watt-hour metering

What you're describing shows AC input voltage. That's okay, if that's what you're looking for. But there's loss too - not being accounted for via such appliances, when AC still needs to be converted to DC storage. Some plugins account for this, to show exactly what the traction pack has - as usable stored energy - thusly .


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huh?

 

i use the cars readout, and add 15% for losses.

 

That works - but your efficiency is likely much better than your allowance.
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i hear you. plugging your evse into the meter should give you a fairly accurate reading. the car should track it as well (mine does) but doesn't account for losses between the wall plug, and the charger. the difference would show the losses.

 

i got that from the pip forums back in the day, by peeps who were tracking both. not sure there was agreement though.

 

I just installed that very meter in my charging outlet a week ago and so far it's working perfectly. I love the cumulative energy display, which is retained even through power failures, so I don't need to log the usage after each charging cycle.

In my case, I am using it to tell me how much energy I'm putting in the car, since I haven't figured out how to get reliable data from the car itself. That should generally work, since I almost always charge at home, but I'm still a little grumpy that the car won't tell me how much electricity I've put in it.

Edit: I just noticed that the original poster said the unit can be mounted in a standard switch plate. It actually can't; it's too big to fit in a single-gang box. I mounted mine sideways in a double-gang box, using a blank faceplate with a hole cut in it to fit the unit.

 

Your years have made you wise, grasshopper

By the way, I just got my first minor disappointment with that meter. The energy display starts off in Wh, as shown in your photos at the top of this thread, and then switches to kWh once you overflow that. When I charged my car last night mine overflowed, and it went straight from showing watt-hours (i.e. a resolution of .001 kWh) to showing whole kWh (a resolution of 1 kWh). I had been hoping it would go through an intermediate phase of showing fractional kWh so that I could track individual charges with reasonable accuracy when I wanted to, but it looks like the only way to do that is to reset the energy display first and lose the accumulated count. Foo.

Still, that's a minor issue for me, and probably less for you if you're just trying to track the monthly usage against your electric bill. Just another way that life manages to be not quite perfect.

 

Are these meters measuring the current at 240V like in the attached image?

 

So which watt meter did you actually buy? (Make and model plz!).

Jim

 

Maybe they were confused because sometimes 240V things have two "hot" and one neutral wire. But in the case of a load that's mainly 240V, the neutral current should be negligible. Sometimes it's just there to power control electronics or something minor that only needs 120V. So measuring current on just one wire is sufficient (plus of course voltage and time as you mentioned).

Last time I thought about it, I wasn't able to derive a way to measure the total power of an arbitrary combination of 120V and 240V loads on a typical split phase system using just a single current meter. But I might have missed something.

 

Some 240 charging stations don't even have a neutral. My Chargepoint Home unit is like that. The plug for it has two "hot" connectors and a ground. The ground is for safety; if any current flows through it, there has been a fault somewhere and the system trips off. Unlike electric dryers, which typically have hot-hot-neutral, and in which the 120V controls run on one of the hot connectors and the neutral, the electronics in the ChargePoint Home just uses 240 V.

 

not unless your Appliance has a GFI also. Plenty of people have been electrocuted (some even to death) with a ground.
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You're right; I meant to suggest that the ground is used in conjunction with a GFI to actually provide the protection.

And a totally pedantic comment on the word "electrocuted". This word means killed by electricity, so everyone who has been electrocuted is dead (unless you count people whose heart has been restarted after an electric shock to be at one time dead but then revived). OTOH, one can receive a non-lethal electric shock. Sort of like everyone who has "drowned" is dead by suffocation in water.