Batt IR Meter Assembly Instructions

User Manual:

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The BattIR Project

Since the author has no control over the

quality or skill level of the persons building

up this project, there needs to be the follow-

ing disclaimer.

The software is provided “As Is” with the au-

thor not being responsible for any claim,

damages or similar issues on the use of this

project.

HOW IT WORKS

The BattIR project uses 14 electronic relays to

connect each battery cell in succession to the

same PicChip A/D input. This way there is no var-

iation in the PicChip between different A/D inputs

since only one PicChip channel is used.

So far, 31 BattIR meters have been built, all work

very well. (I did miss a solder joint on one meter)

A precision 0.2% Voltage reference, part U2 has

been added to the original design in order to im-

prove basic DC voltage accuracy, as compared to

the original BattIR meters.

In addition, each cell voltage is read 10 times, and

an average is taken of those voltage readings. .

The multiple cell voltage readings eliminates volt-

age "jitter" on the last digit of the four digit display

of the battery voltage. Tests on the three proto-

types shows that the voltage read out is accurate

to around 0.3% on voltages between 2.5 VDC and

4.5 VDC as compared to my Fluke 87V meter

while using its Hi Res feature. These units should

hold plus/minus 1% on the measured cell voltag-

es.

The BattIR meter first connects a 5 Ohm 1% re-

sistor across the battery pack, then reads and

saves the individual cell voltage readings to the

first table. Next, it connects a 2.00 Ohm 1% re-

sistor to the battery pack, and reads and saves

the individual voltage readings to a second table.

Last, the BattIR meter applies both the 5.00 and

2.00 Ohm resistors in parallel to the battery pack,

and again reads and saves the voltage readings

to a third table.

The individual cell IR calculation is:

IR = (Volts Low Amps- Volts Hi Amps)

Divided by (High Amps - Low Amps)

The first and third voltage readings are used to

calculate the individual cell IR values and displays

them to the LCD display.

Example, a cell measuring 3.71 Volts at 4.45

Amps and measuring 3.58 Volts at 15.1 Amps

would have a cell resistance of 12.2 MilliOhms.

This meter has a maximum of 999 MilliOhms

range.

The software also has commands to preset the

batteries Mah rating and uses the Mah rating to

calculate the maximum safe current for the bat-

tery.

Credit must be given to Forsyth, Julian, and Giles

for their work in testing countless LiPo batteries,

and coming up with the formula that is used to cal-

culate the maximum safe current for the given

LiPo or LiFe/A123 battery pack. These names are

included on the BattIR LCD display.

Last but not least, the test currents that are ap-

plied to the battery pack are derived by the batter-

ies voltage divided by the resistance of the power

resistors.

If the 1% 5 ohm and 2 ohm power resistors are

not available, 5% units can be substituted with a

slight loss of IR accuracy.

One feature of this setup is that the 5, 6 or 7 cell

packs will pull higher test currents through the

power resistors, compared to much lower test cur-

rents that occur with the 1, 2 or 3 cell LiPo packs.

As a result, those usually smaller 2 cell 200 Mah

battery packs are tested at current levels of

around 5 Amps, compared to the test current of

around 15 Amps for the higher voltage big battery

packs.

This meter also has the capability of displaying

the individual cell voltage of the battery pack on

each of the load currents applied to the pack. It

can also display all cell voltages while connected

to an ESC and motor under full power as an ex-

ample.

Time to start the project!

(Equipment Needed)

This project uses a number of surface mounted

resistors in its design. Surface mounted resis-

tors might be a bit scary for someone that has

not worked with them. But, with a bit of prac-

tice, assembly of a project like this goes much

faster than through hole resistors.

Note the required equipment in the photo at

right that will be used to build up the circuit

board. An old cookie sheet will aid in finding

any surface mounted parts accidentally

dropped. For older folks, a magnifying visor

helps a lot. Then a needle pointed soldering

iron is used along with tweezers to place and

solder the components. I use 0.040 sized rosin

cored solder for these type projects.

What I’ve learned over the years, is to place a

tiny bit of solder on ONE of the pads of the re-

sistor as an example.

Then, place the iron on that bit of solder, and,

using the tweezers, “slide” the surface mounted

resistor into that tiny bit of solder. Wait for the

solder to cool off, then solder the other end of

the resistor. This takes longer to describe than

actually doing it.

Install the electronic relays

Next, insert each of the 16 electronic relays into

the circuit board. Be careful to not have any of

the relay pins bent under the relay, rather than

going into their respective holes. Also, pay at-

tention to the small dot on these relays showing

which is pin #1. Next, install and solder up the

resistor networks that are used with the elec-

tronic relays.

At the right is the components as re-

ceived from www.digikey.com. All

components are placed in individual

bags, properly marked with compo-

nent type and value.

Order extra resistors and capacitors.

Most 10 parts for under 50 cents.

These correspond with the parts list

that is part of the

www.expresspcb.com schematic that

is included along with the PCB layout

that can be downloaded from github.

Install The Microcontroller

Here we install the microcontroller, along with

the 5 Volt regulator that powers the project,

along with the two MosFets that are used to

connect the battery under test to the load resis-

tors.

Be very careful not to fold any of the microcon-

troller pins under the chip. If this happens it will

be difficult to fix after the chip is soldered.

Again, be aware of the location of the dot on

the microcontroller, it should be located to the

bottom left on the photo. (The PCB Pin#1 hole

Install the surface mounted parts on the

back of the PCB

Time to install the parts on the back of the

PCB, paying particular attention to the part

number, part value, and location on the PCB.

For those interested in this project, the au-

thor will make available a limited supply of

the circuit board plus the programmed mi-

crocontroller for 20% over cost of the two

items, plus shipping cost, USA only.

Install the 0.2% voltage reference

with its associated resistor and capacitor. Next,

install the potentiometer that is used to set the

LCD display Contrast.

Note the PCB layout on the voltage reference

has been changed. The author placed the cir-

cuit board order through www.expresspcb.com.

This web site repeatedly warns to verify that the

proper PCB layout is attached.

And, of course, I didn’t include the proper lay-

out! The PCB layout plans in this project has

the corrected circuit board layout.

The final project as installed on a piece of Luan

sheet found at the local lumberyard.

The PCB is mounted along with the LCD dis-

play by four one inch long 2-56 screws, along

with nuts and washers. Note that the PCB is

slightly smaller than the LCD display, requiring

the bottom right screw holding the PCB with a

couple of washers.

The power resistor mounting brackets were

tapped and installed with 6-32 screws. The flat

pads on the PCB are used to connect the #16

wire for the power test lead to the battery under

test, along with connections to the two power

resistors.

When first powered up, the LCD display will be

blank. The top right potentiometer must be

turned counter clockwise until the LCD display

properly displays the information.

The final project. The case was built up from some 1/4 by 2 inch Oak

trim pieces from the local lumber yard. This project will also fit into a

commercial 6X4X2 plastic project box available from many sources.