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      08-03-2023, 12:11 PM   #1
DroMike
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Home Charging Time for i7?

PLEASE FOLLOW THIS PARA BY PARA TO GET TO QUESTION AT BOTTOM:

For my upcoming i7, I've contracted for a dedicated outlet/circuit in my garage, to be installed in the next week or two. Accordingly, I went:

FROM (considering): an existing 240v dryer outlet on 30 amp circuit
TO (be installed): a 240v outlet on a dedicated 40 amp circuit.

I'd LIKE to know is how much faster would my 20-80% charging time now be. However, I keep hearing that an amp circuit can only charge 80% of its amperage (ergo, the 30 amp would be 24 amps, and the 40 amp would be 32 amps). I simply don't know which figure to use (higher or smaller).

I DID find this "Charging Time Calculator" but it requires one to know one's "Charging Time in kW" to make it work. https://www.homechargingstations.com...charging-time/

Happily, I also found an easy formula for kW: (Amperage x Voltage) / 1000

That said, I BELIEVE:

24 x 240 = 5,760 / 1000 = 5.76 kW [dryer, 24 amps]
30 x 240 = 7,200 / 1000 = 7.20 kW [dryer, 30 amps]
32 x 240 = 7,680 / 1000 = 7.68 kW [dedicated outlet, 32 amps]
40 x 240 = 9,600 / 1000 = 9.60 kW [dedicated outlet, 40 amps]

Thus using the "Charging Time Calculator," the actual charging time (going from 20-80% charged) would take:

12 hrs, 16 min (at 5.76 kW) [dryer, 24 amps]
9 hrs, 48 min (at 7.20 kW) [dryer 30 amps]
9 hrs, 12 min (at 7.68 kW) [dedicated outlet, 32 amps]
7 hrs, 21 min (at 9.60 kW) [dedicated outlet, 40 amps]

My QUESTION is, which actual charging time would I have got from the dryer outlet and which actual charging time will I get from the dedicated outlet?.
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      08-03-2023, 03:21 PM   #2
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1. You won't get full 30A charging from a "30A" drier outlet...

For example, in order to get 40A (9.6KW) charging, you actually need a 50A circuit. (Based on efficiencies, mfr recommendations, and safety) If you want a full 50A charge, then a 70A circuit is typically specified... (Both my charger outlets are on 50A circuits, so I am configured for 40A or 9.6 KW each...) Charger Manufacturers typically specify this very clearly in their manuals...

No one really specs out a 30A circuit for a fixed EV charger (although many "portable" chargers will work with one...) As such, I'm unsure of what amperage you would have to limit the charger to. Maybe 25A? (about 6.0KW) You would need to check with the configurable options available for the specific charger you plan on using. ...but it would be less than 30A.

2. The i7 M70 has a battery size of 105.7KW. If you wanted to fully charge a completely drained battery, you BASICALLY divide the battery size by the charger output. I.E 105.7/9.6 (40A) = 11 Hrs 105.7/6.0 (25A) = 17.6 Hrs

3. Not necessarily a meaningful concern for level 2 home charging, but EV's will accept higher charging rates ONLY when close to empty. As the battery charge increases, the charging rate decreases. (IOW: a 350KW Electrify America charger is not going to provide a linear 350 KW charge - even if the car could accept it. Charging tapers off as the battery fills up...) Aagin, not so relevant for home charging...

4. All that being said, no one completely uses their entire battery capacity every day. If you do, then an EV was a bad choice. You will only need to charge up based on what you have actually used...

5. ...and you don't typically charge an EV to 100% every day. Only when you know you have a long trip planned. Most EV suggest a lower charge for daily use. BMW recommends 80% daily charging (on my iXM60), Porsche recommends 85% (on my Taycan Turbo S). You don't really want to charge to 100% every day as it places needless strain on the battery. Only charge to 100% when you really need it!

So all that being said, the typical usage model for EV's with home chargers is simply plug it in when you get home and it should be ready to go (at 80-85%) in the morning. (Like your cell phone). If you have greater range/charging demands then that, then an EV may not be a great choice...

Hope this helps...
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      08-03-2023, 05:11 PM   #3
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Thanks for your thoughtful reply Evan. I guess I really only needed corroboration that my 40A circuit would actually charge at just 32A (instead of the full 40A).

And yes, I'm only talking about charging from 20% to 80% capacity -- I already know not to charge fully to 100% unless taking a rare long trip.

Accordingly, I'm happy enough that we were able to pinpoint it'd then take approximately 9 hrs, 12 mins indicated per the "Charger Time Calculator" times shown -- more or less overnight as you point out.

Last edited by DroMike; 08-03-2023 at 08:58 PM..
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      08-03-2023, 06:48 PM   #4
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Quote:
Originally Posted by evanevery View Post
1. You won't get full 30A charging from a "30A" drier outlet...

For example, in order to get 40A (9.6KW) charging, you actually need a 50A circuit. (Based on efficiencies, mfr recommendations, and safety) If you want a full 50A charge, then a 70A circuit is typically specified... (Both my charger outlets are on 50A circuits, so I am configured for 40A or 9.6 KW each...) Charger Manufacturers typically specify this very clearly in their manuals...

No one really specs out a 30A circuit for a fixed EV charger (although many "portable" chargers will work with one...) As such, I'm unsure of what amperage you would have to limit the charger to. Maybe 25A? (about 6.0KW) You would need to check with the configurable options available for the specific charger you plan on using. ...but it would be less than 30A.

2. The i7 M70 has a battery size of 105.7KW. If you wanted to fully charge a completely drained battery, you BASICALLY divide the battery size by the charger output. I.E 105.7/9.6 (40A) = 11 Hrs 105.7/6.0 (25A) = 17.6 Hrs

3. Not necessarily a meaningful concern for level 2 home charging, but EV's will accept higher charging rates ONLY when close to empty. As the battery charge increases, the charging rate decreases. (IOW: a 350KW Electrify America charger is not going to provide a linear 350 KW charge - even if the car could accept it. Charging tapers off as the battery fills up...) Aagin, not so relevant for home charging...

4. All that being said, no one completely uses their entire battery capacity every day. If you do, then an EV was a bad choice. You will only need to charge up based on what you have actually used...

5. ...and you don't typically charge an EV to 100% every day. Only when you know you have a long trip planned. Most EV suggest a lower charge for daily use. BMW recommends 80% daily charging (on my iXM60), Porsche recommends 85% (on my Taycan Turbo S). You don't really want to charge to 100% every day as it places needless strain on the battery. Only charge to 100% when you really need it!

So all that being said, the typical usage model for EV's with home chargers is simply plug it in when you get home and it should be ready to go (at 80-85%) in the morning. (Like your cell phone). If you have greater range/charging demands then that, then an EV may not be a great choice...

Hope this helps...
This is 100% spot on! You couldn’t ask for a better, more accurate response
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      08-04-2023, 12:50 AM   #5
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Quote:
Originally Posted by evanevery View Post
1. You won't get full 30A charging from a "30A" drier outlet...

For example, in order to get 40A (9.6KW) charging, you actually need a 50A circuit. (Based on efficiencies, mfr recommendations, and safety) If you want a full 50A charge, then a 70A circuit is typically specified... (Both my charger outlets are on 50A circuits, so I am configured for 40A or 9.6 KW each...) Charger Manufacturers typically specify this very clearly in their manuals...

No one really specs out a 30A circuit for a fixed EV charger (although many "portable" chargers will work with one...) As such, I'm unsure of what amperage you would have to limit the charger to. Maybe 25A? (about 6.0KW) You would need to check with the configurable options available for the specific charger you plan on using. ...but it would be less than 30A.

2. The i7 M70 has a battery size of 105.7KW. If you wanted to fully charge a completely drained battery, you BASICALLY divide the battery size by the charger output. I.E 105.7/9.6 (40A) = 11 Hrs 105.7/6.0 (25A) = 17.6 Hrs

3. Not necessarily a meaningful concern for level 2 home charging, but EV's will accept higher charging rates ONLY when close to empty. As the battery charge increases, the charging rate decreases. (IOW: a 350KW Electrify America charger is not going to provide a linear 350 KW charge - even if the car could accept it. Charging tapers off as the battery fills up...) Aagin, not so relevant for home charging...

4. All that being said, no one completely uses their entire battery capacity every day. If you do, then an EV was a bad choice. You will only need to charge up based on what you have actually used...

5. ...and you don't typically charge an EV to 100% every day. Only when you know you have a long trip planned. Most EV suggest a lower charge for daily use. BMW recommends 80% daily charging (on my iXM60), Porsche recommends 85% (on my Taycan Turbo S). You don't really want to charge to 100% every day as it places needless strain on the battery. Only charge to 100% when you really need it!

So all that being said, the typical usage model for EV's with home chargers is simply plug it in when you get home and it should be ready to go (at 80-85%) in the morning. (Like your cell phone). If you have greater range/charging demands then that, then an EV may not be a great choice...

Hope this helps...
i second that, best answer possible!

DroMike
about charging: check this out:
https://evkx.net/models/bmw/i7/i7_xd...chargingcurve/
it might help you in understanding how charging works in general
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      09-26-2024, 02:03 AM   #6
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Following up on this.....

I am thinking of just getting the BMW Wallbox hardwired since a BMW Wallbox comes free this month on all 7 series purchases (just waiting for stop sale work to be performed on mine).

So the BMW wallbox are 40 amp units....meaning it would actually charge at 32 amps, correct (since they do 80% of the total)? As DroMike mentioned....I assume I am looking at 9 hours to charge from 20% to 80%? I just wonder if it's worth it to buy one that is a 50-60 amp unit....or whether the time difference is negligible.

Also, does the BMW wallbox have a built in GFCI like a lot of charger units?
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      09-26-2024, 11:24 PM   #7
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Quote:
Originally Posted by mjr24 View Post
Following up on this.....

I am thinking of just getting the BMW Wallbox hardwired since a BMW Wallbox comes free this month on all 7 series purchases (just waiting for stop sale work to be performed on mine).

So the BMW wallbox are 40 amp units....meaning it would actually charge at 32 amps, correct (since they do 80% of the total)? As DroMike mentioned....I assume I am looking at 9 hours to charge from 20% to 80%? I just wonder if it's worth it to buy one that is a 50-60 amp unit....or whether the time difference is negligible.

Also, does the BMW wallbox have a built in GFCI like a lot of charger units?
I'm far from an expert, but this is what I am almost certain of:

The BMW Wallbox (correctly termed Electric Vehicle Supply Equipment or EVSE) will charge at a maximum of 40 amps. But for you to coax that amperage out of it you will need a 50 amp circuit. Your math however, IS correct, but in this case 80% of 50 amps get your that full 40 amps.

I'm not sure about any unit that is 60 amps. 40amp charging from a 50-amp circuit will be the most you can get in 98% of all scenarios. VERY generally speaking, even charging at 40 amps, it will still be most efficient to do so overnight, as it will take 6-8 or 9 hours depending on your state of charge. Even if you WERE charging at 48amps to your vehicle, you might only shave an hour off that time -- it's of small consequence. Similarly, charging at 32amps might take you another 90 minutes or so. I'm merely saying, that a 50-amp circuit is the most common here and probably most financially efficient or the best value.

The hardwired wallbox does NOT come GFCI protected. But there are two important things to consider however: (1) Your 50amp circuit will have GFCI so you are protected on that 50amp-EVSE circuit; and (2) should you HAVE two GFCI breakers (using a non-hardwired EVSE), you'd more than likely have problems with premature tripping. It's generally know that portable/outlet/14-50 EVSE's coupled with a GFCI-protected circuit/subpanel, etc. "do not play nice" together. Basically, they become OVERLY-sensitive and trip often making charging frustrating and unreliable. The correct terminology for this is called "nuisance tripping." That said, you're probably VERY OK pairing your non-GFCI BMW Wallbox with a GFCI-protected 50amp breaker. This is an ideal setup.

Coincidentally, I am about to post a small treatise here about this very subject matter -- for those with an i7, a 50amp GFCI circuit breaker (or not) and a portable/outlet/14-50 EVSE like mine.

In any event, I'm sure others will chime in with more than my layman's information -- but the bottom line is you'll be golden with a 50-amp GFCI-protected dedicated circuit or subpanel for you EV charging, AND the BMW Wallbox!
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      09-27-2024, 01:11 AM   #8
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Quote:
Originally Posted by DroMike View Post
I'm far from an expert, but this is what I am almost certain of:

The BMW Wallbox (correctly termed Electric Vehicle Supply Equipment or EVSE) will charge at a maximum of 40 amps. But for you to coax that amperage out of it you will need a 50 amp circuit. Your math however, IS correct, but in this case 80% of 50 amps get your that full 40 amps.

I'm not sure about any unit that is 60 amps. 40amp charging from a 50-amp circuit will be the most you can get in 98% of all scenarios. VERY generally speaking, even charging at 40 amps, it will still be most efficient to do so overnight, as it will take 6-8 or 9 hours depending on your state of charge. Even if you WERE charging at 48amps to your vehicle, you might only shave an hour off that time -- it's of small consequence. Similarly, charging at 32amps might take you another 90 minutes or so. I'm merely saying, that a 50-amp circuit is the most common here and probably most financially efficient or the best value.

The hardwired wallbox does NOT come GFCI protected. But there are two important things to consider however: (1) Your 50amp circuit will have GFCI so you are protected on that 50amp-EVSE circuit; and (2) should you HAVE two GFCI breakers (using a non-hardwired EVSE), you'd more than likely have problems with premature tripping. It's generally know that portable/outlet/14-50 EVSE's coupled with a GFCI-protected circuit/subpanel, etc. "do not play nice" together. Basically, they become OVERLY-sensitive and trip often making charging frustrating and unreliable. The correct terminology for this is called "nuisance tripping." That said, you're probably VERY OK pairing your non-GFCI BMW Wallbox with a GFCI-protected 50amp breaker. This is an ideal setup.

Coincidentally, I am about to post a small treatise here about this very subject matter -- for those with an i7, a 50amp GFCI circuit breaker (or not) and a portable/outlet/14-50 EVSE like mine.

In any event, I'm sure others will chime in with more than my layman's information -- but the bottom line is you'll be golden with a 50-amp GFCI-protected dedicated circuit or subpanel for you EV charging, AND the BMW Wallbox!

Thanks Mike, very informative.
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