Posted by Tim on January 13, 2006, 6:04 pm
Apologies if my question seems very basic.
I want to create a small off-grid system to provide lighting and
occasional power to a small stable block. To this end I have purchased
the following:
4 x 110Ahr leisure batteries
1 x 80W solar pannel (which came with a small 8amp charge controller)
1 x 2Kw (modified sine wave) inverter
I have assumed that I can connect the batteries in parallel, and have
done this in what may seem to be an odd way by connecting each one
separately to a common point, i.e. I have four leads for each of +ve
and -ve comming to one junction (for each pole). From that point I have
leads running to the inverter.
I did this so that I could easily remove any one of the batteries for
off-site charging if required, leaving the rest to power the system.
I have also assumed that I can simply connect the appropriate terminals
from the charge controller to the common junctions and the solar panel
will charge all the batteries together.
The charge controller does have a couple of terminals that are supposed
to go to the load (i.e. the inverter) but I don't want to use them as I
will be pushing far too much current through such a small device.
I have read some messages in this group that have worried me as I am
now concerned that connecting my four batteries together will cause
them to either overheat or be somehow not correctly balanced.
Am I doing anything wrong in the set-up I have proposed. By the way I
have not yet actually connected it all together, but I have all the
kit.
Posted by Pop on January 13, 2006, 6:46 pm
In the interest of no responses yet, I'll offer you what I know
and let those with actual experience chime in when they see your
message.
Batteries, I believe, MUST be ISOLATED from each other!! So far,
assuming the batteries are all in about the same condition, you
probably haven't had any damage yet, but I'm pretty sure it's
coming!
Something as simple as a diode can be used to isolate the
batteries. The "trick" is to NEVER let one battery be able to
supply power into another battery. Depending on the
circumstances, not having that isolation could result in anything
from a short battery life to an explosion that might be pretty
but also might be pretty dangerous.
When you tie two batteries together in parallel, they will try
to instantaneously become one battery. If one battery is, say,
12.5 volts, and the other battery is, say, 12.0V, they will
source/sink current until they are both the exact same voltage.
The amount of amperage that will generate will depend on a lot
of things, but mainly the battery's internal resistances. For a
half volt difference, you may or may not notice anything going
on.
Now, let's draw some power off them. They aren't likely to be
perfectly identical, so one will start to "drain" at a different
level than the other. One battery will supply current at a
higher rate than the other. But when the load drops, or is
removed, now the two batteries will again try to come to
equilibrium, which means they will attempt to instantaneously
move to identical charges. Now, THAT situation could be many,
many amps, in the extreme limited only the the very low battery
internal resistances and the wiring resistances. In the extreme
it could be like shorting one of the batteries and super-charging
the other way above its safe charge current. And bloomo;
something has to give. With luck, it'll be a shortened battery
life until it becomes simply a resistor. Without luck, you have
sparks, melting, possible implosion/explosions and lots of acid
flying around in addition to the heat.
I would disconnect the batteries ASAP until you can learn more
about how to isolate them from each other and get a safet setup
in there.
And yes, I know it's possible to parallel batteries in some
battery operated equipment, but that's a different game with
entirely different possibilities in most cases. That's why most
things you see have series battery arrangements vs parallel -
much longer battery lifetimes.
HTH, and I'm sure someone with actual experience will be along
soon.
Pop
: Apologies if my question seems very basic.
:
: I want to create a small off-grid system to provide lighting
and
: occasional power to a small stable block. To this end I have
purchased
: the following:
: 4 x 110Ahr leisure batteries
: 1 x 80W solar pannel (which came with a small 8amp charge
controller)
: 1 x 2Kw (modified sine wave) inverter
:
: I have assumed that I can connect the batteries in parallel,
and have
: done this in what may seem to be an odd way by connecting each
one
: separately to a common point, i.e. I have four leads for each
of +ve
: and -ve comming to one junction (for each pole). From that
point I have
: leads running to the inverter.
:
: I did this so that I could easily remove any one of the
batteries for
: off-site charging if required, leaving the rest to power the
system.
:
: I have also assumed that I can simply connect the appropriate
terminals
: from the charge controller to the common junctions and the
solar panel
: will charge all the batteries together.
:
: The charge controller does have a couple of terminals that are
supposed
: to go to the load (i.e. the inverter) but I don't want to use
them as I
: will be pushing far too much current through such a small
device.
:
: I have read some messages in this group that have worried me as
I am
: now concerned that connecting my four batteries together will
cause
: them to either overheat or be somehow not correctly balanced.
:
: Am I doing anything wrong in the set-up I have proposed. By the
way I
: have not yet actually connected it all together, but I have all
the
: kit.
:
Posted by Steve Spence on January 13, 2006, 8:12 pm
Pop wrote:
> In the interest of no responses yet, I'll offer you what I know
> and let those with actual experience chime in when they see your
> message.
>
> Batteries, I believe, MUST be ISOLATED from each other!! So far,
> assuming the batteries are all in about the same condition, you
> probably haven't had any damage yet, but I'm pretty sure it's
> coming!
> Something as simple as a diode can be used to isolate the
> batteries. The "trick" is to NEVER let one battery be able to
> supply power into another battery. Depending on the
> circumstances, not having that isolation could result in anything
> from a short battery life to an explosion that might be pretty
> but also might be pretty dangerous.
No No No. When using 12 volt batts in a 12v pack, all the positives are
connected to gether, and all the negatives are connected together. There
are no diodes. All the batts need to be identical in type and life.
Your charger wants to see them as one big battery.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html
Posted by SolarFlaire on January 13, 2006, 9:58 pm
I have to agree with Steve on this one. While no
personal experience with doing this it is done on a
quite popular basis. Ever see a diode explode? I have
and you want your face and eyes covered. Little
firecrackers they are. Forget the diodes, too much loss
and resistance.
The start topology is a great idea although probably
not necessary. It may help the sharing of charge and
discharge between the cells. regular equalizing also
helps. The weaker clucters will get brought up to the
level of the stronger ones, avoiding cross charging (if
such a thing even exists)
If the fear mongers really get you down, you insert
large fuses in each lead to the star point. The fuses
will off a few milliohms of isolation between the
clusters and also provide some protection in the rare
case of a shorted cell.
Remember, all the square inches of plate material in a
cell are in parallel already. You are just separating
some of the surface area into different boxes.
> No No No. When using 12 volt batts in a 12v pack, all
the positives are
> connected to gether, and all the negatives are
connected together. There
> are no diodes. All the batts need to be identical in
type and life.
> Your charger wants to see them as one big battery.
> --
> Steve Spence
> Dir., Green Trust, http://www.green-trust.org
> Contributing Editor, http://www.off-grid.net
> http://www.rebelwolf.com/essn.html
Posted by Windsun on January 14, 2006, 2:55 am
That is exactly what they are SUPPOSED to do.
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> When you tie two batteries together in parallel, they will try
> to instantaneously become one battery.....
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> and let those with actual experience chime in when they see your
> message.
>
> Batteries, I believe, MUST be ISOLATED from each other!! So far,
> assuming the batteries are all in about the same condition, you
> probably haven't had any damage yet, but I'm pretty sure it's
> coming!
> Something as simple as a diode can be used to isolate the
> batteries. The "trick" is to NEVER let one battery be able to
> supply power into another battery. Depending on the
> circumstances, not having that isolation could result in anything
> from a short battery life to an explosion that might be pretty
> but also might be pretty dangerous.