Care for your rechargeable batteries
High-current
Battery Balancer
Part 2 – by Duraid Madina
Introduced last month, our new High-current Battery Balancer is an
advanced design which provides high efficiency and fast balancing by
efficiently transferring charge between connected cells or batteries. It
can handle cells or batteries up to 16V, and two units can be combined for
larger installations. This second and final article describes the assembly
and testing steps, and how to use it.
W
e put considerable effort into keeping this
design as simple as possible, while still providing
excellent performance and many useful features.
As a result, the parts count is not especially high. However, we have had to use mostly SMD parts to keep the size
reasonable, and also because many of the best part choices
were not available in through-hole packages at all.
Therefore, while the board assembly is not overly difficult, it is not suitable for beginners – some SMD soldering
experience is desirable.
You will need a decent temperature-controlled soldering
station (and ideally, a reflow oven or hot air rework station),
a syringe of flux paste, some solder wick, fine-tipped tweezers, a magnifier and a strong light source.
None of the SMD parts are especially difficult to handle,
although the smaller six-pin parts in SOT-363 packages are
on the tricker side, along with QSOP-16 ICs, which have
pins that are fairly close together. Finally, the transformers can present a bit of a challenge in making good solder
joints due to their high thermal mass. But with a little care,
the PCB can be built by hand.
Construction
The High-current Battery Balancer is built on a four-layer
PCB coded 14102211 which measures 108 x 80mm. Refer
to the PCB overlay diagrams, Figs.4(a) and 4(b) overleaf,
for details on which parts go where. We suggest you start
construction by populating the surface-mount components
on the board’s underside, followed by the SMDs on the top
side, and then finally, the through-hole parts.
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As touched on earlier, you can use various assembly
methods, including reflow soldering or hand-soldering. We
will describe the hand-soldering method as it requires the
fewest specialised tools, as listed above.
The general procedure is to place each part (with the correct orientation for polarised parts, which is pretty much
all ICs, diodes and MOSFETs) and tack down one pin. You
then check the alignment of the other pins and re-position
the part by melting the tack solder and gently nudging the
part if it is not perfectly aligned with its pads. Once aligned,
it is a good idea to add flux paste to all the pins, as that
greatly reduces the chance of solder not adhering.
You then solder the remaining pins, refresh the initially
tacked pin (if you have added flux paste then all you need to
do is touch it with the tip of the iron), then use solder wick
and flux to clean up any bridges which might have formed.
The order in which components are placed is not critical,
but it’s best to place the most difficult parts on each side
first, so that you do not have to deal with interfering adjacent
components. The following procedure uses that method.
Note that SMD resistors are typically marked with a tiny
code on the top that indicates the value (eg, 47kΩ = 473 [47
x 103] or 4702 [470 x 102]), which you probably need a magnifier to see. SMD ceramic capacitors are usually unmarked.
Finally, note that most of the semiconductor devices used
are sensitive to electrostatic discharge (ESD) – particularly
those in the smaller packages. Therefore, when handling these
devices, try and avoid touching their pins. A grounded anti-static wrist strap will usually ensure you can’t damage any
parts, but there are many other ways of ensuring ESD safety.
Practical Electronics | May | 2022
Assembly details
Start by fitting the eight 1Ω gate-drive resistors, because they are the smallest passive components
on the board and are generally out of the way
of other parts. Next, fit the eight gate-drive
NMOS/PMOS FET pairs: Q27, Q28, Q22,
Q23, Q16, Q17, Q11 and Q12.
These are relatively large as six-pin
SMDs go, so they should not give
you too much trouble, but watch
the orientation! You might need
a magnifier to find the pin 1
dot on the top of each device,
which in each case goes in
the bottom right corner, as shown
in Figs.4(a) and 4(b).
Next, mount the eight 4.7µF capacitors which
are adjacent to these MOSFET pairs. Follow with the
five 330Ω resistors on this side of the board, plus the four
20Ω resistors, then the eight 10µF capacitors alongside the
mounting pads for MOSFETs Q1-Q4.
The components labelled ‘Rsnub’ and ‘Csnub’ are required
if you are balancing 12V batteries, but are not needed for
lower voltage balancing, such as Li-ion/LiPo/LiFePO4 cells.
If you need them, fit them now, using the values suggested in the parts list published last month (30Ω and 470pF).
Now install MOSFETs Q1-Q5. These are in LFPAK56
SMD packages, which are similar to 8-pin SOIC devices,
but with a tab replacing four of the pins on one side. As
such, it should be obvious which way round they go, but
don’t get the BUK9Y8R5-80E used for Q5 mixed up with
the similar BUK9Y4R8-60Es used for Q1-Q4.
In each case, spread a little flux paste on the tab pad before tacking one of the small pins, then solder the remaining three small pins before the tab. You might need to crank
your iron temperature up to solder the tabs as they have a
lot of thermal mass. The flux paste you added earlier should
help draw the solder you feed in under the tab for a good
thermal and electrical connection.
With those in place, fit the eight remaining MOSFETs on
this side of the board using the same technique. They are all
BUK9Y14-80Es (a different type again from Q1-Q4 and Q5).
Now fit the four SMB TVS diodes, ZD1-ZD4, ensuring
that their cathode strips are oriented as shown in Fig.4.
Note that the voltage rating of these parts varies depending
on what type of cells or batteries you are balancing (see the
parts list last month).
Solder them similarly to the passives, but being larger,
they take a bit more heat. Their leads wrap around the sides,
so make sure the solder adheres to both the PCB and the
device leads (flux paste makes this much easier to achieve).
The next job is to solder the four 3A SMD fuses, which
mount similarly to resistors (they are not polarised). That
just leaves two small resistors: one 100kΩ 0.1% resistor, and
another 0.1% resistor, the value of which varies depending
on your application. Make sure you don’t get them mixed up.
Top-side SMDs
Flip the board over and continue assembly by fitting the
four larger, 3.2 x 2.6mm (M3226 or 1210) sized ceramic
capacitors near the transformer T1-T4 footprints. We used
4.7µF 100V capacitors (TDK CNA6P1X7R2A475K250AE)
but you can more than double the capacitance by using
10µF 75V capacitors which cost only a little bit more (TDK
CGA6P1X7R1N106K250AC).
Follow by fitting the five small dual MOSFETs, Q8,
Q18, Q13, Q19 and Q24. In each case, make sure that the
pin 1 dot is lined up correctly first. These are in smaller packages than the ones you mounted on the bottom of
Practical Electronics | May | 2022
the PCB, with more closely spaced pins, so they might be
a little bit trickier. But they aren’t too hard as long as you
remember to carefully check for bridges between pins using a magnifier and fix any bridges you find using flux
paste and solder wick.
MOSFET Q7, in the bottom-right corner, is in the same
package as those five but it is a slightly different device, so
don’t get it mixed up. Again, check its orientation carefully before soldering it in place.
Now is a good time to mount the microcontroller, IC2. It
should be relatively easy compared to the devices you have
already soldered, but make sure that the pins on all four
sides are lined up before soldering more than one pin, and
as usual, be careful to get its pin 1 in the correct location.
Follow with the four isolators: IC4, IC6, IC8 and IC10. In
each case, pin 1 is at upper left. These have a similar pin
pitch to the small dual MOSFETs you already mounted, so
should not be any harder to install.
Next, fit the eight 470nF capacitors, followed by the five
regulators. For the regulators, spread a little flux paste on
the large pad before tacking one of the smaller pins, then
solder the remaining small pins before tacking the tabs.
You might need to turn your iron temperature up a bit
when soldering the tabs.
With those in place, now you can fit the six 1µF SMD
capacitors, the two ferrite beads, plus the 680Ω and 100Ω
SMD resistors. Then mount the two ESD protection arrays, which are in four-pin packages with one larger than
the others. Check Fig.4(a) and to verify their orientation if
you are not sure.
Now install the eight 10kΩ resistors and then the five
1nF, three 100nF and three 10µF capacitors. Follow by
fitting the remaining TVS (the higher voltage one, ZD5).
Make sure it is oriented correctly. Then mount the two
fuses, with the lower-current (0.75A) fuse being F7, near
8-pin header CON15, and the higher-current (3A) fuse near
CON2 at upper left.
In terms of passives, that just leaves the sole 20Ω resistor
near CON10, plus the eight 0.1% resistors.
As we mentioned last month, the lower value 0.1% resistor values need to be changed depending on your battery voltages.
The upper resistor in each pair is 100kΩ. Ensure that the
lower resistor is either 6.8kΩ, for a total stack up to about
24V, or 2.2kΩ for higher stack voltages.
29
Transformer mounting
Due to the significant thermal mass of
the transformers and the large power planes they connect to, we recommend avoiding the use of solder paste
for mounting these parts, unless you
have a very high-quality reflow oven.
Instead, we suggest placing them as
accurately as possible, holding them
in place with Kapton tape, then soldering their four tabs with a hot iron
and flux-cored wire solder.
Once the transformers are fitted, it is
essential to ensure that all flux residues
are removed. This can be challenging
as most residues will be hidden between the underside of the transformers and the PCB.
If flux residues are allowed to remain, the idle current can increase by
orders of magnitude (beyond 1mA).
The flux can break down at higher
voltages, resulting in erratic behaviour
and even arcing through the residues.
Here, an ounce of prevention is
worth a pound of cure, so try to limit
the build-up of flux residue by not allowing too much to accumulate in the
first place. If you have the choice, try
to use a ‘no-clean’ flux. However, if the
flux you are using requires cleaning,
make sure to wash the transformers
thoroughly with a high-quality flux remover and wipe off any visible residue.
Through-hole components
Fit tactile switch S1 now. It has a standard footprint, so switches with various
actuator heights are available. If you
will be frequently adjusting the unit,
you might consider chassis-mounting a
switch and wiring it back to the pads. If
doing that, make sure the wires connect
to one of the upper pair and one of the
lower pair (which is GND).
Then you can fit terminal blades for
battery/cell connection as required.
Most 5.08mm-pitch two-terminal types
will work, but check to make sure your
intended spade connector will fit.
An example blade is Wurth Elektronik 7471286, or use the Altronics parts
suggested in the parts list last month.
It may be preferable to solder wires
instead of spade lugs for some installations, perhaps to reach panel-mounted connectors.
However, the Balancer should not be
directly soldered to batteries. A failure
in either the Balancer or the batteries
will be more difficult to resolve if the
two are permanently connected.
There is no need to use particularly
heavy gauge wire, as balancing currents are modest, but as a rough guide,
they should be able to carry 2A with a
negligible temperature rise. 0.8mm-diameter copper wire (20AWG) is a reasonable option.
30
Fig.4(a): top-side PCB component overlay, with matching photo below.
If you are using spade lugs, then
ensure that no part of the blade, lug
or wire can contact other nearby components. Insulated spade quick connectors are available, and it’s a good
idea to use them.
For some installations, you might
want to mount the board inverted and
have terminals or wires exiting from
the rear of the board.
You can also fit a 5-position 2.54mm
header (either vertical or right angle)
at CON13 for lower-power applications such as balancing smaller lithium-polymer (LiPo) batteries.
CON13 is conveniently located at
the edge of the board. If the board is
mounted right at the edge of a case
with a cut-out in the side, you can plug
a standard balance connector straight
in. However, you do need to be careful
with the polarity!
Now is a good time to fit the 2x4-pin
header for JP1. For some installations,
where the batteries are of a fixed type,
this could be replaced with a soldered
wire link. Follow with trimpot VR1,
ensuring its adjustment screw is located as shown.
If you will be adjusting the balancing voltage frequently, you could instead use a chassis-mount 100kΩ potentiometer and run flying leads back
to VR1’s pads, possibly plugging into
a pin header.
Neither the potentiometer’s accuracy nor power dissipation are critical,
but we suggest using a sealed design
for greater long-term reliability.
Follow with the four LEDs, ensuring that the cathodes face towards
the top as shown. If mounting the
LEDs on the PCB, you will need to
use 3mm types.
Practical Electronics | May | 2022
It’s very important not to program
the device while attached to any kind
of power source (cell/battery or otherwise), so enable the ‘power target from
PICkit’ option.
Test the device in low power/current limited situations after programming, as described below, in case
there’s an error with the newly programmed software.
Fig.4(b): and here’s the underside of the board, again with matching photo below.
Alternatively, you could instead fit
pin headers or flying leads and mount
them in a location that will be externally visible (eg, mounted onto a panel or
case side using bezels), in which case
you could use 5mm LEDs or virtually
any other types.
For some colours, a different value
current-limiting resistor from the 680Ω
specified could be used to raise brightness or lower power consumption.
As the drive voltage is 3.3V, blue
or white LEDs are not recommended,
although you might find that such
types give adequate light given their
high efficiency.
Pin headers CON14 and CON15 are
optional. CON14 is only required if you
need access to the serial port, such as
for debugging or connecting two Balancers to work together (via an isolator) on an 8-cell battery.
Practical Electronics | May | 2022
CON15 is only needed if you have
fitted a blank microcontroller and will
need to program it on-board, or wish
to reprogram it later.
That just leaves the six capacitors.
Don’t get the two different types mixed
up, and make sure to insert the longer leads into the holes marked with
‘+’ signs.
Note that we have specified organic
polymer capacitors, not ordinary electrolytics, for their much superior performance characteristics.
Programming
When it comes to programming IC2,
as mentioned last month, this can be
done with a PICkit 4 plugged into
CON15 (pin 1 to pin 1). This is best
done using the MPLAB X IPE software, which comes with Microchip’s
free MPLAB X IDE.
Testing
Before connecting the Balancer to batteries, it’s essential to test it to ensure
that nothing has gone wrong with the
assembly that could affect the circuit’s
safety or reliability.
The easiest way to do this is with a
pair of isolated, current-limited power supplies. Set their output voltages
to be the same (eg, 4V each) and their
current limits to around 500mA.
Connect one supply between
STACK– (CON7) and CELL1 (CON6),
with the positive terminal to CON6.
Connect the other between CELL1
(CON6) and CELL2 (CON5), with the
positive terminal to CON5.
Ensure that a jumper is installed so
that the control block is powered from
one of these two points, ie, at the positions marked 1 or 2 for JP1 (across pins
1 and 2, or pins 3 and 4).
With an oscilloscope, check to see
periodic pulses on the SENSE_EN and
SAMPLE lines (pins 19 and 20 of IC2
respectively). If these are absent, there
is a fault in or around the microcontroller, or it is not receiving power.
If you don’t have a scope, you might
be able to pick up the pulses using the
frequency counter mode on a DMM, or
even an analogue voltmeter.
If the microcontroller is functional,
tie the top-most cell to the stack voltage rail (connecting CON5 [CELL2] to
CON2 [STACK+]), and slowly make a
small change to the voltage of one of
the cells.
You should see that the voltage on
the power supply with the lower output voltage increases.
If this is difficult to observe, then
you can try using an oscilloscope
to check the CSPWM/SSPWM lines
on the corresponding cell (pins 11
and 17 for the lowest cell or pins 12
and 18 for the second-lowest). You
should see narrow, square pulses on
these lines.
If this test is successful, check the
third and fourth cell sections, but note
that cells must always be populated
in-order from ground; none can be left
empty except at the top.
If you are considering higher-voltage applications, test these carefully,
taking great care to use appropriate
current limits, and ensuring that the
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Safety notes
Working with batteries presents some hazards. The most important thing to do is to be thoroughly familiar with your particular batteries’
safety requirements. In general, having fuses close to the terminals of all larger batteries is a good idea to prevent cables catching fire.
You can buy fuses that connect directly to the terminals, with provision to attach thick wires at the other end. You can also use
inline fuses, but you should ideally keep the section of wire between the terminal and fuse short.
There are a few other things to keep in mind when using the Balancer:
• Always check that the Balancer is working as intended before attaching it to batteries or other power sources. Ideally, this is done
with current-limited power supplies, as described in the main text.
• Don’t leave the Balancer unattended until you are satisfied that it works reliably for your particular application. Take particular
care if setting a lengthy timeout period.
• Keep the Balancer physically separate from the batteries. If they are too close, heat from the Balancer could degrade the batteries, or lead to a hazardous situation.
• Ensure that the Balancer is kept clean and dry at all times.
• Don’t permanently attach the Balancer to batteries or other power sources; if a hazardous situation arises, it is good to have the
ability to quickly disconnect the Balancer.
• Periodically check that your batteries are healthy: if the Balancer is constantly balancing one cell, or if you notice that your batteries are losing their ability to store charge, be sure to test and replace any failing cells.
• Remember that the Balancer can’t stop a battery from being charged or discharged by external circuitry: over-charging and
over-discharging cells can not only damage them, but can lead to hazardous situations.
• Note that in higher voltage applications, some of the voltages present on the Balancer could be dangerous (although its maximum
rating of 60V total is well within the extra-low-voltage or ELV domain) and so the Balancer should not be touched. Additionally,
some components on the Balancer can get hot during operation.
control logic section is powered from
only the lowest possible cell.
This avoids wasted power in the
control regulator (REG1) and potential
damage if its maximum input voltage
is exceeded.
In general, if your lowest expected
cell or battery voltage is above 3.6V,
then you should always leave JP1 in
position 1, so the control circuitry runs
off the lowest cell.
If your lowest expected cell voltage
is lower than this, down to the minimum supported of 2.5V, then it should
always be safe to run the control circuitry off the second cell (position 2
on JP1).
Higher positions are only useful if
you need to ensure that the small current which powers the control section
comes from the whole stack, which
would be unusual.
Final assembly
Once you have finished testing your
High-current Battery Balancer board,
it should be enclosed to protect it from
dust and any other contaminants.
You can use just about any housing or box that’s large enough to accomodate the PCB module, and which
allows cables to be fed through. Ideally, it should offer some method of
exposing the LEDs (eg, a clear lid),
potentiometer and pushbutton (possibly via a screwdriver through small
holes in the lid).
32
Mount the PCB to the bottom of the
case using standoffs so that the board
does not flex, and take care that all of
the components have adequate clearance from the case walls as it can dissipate some heat.
Four mounting holes are provided
to suit M3 machine screws, and plastic or metal spacers can be used. Just
be careful if using metal spacers that
they fit within the copper areas provided around the holes.
Heatsinking is not usually required
on any of the components, but allowing even a modest amount of airflow
will go a long way towards keeping
the Balancer cool, prolonging its life.
In harsh environments, a small temperature-switched fan could be used
(eg, with the thermal switch glued to
transformer T1).
However, in most cases, passive airflow will be adequate – just a few vents
or holes drilled in the bottom and the
top, or the sides of the case, being sufficient for convection to remove the heat.
Using it
Now that you’ve built and tested your
Balancer, how do you use it? Before
connecting it to a battery, run through
the following checklist to make sure
it’s correctly configured:
1) Configure the source of control power. As described above, if balancing
12V batteries, ensure that the con-
trol power source select jumper is
securely installed in the right-most
position (marked 1), so that the lowest cell is providing control power.
If balancing a ~3.6V cell (eg, Liion, LiPo or LiFePO4), you will probably want the power source select
jumper in the second-rightmost position, so that the lowest pair of cells
are providing control power.
2) Connect the battery leads to their
respective terminals. We suggest
connecting them either sequentially
(CELL1, CELL2…) or simultaneously (if using an external connector).
Plug spade quick connects onto
CON8-CON12 for higher-current applications, or a plug designed to mate
with 2.54mm-pitch header pins to
CON13 for balancing up to 1A.
If using CON13, make sure the
plug orientation is correct, with
the negative-most terminal to pin 1!
There might be small sparks when
connecting battery leads, but these
should be momentary.
3) Finally, connect the stack leads
(STACK– to CON7 and STACK+ to
CON2). If balancing, you can simply
bridge the positive stack voltage terminal to the top-most cell terminal.
For charging, connect the negative stack terminal to the negative
end of your power source, and the
positive stack terminal to the posPractical Electronics | May | 2022
itive end.If available, we recommend setting a reasonably low current limit on your power source, to
help prevent damage to batteries in
case of malfunction.
Making adjustments
Operation is essentially automatic,
with the Balancer simply transferring charge based on the differences
it senses in voltage across the batteries or cells. However, there are some
options you can set, either using trimpot VR1 and pushbutton S1, or via the
serial interface.
The options include the minimum
difference between battery/cell voltages for balancing to start, the maximum
balancing current and the minimum
and maximum battery/cell voltages
outside which balancing will cease.
The defaults are for the maximum
possible balancing current (about
2.5A), to begin balancing with a 50mV
imbalance for 12V lead-acid batteries
or a 10mV imbalance for Li-ion cells,
and for an operating cell voltage range
of 2.5-4.3V for Li-ion applications and
10-14.8V for nominally 12V batteries.
You can change most of these settings using trimpot VR1 and pushbutton S1, although a larger range of configuration and calibration settings are
available via the serial/USB interface.
Table 1 shows the various commands which can be issued by pressing pushbutton S1 in various ways – either a single, long press or with several
short presses in a row. Some of these
control the unit while others adjust settings in combination with the current
rotation of trimpot VR1.
Unfortunately, making settings
changes this way is a bit imprecise. You
can measure the voltage at the wiper of
VR1, either by probing its centre pin
on the bottom of the board with a DVM
or by probing pin 3 of nearby MOSFET
Q7 relative to GND. You then need to
divide that reading by 1.65V (or better,
the actual measured 1.65V ADC reference voltage) and then multiply by the
range given in Table 1 below.
If you can hook up the serial interface, you are much better off making
changes that way as they will be exact, and you can also calibrate the unit
From Practical Electronics, March 2022:
this Isolated Serial Link is ideal for
connecting two Balancer boards together.
Practical Electronics | May | 2022
Screen1: sample serial output.
properly that way. Read on for further
details on the serial interface.
Monitoring its operation
The simplest way to do this is visually. One of the four LEDs on the board
will flash to indicate when balancing is occurring, with the right-most
LED (LED7) corresponding to the bottom-most cell, LED8 to the next cell
up in the stack and so on.
They blink slowly if a battery/cell is
being charged, or rapidly if a battery/
cell is being discharged.
If no balancing/charging is occurring, LED7 will occasionally flicker
very lightly, just to let you know that
the circuit is ‘alive’, while consuming
as little power as possible.
If there is an over-voltage error, all
four LEDs will flash simultaneously at
1Hz, with a 50% duty cycle.
If an under-voltage error is detected, then the unit simply shuts down
and does not flash the LEDs at all (not
even a heartbeat).
If you are paying attention, the lack
of heartbeat will tell you something is
wrong, and by leaving the LEDs off,
we don’t risk discharging an already
over-discharged cell or battery.
If you want more details of the unit’s
operation and be sure that it is doing its
job, you can monitor the serial port at
CON14. Ideally, this should be connected to your computer via an isolating interface (a good one is described below).
You can then wire the output of
that isolating interface to a USB/serial adaptor.
Set a terminal emulator to 38,400
baud N,8,1 and you should see a stream
of information, like that shown in
Screen1. This shows you the measured
voltage at each input, plus the whole
stack, whether it is currently moving
any charge into or out of a battery/cell,
and how fast it is doing so (0-100%).
The data is both human-readable and
machine-readable, so it would be quite
easy to create software to parse the information and display it differently, or
take actions depending on the results.
As shown in Table 2, you can also
send commands to pause or resume
balancing, change the settings, or even
force it to transfer charge into or out of
a given battery/cell. This means that
you could centralise the control via
a computer program if you are using
several Balancer boards.
Combining multiple balancers
You can use two Balancer boards to
balance up to eight batteries or cells,
as long as the total stack voltage is still
within the 60V DC maximum rating.
The only extra hardware that you need
to do this is an isolated serial link.
Fortunately, we published just such
a design in March 2022 (see page 14
for the Mini Isolated Serial Link project). PCBs are available for this design
from the PE PCB Service.
Function
Check that unit is powered up
Pause/resume balancing
Switch between Li-ion and lead-acid presets
Set allowable voltage delta (0-300mV/0-1V)
Set maximum balancing current (0-2.5A)
Set minimum battery/cell voltage (0-5/0-15V)
Set maximum battery/cell voltage (0-5/0-15V)
Number of S1 presses
One short (<500ms)
One medium (1-2s)
One long (5s+)
Two short
Three short
Four short
Five short
Table 1: functions accessible by pressing pushbutton S1
33
Example
Result
p
r
t 600
l 3000
h 4300
d 50
i2 50
o3 25
c2 100000 6790
st 100000 6812
v 3280
Pauses automatic balancing
Resumes automatic balancing
Set balancing timeout to 600s; if balance not reached in this time, shut down
Set low battery/cell threshold to 3V (3000mV); below this, it shuts down
Set high battery/cell threshold to 4.3V (4300mV); above this, it shuts down
Batteries/cells can vary by up to 50mV before balancing starts
Move charge into battery/cell #2 (1-4) at 50% of maximum rate (1-100)
Move charge out of battery/cell #3 (1-4) at 25% of maximum rate (1-100)
Calibration – set battery/cell divider #2 to have a voltage division ratio of 100kΩ:6.79kΩ
Calibration – set stack divider to have a voltage division ratio of 100kΩ:6.812kΩ
Calibrate – set the typical supply voltage to 3.28V (3280mV)
Table 2: Serial commands
Build that board, but leave off the
headers, and set both jumpers (JP1 and
JP2) to the 5V position (they will actually be supplied with 3.3V, as that is
the only low-voltage rail available on
the Balancer boards).
You can then solder pins 3-6 of either
CON1 or CON2 directly to CON14 on
one of the Battery Balancer boards, as
the pinout is an exact match.
Run a ribbon cable or similar from
the other end of the board to CON14
on the other Balancer board. The wiring will be the same as the other end
and you should have the TX pin on the
Balancer connected to the TX pin on
the Isolator board.
Similarly, the RX pin on the Balancer connects to the RX pin on Isolator. The reversal is effected within
the Isolator.
Then, all you have to do is connect
between one and four contiguous cells/
batteries in your stack to one Balancer
board, starting with the CELL1 connection, and join the remainder to the other.
Connect both full stacks across the
STACK– and STACK+ terminals on
both boards.
The two units will power up and negotiate over the serial link, automatically detecting that they are talking to
each other.
They will then balance as if they are
one eight-input Balancer instead of two
four-input Balancers.
Teach-In 8 CD-ROM
Exploring the Arduino
This CD-ROM version of the exciting and popular Teach-In 8 series
has been designed for electronics enthusiasts who want to get to
grips with the inexpensive, immensely popular Arduino microcontroller,
as well as coding enthusiasts who want to explore hardware and
interfacing. Teach-In 8 provides a one-stop source of ideas and
practical information.
The Arduino offers a remarkably effective platform for developing a
huge variety of projects; from operating a set of Christmas tree lights
to remotely controlling a robotic vehicle wirelessly or via the Internet.
Teach-In 8 is based around a series of practical projects with plenty of
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in many different ways in order to build more complex systems that can
be used to solve a wide variety of home automation and environmental
monitoring problems. The series includes topics such as RF technology,
wireless networking and remote web access.
PLUS: PICs and the PICkit 3 – A beginners guide
The CD-ROM also includes a bonus – an extra 12-part series based around the popular
PIC microcontroller, explaining how to build PIC-based systems.
Reproduced by arrangement with
SILICON CHIP magazine 2022.
www.siliconchip.com.au
EE
FR -ROM
CD
ELECTRONICS
TEACH-IN 8
£8.99
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SOFTWARE
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8
SERIES
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INTRODUCING THE ARDUINO
• Hardware – learn about components and circuits
• Programming – powerful integrated development system
• Microcontrollers – understand control operations
• Communications – connect to PCs and other Arduinos
PLUS...
PIC n’MIX
PICs and the PICkit 3 - A beginners
guide. The why and how to build
PIC-based projects
Teach In 8 Cover.indd 1
04/04/2017 12:24
PRICE
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Includes P&P to UK if
ordered direct from us
SOFTWARE
The CD-ROM contains the software for both the Teach-In 8 and PICkit 3 series.
ORDER YOUR COPY TODAY at: www.electronpublishing.com
34
Practical Electronics | May | 2022
