# How much current will actually flow from panels to battery ?

D

#### daveem Dave M

Jan 1, 1970
0
I have a question that I hope some one here can help me with.

I understand that due to the internal resistance of a led acid battery,
one can never expect to get the full charge potential to go from your
Solar Panels to your batteries, and I have observed that the current
flow to the batteries also depends on the state of charge in the
battery. but given that a battery is 50 percent discharged, using a
conventional solar panel designed to charge 12 volt battery, how much
current will actually flow from the panel to the cells, and how much
does it vary from an L16 battery Vs a T105? I suppose it goes with out
saying that more batteries will result in a better transfer of power,
but it would help me to know what kind of losses in current to expect.
excluding the other chemical inefficiencies.

The bottom line here is I was wondering if I could get away with a 20
amp charge controller, if my panels had the potential to put out 22
amps, since only so much current will actually pass to the batteries.
Thanks. Dave

G

#### Gymy Bob

Jan 1, 1970
0
There are too many variables involved to pre calculate this.

Temperature of the solar cells and battery
Age of the solar cells and battery.
Impedance of the battery.
Impedance of the wiring.
Capacity of the solar cells.
Nature of the charger control circuit.
etc...etc...

M

#### m II

Jan 1, 1970
0
daveem said:
The bottom line here is I was wondering if I could get away with a 20
amp charge controller, if my panels had the potential to put out 22
amps, since only so much current will actually pass to the batteries.

I have two BP 85 watt panels. They are rated at roughly 4.6 amperes
each. They are paralleled, so I'd expect 9.2 amps maximum.

On a very clear day last month, I had a reading of roughly 10.8 amps
going into the 12 volt battery bank.

Be careful with your controller, as it may be subjected to MORE than
the rated amperes on the panels. If you expect 22 amps. then go with a
thirty amp or higher controller. Also, consider the future. What
happens if you get more panels? You will then have to get another
controller to replace or use with your 20 ampere unit. Get a bigger
one now and save grief down the road.

mike

G

#### Gymy Bob

Jan 1, 1970
0
Aren't we talking about a DC-DC charge controller here that actually
transformers the voltage to the desired charge voltage and increases the
current in the process to get full VA capacity out of the solar cells?

M

#### m II

Jan 1, 1970
0
Gymy said:
Aren't we talking about a DC-DC charge controller here that actually
transformers the voltage to the desired charge voltage and increases the
current in the process to get full VA capacity out of the solar cells?

I don't know. I could have mistakenly assumed it was a regular charge
controller and NOT one of those 'maximizer' sorts.

mike

S

#### Steve Spence

Jan 1, 1970
0
That would be a mppt controller. Very few charge controllers have that
capability.

Steve Spence
Dir., Green Trust
http://www.green-trust.org

Replies
2
Views
2K
Replies
5
Views
2K
Replies
2
Views
2K
Replies
9
Views
1K
Replies
8
Views
2K