12V in, gel cell out?

W

Wong Sy Ming

Guest
Hi, does anyone have any links/circuits for a gel cell charger that will
take a 12V input from a vehicle battery to charge a smaller 12V battery? I
saw one in a distant issue of Silicon Chip magazine, but I don't think
that's available anymore.

Or, can I just connect the gel cell to something like a cigarette lighter
output with a diode in series to prevent back flow of current? How would the
charging current be limited?

TIA...
 
In article <c92k6v$1h7$1@mawar.singnet.com.sg>,
Wong Sy Ming <simingx@anti_yahoo.com> wrote:
Hi, does anyone have any links/circuits for a gel cell charger that will
take a 12V input from a vehicle battery to charge a smaller 12V battery? I
saw one in a distant issue of Silicon Chip magazine, but I don't think
that's available anymore.

Or, can I just connect the gel cell to something like a cigarette lighter
output with a diode in series to prevent back flow of current? How would the
charging current be limited?
Click to expand...
You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the glow
tells you whats happening. If you hook up backwards, the light is at full
brightness. If the battery is flat dead, the bulb looks orangish. When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.

--
--
kensmith@rahul.net forging knowledge
 
Ken Smith wrote:

You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the glow
tells you whats happening. If you hook up backwards, the light is at full
brightness. If the battery is flat dead, the bulb looks orangish. When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.
Click to expand...
I doubt that this works at all...

It takes a voltage of about 14V to charge a nominal 12V gel cell.
How does a Lead acid car battery whose steady-state terminal voltage
is 12.65V cause the gel cell to be charged?

If the car is running, then the alternator raises the car battery
voltage to about 14.2V, so that would charge the gel cell too...

MikeM
 
On Wed, 26 May 2004 17:12:45 -0600, MikeM <trashcan@yahoo.com> wrote:
Ken Smith wrote:


You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the glow
tells you whats happening. If you hook up backwards, the light is at full
brightness. If the battery is flat dead, the bulb looks orangish. When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.

I doubt that this works at all...

It takes a voltage of about 14V to charge a nominal 12V gel cell.
Click to expand...
It takes a voltage of just over 12V to charge a 12V gell cell.
Set the series resistor to get the proper charging current.

How does a Lead acid car battery whose steady-state terminal voltage
is 12.65V cause the gel cell to be charged?
Anything over 12V will charge a gel cell.
Click to expand...
 
In article <c9389i$rq3$1@coward.ks.cc.utah.edu>,
MikeM <trashcan@yahoo.com> wrote:
Ken Smith wrote:


You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the glow
tells you whats happening. If you hook up backwards, the light is at full
brightness. If the battery is flat dead, the bulb looks orangish. When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.

I doubt that this works at all...

It takes a voltage of about 14V to charge a nominal 12V gel cell.
How does a Lead acid car battery whose steady-state terminal voltage
is 12.65V cause the gel cell to be charged?
Click to expand...
Take a DVM to a car battery that is freshly charged. You will see
something like 13.5V for a while after the charging stops.


:Stolen from http://www.qsl.net/wb3gck/gel-cell.htm
:
:Float Charging (aka Standby Service)
:
:In this mode, the battery is connected to a constant voltage source of
:2.25 to 2.30 volts per cell (13.5 to 13.8 volts for a 12-volt battery) at
:20° C. Provided that the charging source is regulated at the proper float
:voltage, the battery will establish its own current level and will be
:maintained in a fully charged condition. Gel cell batteries can be left
:in the float charge mode for extended periods of time without damage. This
:mode is often used to maintain gel cell batteries used in backup power
:applications.


--
--
kensmith@rahul.net forging knowledge
 
In article
<slrncbabiu.epq.The-Central-Scrutinizer@linux.client.comcast.net>,
TCS <The-Central-Scrutinizer@p.o.b.o.x.com> wrote:

On Wed, 26 May 2004 17:12:45 -0600, MikeM <trashcan@yahoo.com> wrote:
Ken Smith wrote:


You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the glow
tells you whats happening. If you hook up backwards, the light is at full
brightness. If the battery is flat dead, the bulb looks orangish. When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.

I doubt that this works at all...

It takes a voltage of about 14V to charge a nominal 12V gel cell.

It takes a voltage of just over 12V to charge a 12V gell cell.
Set the series resistor to get the proper charging current.

How does a Lead acid car battery whose steady-state terminal voltage
is 12.65V cause the gel cell to be charged?
Anything over 12V will charge a gel cell.
Click to expand...
Holding a gel-cell at 12V will actually kill it. As the other poster
said, the normal output is around 12.65V.

A DC-DC inverter with a 13.6 to 14.4 volt output is what's needed. They
can be found online. The schematics are non-trivial if you want enough
efficiency for more than a few mA output.
 
On Thu, 27 May 2004 01:52:14 +0800, "Wong Sy Ming" <simingx@anti_yahoo.com>
wrote:

Hi, does anyone have any links/circuits for a gel cell charger that will
take a 12V input from a vehicle battery to charge a smaller 12V battery? I
saw one in a distant issue of Silicon Chip magazine, but I don't think
that's available anymore.
Click to expand...
Yep. SC 7/89. Look no further, it is still available from Altronics, listed on
p279 of their current cattledog. Kit K1685 $26.50.

Note that this kit uses the Unitrode/TI UC3906 charge controller, which IMHO
offers one of the best charge regimes for SLA's.
Or, can I just connect the gel cell to something like a cigarette lighter
output with a diode in series to prevent back flow of current? How would the
charging current be limited?

TIA...
Click to expand...
 
TCS wrote:
Anything over 12V will charge a gel cell.
Click to expand...
WRONG!!!

go to: http://www.power-sonic.com/

click on "12 Volt"

click on PS-1250 (for example)

scroll down the spec seet where it says "Charging", read and learn!

also be sure to read the section on float charging.

MikeM
 
Ken Smith wrote:

Take a DVM to a car battery that is freshly charged. You will see
something like 13.5V for a while after the charging stops.
Click to expand...
A very shor while...

Now repeat the measurement one hour after charging stops,
" " " " 12 hours " " "
" " " " 24 hours " " "

Within just a few hours, the voltage will be down to 12.65V.

MIkeM
 
For what it's worth, I have a pair of 12V 7 AH gel cells that sit across my
car battery.
They are charged through a light bulb, similar to the previous
reccomendation.
They've been in place for two years now, and are working just fine, powering
half of the radios in my car. They are charged when the vehicle is running,
and add capacity to the system when not running. The lamp prevents excessive
charge current when dead, or discharge current when starting.

I'd prefer a boost reg with 5A output and a 12.5V UVLO, but I haven't
bothered to build one, since this seems to work just fine, summer and winter
(+130ish to -20ish)
 
"TCS" <The-Central-Scrutinizer@p.o.b.o.x.com> wrote in message
news:slrncbabiu.epq.The-Central-Scrutinizer@linux.client.comcast.net...
On Wed, 26 May 2004 17:12:45 -0600, MikeM <trashcan@yahoo.com> wrote:
Ken Smith wrote:


You can get away with connecting the gel cell through a 24V bulb to the
car battery. The resistance of the bulb limits the current and the
glow
tells you whats happening. If you hook up backwards, the light is at
full
brightness. If the battery is flat dead, the bulb looks orangish.
When
the battery is open or charged the light goes out.

It only works if the car battery is freshly charged.

I doubt that this works at all...

It takes a voltage of about 14V to charge a nominal 12V gel cell.

It takes a voltage of just over 12V to charge a 12V gell cell.
Set the series resistor to get the proper charging current.

Not any gell cells that I have owned. I found that it takes a voltage of
Click to expand...
around 14.3V to charge a gel cell at 10% of rated current.

Tam
How does a Lead acid car battery whose steady-state terminal voltage
is 12.65V cause the gel cell to be charged?
Anything over 12V will charge a gel cell.
Click to expand...
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top