From: John
Pfeifer
Sent: Thursday, March
18, 2010
11:52 AM
Here is the
answer to your question in the
form of an FAQ which we can clean up and then publish it on our
website.
Question:
How
does the State of Charge
energy meter determine when the battery is full?
Answer: The
State
of Charge
readout
or Energy Meter works exactly like the ever popular Tri-Metric meter
from
Bogart Engineering. Apollo Solar licensed the technology from Bogart
Engineering so our T80 would display the same numbers as everyone’s
Tri-Metric. When the T80 is first installed, it has no way of
knowing the state of the battery so it displays ??? on the front panel
LCD. The battery is charged through the normal cycles of Bulk and
Absorb and when it finishes the Absorb stage, and the battery is full
by definition,
it goes into the Float stage. At this point, the T80 tells the
internal State of Charge
software that the battery is at 100%. We often look at this like
filling the gas tank of a car: the only way to really know that the gas
tank is full is when the gas is dripping from the filler port.
By the same
gas tank
analogy, when the T80 is set up it has to be told how many gallons the
gas
tank will hold. This is the Amp Hour capacity of the battery. There
is some elegance in integrating the State of Charge meter into the charge
controller
since only the charge controller knows exactly when the battery is full
as it
goes into the Float stage.
While we are
on the
subject, we should describe how the Energy Meter follows the actual
State of Charge
of the battery
and why it is the best method. A current shunt is required in the
system
which is wired such that all the current that goes into and out of the
battery
must pass through it. Starting from the 100% full state at Float,
the T80 software counts current that is discharged from the
battery and subtracts it from the total Amp Hour Capacity that was
programmed
in as the full battery capacity. When the battery is charged, all
the current going into the battery is measured and added to the total.
Even though this running total can sometimes get a little off when the
battery
is old or has some weak cells, it is much better than measuring the
battery
voltage. First of all the running total is reset to 100% every time
the battery goes into float mode. In order to get an accurate state
of charge reading by measuring the battery voltage, all the charging
sources
and loads must be disconnected from the battery and it must rest for
about 20
minutes. Since this is not practical in a real installation, the
battery
voltage is often measured under load or while charging, which give
totally
erroneous readings.
-------- Original Message --------
I'm sure that's all
cleared up for current versions,
by now.
Now a couple of years
later, we've had zero trouble,
and we are running well over 70 amps continuous.
The wireless Trimetric
meter option is a pretty good
reason to use Apollo for off grid projects, too.
So do the charge
controller and amp hour meter communicate so they agree
on when the batteries are fully charged?
Todd
On Wednesday, March
17, 2010 12:02pm, "R Ray Walters" <[email protected]>
said:
We have a couple out in the field. A bit of hassle to upgrade the
firmware at
first, but Apollo was very helpful, and sent us a free interface to do
the
update.
is a pretty good
reason to use Apollo for off grid projects, too.
