Solar Charge Controller Notes

A solar charge controller of any type should have Temperature compensation, However,
only the better controllers have it. The best temperature comp is an external temperature sensor
(normally sold separately). With an external sensor the battery temperature is checked and
adjusted for and not the room temp. Batteries are full of mass so it takes a while for them to adjust
to room temp. You need a higher voltage in the cold and a lower voltage in hot areas.

Digital readout is a great way to check charge efficiency. Input Voltage times Amps = Wattage.
Then do the same for the output voltage and amps.Compare these two numbers and you have
your controller efficiency. Wattage is the best way to check efficiency. Divide the out put watts
by the input watts.

Power requirements for charging a battery bank are 5% to 10 % of the total amp hour rating of
the bank. 10% is better but double the cost. Charge controllers come in sizes to charge from 12
volts to 48 volt battery banks. In multiples of 12 volts. Don’t pick 36 volts because there are not
any power inverters that I know of that will use that voltage.

Just a note from my observations: Some controllers will allow your battery voltage to drop to
12.4 volts before it will start charging. The better charge controllers will hold the battery voltage
at the set float voltage. What I see is a problem with this is if your batteries were fully charged by
noon and a light was on somewhere, It might make it till dark or late after noon to reach 12.4 volts
and you start the night with a low battery bank. It should have been holding the float voltage from
the time it reached full charge at noon.

When you set the float voltage the controller should hold that voltage if it has the input
power to do it. It should not allow the battery to discharge or even use the battery voltage as long
as the sun is shining. Your load should first be supplied by the solar panels and if the
requirement was too high then tap the battery bank. Your batteries are your battery backup and
not meant to be used unless there is not enough light for the solar panels. The panels should
recharge them every morning and then maintain them the rest of the day at float voltage. This all
leads into the charging cycles. Bulk charge, Absorb and Float. One other charging type is the
Equalization charge. Everyday your charge controller will start a bulk charge by putting
everything it can into the batteries to reach your set bulk charge voltage. Normally about 14.8
volts depending on the brand and type (lead acid or gel etc..) of the battery. Same for the float
voltage based on the battery brand and type.

The bulk charge brings the batteries up to a bubbling state which helps clean the lead
plates in the battery. At this point it goes into the absorb mode which holds that voltage for an
hour or two depending on your settings. After the absorb time say 2 hours it will switch to the float
stage where it just holds the voltage you pre-set. Your panels are at idle at this point or only
using a few amps from them. Un-like windmills or hydro generators will not need a diversion load.
Most charge controllers have a hookup and or setting for this. Not having diversion will not hurt
your solar panels in anyway. Just means you waste your extra solar electric. You will find
something to use it for I’m sure.

Battery Equalization or "EQ" is a once every 4 month to twice a year thing for lead acid
batteries only. It depends on how hard you are using them. Equalization charging is the deliberate
process of charging a battery or battery bank at a high voltage for a set period of time to remix the electrolyte and destratify the internal plates. Equalize charging helps to remove sulfate buildup on
battery plates and balances the charge of individual cells. The charge controller Equalization holds
the voltage above the bulk setting for 1 to 2 hours by 1 volt at 12 volts or double for 24 volts times
four for 48 volts.