TerryL
Posts: 2
Joined: Mon Mar 21, 2016 11:03 pm

Re: Detecting Electric Current

Mon Mar 21, 2016 11:37 pm

I know almost zero about the raspberry pi but I do know lots about power measurement using the Owl CMA113 current sensor and using it to feed controllers for using the spare power from solar panels.
One of these sensors is supplied with the Owl power monitor and extra sensors are available from Owl for use with three phase systems.
The sensor produces 32mV AC for each amp flowing in the cable passing through it. If it is assumed that the voltage is 240V AC then each 32mV corresponds to 240W (assuming a power factor of 1). A domestic property will not normally consume more than 100A (or 42kW) so the maximum output from the CMA113 would be 3.2 volts AC. This would need to be rectified and possibly amplified before feeding into an A to D convertor for the pi.
The above will not differentiate between power flowing into the property or out of it. In order to do this the current needs to be measured during either the positive or negative half cycle of the mains voltage. If anyone is interested in this or wants me to try to post some circuits then I can try to do this. The system I designed worked on three phases to use excess solar power (but this opens another can of worms as most three phase electricity meters cannot cope with partial export of power on individual phases).

RDS
Posts: 739
Joined: Tue Oct 06, 2015 8:17 am
Location: Lancashire, UK

Re: Detecting Electric Current

Tue Mar 22, 2016 8:34 am

Terry
Thank you for your response.
I am extremely interested in any further information you could supply. I have only had my panels since the end of August last year and I am very keen to be able to use at least some of the excess electric that they are generating.
I am personally only interested in single phase.

TerryL
Posts: 2
Joined: Mon Mar 21, 2016 11:03 pm

Re: Detecting Electric Current

Thu Mar 24, 2016 3:04 pm

Hi RDS,

I have tried to attach a couple of “back of the envelope” diagrams (Diag 1 and Diag 2) but there is a limit of 64k :-(
Try: http://s955.photobucket.com/user/terzo_ ... rary/Power

Diag 1 shows how the signal from the CMA113 is sampled only during the negative half cycle of the mains voltage. The average of this is stored in a capacitor and amplified to produce Vout. Vout varies with the current I1 flowing through the sensor. I assume you could use this voltage to feed an analogue input into your Pi and then switch heaters once there is excess exported energy.

Diag 2 shows how you could also use Vout to produce a visual display either using a centre zero meter or a bi colour LED that glows brighter red as more power is imported (or brighter green as more power is exported). Diag 2 also shows how to control a proportional circuit that will feed all excess power to a heater. Whenever there is exported power the capacitor charges and increases the voltage to the controller and the power to the heater. The pot allows the “zero point” to be fine tuned so the electricity meter just stops registering (if you are using a bi colour LED this is the point it changes from red to green). The power indicator LED glows brighter as more power is fed to the heater. You may want to consider using an EMC filter in conjunction with the phase angle power controller.

Some useful bits I used are:

Sockets to plug the CMA113 into:
Switchcraft 732RA 1.3mm Power Socket
http://www.rapidonline.com/cables-conne ... et-20-1084
TruConnect 1.3mm DC PCB Power Socket
http://www.rapidonline.com/cables-conne ... cket-63538

Crydom 10PCV2425 Proportional Power Controller
http://uk.rs-online.com/web/p/solid-sta ... s/2181870/

Heatsink
https://uk.rs-online.com/web/p/heatsinks/1898050/

United Automation F165 15A Filter Module
http://www.united-automation.com/f165-1 ... 30v-15amp/

Kingbright L-57EGW Bi-colour Green, Red LED (25mA)
http://uk.rs-online.com/web/p/visible-leds/2285720/

grahamed
Posts: 277
Joined: Mon Jan 30, 2012 7:01 pm

Re: Detecting Electric Current

Thu Mar 24, 2016 7:24 pm

Hi

just a couple of quick points -

I often find that a scope produces a lot of information much of which is, in fact, irrelevant. Wood and trees spring to mind.

the output of a current transformer must be a (rough) sinusoid at 50/60V, generally meters are quite good at reading this.

as to direction of power flow, have a look at 4-quadrant multiplier.

apologies if any/all of this has been said before.

User avatar
Cancelor
Posts: 768
Joined: Wed Aug 28, 2013 4:09 pm
Location: UK

Re: Detecting Electric Current

Thu Mar 24, 2016 8:34 pm

Thought for the day ... use a 3Kw heater element but divert a variable amount of surplus PV Power using a Triac ...
see http://www.openenergymonitor.org/emon/mk2/switchdev

http://www.openenergymonitor.org is a good site for info and ideas.

also see http://www.openenergymonitor.org/emon/modules/emonpi
Last edited by Cancelor on Wed Aug 24, 2016 5:39 am, edited 2 times in total.
Can't find the thread you want? Try googling : YourSearchHere site:raspberrypi.org

RDS
Posts: 739
Joined: Tue Oct 06, 2015 8:17 am
Location: Lancashire, UK

Re: Detecting Electric Current

Tue Apr 12, 2016 10:28 pm

Sorry for the very delayed response.
@TerryL - Thank you very much for the time you have taken to compile such a comprehensive reply. I will look into the points you have raised.
@grahamed - OK, Thanks.
@Cancelor - Thank you, I will study the links you have provided. That sounds an interesting idea about the possible use of a 3Kw heater. I have no experience of Triacs though.

RDS
Posts: 739
Joined: Tue Oct 06, 2015 8:17 am
Location: Lancashire, UK

Re: Detecting Electric Current

Wed Apr 13, 2016 6:21 pm

@Cancelor
I have now looked at those links and there is plenty to go at. Thanks again.

Northland
Posts: 8
Joined: Fri May 06, 2016 6:07 am

Re: Detecting Electric Current

Sat May 07, 2016 9:15 am

http://s.aliexpress.com/yYZ7VZbm

I use one of these to control my element. I bypass the varistor and use relays to provide different resistances

mspark
Posts: 2
Joined: Tue Aug 23, 2016 12:08 pm

Re: Detecting Electric Current

Tue Aug 23, 2016 2:50 pm

Hi

I'm completely new to raspberry pi but have installed solar panels and also fitted solar immersions. Do a search for solar immersions, the units I fitted came from immersun but other manufactures are out there. I use very little gas during the summer as most of my hot water is heated via my 4kWp solar panel system.

RDS
Posts: 739
Joined: Tue Oct 06, 2015 8:17 am
Location: Lancashire, UK

Re: Detecting Electric Current

Tue Aug 23, 2016 9:43 pm

mspark wrote: Do a search for solar immersions, the units I fitted came from immersun but other manufactures are out there.

Thanks but when looking for details about Immersun, I came across this page: https://www.immersun.co.uk/

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