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https://github.com/tdittr/tripple-current-shunt

PCB design for three current shunt measurements
https://github.com/tdittr/tripple-current-shunt

kicad pcb

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PCB design for three current shunt measurements

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README 

        
# Tripple Current Shunt



This is a small PCB project to measure current consumption and voltages in a multi battery camper van environment.



To do this it hosts three [INA219](https://www.ti.com/product/INA219) power monitors,

one [ADS1015](https://www.ti.com/product/ADS1015) four channel ADC to measure ground offsets,

one [MCP9808](https://www.microchip.com/en-us/product/MCP9808) temperature sensor and

a [M24C02](https://www.st.com/en/memories/m24c02-r.html) EEPROM to store calibration data.



![3D Model of the board](doc/3d-model.jpg)



## Interfaces



The board has three different interfaces. A [I2C](#i2c) digital interface for reading the measurements.

Three [Current Inputs](#current-input)

to measure the current flows into and out of the batteries. Three [Voltage Inputs](#voltage-input) to measure the ground

offset of the batteries.



### I2C



The I2C interface is wired to two JST-PH connectors with a pin-out compatible

to [Adafruits Stemma](https://learn.adafruit.com/introducing-adafruit-stemma-qt/technical-specs) connection. The

footprint also fits the connector and pin-out

of [Seedstudios Grove System](https://wiki.seeedstudio.com/Grove_System/#grove-i2c). The two connectors are wired in

parallel to allow for daisy-chaining. The power is also supplied via this connector (from rev2 onwards).



**Note on using Grove Connectors:** The 90 degree version of the grove connector seem to count their pins from right to

left - so inverse to how JST counts their pins. To use the Grove connectors you can either mount them on the backside of

the board or use the upright connectors with the clip facing to the edge of the board.



#### I2C Addresses



The six I2C slaves on the board are configured to follow a schema where the lowest two bits of the address are defined

per board. This allows usage of up to four boards with a total of 12 channels on a single bus. The individual addresses

are listed below. *xx* marks the bits set via jumpers (see screenshot below).



| Device      | Address Pattern | Board 0 | Board 1 | Board 2 | Board 3 |

|-------------|-----------------|---------|---------|---------|---------|

| MCP9808     | 0b001_10*xx*    | 0x18    | 0x19    | 0x1a    | 0x1b    |

| INA219 Ch A | 0b100_00*xx*    | 0x40    | 0x41    | 0x42    | 0x43    |

| INA219 Ch B | 0b100_01*xx*    | 0x44    | 0x45    | 0x46    | 0x47    |

| ADS1015     | 0b100_10*xx*    | 0x48    | 0x49    | 0x4a    | 0x4b    |

| INA219 Ch C | 0b100_11*xx*    | 0x4c    | 0x4d    | 0x4e    | 0x4f    |

| M24C02      | 0b101_00*xx*    | 0x50    | 0x51    | 0x52    | 0x53    |



| ![Address selection jumpers screenshot](doc/address-selection.jpg)                                                                                                                                     |

|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| There should always be one of JP1, JP2, JP3 or JP4 closed. Then close JP11 or JP12 when the matching box is filled. To select for example the address *10* for the board you would close JP3 and JP12. |



### Current Input



The current inputs are connected inline between the batteries and the consumers. They can be connected using

either [Wago 2604-1103 terminal blocks](https://www.wago.com/global/pcb-terminal-blocks-and-pluggable-connectors/pcb-terminal-block/p/2604-1103)

or a single row terminal block with 5mm pin spacing.



The board offers the option to place a [miniOTO fuse holder](https://imaxx.nl/product/minioto-holder-h7810/) in line to

protect the board and connections.



The current is then converted to a voltage using a current shunt. The different options for this are described

in ["Choosing a Shunt Resistor"](#choosing-a-shunt-resistor).



### Voltage Input



To measure the voltage offset between the board ground and the battery ground the connector used for

the [Current Input](#current-input) offers an extra connection. The input can tolerate a maximum voltage of ±20V but can

only measure about a ±5V offset. This can easily be adapted to other needs,

see [Adapting Voltage Dividers](#adapting-voltage-dividers).



## Design considerations



The board is designed to be easily adaptable to different situations. The easiest adaptions are to just leave parts out:



* Remove the fuse holders (e.g. because you already have a fuse box), and bridge that footprint

* Remove the temperature sensor and/or EEPROM to save cost

* Remove the EMI filter by not populating the capacitors and bridging the ferrite-beads



For the more complex considerations see below:



### Choosing a Shunt Resistor



**1. Choosing a footprint:** The board offers four different footprints for the shunt resistors:



* Single-Inline 4-pin through-hole

  for [Isabellenhütte PBV](https://www.isabellenhuette.de/fileadmin/user_upload/PBV.PDF) resistors

* SMD 2512 resistors

* SMD 1206 resistors

* Off-Board Shunt like [Vishay RTOP](https://www.vishay.com/product/50045/)



When using any other resistor footprint then the Single-Inline one the two jumpers next to the resistor footprints needs

to be closed. This connects the voltage sense terminals to the current terminals.



![Shunt resistor footprints and jumpers](doc/current-shunt.jpg)



The screenshot shows the resistor footprints for channel A. R5 is for the *Single-Inline 4-pin through-hole* and R2 for

either SMD 2512 or SMD 1206. To use an external shunt do not populate any of the two. If you want to use any shunt that

is not the Single-Inline 4-pin close the two jumpers below R2.



**2. Check maximum values:** Calculate the maximum resistor value for a given current and power rating:



$R \leq \frac{P}{I^2}$



**3. Check voltage over shunt:** The INA219 can work with up to 26V but can measure a either ±40mV, ±80mV, ±160mV or

±320mV of shunt voltage. Using a lower shunt voltage will give a lower power loss on the shunt while aiming for a higher

shunt voltage increases signal-to-noise ratio.

You can calculate the voltage over the shunt by $U_{shunt}=R_{shunt} \cdot I$.



**Note:** Check whether the trace width is sufficient for your current. You can add extra solder and copper to the

traces on the bottom side to improve the current capabilities.



### Adapting Voltage Dividers



The voltage dividers for the ground offset are set to allow for ±5V input. This is achieved by building a voltage

divider between the input voltage and 5V. The output voltage can then be calculated by:



$U_{out} = \frac{5V + U_{in}}{2}$



There are however footprints to form a voltage divider between the input and ground. So it could be used to measure

another bus voltage.



**Note:** When adapting this take care to not overload the clamping diodes or the resistors in the voltage divider.



### Adapting Low Pass Filters



The current and voltage inputs host capacitors to form RC low-pass filters. The calculations for these can be found in

the schematic.



# License



Licensed under the CERN Open Hardware Licence Version 2 - Permissive.

Unless you explicitly state otherwise, any contribution intentionally submitted by you, shall be licensed as above,

without any additional terms or conditions.