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MPPT QUICK START PROCEDURE
The LTC4013 has a maximum power point tracking feature
that regulates the input voltage to the maximum power
voltage (V
) by adjusting the output of the charger.
PM
The LTC4013 MPPT function periodically stops charg-
ing, measures the open circuit voltage (V
continues charging while regulating the input voltage. As
the sunlight changes, the V
board is setup to regulate a V
measured V
. This ratio can be changed to match the
OC
solar panel by changing R2, R8, and R10. To change the
V
/V
ratio, follow the procedure listed in the Maximum
OC
PM
Power Point Tracking section in the LTC4013 data sheet.
There are a number of ways to test the MPPT function of
the LTC4013. The most accurate way is to use a solar panel
in sunlight, however it is difficult to control the sunlight
conditions. Another method is to use a covered solar panel
(dark panel) biased thru a controlled current source from
0A to the short circuit current (I
in Figure 3. The solar panel can be replaced with a string
of silicon rectifier diodes that can handle the power dis-
sipation of V
• I
. With these methods, increasing the
f
SC
current on the panel to I
for a full light condition. Reducing this current simulates
lower light conditions.
A more simple method is to supply a voltage to DCIN with
a series input resistor (R
calculated by (V
– V
)/IMP where IMP is the maximum
OC
PM
power current. The supply current limit is set to I
voltage of the supply is set to the desired V
the desired sunlight. Set the power supply to the maximum
V
to produce a full light condition. Reducing the supply
OC
voltage simulates lower light conditions.
To evaluate the LTC4013 MPPT function follow the pro-
cedure below:
1. Set the DC2374B to operate in MPPT mode with a three
stage lead acid battery charging mode by positioning
the jumpers as listed below:
JP1
ENABLE - ON
JP2
MPPT - ON
JP3
MODE2 – LO
JP4
MODE1 – HI
), and then
OC
and V
also change. This
OC
PM
voltage of 83% of the
PM
) of the panel as shown
SC
produces the maximum V
SC
) as shown in Figure 4. R
IN
SC
representing
OC
DEMO MANUAL DC2374B
JP5
NTC – INT
JP6
TIMER – CAP
JP7
PULL_UP PWR - DCIN
2. With power off, connect a 0V to 16V, 6A power supply
(PS2) to BAT and GND terminals with a series ammeter
and a voltmeter as shown in Figure 1.
3. With power off, connect a 5.1A load (LOAD1) to BAT
and GND terminals in parallel with PS2 as shown in
Figure 1.
4. Set PS2 to 10V and turn on PS2 and LOAD1.
5. With power off, connect a solar panel or solar panel
simulator as previously discussed and refer to Figure
3 and Figure 4 as needed.
6. With a full or close to full light condition, observe that
the battery charger current is only about 1A, 20%, and
the voltage on the ISMON terminal measures about
0.2VDC. DCIN is also above the V
time. This is because the battery voltage is below the
Low Battery threshold. If the battery voltage remains
OC
below low bat for 25 minutes then the charger cycle
is terminated. The solar panel can supply more power
to the charger than needed at this point.
7. Slowly increase PS2 until the battery current jumps
is
IN
up to above 1A. The battery voltage is now above
the low battery threshold. If the IMP is less than the
and the
input current needed to provide full charge current,
the LTC4013 will regulate the charge current below
full load to obtain a DCIN voltage near the V
for the measured V
8. If possible, vary the light conditions for the solar panel
or simulator and observe the charge current is adjusted
to maintain the VMP for the measured V
NOTE: If the charge current is reduced below C/10,
~ 500mA, and the battery voltage is over the low battery
threshold, then the TEOC timer will start even if the battery
voltage is not approaching the absorption voltage.
9. If possible, return the light source to near full light
condition.
point at this
PM
.
OC
.
OC
point
PM
Rev. 0
7
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