The Harvi has an internal burden on each channel. It periodically switches the burden in and out of circuit as you’ve seen. Burden in when it’s measuring, out its harvesting. It relies on the peak voltage when the burden is out to then rectify the AC and then charge a capacitor to power the Harvi. The capacitor stores enough energy to maintain operation during burden cycling. A CT without a burden has an equivalent circuit of a constant current generator and will try to drive the constant current through an extremely high impedance value (CT is open circuit) and therefore could give anyone a very nasty (lethal) shock. But luckily most are sold with a varistor fitted across the CT winding, thereby limiting the open-circuit voltage to a safe level. At first I thought you were measuring the DC voltage and current from the panels, but I need to watch your video again. If so it would be exceptionally dangerous to do so as the panels will be producing voltages (with solar) that are of extreme lethality, if so you may have got lucky so-far! I’m also interested to see how you’ve solved the Power Factor aspect of the power calculation, but I expect the EMONPi code is handling all that. I think you owe it to your viewers to keep reminding them of the lethal nature of what you’re doing, it is quite unlike any AC work and requires special skills.

@routercnc9517

9 ай бұрын

Hi. Thanks for the comments, I've only been on the Myenergi forum a few times but I think I've seen you are a knowledgeable contributor there so I humbly welcome your input. Yes, this video is from the beginning of the project and I've since learnt a lot more about the Harvi and how it works. I have the datasheets for a number of the key components and it make a bit more sense now. Interestingly the microprocessor they are using can communicate in about 10 or so protocols, including i2c. The Arduino I'm using also uses that as one of the standards so it makes you think how much easier this could be if they could talk directly! So this video is just the intro and at that time (~May) I had not quite got it working . I did have a long bit of footage of me drawing out the block diagram and logic flow but it got cut out. Maybe I'll see if I can drop it in another video. This means I did not get into the safety side so let me add a bit here (I'll include it in the next video). This is all very low voltage, the Arduino is 5V, the output side generating a few mA of current into the Harvi is 12V, and the sensors are Hall Effect DC CT clamps (these are homemade, but later on I did find some commercial versions). These clamp around the DC cables in the same way as the AC CT clamps, so I'm not breaking into any of the high voltage side, just inducing a current. They use the Hall Effect sensor so you just get 5V max output. Hopefully later videos will explain it better. I really wanted to keep this safe using passive components and low voltage and I have got it to work that way. You mentioned power factor and the solution I came up with was quite ingenious (if I may say so!), as I'm sure you know that internally the Harvi will multiply the current and the voltage to obtain the power, but of course with them both being AC the phase is important. This not only determines the real and imaginary parts, but for the user it will display the current direction (important for charging and discharging the battery). This was the key to the project really as the voltage reference is the house mains (which I'm not measuring). The current reference which I artificially create is based on the level of DC current in the DC CT clamp (of the panels or battery cables into the inverter), but it must be phase locked to the mains voltage, otherwise the power level will be incorrect, and the direction of current will be probably random. I will show you in a later video how it did that because trying to lock onto the mains voltage and artificially create the correct current signal proved to be very difficult, so I sort of cheated! But again all safe and passive and works well (to a level of accuracy I'm happy with anyway). I'll show lots more in the next videos, touch on the calculations, and start to show the graphical result so it is easier to see how it performs. It is currently running open loop, so just reads signals in, runs the calcs, and outputs the signal to the Harvi. It assumes it has output the correct signal but it cannot check, although it is pretty good. So I've been working on a closed loop version which monitors the output current and feeds this back to iterate the required output, and this ran for the first time yesterday. This is even better than the open loop version as it can correct itself, but I did see a few glitches which I need to work on. OK thanks for following along.

@G6EJD

9 ай бұрын

@@routercnc9517 some more Harvi information, it only measures and sends current values aligned to the zero crossover, that then gives the Master device the ability to calculate the phase angle based on its reference of the incoming supply voltage, so the Master calculates the Power and Power-Factor (phase angle). I’m beginning to see that your using a Hall effect device clamped to the Solar DC feed to get a non-intrusive measurement of DC current, and await with interest how your measuring the DC voltage. BTW the Harvi input is also designed to be a parallel tuned circuit comprised of the CT inductance and a Harvi mounted capacitor. They are doing this to allow very low energy flows to be measured by utilising the Quality Factor (Q) of the tuned circuit to then enable sufficient energy to run the microcontroller and RFM69 for the RF transmissions. Looking forward to see the next chapter.