charger to use with the solar
panel than to buy one from the same store that sells the panels.

other than using something from the junkbox.

NT

 

[Phil Allison]

"Mac"

AIUI, the diode consumes more power than the solar cell.

** Then you don't understand much.

I lived on a boat with solar cells for 2 years, and I had no diodes. It
didn't seem to be a problem.

** A series Schottky diode is often built into the solar panel itself.

There is a 0.5 volt loss during charging, but this is trivial as panels
typically output 20 volts in bright sun.



......... Phil

 

[Pooh Bear]

"Mac"


** Then you don't understand much.


** A series Schottky diode is often built into the solar panel itself.

There is a 0.5 volt loss during charging, but this is trivial as panels
typically output 20 volts in bright sun.

Please explain how they can output 20V when loaded with a lead-acid battery.

Graham

 

[[email protected]]

Phil Allison wrote:

Please explain how they can output 20V when loaded with a lead-acid battery.

Graham

8kW of panels on a 6Ah SLA might manage it

NT

 

[Kevin]

A solar cell can be modelled as a current source with a current
proportional to the amount of light falling on it, in parallel with a
silicon diode.

As such it tends to have an output voltage that is proportional to the
logarithm of the solar intensity that drops with increasing temperature
(~2mV per degree). The individual cell voltage will be a maximum of
about 0.5V and because of the logarithmic effect of the diode does not
drop greatly as the intensity reduces.

A typical solar array will consist of 36 cells in series giving an open
circuit voltage of about 18V. When this is fed to a 12V lead acid
battery through a diode the voltage will drop to about 13-14V depending
on charge level - it will act as a constant current generator so the
series diode will have little effect on charging current except at low
intensity levels or high-temperatures.

At nighttime the solar panel will act act like 36 forward biased
silicon diodes in series - with ~13V from the battery each diode will
only have about 360mV across each and the current will be pretty low,
usually the array temperature will be lowest at night so this increases
the voltage required for the diodes to conduct helping reduce the
current.

So it is usually acceptable to not have a reverse blocking diode but it
will not significantly affect the charging current except when the
array temperature is high (under midday sun).

I like to have a blocking diode as a safety measure to avoid dangerous
currents from the battery if the array wiring that is exposed to the
elements has a short ( you should put a fuse in series with the battery
physically close to the battery as well - even a small battery can have
short-circuit currents of hundreds of amps).

Some solar arrays do have diodes included in the array but they are
usually in parallel rather than series - this is to avoid problems when
arrays are placed in series and one array gets shaded while the others
don't. Without the diode the shaded array would be reverse biased by
the voltage from the other arrays and be damaged (a similar problem can
occur with series cells in a battery when one is discharged before the
others.)

It is usually advisable to have a charge controller - if the voltage
goes above ~14V the electrolyte in the battery will be electrolyzed
away pretty quickly - in the case of sealed lead acid batteries there
is no way of replacing it and so the battery will be damaged.

There are some solar arrays available with fewer cells that claim to be
self regulating - these usually just have fewer cells (33 rather than
36) so that the charging current drops off as the battery is charged.
These are not usually completely effective.

These days small charge controllers only cost $20-30 and are easily
available - my local Fry's has them.

kevin

 

[Jasen Betts]

8kW of panels on a 6Ah SLA might manage it

are those cells connected directly to the battery?

Bye.
Jasen

 

[Ken Smith]

8kW of panels on a 6Ah SLA might manage it

Or less pannels on a totally dead 24V SLA of any size.

 

[Rich Grise]

Even if such batteries exist, they won't have a cost-effectiveness
advantage over car batteries.

They do, and they do, and they do.

They're called "deep-cycle" batteries, or "marine", or sometimes "golf
cart" batteries. They're designed to provide moderate current for a long
time, whereas car batteries are designed to stay at the ready on float
while in use, and provide hundreds of amps of starting current when needed.

Please don't mislead the children.

Thanks!
Rich

You are thinking that by trading in