Black box project (BBP) sensing modules

[Gregy]

Started a new thread to let separate discussion

I've been thinking thru the automation aspects of RE system, given that I have existing HA - albeit
For more traditional aspects (no RE type inputs at present)

So herewith my attempt at defining "RE" sensing/automation requirements (as distinct from
More traditional HA inputs and outputs)

I've tried to structure below In a logical way we can then discuss each "block" prioritize effort
As we think best, and use a structured approach to how we gather and display data

RE sensing/automation blocks
1) PV array
2) Charge controller
3) Inverter /charger
4) battery bank
5) Generator
6) Weather
7)Solar radiation
(it's probably part of weather, but I include it separately because of it's complexity)
8 ) Loads DC and AC
9) Environmental sensors

What/how to get from each block

1) PV array
a) Fixed array
b) tracked Array
general: most useful/important data can be accessed via CC via modbus BBP
- PV string voltage and current (given its DC, and very high voltage and current)
options here are expensive and limited. .. And aside from fault monitoring - possibly don't yield ROE/I
Summary : at present IMHO we "leave it up to the CC" to manage and report
- panel temp (very useful and important) via a simple temp sensor glued to rear? Of panels
(Suggest a few to be able to get an averaging across each array)
Need to support More than one array for those with multiples
Suggest we allow for n sensors per array and x arrays (pick some reasonable number for n and y)

2) Modbus data from CC into BBP - "done" (zoneblue/Ross pls take a bow)

3) inverter /charger
a) inverter
load
status
etc
b)charger
load
status
etc

4) battery bank
a) Bank voltage (CC) - done
b) cell voltages (see other forum posts),
c) cell temps simple sensor attached to batteries
- glued on side of cell
- attached to terminal ... This measures the conducted heat out of battery onto battery terminal
Note the temp sensors are so cheap, could put one "between each cell"

5) generator
Needs a mix of voltage, current and environmental
a) start battery (voltage)
B) AC voltage,current and power output ;
AC current transformer CT  (lots of work already done on this)
c) status : running, standby, manual,
d) oil and water temp
e) room temp
F) CO gas sensor
Note some generators likely provide some of above  already via a status panel etc
However we can plan for worse case and assume all above need to be sensed

6) weather
A very well (over done) aspect in HA already ... So many options, hard to summarise "how"
As a minimum the RE block needs
a) ambient temp (near  array, possibly "under array" also
b) humidity
C) atmospheric pressure (barometer)
d) wind speed and direction (not sure the relevance for PV?)
As a minimum BBP can have its own sensors for a) b) c) , or access a separate weather
Station .. As ZB points out ... Can use off shelf weather station and sniff it's RF (eg 433MHz )
But there are myriad of options around
(Happy to separately share my experience on this)

7) solar radiation and insolation
(Other thread topic)
a) pyranometer
b) solar "test array"
c) simple solar (eg photodiode ambient light )
Note some weather stations also have above "built in"

8 ) Loads
A) DC loads
Use low cost Hall effect breakouts circuits to measure DC current
Various modules avail off shel, to measure up to 30A + per circuit
Can measure individual circuits and look for faults and monitor loads
B) AC loads  (see generator 5b above)
Plenty of ready avail options .. Just need to "read" into BPP

9) environmental
Mostly covered above
a) room temp sensors (battery room, inverter room)
b)  gas sensors (CO, hydrogen, fire, smoke ) as applicable for each location
There are low cost breakouts boards that can achieve each of above

As you can see - the list is biggish - hence need to "prioritise" .. Hope I haven't scared Zoneblue 
I will separately document my thoughts on the various methods to achieve each of above

We can use above list as a reference start point - and add to it as required

*********
Edits
- split item 1) into fixed  and  tracked
- Inverter (deleted inverter specific comments)
22/10 split module 3 into inverter and charger

[Gregy]

BBP sensing modules vs BBP "itself" (the core)

BBP Core
- the heart of the system
- designed for always ON
- low power
- capture and log data
- display data
- ARM platform
- Linux based
- centrally located (in protected environment)
- limited onboard IO for local sensing
- scaleable capability (memory, processing)

Sensing Modules
- distributed (possibly many)
- remote to BPP core
- harsh environments
- ultra low power
- wireless option
- various IO and sensor options
- scaleable IO
- low cost

BPP Core : options
( refer separate thread by zoneblue "ARM board evaluation"
Don't post replies here on the core)
- cubieboard
- beaglebone black
- RPi
- others

Sensing module : options
- Arduino family (ATMEGA based)
Many different modules available with various IO
Interface to BBP via:
Wired (USB, I2C, SMB, SPI)
Wireless (xbee, RFM12, many other low PWR options)
-PIC
-xbee
Wireless with some limited onboard DIO ADC
-Rpi
Could fit into this category also but ..
It kinda sits between the core (memory and processing lower than other options)
And sensing module (where it higher cost makes it less attractive as c/w other options above)
- above list far from exhaustive (more a reflection IMHO of where the optimum choices lay)

IMHO
we should logically separate BBP sensing from the BBP core functions
Sensing in many cases will be physically separated also (except where using the
More limited Onboard IO on whichever  BBP core platform used)
We need to keep the number sensing module variants manageable for BBP core
And re-use available "libraries" and support as much as possible

[Gregy]

ZB
Per one of your posts in other thread

Pls feel free to use any of above in TBB wiki - as you think relevant
I agree that it may be better to maintain some things via the wiki and have them tracked and updated
In wiki
Eg the "sensing module" structure

Just a thought

[Gregy]

Module 6a :  weather Temperature Sensing

.These are simply a readily available selection I've found, from what appears
To be popular sites - to provide a starting point for information

1) DS18XX. : Dallas 1wire interface
DS18S20 : parasitic powered,  ±0.5°C Accuracy from -10°C to +85°C
DS18B20 ; non-parasitic or parasitic,   Â±0.5°C Accuracy as above
( -55°C to +125°C measurement range)
Ds1822 : parasitic/non-para. "Eco version" ±2°C Accuracy from -10°C to +85°C
Pricing
DS18B20
- component only $4 (used on many breakout and other boards)
- waterproof housing with PVC lead $10
- high temp waterproof with PTFE lead $15
(Sparkfun.com.    Adafruit.com)

2) TMP36. : analog interface (ADC)
Power supply voltage 2.7 V to 5.5 VDC
Output voltage 0-1.75V
10 mV/°C scale factor
±2°C accuracy over Operating Range: âˆ'40°C to +125°C
Price $2 raw component
(Sparkfun.com)

3) Tm102. : 2wire Bus SMB
Mounted on PCB
Accuracy: 0.5°C (-25°C to +85°C)
$6. (Sparkfun.com)

Summary: 
for temperature only sensors that are collocated or remote to the sensing module,
Dallas 1 wire interface appears the most popular and functional, it's easy to daisy chain and only requires a pair of wires, the sensors are cheap and available
In various options (bare, waterproof etc), good accuracy and temp range.
For local sensor on ADC input, TMP36 feasible but with lower accuracy.

Disclaimer
I am not in any way affiliated with any of the above companies, web sites, or
Manufacturers of the modules or components
There are no doubt other ways to achieve these outcomes, and other web
Sites and suppliers that stock these and/or comparable units

[Gregy]

Module 6b/c/d weather sensing : humidity/barometer and temperature combos

1) commercial weather stations
Various models from various manufacturers
- hard wired proprietary interface
- 1wire interface
- RF (433MHz, 900Mhz, and various) Proprietary protocols, but in many cases are published or reverse engineered
Too many options to document here
note 1wire weather instruments and sensors are popular and low cost
Where a base station display/monitoring unit is not required
(A good low cost solution for sensors only)

2) Combo sensors : humidity + temperature

A) RHT03  : "maxdetect" 1wire bus (NOT. Dallas 1wire)
Humidity from 0-100% RH
-40 - 80 degrees C temperature range
+-2% RH accuracy
+-0.5 degrees C
$ 10. Sparkfun.com

B) DHT22 : " maxdetect"1wire bus (NOT Dallas 1wire)
Similar to RHT03 above
$13 Adafruit.com
DHT11 $5 lower  precision version of DHT22

C) SHT15. : 2wire serial bus
Measurement range: 0-100% RH
Absolute RH accuracy: +/- 2% RH (10...90% RH)
Repeatability RH: +/- 0.1% RH
Temp. accuracy: +/- 0.3°C @ 25°C
$42 sparkfun.com

D). HIH6130  : I2C bus
Breakout PCB
Operating Voltage: 2.3-5.5v
Compensated humidity range: 10-90% RH
Compensated temp. range 5-50°C
True temperature-compensated digital I2C output
$30 sparkfun.com

E) HIH4030. (Humidity only ).  : ADC
humidity analog voltage output
PCB
$17. Sparkfun

F). HH10D. : I2C
Breakout board
$10.  Sparkfun.com

G). SHT11. : 2wire serial
$35 Adafruit.com

H)  HT3-R1-A.  Humidity/temp  : Dallas 1wire
$58   Hobby-boards.com

3) combo sensors  : barometer and temperature

A) BMP085 : I2C
Pressure sensing range: 300-1100 hPa (9000m to -500m above sea level)
Up to 0.03hPa / 0.25m resolution
-40 to +85°C operational range, +-2°C temperature accuracy
$20 Adafruit.com   Sparkfun.com

B) MPL115A2. : I2C
Lower precision than BMP085
$12. Adafruit.com

C). MPL11-5A1. : SPI
$13. Sparkfun.com

D)   B1-R1-A  barometer only :  Dallas 1wire
$60 hobby-boards.com


Summary : a range of different interfaces are available, most are
Local only (where module/sensor is co-located with interface ).
Dallas 1wire is proven to operate over long distances, maxdetect also
Claimed to allow 100m
There are no ADC options available for barometer.
selected options for BBP need to depend on
- core platform onboard support for one or more of noted interfaces
- BBP. support for arduino/PIC interfaces (sensors dont connect direct)
This will be important for distributed/remote sensors

notes
1) all above sensors have arduino library available
Library availability for other OS (eg Linux) needs research
2) RPi shields have not been listed

Disclaimer ; same as previous (see temp sensors)

[mtdoc]

Wow - to paraphrase the movie Jaws  "You're gonna need a bigger acronym". How about VBBBP. For very big .....

[Gregy]

Just to be clear - I'm not suggesting that it should support all of these modules
I wanted to show the range - and in particular show the range of different
INTERFACES
Eg ADC, i2c, SMB, SPI, 1wire
That they use ... Which presents the dilemma as to which "interfaces" to support in BBP

Hence my suggestion that we initially standardized on a minimal number of
Interfaces

In respect to the number of sensors connected - this shouldn't be too bad - if it's mainly a
Capture/log/graph/display function in BBP .. It should scale to some reasonable number
Eg database entry gets setup for each sensor and simply stores the data .... Then it can be
Called up to display accordingly

However - again I'm thinking a modular approach by using arduino or similar "sensing modules"
Is best

And have them report to BPP in a "common format" - thus reducing the load on BBP to
Do any low level sensor computations (do that in arduino)  .... And reducing the number
Of physical interfaces BBP needs to support to
"Listen for arduino sensor reports"

[zoneblue]

Quite a comprehensive outline there. I for one am quite keen to have the option to integrate weather in some optional form into this thing, and i like your idea of  scalable remote sensor satelite units.

In general, in my ideal world the central arm board, would interface with everything else via ethernet. The reasons are these:
- with switchs, scalable to 255 devices.
- robust
- high voltage isolation.

However its not an ideal world, and ethernet isnt exactly a low power means of communication. I recently measured a 5 port switch and found it used 0.6W idle, plus 0.6W per connected link. Its the rj45 isolation transformers im told.

Some inverters etc only have serial/usb/bluetooth. So we will clearly need to provide support for those. Most arm boards have a 4 pin serial header, which could be used to get reliable serial interface independent of the usb implementation on board. But how to cope with more than one? I know squat about that. Most baords also have one or more of gpio, i2c,spi. Can we have a daughter board of some kind with interfaces to the remote units?

In terms of the BB software its modular, you just add a module for each RE device, but i define module loosely, ie a module for each unique remote sensor unit, or online query, online publish, whatever.

I will start another thread on the project scope.

[Gregy]

Yes agree Ethernet would be nice ... But for some installations where distances between
Various units (eg generator locate some distance away, likewise panels in a convenient ground location,
Water pumps at damn/well, storage tank .... You get the idea I'm sure)

To run Ethernet cabling presents some issues
- cost of cable
- cost and effort for conduit and or burial
- lightning!! (Ethernet cable is yet another way to bring lightning into the "control room" )
And presents more earthing and SPD issues potentially
but wifi presents an interesting alternate (yes there are self contained wifi compliant sensor modules out there ..)

Consider a fully self contained low PWR wireless sensor module for perhaps $25 + LiPo battery + small local solar cell With a distance of 100m Tx range
.. All up cost maybe $45  .... Now compare to cost of 100m cat5e, plus conduit plus burial effort!
.... Hmm I know Which way I'm going to go ! (Not lazy, just practical)
And the sensor module will NOT send the lightning back ... And when it does get fried, it's fast to
Replace (imagine digging up that 100m of cat5e when lightning fries  it ... Somewhere along its length)
I'm working on my "dissertation" for this thread on wireless modules ... Just haven't got there yet

[RossW]

Consider a fully self contained low PWR wireless sensor module for perhaps $25 + LiPo battery + small local solar cell With a distance of 100m Tx range
.. All up cost maybe $45  .... Now compare to cost of 100m cat5e, plus conduit plus burial effort!

There's direct-burial cat5 cable. Saves on the conduit. Perhaps.

I chose to run an old WRT54GL, re-flashed with dd-wrt, as my ethernet connection to the battery room.
I had ethernet there already, but decided to use wireless:
1. I already had access point(s) available
2. I needed 4 devices, the WRT54GL already has a 5-port switch.
3. I wanted galvanic isolation and a bit of an air-break

Cost: picked up a bunch of them for about $15 each.

Oh, additional: the WRT54GL actually has two TTL RS232 serial ports onboard.
Using OpenWRT and a $3 converter from ebay, you've got a linux-capable device with ethernet, wifi, multiport switch and RS232 for almost nothing.

[Gregy]

Measuring AC power/energy sources and loads in off grid setup
Module 3b (inverter source/load)
Module 5B (generator source)
Module 8b (AC loads)

****** What to measure and where ****

METHOD 1
Inverter data
Power/energy
- input from generator (any AC source)
- used by inverter for battery charging
- supplied to AC loads (output)
This data should be available from inverters I would expect, But that will be inverter specific, and dependant on capability
To access data from inverter

METHOD 2
Using qty 2 (or 3) separate power/energy sensors
1) Generator
AC energy/power (ouput) delivered
One Uni/directional energy/power sensing unit
Easy to locate at AC load/source panel (or generator output)

2) Inverter/charger
AC power/energy (input/output)
a) consumed by inverter specifically for battery charging
(eg when Using generator or other AC source)
b) Generated from batteries = supplied from inverter AC ouput to system (all AC loads)
this would be one bi-directional (power/energy) sensing unit

scenario 1
a) no generator or other AC power sources,  only one sensor on 2) above required
b) separate inverter and charger, two sensors required (one each on inverter and charger)

Scenario 2
Use a additional sensor on generator output
Assumption is that by using subtraction, it's possible to determine Power/energy supplied from generator to :
a) battery charging
AND
b) AC connected loads
( some of the generator power flows to Both depending on respective demands)
Note : there are different methods for achieving the subtraction method Depending on where sensors sniff power

Scenario 3
Use three (or more) sensors and possibly avoid the subtraction method or cater for various combinations to Sniff all power flows
(Generator, inverter, charger,  "all" AC loads)

3) power/energy consumed by individual AC. Loads
Additional Uni directional power/energy sensors as required for individual AC load circuits
(Eg heater, different sections/circuits of house, individual appliances)


******* how to measure ********

there are many of "Off shelf" systems for monitoring power/energy
All typically use a "non invasive" method to measure AC power with Current transformers "CT"
Measuring power and energy has a lot of complexities - that others have already "Solved".
.... So lets not reinvent the wheel here!

What we are seeking IMHO - is a way to get this data into BBP  (Again my "modular sensing" thinking ) so we can Log/display/use as part of BBP decision making

So IMHO we use an available off shelf system that we can "capture" the data ..
Which brings me to
  openenergymonitor.org. Project

Which is very impressive and has done a LOT of work on power/energy monitoring
Including work on Solar PV energy monitoring and control,
However it appears to be Focussed (to date) on
- monitoring grid tie PV systems with nett metering /feed in tarrifs
- using excess PV energy for local AC heating loads and decision making on when to use
Note however - with No local battery storeage the decision making process is quite different  than our off grid scenario, and also the monitoring requirements for power flows differ considerably

Here are a couple of links that give a. Idea of how monitoring is being used
In grid tied PV systems

"Solar PV Monitoring System Application ....... For wireless web-connected solar PV monitoring system that monitors both generation and grid import/export"
http://openenergymonitor.org/emon/applications/solarpv

"A project to design and build a controller to route surplus P.V. energy into the domestic hot water supply"
http://openenergymonitor.org/emon/mk2

**********
Using   Openenergymonitor.org.  for module 3b 5b 8b Sensors for BBP off grid

1) emonTX v2 kit "sensing node"
http://openenergymonitor.org/emon/emontx
Apparent Power, Real Power*, Power Factor* and AC RMS voltage readings*
3 x CT Current Sensor input (measure power in 3 separate circuits)
Optimized for Low PWR operation, can be powered from 5V USB (or 3.3V)
Onboard low PWR Wireless transceiver
Up to 16 DS18B20 Dallas 1 wire temp sensors
Atmega328 "arduino" onboard (with its GPIO exposed)
Arduino sketch (program)  "ready to go"
Only "downside" is that the units are supplied in kit form (ok for those
Of us comfortable with soldering)
EmonTX v2 kit £27. Plus CT £10ea. (CT source able elsewhere also for $12)

** Edit 21/10  **
emonTX V3 fully assembled version due any moment
Note it has onboard support for 3xCT + 1xCT (4 in total)
http://openenergymonitor.blogspot.com/2013/08/emontx-v3-progress-update.html

2) emonBASE. "Wireless base station transceiver"
Ethernet network interface
"Send data packets to a web server"
communication with emonTX nodes
Four different options available
"Nanode"kit  £35 (bout again needs building)
"Nanode RF SMT" .£35 fully assembled from Nanode.eu (the developer)
Raspberry Pi plus RFM12 expansion board (more expensive than above options, Although more powerful, but claimed to be more difficult to setup)

3)  emonGLCD. "Display unit"
LCD display of power, energy etc
Wireless transreceiver (receive data from nodes, transmit to base)
It appears the energy computation (integrating power over time to calc energy) Is done in this device? TBC
It also communicates with emonBASE to send temp to server, and get "time" from Internet To sync it's local clock
Very simple "add on" that gives an instant dIsplay!
£55 (kit)

Question/details as yet unclear (I am still researching)
1) is it possible to hardwire interface direct to emonTX sensor node and get data
Via serial interface (USB? I2C?  SPI? Etc) into BBP
2) where is the energy calculation done? Possibly in emonBASE? or as I suspect in either or both emonGLCD and emonBASE

Summary:  Whilst it's possible for us to "hang a CT of some ADC inputs" on BBP ...
There is a LOT of work behind the scenes to measure Instantaneous voltage, current, calculate power, integrate to get energy et al
So why not use an emonTX and emonBASE to do all the work - and let BBP capture and Log the data from the Ethernet interface on emonBASE
As the data is already in the "Ethernet domain" - shouldn't be too difficult To get the data into BBP (it's all open source !)
Wireless is an advantage (for adding more remote modules - another topic To come )
and separating BBP From inverters and other equipment

Zoneblue - I believe this answers the questions you posed to me
IMHO - we absolutely re-use the existing Openenergymonitor.org project,
It's very complementary to BBP with minimal overlap
(Note I haven't as yet searched their development threads to determine if there
Are off grid versions under development.. But as it exists now it can pretty much deliver All we need)

And my final caveat ... Of course if the inverter provides the data (as it should, But often may not)
then just stop reading at method 1 at top

Wow big post !

Thoughts?

edit history :
21/10 updated scenarios for split inverter charger, number power flow/CTs  and cleaned up formatting etc
21/10 added link to forthcoming emonTX V3

[Gregy]

Ross

Wrt54gl  All good points - I will rethink further - I think I may even have one in my discarded
Items box

Agree that it provides lots of functionality and of course Ethernet connectivity.

But if it's wireless how do you power it remotely?

I'm thinking of a very low power wireless node with onboard GPDIO ADC - that needs
5V @40mA when transmitting - and way lower when it goes into sleepy mode
That can be powered from a. LiPo and charged with a smallish solar cell
The lipo can power it for days without charging ! And it can even report it's own battery state
Wirelessly

The wifi/Ethernet router gives much different and greater capability for sure.
But no wifi router is going to achieve the above power consumption where only limited
Connectivity is required - and can be delivered via small wireless module

we are comparing different requirements .. Apples and grapefruit

[Gregy]

Measuring DC loads (DC current)
Module 8a

A selection of sensors/circuits available to sense DC loads (DC current flow)

1) DC current under very high voltage using non invasive current transformers
Uses a special CT and circuit to sense DC current with high voltage isolation
Could be used for measuring PV array current total (or from individual strings/arrays)
Discounted because of cost ($120 fixed core CT; $150 split core CT)
CC should provide enough details for Its high voltage (PV array) input

2) DC current shunt
Very low resistance ("shunt") generates a small voltage across it
(Ohms law applies - voltage generated is directly proportional to current flowing)
Eg 500Amp 50mV is common in solar PV battery installations
When current shunt is connected to battery negative it's termed "low side"
For low side shunts, measure voltage to ground across shunt (no common mode
Issue to deal with)
Low side seems to be the more common is solar PV Battery installations
Current can flow either direction (charge vs discharge) so voltage can swing +/- as measured referenced to ground across the shunt
note this referenced to ground, and not battery negative - which is not connected to ground directly, but is connected to ground via the shunt)
Voltages are very low and cannot be measured by ADC directly, but need
An amplifier
(Note a good quality DMM can accurately measure 0.1mV ranges, however
5A = 0.5mV  which is quite a low voltage to measure)
A CC with a battery shunt monitor (eg midnite wizbang JR)  does all the work
Summary:  how to measure
A) for CC it's assumed BBP will be able to access (wizbang) shunt current flow
Data via modbus
B)  inverters with current shunt measurement (eg battery monitor kits)
Should likewise enable access to this data
C) systems without access to current shunt data, it's possible to amplify
And measure shunt voltage (further details available )

3) DC loads
Hall effect devices allow monitoring DC (and AC) current "through" a special IC That is isolated from its ouput - which could be analog voltage of one of the Various serial interfaces
The DC current flows through the Hall effect chip (it's effectively in line with The circuit)
Various modules/breakout boards available ; below a selection I've found
Current shunts use a measurement resistor - below a selection of devices with "onboard" shunt,
But in some cases can be removed to use external shunt

A)  various Hall effect sensors with ADC ouput
* ACS709. : 30A. ADC
Bi-directional current 30A "continuous " (but needs heat sinking)
70A (max short term transient)
Note the warnings about temperature and heat generation
2.1kv isolation
Output voltage proportional to current (can use ADC to read)
$10   Pololu.com
* ACS711EX. :    ADC
100v isolation
bi/directional +/- 31A version
bi/directional +/- 15.5A version
Output voltage proportional to current (can use ADC to read)
$4 pololu.com
* ACS714.
G* ACS 715  0-30A (Uni directional) $10

D) attopilot DC Voltage and AC current sensor with analog output (ADC)
Three diff versions using inbuilt current shunt
50V/180A
50V/90
13.6V/45A
$20.  Sparkfun.com

E). ACS712. 0-5A AC or DC current
With opamp for gain for improved accuracy
$10. Sparkfun.com

F) INA219  : I2C
High side DC Current and voltage shunt sensor 26V +/-3.2A
Inbuilt 0.1ohm shunt resistor (can be removed and replace with external shunt for Higher currents)
I2C interface
$10. Adafruit.comp

G) INA169. High side current shunt monitor.  ADC
Onboard shunt resistor for 5A  (for 5V ouput)
$10 Adafruit.com

Summary ; majority of DC current sensors provide analog ouput  (suitable for ADC)
All above boards supported by arduino with respective sketch available
can also be read directly into ADC if available on BBP core platform
Many different options for various DC Currents (and voltages)

Disclaimer (see above posts)

[Westbranch]

In reply #10
Method 2
2) inverter
Scenario 2......
Assumption is that by using subtraction, it's possible to determine
Power/energy supplied from generator to :
a) inverter battery charging
AND
b) AC connected loads



There is also the variant where the Off Grid system has Inverter and Charger as separate units.

ADD #1
Using   Openenergymonitor.org.  Sensors for BBP off grid

in link from Openenergy I found this,  the JEENODE

http://jeelabs.net/projects/cafe/wiki/

sold here:   http://jeelabs.com/

[Gregy]

Westbranch
Good point.
If I understand correctly,
In this scenario it also includes a generator? And the inverter and charger are separate units.

If so, then I think it needs the three sensor scenario? To measure all the respective power flows.

1) generator output
(current can flow into battery charger AND AC loads directly)
2) Battery charging input
(AC power used by charger to recharge batteries)
3) Inverter output
(Power supplied to AC loads from inverter using batteries)

Is my above assumptions correct?
Or can it still be done with two sensors and subtraction? (I need to make a diagram for myself)