function of a controller or regulator is to fully charge a battery
without permitting overcharge. If a solar array is connected to
lead acid batteries with no overcharge protection, battery life
will be shortened. Simple controllers contain a relay that opens
the charging circuit, terminating the charge at a preset voltage
and, once a preset low voltage is reached, closes the circuit,
allowing charging to continue. More sophisticated controllers
have several stages and charging sequences to assure the battery
is fully charged. The first 70 to 80 percent of battery capacity
is easily replaced. It is the last 20 to 30 percent that requires
more attention and therefore more complexity.
controllers work and available options
The circuitry in a controller reads the voltage of the batteries
to determine the state of charge. Desig
ns and circuits vary, but
most controllers read voltage to reduce the amount of power flowing
into the battery as the battery nears full charge.
that can be included with controllers:
- Reverse current
leakage protection by disconnecting the array or using
a blocking diode to prevent current loss into the modules
load disconnect to reduce damage to batteries by avoiding
- System monitoring
analog of digital meters, indicator lights and/or warning
protection with fuses and/or circuit breakers.
- System control
control of other components in the system; standby generator
or auxiliary charging system, diverting array power once batteries
are charged, transfer to secondary batteries.
compensation utilized whenever batteries are placed in
a non-climate controlled space. The charging voltage is adjusted
to the temperature. Recommended on most systems.
Sizing a Controller
Charge controllers are rated and sized to the systems they protect
by the array current and voltage. Most common are 12, 24, and
48 volt controllers. Amperage ratings run from 1 amp to over
For example, if one module in your 12 volt system produces 3.5
amps and four modules are utilized, we produce 14 amps of current
at 12 volts. Because of light reflection and the edge of cloud
effect, sporadically increased current levels are not uncommon.
For this reason we increase the controller amperage by a minimum
25 percent bringing our minimum controller amperage to 18.7.
Looking through the products available, we find a 20 amp controller.
There will be no problem using a 30 amp or larger controller,
aside from the additional cost. If you think you may increase
the system size, a larger than needed controller may be the