tracking charging costs

Ok I have been using the 12 amp EVSE upgrade since Tuesday. I hate not knowing exactly bow much power I am using so wondering what formula I should use to track my costs.
When using only 120 volt charging I was a rock solid 75% efficient. Against the mpk from the car which I reset daily.

Others have reported various efficient iencies running from 85-88%.

Now I am charging ar
T a slower rate so curious as to anyones thought as to was efficency I should expect.

I began by obsessively tracking costs, although for my Prius with driving cost 6X higher I had long since stopped tracking at all, and instead just paid the $4.20/gallon at the pump. Whatever the total it was much less than the $100 the SUV before me had rung up. I guess I started tracking so closely because I wanted to reassure myself that I really am saving something after the big outlay to buy the car.

So I recorded kWh from Carwings, bars and DTE from the car, kWh from the Blink front panel and from the Blink web site, and kWh from the utility meter - the only one that matters in the end. I think I have enough data now to estimate how Carwings kWh relate to Blink kWh and to SDG&E kWh, for me. So now I think I'll just record it from Carwings because it's easiest to retrieve day by day data, and from the utility bill. As for resulting inaccuracies, I really don't need to know if I actually spent an extra dime on power yesterday and a nickel less today.

So I can take that to mean you do not agree with the 85 percent

DaveinOlyWA said:

So I can take that to mean you do not agree with the 85 percent

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No, 85% is probably about right. I just mean that having once determined what I think are my ratios of Carwings-kWh/Utility-kWh and Blink-kWh/Utility-kWh then I'll be satisfied to estimate utility from Carwings and check it once a month when the bill comes.

I get about 80% efficiency from Blink (AC) to Leaf "meter" display (DC) above the steering wheel. Haven't checked Carwings against them.

When they installed my blink, I had them install a second meter as well. Not for the power company, just for my own use. I bought one online for under $30, and they installed it between the breaker panel and the Blink, so it's recording all power going to the Blink. That's the only number I care about, and I record it once a month when I get my PSE bill. Using the number from my meter, the PSE bill, and the Leaf's odometer, I can record exactly how much I'm paying to operate the car.

The only other factor that would come into play is if I were paying for charging somewhere else. In that case I'll also record that price each time, just like I record each tank fill on the ICE vehicles. If I get a free charge somewhere, I don't really care to record that because it doesn't factor into my cost. I'll have to decide if I really want to record it just to have the data or not. So far that hasn't come into play, though.

I recommend a second meter like I have for anyone that's anal about this like I am. I'm just a data junkie. But then again, I think most people on this forum suffer from this same obsession! Any electrician should be able to install a meter like this. You could probably even do it yourself but if you end up electrocuting yourself don't have your family come whining to me...

Here's where I got my meter: http://www.hialeahmeter.com/

blorg said:

When they installed my blink, I had them install a second meter as well. Not for the power company, just for my own use. I bought one online for under $30, and they installed it between the breaker panel and the Blink, so it's recording all power going to the Blink. That's the only number I care about, and I record it once a month when I get my PSE bill. Using the number from my meter, the PSE bill, and the Leaf's odometer, I can record exactly how much I'm paying to operate the car.

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Have you found any difference between Blink numbers and your meter ? BTW, blink has an actual 3rd party meter inside to get the reading.

evnow said:

Have you found any difference between Blink numbers and your meter ?

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I see my SDG&E meter about 20% higher than Blink and 50% higher than Carwings.

evnow said:

blorg said:

When they installed my blink, I had them install a second meter as well. Not for the power company, just for my own use. I bought one online for under $30, and they installed it between the breaker panel and the Blink, so it's recording all power going to the Blink. That's the only number I care about, and I record it once a month when I get my PSE bill. Using the number from my meter, the PSE bill, and the Leaf's odometer, I can record exactly how much I'm paying to operate the car.

Click to expand...

Have you found any difference between Blink numbers and your meter ? BTW, blink has an actual 3rd party meter inside to get the reading.

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I thought the meter in the Blink was only recording power going out through the cord and did not include any losses that the Blink itself has, which I would assume is NOT negligible since the damn thing reboots about every 6 hours.

Honestly, I haven't even compared them. I just went out to check on it now, and the Blink only tells me numbers for May and June, I can't get it earlier than that (which seems stupid). Am I just missing something? Is there a way to get total numbers off the Blink rather than only monthly numbers? I'd trust my wall meter more than the Blink anyway, though.

Carwings is worthless to me. I determined early on that it didn't hold that great of data for me, so I almost always bypass the neg screen by hitting some other button. But just for kicks I logged in there just now and it has me down for a total of 152.2kwh, so it's certainly not getting all my data!

blorg said:

I thought the meter in the Blink was only recording power going out through the cord and did not include any losses that the Blink itself has, which I would assume is NOT negligible since the damn thing reboots about every 6 hours.

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Incorrect on both. It records all power going into the EVSE, and... it doesn't matter much. The Blink now draws about 11 Watts on standby. That's not much compared to the 3750W when it's actually doing its thing.

For my first full month of having a second meter in and charging exclusively on the Blink, I paid $18 for the month. I did not write down the mileage at the beginning of the billing period, but did capture it for this one. It was roughly 500-600 miles. $18/500 = $0.036/mile $18/600 = $0.03/mile. Next month I will have an accurate number.

To me CARWINGS stats don't matter, Blink stats don't matter. How far did I drive, and how much did I pay? Simple.

Per the drifting topic, my SDGE meter shows about 4-5 percent higher than Blink. (I just went and added this column to my spreadsheet. I'm surprised that it's the same percentage every time I check. I expected it to be higher but getting better since the update. Nope; stays about the same.) I also thought Blink excluded its own power use, but now I remember reading that the Blink could be used as an actual power meter. But that suggests this question: Should it include the overhead, because you pay for everything you use, or should it exclude it because "I shouldn't pay for what the utility's meter eats". So, another question, then. What's the overhead in the real SDGE meter and do I pay for that?

As to Dave's original question. I'm not sure what you are asking. You state with confidence that you had 75% efficiency. I think what you're implying is that you had a Kill-A-Watt on your 110 circuit, but you can't do that now that you've got a 220-capable EVSE. If that's the question, all I can offer is that we are stuck judging our recorded power use against the percentage charge applied to a mythical battery pack. If you want to say what kWh capacity you base your 75% figure on, we can probably run our own numbers and give you an answer. I'm pretty sure that's how we got our 85-87% figure originally.

SDG&E's TOU meter itself is rated for 0.2% accuracy (ANSI 12.20).
I haven't seen a spec for how much power it (itself) consumes, or which side of the meter it loads. I'd be surprised if it was more than a couple watts.

My 75%EVSE capacity was based on actual power from the wall divided by the miles per kwh from the car which the difference should be charging losses from conversion and cooling

Based on kill a watt reading when on 120the volts. Now that I am charging at 240 volts my efficiency should go up due to shorter charging time and a static cooling overhead penalty.

But charging at 12240 amps would increase that time and the penalty for the cooling overhead.

Now I do like that the Leaf has recognized the lower amperage and adjusted its estimated charge time accordingly

walterbays said:

evnow said:

Have you found any difference between Blink numbers and your meter ?

Click to expand...

I see my SDG&E meter about 20% higher than Blink and 50% higher than Carwings.

Click to expand...

Something wrong there. Blink can't consume 20% power without melting. Either your Blink is not properly calibrated or your SDG&E meter is faulty.

ps : If you charge 2 hours per day - and Blink consumes about 15 watts when idle, that is still a small number. 7.5kwh vs 0.4kwh or 5%.

evnow said:

walterbays said:

evnow said:

Have you found any difference between Blink numbers and your meter ?

Click to expand...

I see my SDG&E meter about 20% higher than Blink and 50% higher than Carwings.

Click to expand...

Something wrong there. Blink can't consume 20% power without melting. Either your Blink is not properly calibrated or your SDG&E meter is faulty.

Click to expand...

Or, as mine has done, the Blink resets partway through charging and "forgets" the energy used in the first part of the charge.

This is usually what results in the Blink total (via Blinknetwork) being far off from the observed SDG&E total for the charge session.

When the Bink is working correctly, it seems to be consistently 1.4% low in the value it reports (compared to meter).
When it's wiggin out, it can be absurdly low. The "-5%" is the confusing one, where I have to assume it rebooted early in the charge cycle.

I have never, ever, seen it match the SDG&E meter exactly or read higher. It's always low (optimistic) by some amount, usually 1.4%.



Yesterday's charge was from an SOC reading of 74 to 280 (100% charge), after driving 52.1 miles since the last full charge.

SDG&E: 18.9264875
Blink: 18.6554
Mileage: 52.1
SOC: 280-74 = 206 = 92 Watt-hours per step

Average: 363 Watt-hours per mile, 2.75 Miles per (wall) kWh
THIS is the true and correct number for the driving I did yesterday. Everything else is rose-colored eco-pumping.

Bringing in my own local power rates, it works out to $1.50, or 3 cents per mile. There is no need to sugar-sweeten these numbers -- they're astounding and speak for themselves!
A 50mpg Prius burning $3.59 fuel is more than twice as expensive.

The more we, Nissan, Carwings, and Blink do to confuse the costs and underreport the energy consumption, the less convincing the whole EV proposition becomes.

DaveinOlyWA said:

My 75%EVSE capacity was based on actual power from the wall divided by the miles per kwh from the car which the difference should be charging losses from conversion and cooling

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Care to restate that, Dave? (wall kWh) / (m/kWh) = (kWh)^2 / mile which doesn't sound like a very useful measurement.

I trust you were actually calculating ((odometer miles) / (wall kWh)) / (m/kWh)

Ray

GroundLoop said:

SDG&E: 18.9264875
Blink: 18.6554

Click to expand...

That difference of 271 watts would be consumed by Blink @ 15W, in 18 hours.

Or, as mine has done, the Blink resets partway through charging and "forgets" the energy used in the first part of the charge.

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I don't think that happens. Since Blink has an actual 3rd party power meter, it doesn't lose the accumulated monthly reading after resets, crashes, reboots. I've seen this to be the case after all those events numerous times.

As I said earlier, upto 5% difference should be expected based on the idle draw of Blink. In a month Blink would draw about 10kwh - so in my case it last month, the utility meter would have shown about 6.1% higher than Blink.

Efficency=AMPK /DMPK

AMPK= AC miles per kwh
DMPK= DC miles per kwh

AMPK was calculated by miles driven divided by charge calculated

DMPK was recorded from energy screen that is reset daily with trip meter