Measuring AC energy flow direction

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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Measuring AC energy flow direction

    Not sure what they are promoting but I looked at their battery info section and, don't know where they get their info on AGMs but they state a MTBF of 2 - 5 yrs for AGM???http://powerrouter.com/faq/what-batteries-do-we-need
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    westbranch wrote: »
    Not sure what they are promoting but I looked at their battery info section and, don't know where they get their info on AGMs but they state a MTBF of 2 - 5 yrs for AGM???

    Maybe based on the way their system treats them???
    SMA SB 3000, old BP panels.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Measuring AC energy flow direction

    Ya, that being the case, it would be rather severe treatment... despite their (correct) cautionary statement re AGMs requiring lower charging voltages. Almost like they assume abuse will occur.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Measuring AC energy flow direction

    HI Forum

    Although slowly, we've made some advances in detecting AC flow direction. With an hall-effect ampmeter and circuit for measuring AC voltage, we can see the current phase and the voltage phase on the oscilloscope. The next step will be programming the arduino to multiply to two waveforms and give the power level and its direction.

    So i'm confident that we will be able to detect which way the power is flowing (in or out) and in what quantity and program the arduino to that effect.

    The next big challenge is to dissipate the power in a linear fashion for the exact amount that would be injected into the grid... why? you ask... because Spain has quasi-mafia monopolies, who control the politicians, that dont want citizens producing their own energy. Yes it's a waste of good, clean electricity, but it's better than not producing any at all.

    As far as I can tell there are 2 options to solve this problem:
    1. Reduce the production from the PV system to never exceed the consumption at any time within the house. There are inverter manufacturers working on modules that do exactly that, but they are a significant added cost. I think they push the system either up or down the IV curve away from the Maximum Power Point and hence reduce production accordingly.
    2. Invent a power-consuming aparatus with whose power can be controlled linearly (and controlled by an arduino). The problem with resistance heaters, for example, is that they are on or off. The problem with dimmer-type switches is they use triacs which cut the wave form, and dont vary the power linearly.

    Anyone got their thinking caps on? :p

    Cheers
    Larry
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    Invent a power-consuming aparatus with whose power can be controlled linearly (and controlled by an arduino). The problem with resistance heaters, for example, is that they are on or off. The problem with dimmer-type switches is they use triacs which cut the wave form, and dont vary the power linearly.

    You would need to have a set of heaters of different size, which differ by a power of 2. Say, 100W, 200W, 400W, 800W, 1600W, 3200W etc.

    Then, you switch them on and off to dial the exact amount you want. For example, if you need 1100W, you switch on 100W, 200W and 800W heaters and turn everything else off.

    These heaters should have resistance that is not affected much by their temperature, or you may need to compensate for the temperature effects.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Measuring AC energy flow direction

    How are the Hall effect devices working out for you? I would suggest a Current Transformer with a voltage shunt (precision resistor)--Then all you have to do is measure a few volts (or whatever your CT winding and resistor value works out to be for your needs). Should get rid of the variability of the Hall effect device.

    Just be sure that the shunt is always on the CT when in operation--You could get thousands of volts from a CT if there is no load attached.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    BB. wrote: »
    I would suggest a Current Transformer ...

    I would second this. I used these and, when calibrated, they measure with better than 0.1% FS precision.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    ...
    Invent a power-consuming aparatus with whose power can be controlled linearly (and controlled by an arduino). The problem with resistance heaters, for example, is that they are on or off. The problem with dimmer-type switches is they use triacs which cut the wave form, and dont vary the power linearly.
    ...
    Anyone got their thinking caps on? :p
    As long as the drive to the triacs is continuously controllable, it does not matter whether the output is linearly proportional to the input, since you will have the capability for feedback via the Arduino.
    The n-bit heater-based D-to-A convertor has merit too!
    SMA SB 3000, old BP panels.
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Measuring AC energy flow direction

    HI, thanks for all your replies.

    Hall effect is working fine as far as I know. It's this type: http://www.ebay.co.uk/itm/50A-100A-150A-200A-Bi-Uni-AC-DC-Current-Sensor-Module-arduino-compatible-/110894073072?pt=LH_DefaultDomain_0&var=&hash=item19d1cd44f0

    Turning on various heaters is not practical nor is it sufficiently linear unfortunately.

    As for inetdog's reply, sorry I dont understand what you're saying about the triac etc, what's an n-bit heater?... could you give me a version for dummies?

    cheers
    Larry
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    inetdog wrote: »
    As long as the drive to the triacs is continuously controllable, it does not matter whether the output is linearly proportional to the input, since you will have the capability for feedback via the Arduino.

    You cannot control triac continuously. Once triac is switched on, you cannot switch it off. You have to wait for the end of the half-wave where it switches off by itself.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    NorthGuy wrote: »
    You cannot control triac continuously. Once triac is switched on, you cannot switch it off. You have to wait for the end of the half-wave where it switches off by itself.

    What I meant, of course, was continuous (phase based) control of the on time of the triac. If you know when it will switch off, you just need to control when you switch it on. Either via phase shift circuitry as in light dimmers or by controlling the timing of the trigger pulse.
    And in the later case, the energy delivered will not be directly proportional to the on time, but you can still get any fraction you want using either a scaling table or software feedback.
    SMA SB 3000, old BP panels.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    inetdog wrote: »
    What I meant, of course, was continuous (phase based) control of the on time of the triac. If you know when it will switch off, you just need to control when you switch it on. Either via phase shift circuitry as in light dimmers or by controlling the timing of the trigger pulse.
    And in the later case, the energy delivered will not be directly proportional to the on time, but you can still get any fraction you want using either a scaling table or software feedback.

    If I understood OP correctly, he didn't want to alter the waveform to make sure that her activity goes undetected.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    NorthGuy wrote: »
    If I understood OP correctly, he didn't want to alter the waveform to make sure that her activity goes undetected.

    I really do not think that even a smart meter for residential use will record anything out of the ordinary as a result, and a mechanical meter certainly would not. The whole idea is not to return any power to the grid, so the controlled opportunity load will most of the time be small compared to the normal load. A commercial meter which has both demand and power factor monitoring might raise a flag over the triac load profile, but I seriously doubt even that. Even it could not easily tell the difference between a low power factor load powered by triacs to dump energy and a low power factor load which is running for some other purpose.
    I admit that since the real net power delivered inward through the meter would be so close to zero that the power factor of the extra VA going back and forth could be really large by comparison. Somebody needs to borrow a smart meter and try the experiment. :-)
    The utility might figure out just from the fact that power utilization goes to zero whenever the sun is shining that there is a solar system involved, whether GTI or off-grid with the loads being transferred. But that would happen with any kind of diversion load the OP uses.
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Measuring AC energy flow direction

    My last digital meter was able to report power factor and other power quality issues.

    So--I would think that a triac chopping up the current wave form is not really what a utility has in mind for solar power. If this was a commercial installation in the US, many utilities will log PF and charge for poor power factor.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    BB. wrote: »
    So--I would think that a triac chopping up the current wave form is not really what a utility has in mind for solar power. I-Bill
    But remember, the proposed situation is one in which the utility is not aware that there is a solar GTI installation and the goal is to keep it that way. :-)
    Would it be a big enough anomaly that they would investigate?
    If necessary, add a large harmonic filter to the triad diversion load?
    SMA SB 3000, old BP panels.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Measuring AC energy flow direction
    inetdog wrote: »
    But remember, the proposed situation is one in which the utility is not aware that there is a solar GTI installation and the goal is to keep it that way. :-)
    Is that legal? If not, should we in this forum be disseminating advice on how to circumvent the law, even if it is in another country?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Measuring AC energy flow direction
    ggunn wrote: »
    Is that legal? If not, should we in this forum be disseminating advice on how to circumvent the law, even if it is in another country?

    It is an experimental circumstance.
    So long as the grid is not actually ever back-fed (the intent) it is little different from taking the home off-grid and using the utility only when necessary.
    Simply a different way of doing something people often do.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    ggunn wrote: »
    Is that legal? If not, should we in this forum be disseminating advice on how to circumvent the law, even if it is in another country?

    Backfeeding might be illegal with they power grid. Therefore, avoiding backfeeding has to be legal.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Measuring AC energy flow direction
    NorthGuy wrote: »
    Backfeeding might be illegal with they power grid. Therefore, avoiding backfeeding has to be legal.
    I was addressing the issue of the OP wanting to interconnect with grid surreptitiously. Was that in jest?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Measuring AC energy flow direction
    ggunn wrote: »
    I was addressing the issue of the OP wanting to interconnect with grid surreptitiously. Was that in jest?

    It isn't surreptitious if the grid connect remains a "load" rather than a "source". Keeping it isolated as that is the whole issue here.
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    HI, thanks for all your replies.

    Hall effect is working fine as far as I know. It's this type: http://www.ebay.co.uk/itm/50A-100A-150A-200A-Bi-Uni-AC-DC-Current-Sensor-Module-arduino-compatible-/110894073072?pt=LH_DefaultDomain_0&var=&hash=item19d1cd44f0

    Turning on various heaters is not practical nor is it sufficiently linear unfortunately.

    As for inetdog's reply, sorry I dont understand what you're saying about the triac etc, what's an n-bit heater?... could you give me a version for dummies?

    cheers
    Larry

    Cool!

    I'm currently working on a project to more accurately log both my DC and AC current data using an Arduino as well. I'm experimenting with the same Allegro hall effect sensor for my DC current as well but also am going to try out a 24 bit ADC chip to measure voltage across a shunt (the Arduino's 8 bit ADCs won't cut it). Not sure which will win out yet.

    I hadn't seen that Allegro HE IC on a breakout board for Arduino before - looks good and will simplify things if I end up going that route. Currently I've been playing with the bare HE IC. Thanks for the ebay link!

    For AC current, I plan to use a CT - but haven't gotten there yet.

    I'll look forward hearing more about how your project progresses.:cool:
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Measuring AC energy flow direction

    Thanks for all your replies... phhh.. that triac stuff is hard to get my head round... could anyone show diagrams of what would happen to the wave forms with a grid-tie inverter producing say 300W more power than required and a triac-controlled device consuming 300W load in order to compensate??

    On the question of legality- the whole point is to make sure that any pv system with grid connection stays within the law... the problem is the minute that you inject power, this becomes legally questionable (although it's currently alegal rather than illicit)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Measuring AC energy flow direction

    From a functional point of view... Think of a silicon switch that can turn on any time during the voltage cycle of the sine wave (when non-zero). And turns of automatically when the tail end of the sine wave hits zero volts.

    http://en.wikipedia.org/wiki/TRIAC

    So, one way to implement would be to setup a triac (aka lamp dimmer circuit) to a resistive heater bank. If you decide that your local loads are 1,000 watts and the solar output is 1,500 watts, then turn on the resistance heater for 500 watts (or about 1/3 of the average current for a 1,500 watt heater).

    The down side is that you are pulling current for only 1/3rd of the cycle. So for 2/3rds of the cycle you are pushing "energy" to the grid and 1/3rd of the cycle you are drawing energy from the grid. Very poor power factor (should be easily detected by a "smart/digital meter", if programmed to look for this) and you are injecting some power for a part or each cycle. Probably "a-legal" at least.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: Measuring AC energy flow direction

    Apologies if this has already been suggested or is irrelevant (I haven't digested this entire thread) - but if I understand correctly you're trying to divert some of your power production to prevent (illegal) sell back to the grid when your production exceeds your normal loads - correct?

    Have you considered using PWM output from the Arduino to control an AC load via a SSR?. This would be similar to what Chris Olsen and others are doing with the PWM output of the Classic CCs Aux to control water heating? Might be a simpler solution....:confused:
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    that triac stuff is hard to get my head round...

    If you're going to use it for diversion load, you do not have to use triacs, because you can rectify first. For a resistive load, it will make no difference wether you use AC or DC, but DC is easier to deal with.

    With DC you can use a MOSFET or BJT to switch it on and off as you please.

    Or you can use BJT in linear mode to control the amount of current you send to your diversion load instead of switching.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    As for inetdog's reply, sorry I dont understand what you're saying about the triac etc, what's an n-bit heater?... could you give me a version for dummies?

    Sorry I did not get back to you sooner on this question. I overlooked it.

    The same way that an 8 bit digital to analog convertor uses each bit to control a voltage or current source whose value corresponds to the bit position, you can turn on separate heaters. I was using that as a short-cut description.
    Here is a concrete example which extends the suggestion made earlier:

    If you have eight heaters of 10, 20, 40, 80, 160, 320, 640, 1280 watts, then by turning them on in various combinations you can make any wattage between 10 watts and 2550 watts in 10 watt steps. That means that you could make sure that no back feeding would occur and you would waste at most 10 watts in the process. This is what I would call an 8-bit heater. :-)

    Each heater would be drawing current uniformly over the entire AC waveform and so its presence would not upset the current flowing through the meter in any recognizable way. It would just be a variable load like any other.

    I think the triac has been covered by others as well as it can be in conversation of this type. To understand it more, you will have to look at longer explanations and should know some basics of semiconductor operation and AC power measurement.
    SMA SB 3000, old BP panels.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    NorthGuy wrote: »
    Or you can use BJT in linear mode to control the amount of current you send to your diversion load instead of switching.

    But if you do this, you are dissipating a LOT of heat in the BJT. Much more than when just switching, and sometimes even more than you are sending to the load.
    SMA SB 3000, old BP panels.
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Measuring AC energy flow direction
    BB. wrote: »

    The down side is that you are pulling current for only 1/3rd of the cycle. So for 2/3rds of the cycle you are pushing "energy" to the grid and 1/3rd of the cycle you are drawing energy from the grid. Very poor power factor (should be easily detected by a "smart/digital meter", if programmed to look for this) and you are injecting some power for a part or each cycle. Probably "a-legal" at least.

    -Bill

    Sorry , what would cause the very poor power factor?
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Measuring AC energy flow direction
    lazza wrote: »
    Sorry , what would cause the very poor power factor?
    It depends on the design of the VA counter. If the meter integrates RMS volts and RMS amps, the Volt-Amp figure would be large positive number, since it would add in amps in both directions. But the wattage would be close to zero if the inward power and outward power were nearly equal.
    Since total PF = Watts/VA, the result would be close to zero.

    If the meter measures RMS volts and average amps, then it would end up with a low VA number too, but because the current waveform is far from sinusoidal, what is called the distortion power factor would still be high.

    As I said, it all depends on how the meter measures it, but from a theoretical/definition viewpoint, the PF will be low.
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Measuring AC energy flow direction

    From the utility and wiring point of view, they supply current. Say for example, you use 100 amps during 1/2 a cycle and consume 100 amps during the other 1/2 cycle. From the kWH point of view, the power used is Zero kWH. But, from the wiring and utility point of view, there is 100 amps of current flow heating the wire and the generator has to source/sink that current--taking generating/distribution resources "without payment".

    So, technically, in the above example, you actually have 1.0 PF because the current is perfectly in phase with the voltage (definition of PF), but, I would argue violates the "no generation" policies of most utilities. And at high power levels can create "flickering" as the voltage differences between the output/loading parts of the cycle.

    A Triac would just be a "variation" of this, breaking the current flow into "fractions" of a cycle.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset