7
Rev. 0
DEMO MANUAL DC2374B
MPPT QUICK START PROCEDURE
TheLTC4013hasamaximum power point tracking feature
that regulates the input voltage to the maximum power
voltage (VPM) by adjusting the output of the charger.
The LTC4013 MPPT function periodically stops charg-
ing, measures the open circuit voltage (VOC), and then
continues charging while regulating the input voltage. As
the sunlight changes, the VOC and VPM also change. This
board is setup to regulate a VPM voltage of 83% of the
measured VOC. This ratio can be changed to match the
solar panel by changing R2, R8, and R10. To change the
VOC/VPM ratio, follow the procedure listed in the Maximum
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 (ISC) of the panel as shown
in Figure 3. The solar panel can be replaced with a string
of silicon rectifier diodes that can handle the power dis-
sipation of Vf• ISC. With these methods, increasing the
current on the panel to ISC produces the maximum VOC
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 (RIN) as shown in Figure 4. RIN is
calculated by (VOC – VPM)/IMP where IMP is the maximum
power current. The supply current limit is set to ISC and the
voltage of the supply is set to the desired VOC representing
thedesiredsunlight. Set the power supply to the maximum
VOC to produce a full light condition. Reducing the supply
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
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 VPM point at this
time. This is because the battery voltage is below the
Low Battery threshold. If the battery voltage remains
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
up to above 1A. The battery voltage is now above
the low battery threshold. If the IMP is less than 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 VPM point
for the measured VOC.
8. If possible, vary the light conditions for the solar panel
orsimulator and observe thechargecurrentis adjusted
to maintain the VMP for the measured VOC.
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.
