Public pay charging near my home and some math

[Teddydogno1]

I just put in an order for my Mini SE and I'm planning for my own charging and seeing what public chargers are near me.

I knew that there are 3 EVGO chargers at the ACE Hardware right where we get on the freeway (I live in a small bedroom community where we have to get on the freeway to go just about anywhere). They list the price on their website as one charger at $0.29 per minute for 50 kW charging and the other fast charger at $4.95 plus $0.20 per minute. Anyone familiar enough with EVGO to know if that is a membership charge, or a choice to make depending on how much juice you need? If charge for each use, then it seems that about 55 minutes is the break-even point between the two options, which the Mini should really never need.

The only other public charger close by is a stand of Electrify America units at the Walmart about 10 miles up the freeway. For non-members they charge $0.43 per kW/h (or $0.31 with the $4 monthly membership). I think the non-member price works out to about $6.24 to charge an SE from 30% to 80% (half a battery). Does this sound about right? I compared this to a tank of gas in our 40 mpg RAV4 Hybrid and it doesn't seem to favorable.

RAV4: 11 gallons at $3.60 / gal yields a range of 440 miles for $39.60, or $0.09 per mile

Mini: 50% battery is about 60 miles range, so would need about 7.3 30-80% charges to equal the range of the RAV4 at a cost of about $45, or $0.103 per mile at EA. (The math works the same if we assume 120 miles for a full charge range to get 3.67 charges to do the same 440 miles).

Obviously home charging is more cost effective.

Here in WA, PSE charges me a flat monthly "Base Rate" of $7.50. Then the first 600 kWh per month are billed at $0.094437 ea. All kWH over that are "Tier 2" and billed at $0.113903. Then there are several credits relating to Hydro and Wind Power, but no "transmission" charges or anything like that. No time-of-day rates. We always use over 600 kWh per month now without an EV, so it is pretty easy to say the any EV charging will cost the Tier 2 rate, or 11.4 cents.

At this rate, the same 3.67 full charges (or 7.3 half charges) of 29 kWH at home would cost about $12.14, which is way better at $0.028 per mile.

Using this same data again and charging at EVGO, lets assume the same 50% charge takes 36 minutes as stated by Mini... That's 36 min at $0.29 for $10.44, which is a whopping $76.12 for the required 7.3 charges to get the 440 miles. That's over $0.17 per mile. But I think this is wrong because the 36 minute figure is probably not for 30% to 80%.

Does this all sound about right?

Rob

 

[Godfrey]

One adjustment to make is to take into account the charging efficiency (or maybe inefficiency). It takes more than 29 kWh of electricity to fully charge the car. I've had mine for less than two weeks and so don't have much charging data available yet, but so far I'm seeing about 83% efficiency. The MINI app reports that my charge yesterday took me from 37% to 100% (28.9 kWh x 63% = 18.2 kWh) using ~22 kWh of electricity. 18.2/22 = 83%. Maybe the 83% efficiency number would be higher if I stopped before getting to 100% charge, but I haven't tried that yet.

 

[MatthewL]

Don't spend to much on a level 2 charger. The mini max amps on level 2 is 16 amps. So instead of paying for a 50amp service and a wall mounted level 2 charger just put in a 30amp service (dryer plug) with the appropriate nema connector and order a cheaper level 2 charger with a max output of 16amps.

 

[ColdCase]

I dunno, but my Level two charger reports that the mini is taking 32 amps, 8 - 9kw per hour, until it reaches near capacity where it drops off.

It reports I've been getting about 4.9 mile per kWh in our driving conditions (mostly back roads). Our overall electric rate is about 17 cents per kWh, so thats roughly 3.4 cents per mile or so without charger inefficiency. Probably better if I consider tiering. Current fuel cost here, you would need a ~100 mpg vehicle to match. Your mileage may vary.

 

[Carsten Haase]

The mini max amps on level 2 is 16 amps. So instead of paying for a 50amp service and a wall mounted level 2 charger just put in a 30amp service (dryer plug) with the appropriate nema connector and order a cheaper level 2 charger with a max output of 16amps.

It's definitely more than 16A... 7.4kW at 240V is 30.8A.


Also, for a continuous duty appliance (like an EV charger) you are only allowed to use 80% of the rated circuit capacity so a 30A dryer plug only supports 24A charging. Plus there's always the argument that if you're paying for the installation labor you might as well make sure it's future proof.

Oh and if you're in the US, you only qualify for the 30% tax rebate if you install a UL listed (not cheap) EVSE (at least until the end of this year)

 

[MatthewL]

I dunno, but my Level two charger reports that the mini is taking 32 amps, about 9kw per hour, until it reaches near capacity where it drops off.

It reports I've been getting about 4.9 mile per kWh in our driving conditions (mostly back roads). Our overall electric rate is about 17 cents per kWh, so thats roughly 3.4 cents per mile or so without charger inefficiency. Probably better if I consider tiering. Your mileage may vary.

That's interesting because even in the owners manual it says, Level 2 charging cable The Level 2 charging cable makes it possible to quickly recharge at sockets of designated Level 2 charging stations using a special plug. Charging is performed with alternating current at designated Level 2 charging stations. The charging process can be completed faster than at household sockets. A charge current strength of up to maximum 16 A is possible. The charging cable may be permanently installed at the charging station.

 

[MatthewL]

Does the mini tell us how many amps are being pumped in? I have yet to find that data in the displays anywhere?

 

[Carsten Haase]

That's interesting because even in the owners manual it says, Level 2 charging cable The Level 2 charging cable makes it possible to quickly recharge at sockets of designated Level 2 charging stations using a special plug. Charging is performed with alternating current at designated Level 2 charging stations. The charging process can be completed faster than at household sockets. A charge current strength of up to maximum 16 A is possible. The charging cable may be permanently installed at the charging station.

It doesn't say "level 2", it says "mode 2" which is not the same thing. It's rather confusing but that section of the manual is specifically talking about charging on a "household" socket which is a standard 120V outlet here in the US.

 

[Teddydogno1]

Thanks for the discussion so far. Seems my math is OK except for ignoring efficiency then?

I didn't mention my home charging, but didn't want to until I was back at home and could look at the 240V service in my garage. When we had the house built, I did opt for a such an outlet in there. I don't recall what receptacle was used, though, or the size of the breaker and wire. I have only used it for my H-F Mig welder so far. It is located in the middle of one wall behind my table saw. Not sure if the location will be OK with a 25' charging cable, or if I'll need to buy or build a heavy-gauge extension cable so the Level 2 charger can be closer to the garage door. No vehicles live in the garage...it is more warehouse and shop than vehicle hotel.

I also have several dedicated 20A 120v outlets in the garage. After adding A/C a few years after moving in, my panel is maxed out in terms of breaker slots. No adding without making other changes, so whatever I do will have to be done with what is already there. We only plan to be there a few more years anway.

A question about the Federal Tax Rebate for EV equipment. Since I already have a 240V outlet in the garage, can I apply for and get that rebate on just a Level 2 charger that I plug in myself, or is professional installation required?

Rob

 

[ColdCase]

The federal's charger hardware tax credit does not require professional installation. Dunno about local credits. Your homeowner insurance or local codes may, however.

Properly rated extension cables that support 32amp charging are expensive, look for RV type not welding (short duty) extensions. To support 32 amp charging, it may cost less to run a cable from the the entry panel or outlet box (hard wire the charger).

The grizzly charger lets you set a lower max amp charging rate, one that your wiring may be able to safely handle. Its a common practice. It would just take longer to charge at 16 or 24 amps instead of 32. Most level 2 chargers are probably configurable.

 

[Puppethead]

You should be able to determine the amperage of your welding receptacle from the breaker. EVSEs on an outlet can't be more than 12 inches (or so) from the outlet, so an extension cable is a bad idea.

The federal rebate on installs is 30% up to $1000, so you need to spend at least $3333 to get the full rebate. But buying an EVSE and setting it up yourself does qualify. In your case I'd consider putting in an outdoor outlet or hardwired EVSE if you can't fit the car in the garage. Since you'd be extending the existing circuit I can't imagine it'd be too costly.

 

[ColdCase]

If I recall correctly, if the outlet was configured for intermittent use, like welding, it may be using smaller gauge wiring than what the code requires for continuous duty, like EV charging... regardless of breaker size. So you need to look at the wire gauge and distance from the breaker panel along with the breaker. There is a wire gauge chart around here somewhere.

If you want to be code compliant and safe, you may want to consult a local electrician. Its not rocket science, but its not straight forward.

 

[Carsten Haase]

Its not rocket science, but its not straight forward.

Absolutely lol

In addition to just amperage and run length there's also a bunch of de-rate factors in addition to the 80% continuous duty one which could reduce the ampacity further. (Here's a good explanation)

Then there's the whole GFCI requirement for non-hardwired installation depending on whether your state adopted that section of the NEC or not

 

[F14Scott]

If you have a dedicated 20A, 120V outlet, you are in a perfect position to add very adequate L2 charging, very inexpensively.

Have the electrician replace the single pole 120V breaker with a double pole 240V one. The wiring in the wall is already good for 20A (16A of continuous charging). Swap the plug for a 6-20 or hardwire a connector and you've got 3.8kW, enough to take your SE from 0 to 100% in eight hours. It should cost under $300, plus the price of your L2 connector.

Starting every day with 120 miles of range for $0.03 a mile is one of the great joys of owning an EV. Have fun with it!

 

[Teddydogno1]

Back to my thread now after a week.

I have done more digging into what public/pay chargers are available around me and found there in addition to the 2 DC fast charging stations I mentioned, there are a couple more of those and a lot of public Level 2 chargers. Many are even free for the first couple of hours (like ones by the Target store).

I checked my home 240v plug in the garage and it is a NEMA 14-30R with a 30A breaker in the box.

This seems to maybe be an uncommon plug type? I know the current draw is limited by the breaker and that size is limited by the wire size installed. I could pretty easily shut down the outlet and check the wire size, I think. Someone commented that it might be an "intermittent use" circuit since it was used for a welder, but I highly doubt that as the home builder installed it when we ordered it without any stated purpose. That would not have been safe or to code, I would thing.

I'd like to kind of future-proof buying a "better" EVSE, even if my current outlet and it's rating can't fully use it. I like the Chargepoint, I think, but they come designed for 40A and 50A service:

"Plug-in installation with NEMA 6-50 or 14-50 outlet (14-50 currently selected) requires circuits rated 40A or 50A. "

Since the EVSE and car can only use what the outlet gives it, why couldn't you use a 30A outlet and and adapter to use the Chargepoint with my 30A circuit (https://www.amazon.com/ONETAK-Weldi...ug+adapter+male+14-30&qid=1629424409&sr=8-6)? Or replace the outlet with a 14-50 but only back it with the 30A wire and breaker? Obviously I would need to be able to limit the EVSE to a max draw of 24A on this circuit.

I think I should move these home charger questions to the thread for that.

Rob

 

[F14Scott]

Back to my thread now after a week.

I have done more digging into what public/pay chargers are available around me and found there in addition to the 2 DC fast charging stations I mentioned, there are a couple more of those and a lot of public Level 2 chargers. Many are even free for the first couple of hours (like ones by the Target store).

I checked my home 240v plug in the garage and it is a NEMA 14-30R with a 30A breaker in the box.

This seems to maybe be an uncommon plug type? I know the current draw is limited by the breaker and that size is limited by the wire size installed. I could pretty easily shut down the outlet and check the wire size, I think. Someone commented that it might be an "intermittent use" circuit since it was used for a welder, but I highly doubt that as the home builder installed it when we ordered it without any stated purpose. That would not have been safe or to code, I would thing.

I'd like to kind of future-proof buying a "better" EVSE, even if my current outlet and it's rating can't fully use it. I like the Chargepoint, I think, but they come designed for 40A and 50A service:

"Plug-in installation with NEMA 6-50 or 14-50 outlet (14-50 currently selected) requires circuits rated 40A or 50A. "

Since the EVSE and car can only use what the outlet gives it, why couldn't you use a 30A outlet and and adapter to use the Chargepoint with my 30A circuit (https://www.amazon.com/ONETAK-Weldi...ug+adapter+male+14-30&qid=1629424409&sr=8-6)? Or replace the outlet with a 14-50 but only back it with the 30A wire and breaker? Obviously I would need to be able to limit the EVSE to a max draw of 24A on this circuit.

I think I should move these home charger questions to the thread for that.

Rob

Some home "connectors" (I use the Tesla term because I think it is the most accurate, since it only connects the car's internal charger to the 240V power) allow the user to manually dial in their max draw, such as the Tesla High Power Wall Connector. I have two of these in my garage.

Other home connectors limit their draw based on their physical plug, assuming the plug will be used in a properly wired outlet. Teslas come with a portable connector whose plugs can be swapped out with different sizes, thereby notifying the connector the max Voltage and Amperage to draw.

You have an outlet and breaker (and, presumably, wiring) rated for 30 Amps. As you noted,, they can supply your car a maximum of 24 Amps continuously, per code. If you buy a connector bigger than 24 Amps that cannot be throttled down via a physical switch or other physical means, your connector will try to draw too much juice and you'll trip your breaker, start a fire, or both!

One cannot put a 14-50 outlet on 30 Amp wiring, as the presumption is that a 14-50 outlet may be plugged into freely by any 50 Amp appliance. (There is a 40 Amp breaker exception to the 14-50 for dryers that are not continuous draws, but the electrician must clearly label the outlet and wiring so the home's next owner doesn't inadvertently burn his new house down.

I'm afraid you have the whole "draw" paradigm backwards: the appliance will draw all it can from the outlet, up to and even over the outlets' and breaker's rating. Plug in a power strip with three, 1500 watt hair dryers connected to it into a standard 5-15 (120V, 15A) outlet and the power strip will pull 4500 Watts (37.5A at 120V) , immediately tripping the breaker.

Conversely, the outlet will supply only as much as the appliance needs and draws, so it is perfectly safe to plug a 4 Watt night light into a 120V, 15A socket; the outlet won't send any more than the little bulb pulls.

The good news is that your 24A continuous will fill your SE from 10 to 100% in under 5 hours, and would fill my 75kW Tesla from 10 to 90% in under 12 hours. In other words, a 240VAC, 30A breaker is plenty!

 

[Teddydogno1]

I'm sorry. I do understand how power draw works but I was absolutely guilty of sloppy and imprecise writing (Mechanical Engineer by education). I was trying to say that if the EVSE was SET to only draw 24A, then it shouldn't matter what type of outlet was on the wall being fed by a 30A breaker and appropriate wiring. Totally recognize that it would be an unsafe practice to put a 50A rated outlet on that circuit as someone other than me would not know the difference.

By "Since the EVSE and car can only use what the outlet gives it", I meant that the 30A breaker would trip if the car and EVSE tried to draw more. Again...very poorly stated and bad practice. And my comment about the wire size was meant to say that the wire is a limiting factor to amp rating.

So...lot of sloppiness up there. Sorry.

Someone else mentioned that the Grizzl-e would be better than the Chargepoint for this case because the Grizz can be PHYSICALLY set to a limit of 24A, which should prevent any attempt to pull at the limit of this circuit.

Rob

 

[F14Scott]

I'm sorry. I do understand how power draw works but I was absolutely guilty of sloppy and imprecise writing (Mechanical Engineer by education). I was trying to say that if the EVSE was SET to only draw 24A, then it shouldn't matter what type of outlet was on the wall being fed by a 30A breaker and appropriate wiring. Totally recognize that it would be an unsafe practice to put a 50A rated outlet on that circuit as someone other than me would not know the difference.

By "Since the EVSE and car can only use what the outlet gives it", I meant that the 30A breaker would trip if the car and EVSE tried to draw more. Again...very poorly stated and bad practice. And my comment about the wire size was meant to say that the wire is a limiting factor to amp rating.

So...lot of sloppiness up there. Sorry.

Someone else mentioned that the Grizzl-e would be better than the Chargepoint for this case because the Grizz can be PHYSICALLY set to a limit of 24A, which should prevent any attempt to pull at the limit of this circuit.

Rob

Ahh. All good, then, and I agree with all your points in your correction. This is such a great forum, where friendly advice and helpful corrections are almost always taken in the spirit they are given. Cheers!

 

[MatthewL]

Back to my thread now after a week.

I have done more digging into what public/pay chargers are available around me and found there in addition to the 2 DC fast charging stations I mentioned, there are a couple more of those and a lot of public Level 2 chargers. Many are even free for the first couple of hours (like ones by the Target store).

I checked my home 240v plug in the garage and it is a NEMA 14-30R with a 30A breaker in the box.

This seems to maybe be an uncommon plug type? I know the current draw is limited by the breaker and that size is limited by the wire size installed. I could pretty easily shut down the outlet and check the wire size, I think. Someone commented that it might be an "intermittent use" circuit since it was used for a welder, but I highly doubt that as the home builder installed it when we ordered it without any stated purpose. That would not have been safe or to code, I would thing.

I'd like to kind of future-proof buying a "better" EVSE, even if my current outlet and it's rating can't fully use it. I like the Chargepoint, I think, but they come designed for 40A and 50A service:

"Plug-in installation with NEMA 6-50 or 14-50 outlet (14-50 currently selected) requires circuits rated 40A or 50A. "

Since the EVSE and car can only use what the outlet gives it, why couldn't you use a 30A outlet and and adapter to use the Chargepoint with my 30A circuit (https://www.amazon.com/ONETAK-Weldi...ug+adapter+male+14-30&qid=1629424409&sr=8-6)? Or replace the outlet with a 14-50 but only back it with the 30A wire and breaker? Obviously I would need to be able to limit the EVSE to a max draw of 24A on this circuit.

I think I should move these home charger questions to the thread for that.

Rob

This is what I purchased, same situation as you, and it works great.

https://www.amazon.com/gp/product/B0922R5MYH/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

 

[Torrey]

Back to my thread now after a week.

I have done more digging into what public/pay chargers are available around me and found there in addition to the 2 DC fast charging stations I mentioned, there are a couple more of those and a lot of public Level 2 chargers. Many are even free for the first couple of hours (like ones by the Target store).

I checked my home 240v plug in the garage and it is a NEMA 14-30R with a 30A breaker in the box.

This seems to maybe be an uncommon plug type? I know the current draw is limited by the breaker and that size is limited by the wire size installed. I could pretty easily shut down the outlet and check the wire size, I think. Someone commented that it might be an "intermittent use" circuit since it was used for a welder, but I highly doubt that as the home builder installed it when we ordered it without any stated purpose. That would not have been safe or to code, I would thing.

I'd like to kind of future-proof buying a "better" EVSE, even if my current outlet and it's rating can't fully use it. I like the Chargepoint, I think, but they come designed for 40A and 50A service:

"Plug-in installation with NEMA 6-50 or 14-50 outlet (14-50 currently selected) requires circuits rated 40A or 50A. "

Since the EVSE and car can only use what the outlet gives it, why couldn't you use a 30A outlet and and adapter to use the Chargepoint with my 30A circuit (https://www.amazon.com/ONETAK-Weldi...ug+adapter+male+14-30&qid=1629424409&sr=8-6)? Or replace the outlet with a 14-50 but only back it with the 30A wire and breaker? Obviously I would need to be able to limit the EVSE to a max draw of 24A on this circuit.

I think I should move these home charger questions to the thread for that.

Rob

Just responding to point out that is a very common plug type to have in a garage. 240V / 24A is standard for electric dryers. The NEMA 14-50 that everyone likes for EVSE is most commonly used for electric stoves so you don't often find them in garages.