Water works for some things but not all things. There's no perfect analog for electricity because, well, it's its own thing. My wife got those posters for me because I'd been looking for the originals for the longest time. Those are reprints on a wooden backing, but they'll last. Glad you enjoyed the video, thanks for the view, and may the force be with you, always!
Shelly 2EM can be used in the US to measure split phase with 180°. To do this, one current clamp must be reversed. Shelly 2EM cannot measure three-phase current with 120°. Then Shelly 2EM can measure two currents on only one phase ( 1 hot wire !). This can be used when only one phase (hot wire or hot line) is available. In countries with 240V/400V three-phase current, the Shelly 3EM is used. This has 3 current clamps and measures all three voltages. But where Shelly are very sensitive is inductive loads on the line. This often destroys the built-in power supply.
Yes. They offer additional buffer devices for the induction load issue, though I've not had many issues with this myself as most of the devices I'm using either already have smoothing circuitry, or use an intermediary contactor.
This was a helpful video for those of us trying to use the system in North America. I was wondering if you've given much thought to how you will power all of the Shelly devices when you fill up your panel. I'm debating that currently. Also, any issues with Wifi accessibility with the Shelly inside the panel, or must it be located outside the panel? I was worries the metal panel box would be an issue getting signal out.
It certainly could interfere, worth some testing, but I think the bigger issue is the space constraint--at least in my case. As far as powering them all, since the clamps are independent of the AC side, you could power them all on one run.
Hi. Nice video. Thank you. Consider a house panel with one of its breakers being a 40Amp feeding a sub-panel. The sub-panel has a number of 120V and 240 breakers, including a 40Amp breaker tied to the main panel. Now in the main panel, when I install the Shelly EM onto one of the two wires coming out of the 40A "to-sub-panel" breaker, will I measure the whole current of the sub-panel? I am asking this because the sub-panel shouldn't behave like one 240V appliance, since it has some 120V loads on each phases as well as regular 240V loads. I'm losing sleep over this. Thanks.
First, thanks for watching! Ok, let's start with the numbers: Let's say you've got two circuits on the sub-panel, one 120V pulling 20A and one 240V pulling 10A. What do you think the meter will read? Well, you're intuition is probably not too far from the truth. The answer is 4800 Watts. Just like the main panel related to the transformer at the pole, the number of 120 and 240 circuits doesn't matter at all to that transformer because the work is the same. We'll start with our single big chain moving back and forth--the single-phase power running to your house. Then, we'll start putting gears on it--our circuits. Some of those gears only have teeth around half of the gear and the last teeth at either end are capable of grabbing back onto the chain when it goes the opposite direction (bear with me, I'm wingin' it here). Some of your gears are normal with all of their teeth (those gears avoid soda and brush regularly). The gears with half the teeth are your 120 and the other obviously the 240. For purposes of measuring force applied, let's assume that connected to these gears is a ratchet mechanism of some kind that turns a wheel in one direction--applying the force of either direction of the gear to the wheel (rectifying it, but that's not what we're talking about). If the wheels are the same size, the force it would take to move the 120 gear as fast as the 240 gear will be doubled because it only applies half the time, but the force on the big chain is still the same. Also, the big chain is being driven by one big gear at the power company that turns 360 degrees one way, then 360 degrees back, never going beyond a single rotation. When you get into three-phase, this gets a bit more complicated and harder to explain with the chains because there are three big gears and one side of the chain of all three is the same chain, so... yeah... let's stick to residential single split-phase. Remember, this is split phase, so it's a single sine wave that's being split in the middle. When the wave crosses the 0 threshold into or out of the positive, it's moving electrons on one side or the other of the two hot lines (hence the gears with the dental hygiene problem). The entire wave represents your 240V single-phase power to the transformer, but the pole in the middle of the transformer coil allows you to only use half of the force--which can only do half as much work over time as the full current (keyword there). Bonus round: We use 60 Hz power in this country, which simply means the big power gear goes back and forth 60 times per second. Even when you split this--because you still only reach the full potential of the force applied 60 times per second--the frequency remains the same on either side of the panel, but they will peak at alternating intervals, which is why people *say* that it's 180 degrees out of phase, but that's not entirely accurate; It's simply only 180 degrees *of* the phase. I hope this small novel helps you wrap your head around it a little better. The most important thing to accept is the force required. The Watts. 240 VAC @ 10A = 120VAC @ 20A because the 120VAC only gets the force applied half the time, but the wave rolls on regardless of when you jump on--it just only costs you when there's a load on the wave, up or down or halfway up or down. If you're running downhill on a bike, but still moving the pedals, you don't need any real force, so your legs don't charge you for their provided service--just a base fee to cover the expense of the bike and occasionally greasing the chain. I'm probably going to do a quick video on this because I'm certain it will come up again. Thanks again for watching the video!
Great video. I'm thinking of buying a couple of these but can't find anywhere in the literature the recording cycle time. I've read it outputs every minute but how many or how often are the individual readings taken in that minute?
Thanks! The one I have polls every 15 seconds out of the box, but there's an Eco Mode that is on by default to save power. I've turned that off to see if it polls more often or not. There doesn't seem to be a setting to adjust the polling time, but I also haven't updated the firmware for the last couple updates, so I'm also doing that now to see if it gives me an extra setting--they often add more accessibility to hardware as they make firmware changes. I'll drop another reply here after the update to let you know. I'm having trouble getting a wifi signal from a new wireless access point I installed, so I'll have to get that sorted first.
I waited to hit send on that last reply until I tried connecting to the Shelly EM three times. No sooner did I hit reply, it loaded. After updating the firmware, I still see no option to adjust the reporting interval (I should've said reporting rather than polling in the last comment because it very well could be testing the current more often than it reports). Also, I was wrong about the interval anyway, it's reporting every 5 seconds, I just didn't have my graph zoomed into a small enough time frame in my Home Assistant. So, to summarize my small novel here, it reports every 5 seconds. Eco Mode doesn't seem to affect this at all, but I'm not sure if the device is testing more often than it is reporting.
@@smartercircuits Thanks very much for responding to my query. I have Solar/Battery setup and use an RS485 logger (via mqtt) which reports every 10 seconds. Switching to the shelly wouldn't substantially increase the accuracy of the reported values. If it had been reporting every 1 or 2 seconds, I would have made the jump. Thanks again.
@Bananaskin1 Glad I could help! Haven't seen RS485 in a while--most of my serial stuff is RS232 but it's also close proximity. I might do a video in the future on the various serial communications and why they're still great.
What, you didn't mount it in opposite direction first time you mounted it - and got negative values? I've noticed arrow on clamp about 5 hours after I've installed it (wrong). :D
I have an outlet wired with a Shelly 1PM that I can turn on and off that the power supply for my switch system (which runs on 12VDC) is plugged into, I just ran wires from that to power my meter because it was convenient, but you could just run a hot from one of the breakers.
