Hi everyone.
I'm a manufacturer of power bikes (energorower.pl) - e.g. bikes generating power from human muscles. I use DC generators delivering 10-20V and up to 15 A. Currently all energy is stored in 12V batteries or used right away to power various DC appliances - I do not use grid tied inverters.
I'm interested in using open energy monitor together with my bikes - for example in fitness clubs, during ecological events, even home/emergency users would happily use some way of monitoring wattshours generated.
I did my share of research and found out that open energy monitor setup will not work with DC current out of the box - some modifications are needed.
But then I found that some people have successes with DC current and open energy monitor (for example http://www.appropedia.org/Measuring_DC_electrical_energy_production_from... ) so it is technically possible.
There are DC meters with free DIY plans (for example http://wattsview.com/?page_id=177) which can be probably used together with Open energy monitor (it uses Hall efffect sensors).
My questions are:
1. Is it indeed possible at all (to measure DC current with OEM)?
2. If so, maybe there is someone able to help me with the design and prototype (pay work)
My email: biuro at energorower.pl
Re: DC current monitoring - help needed
I believe there are users who are monitoring direct current - usually from PV arrays, though that is irrelevant - as well as mains electricity. As you say, the system won't work 'out-of-the-box' (and especially as bought from the shop it is a kit that needs assembly!) but that does allow you the flexibility to take the basic design and customise it to suit your needs. And of course you can customise the software.
Hall effect devices would be a good choice, and especially if they give you a 5 V output that would interface directly to an Arduino running on 5 V, and it is even simpler to divide down the voltage. Then you just need a sketch to calculate watts and accumulate watt-hours, and presumably you'd want a display to communicate that to the user. Would I be right in thinking this would be both a single stand-alone unit and you are going to be networking many of these and recording the data remotely?
Re: DC current monitoring - help needed
First, Robert, thank you for your remarks.
Yes, you are right - I'm thinking about installing single meters on each power bike and then networking them wirelessly to record and display data on screen. That is my basic idea.
As for Hall effect sensor - that one would be suitable for my needs I think - http://www.ebay.com/itm/Hall-Effect-Current-Sensor-For-Hobbyist-Arduino-Compatible-AC-DC-10A-75A-/230991057211?pt=LH_DefaultDomain_2&hash=item35c823d13b
The problem is I'm not electrician nor software developer - I can not customize the design myself...
Re: DC current monitoring - help needed
That sensor looks to be suitable. However, I think you need to find someone local to you who knows how to assemble and test these things. I can tell you what to do in theory at the input end, and I could write the code to handle that part, but I'm no networking expert, I have no knowledge of Arduino networking and so I couldn't help there.
I wonder, is there a technical college or University near you who could use this as a student project?
Re: DC current monitoring - help needed
I'm just wondering if CT nodes (clamps) used in standard OEM setup to measure AC current use Hall effect sensors? If so - maybe only code part need to be adjusted...
Additionally - I found commercial project http://www.theowl.com/products/intuitionpv.php - is it based on OEM? It definitively looks very familiar.
@Robert - could you tell what in theory should be done at the input end?
Re: DC current monitoring - help needed
"I'm just wondering if CT nodes (clamps) used in standard OEM setup to measure AC current use Hall effect sensors? If so - maybe only code part need to be adjusted..."
No, they are what they say they are: current transformers. And transformers don't work on direct current. ("Clamp" isn't a word used in the UK in Electrical Engineering anyway - I always think you mean "Busbar clamp", a mechanical clamp for making a temporary connection to a busbar - when anyone uses that term).
I've no knowledge of Owl products, you might have the convenience of a commercial product but you won't have the flexibility that you could have here.
What you need to at the input: You need to connect the GND of your Arduino to the battery negative. You need to connect the 5 V supply to the Hall effect sensor, and the output to one of the Arduino analogue inputs. Also, you need to connect a voltage divider (two resistors) across the 12 - 20 V battery and the midpoint to a second analogue input, the resistor ratio is chosen to give you 5 V at max battery voltage. Those two inputs then give you current and voltage respectively (I could do a diagram but I'm lazy! ) If you want to power the Arduino off the battery, you might need a second voltage regulator, depending on the battery voltage, to provide the 7-12 V that the Arduino needs.
In terms of the code, in the main program loop you would at regular intervals (probably some tens of times per second) read current and voltage, scale the readings into engineering units (i.e. calibrate them) and do whatever sums you need for charge rate, total charge, etc; then at less frequent intervals (maybe 1/2 second or so) send the values you need to your display or the network (or both) depending on how often you want to update those.