This is only a preview of the January 1994 issue of Silicon Chip. You can view 29 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Articles in this series:
Items relevant to "40V 3A Variable Power Supply; Pt.1":
Items relevant to "A Switching Regulator For Solar Panels":
Items relevant to "Printer Status Indicator For PCs":
Items relevant to "Simple Low-Voltage Speed Controller":
Items relevant to "Computer Bits":
Articles in this series:
Items relevant to "Control Stepper Motors With Your PC":
|
Are you interested
in charging batteries
from a solar panel?
Here is a regulator
designed especially
for the job. It can be
built in two versions
(10-amp or 20-amp)
& can be used to
charge a 12V or 24V
battery bank.
I
N THE SIMPLEST solar panel plus
battery setup, all you need is a
diode to isolate the panel from
the battery. This prevents the battery
from discharging via the solar panel
when it is not illuminated by the Sun.
This is OK for a temporary setup but
unless the solar panel is only trickle
charging the battery, you will eventually run up against the problem of
over-charging.
To avoid over-charging the battery
you need a regulator circuit so that
the panel can charge the battery at
its maximum current output until it
reaches full charge. At that point, the
regulator disconnects the panel from
the battery and no further charging
takes place. That is the function of the
circuit presented here.
As depicted in the photos in this
article, this regulator is built up on
a small PC board with a number of
power semiconductors which need to
be mounted on a heatsink. The board
itself would normally be mounted
inside a plastic case with the heatsink
on the outside.
How the circuit works
In effect, this circuit works like a
switch. If the battery voltage is below
13.6V, the solar panel is connected.
Once the battery voltage rises above
that point, the solar panel is dis
connected. A Schottky power diode,
used because of its low forward voltage loss, prevents the battery from
discharging back via the panel when
there is no sunlight. To see how the
circuit works, have a look at the diagram of Fig.1.
Switching regulator
for solar panels
Design by OTTO PRIBOJ
The regulator circuit can be housed in
a plastic case but note that the power
devices must be mounted on a large
finned heatsink to provide cooling.
The two indicator LEDs protrude
through the lid of the case near one
corner of the heatsink.
40 Silicon Chip
D1
1N4148
C
10k
Q1
BC337
IC1
78L05/7805
OUT
IN
E
GND 100k
22
B
BC--B
C
E
0.1
K
A
7805
78L05
OUT
IN
ZD1
15V
GND
VIEWED FROM
BELOW
I GO
GDS
K
A
D4
K
A
D5
LINK FOR
12V
K
22
22k
1%
2
+6V
12V
OR
24V
2xPBYR1645
ZD2
30V
39k 1%
3
VR1
5k
+4V
D2
1N4148
8
1
IC2a
TLO62
6.8k
Q2
BC557
B
E
D3
1N4148
C
4
4.7k
330k 1%
12k
1%
1k
LED1
GREEN
1
8.2k
K
A
LED2
YELLOW
100k
220k
SOLAR
PANEL(S)
Q3
STP60N05
S
G
10k
Q4
STP60N05
G
S
4.7k
A
A
D
D
K
SOLAR PANEL REGULATOR
Fig.1 (above): the circuit is based on
comparator IC2a. When the battery
voltage is below 13.6V, IC2a’s output
is low & so Q2 turns on Q3 & Q4 to
connect the solar panel. Conversely,
when the battery voltage is above
13.6V, the output devices switch off &
the solar panel is disconnected.
While the circuit may look a little
daunting, it is really quite simple in
operation. Notice that the positive
terminal of the solar panel connects
via Schottky diode D4 (and D5 for a
high current version – ie; greater than
10 amps) to the positive terminal of
the battery. The negative terminal of
the panel connects to the negative
terminal of the battery via Mosfet Q3
(and Q4 for the high current version)
and it is the Mosfet which is the
switching element. It is turned on or
off, depending on the charge state of
the battery.
Op amp IC2a is the heart of the
circuit and it is connected as a comparator. It compares a reference voltage
produced by a 5V 3-terminal regulator
(IC1) at pin 2 with a proportion of the
battery voltage at pin 3. When the
voltage at pin 3 is above the reference
voltage at pin 2, the output at pin 1 is
high and transistor Q2 is off. Hence
Mosfet Q3 (and Q4 if used) is also off
and so the solar panel is effectively
disconnected from the battery.
Conversely, if the voltage at pin 3 is
below the voltage on pin 2, the output
The power devices (D4, D5, Q3 & Q4) are
connected to the PC board via insulated flying
leads. Use heatshrink tubing or plastic sleeving
to insulate the leads of these devices, to prevent
accidental shorts.
January 1994 41
been designed around a TL062 dual
low current Fet-input op amp but only
one op amp, IC2a, is actually in use.
The other op amp is disabled by tying
its inputs (pins 5 & 6) low.
24V operation
As noted above, the circuit can be
used for 24V systems and for this you
would need two 12V solar panels in
series and a 24V battery (or two 12V
batteries in series).
When 24V operation is required,
the input voltage divider from the
battery is changed, to take account
of the higher voltage. Note the 39kΩ
resistor connected to the positive side
of the battery. This is in circuit for 24V
operation or replaced with a link for
12V operation.
Finally, D1, Q1 and ZD1 form a
nominal 15V regulator to supply op
amp IC2a and transistor Q2. For 12V
operation, this circuit can be omitted
or left in place – the circuit will function either way. The voltage at the
emitter of Q1 will be only about +10V
for a 12V battery input.
Current capacity
The assembled PC board is mounted on the lid of the case on 10mm tapped
standoffs. Note that a small slot must be cut in the base opposite the terminal
block to provide entry for the leads to the battery & to the solar panel.
at pin 1 is low and so Q2 turns on Q3
(and Q4 if used) so that the solar panel
is now connected.
The rest of the circuit really amounts
to a few frills. LED 1, at the output of
IC2a, indicates “float/full charge”. It
turns on when the solar panel is disconnected. LED 2, driven by transistor
Q2, is turned on while ever the solar
panel is connected to the battery. It
indicates “on charge”.
We should note that the circuit has
As noted above, the circuit can be
configured to handle the output of
panels rated up to 10 amps with one
Mosfet (Q3) or increased to 20 amps
with two Mosfets (Q3 & Q4). If two
Mosfets, are used then two Schottky
diodes will also be required. (D4 &
D5). If more than one solar panel is
used, then an alternative arrangement
of one Schottky diode in series with
each panel should be used.
Construction
All parts with the exception of Mos
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
No.
1
1
2
1
1
1
2
1
1
2
1
42 Silicon Chip
Value
330kΩ
220kΩ
100kΩ
39kΩ
22kΩ
12kΩ
10kΩ
8.2kΩ
6.8kΩ
4.7kΩ
1kΩ
4-Band Code (1%)
orange orange yellow brown
red red yellow brown
brown black yellow brown
orange white orange brown
red red orange brown
brown red orange brown
brown black orange brown
grey red red brown
blue grey red brown
yellow violet red brown
brown black red brown
5-Band Code (1%)
orange orange black orange brown
red red black orange brown
brown black black orange brown
orange white black red brown
red red black red brown
brown red black red brown
brown black black red brown
grey red black brown brown
blue grey black brown brown
yellow violet black brown brown
brown black black brown brown
8.2k
0.1
4.7k
1uF
D3
100k
12k
6.8k
1
IC2
TLO62
VR1
330k
100k
39k
PARTS LIST
4.7k
10k
ZD1
ZD2
LED2
D2
22uF
22k
220k
SOURCES Q3, Q4
SOLAR CELLS
ANODES D4, D5
22uF
Q1
D1
DRAINS Q3, Q4
BATTERY
CATHODES D4, D5
LED1
IC1
1k
Q2
GATES
Q3, Q4
10k
Fig.2: install the parts on the PC board as shown in this wiring
diagram. The connections to the power devices (D4, D5, Q3 & Q4)
are made via flying insulated leads which are soldered directly to
the pins of the terminal block on the back of the PC board.
1 PC board, code OP-004
1 PC mount 4-way terminal block
1 heatsink (see text)
1 5kΩ multiturn trimpot (VR1)
Semiconductors
1 78L05 3-terminal 5V regulator
(IC1)
1 TL062 Fet-input op amp (IC2)
1 BC337 PNP transistor (Q1)
1 BC557 PNP transistor (Q2)
1 STP60N05 N-channel Mosfet
(Q3; add Q4 for 10A version)
1 PBYR1645 Schottky diode
(D4; add D5 for 10A version)
3 1N4148 diodes (D1,D2,D3)
1 BZX79C15 15V Zener diode
(ZD1)
1 BZX79C30 30V Zener diode
(ZD2)
1 green LED (LED1)
1 yellow LED (LED2)
Capacitors
2 22µF 35VW PC electrolytic
1 1µF 35VW PC electrolytic
1 0.1µF monolithic
Resistors (0.25W, 1%)
1 330kΩ
2 10kΩ
1 220kΩ
1 8.2kΩ
2 100kΩ
1 6.8kΩ
1 39kΩ
2 4.7kΩ
1 22kΩ
1 1kΩ
1 12kΩ
The power devices must be insulated from the heatsink using suitable mica
washers & insulating bushes. Smear all mating surfaces with thermal grease
before bolting the assemblies together, then use your multimeter to confirm that
each device is indeed correctly isolated.
fets and Schottky diodes are mounted
on a small PC board measuring 78 x
54mm. A 4-way insulated terminal
black is mounted at one end for the
four external connections to the battery and solar panel.
Trimpot VR1 is a multi-turn top
adjust type which gives easy and
precise setting of the “end-of-charge”
battery voltage. The 3-terminal 5V
regulator may be a 7805 or a 78L05
type, although the latter is preferable
since its current drain is lower which
could be important in this application.
Two prototypes are depicted in the
photos accompanying this article. One
is shown as a board only, with the power semiconductors attached by flying
leads. They will need to be mounted
on a suitable heatsink with the usual
insulating bushes, mica washers and
thermal grease.
The second prototype is shown with
the PC board mounted in a plastic box
and the two LEDs have been taken off
the board and mounted so that they
protrude through the lid of the case.
Where to buy the parts
Short form kits for this project are
available only from the designer,
Otto Priboj. The kit consists of
the regulator PC board plus
components and is priced at
$54. Additional components to
make a 20A version are priced as
follows: STP60N05 $8; PBYR1645
Schottky diode $5.00; postage &
packing, $4.00. Mail orders with a
cheque or money orders should be
sent to Otto Priboj, PO Box 362,
Villawood, NSW 2163. Phone (02)
724 3801.
Setting up
To set the circuit up you will need a
power supply to substitute for a solar
panel and a 12V battery (since the
circuit will not work unless a battery
is connected).
Turn on the power supply and wind
up the voltage. Note that no current
will flow until the power supply exceeds the battery voltage. Turn up the
supply voltage so that it is a few volts
higher and measure the voltage across
the battery. Adjust trimpot VR1 so that
the battery voltage does not exceed
13.8V while on charge.
For a 24V system, the approach is
the same except that the cutoff voltage
SC
is adjusted to 27.6V.
January 1994 43
|