Home L2 Charging: 40A versus 48A

[ridgebackpilot]

When I acquired my Tesla Model 3 a couple of years ago, I installed a Tesla Wall Charger in my detached garage. Since the garage was built in the 1980s, it had only a 50-amp feed so I had to limit my charging to 40 amps continuous. I used #6 Romex to hardwire the charger on its own 50 amp breaker.

My MME charges just fine using the Tesla Wall Charger and a Tesla Tap Mini 60 amp adapter. Since I can't install another Level 2 charger without rewiring the entire garage, I simply swap the charger between the Tesla and the MME.

I have a solar array, Tesla Powerwall battery backup, and NEM EV electric rates, all of which allows me to charge only during off-peak hours. (Indeed, I draw from the grid at all only during off-peak hours; the Powerwalls run the house during peak and mid-peak times of day). That minimizes the cost of charging the cars; it's about half the price of fast DC charging.

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[ridgebackpilot]

Yep. Charging the MME at 48A is like filling an ICE vehicle with a NASCAR fuel can. Most times it is unnecessary and can make a mess of things.

? Love that analogy. But I thought the EV equivalent to the NASCAR fuel can would be DC fast chargers!

 

[SnBGC]

? Love that analogy. But I thought the EV equivalent to the NASCAR fuel can would be DC fast chargers!

DCFC is more like a fire hose.

 

[Eric_C_Boston]

In my case, there was an existing NEMA 10-50 outlet on a 50 Ampere Breaker. Fortunately the outlet box was grounded with a separate ground wire, so the old outlet was swapped with a NEMA 14-50.

40 Amperes meets my needs and I might consider dropping down to 32 Amperes as an overnight charge usually finishes around 5 AM. As for future needs, I am retiring soon so no need for the faster charge even if my next BEV has double the battery of my current MME.

 

[Mosworthy]

I have two chargers on two seperate 30amp circuits, depends where I park.
Always full in the morning, I couldn't care less.

 

[Larry Paul]

My 2¢:

Based on my and my wife's last 23+ years and 330K+ miles of BEV driving (including a 20 year old Toyota Rav4EV with 20 year old batteries in it), my plan is to continue using our existing 32A (6.6kWh) Clipper Creek chargers (each with 40A circuits). At 32A, it should recover about 20 miles of driving per hour of charge, so with 8 hours of charging that is about 160 miles (more than I ever go a day after I went a longer distance from the day before). In worst case I would stop to use a charger on the road, but based on my driving habits, I am not expecting this scenario to occur.

A slower charge rate will increase battery longevity and it will charge fast enough for me to get anywhere I need to be the next day even if it is not "topped off" before I need to depart. My goal is to extend the battery life for as long as practical, while still enjoying the performance for occasional spirited driving of a GTPE.

https://www.vehiclesuggest.com/how-long-does-an-electric-car-battery-last/

 

[Tell It Right]

When I acquired my Tesla Model 3 a couple of years ago, I installed a Tesla Wall Charger in my detached garage. Since the garage was built in the 1980s, it had only a 50-amp feed so I had to limit my charging to 40 amps continuous. I used #6 Romex to hardwire the charger on its own 50 amp breaker.

My MME charges just fine using the Tesla Wall Charger and a Tesla Tap Mini 60 amp adapter. Since I can't install another Level 2 charger without rewiring the entire garage, I simply swap the charger between the Tesla and the MME.

I have a solar array, Tesla Powerwall battery backup, and NEM EV electric rates, all of which allows me to charge only during off-peak hours. (Indeed, I draw from the grid at all only during off-peak hours; the Powerwalls run the house during peak and mid-peak times of day). That minimizes the cost of charging the cars; it's about half the price of fast DC charging.

I don't have an EV yet but I'm in the market for one. Also, I have s solar system too (10 kW panels, 30kWh storage, 9kW continuous power from my inverter). One thing about a higher amp charger is the demand it puts on the inverter. A 240V/32A charger demands 7.7kW -- meaning my 9kW inverter can supply that plus 1.3kW more (for the house's other electrical needs) before pulling from the grid. A 240V/48A charger will pull 11.5 kW -- I'll automatically pull at least 2.5kW from the grid (plus whatever else the house needs at that time).

I'm planning to upgrade my solar system (including doubling my inverter) to reduce this issue. I bring it up because it might be best to have two charger outlets: a lower amperage charger and a higher one (more liable to pull from the grid, but if you need the power you need it). If you come home near empty and have a long trip soon -- use the higher amperage one. If you come home with 3/4th's of a "tank" and have nothing but a 40 mile round trip commute planned the next day, user the lower amperage one (less likely to pull from the grid).

And that's not even getting into if your solar inverter has a "smart load" feature or something like that where it'll power a certain circuit panel only if your home batteries are charged to at least a certain percentage (more then enough power to make it through the night on stored solar power, might as well use some of that for charging the EV, but only as long as the home batteries are charged above that threshold).

 

[nor3bo]

I second the advice of going wiring for 60 amp, and then setting the EVSE to charge at 40 amps. If you need the higher rate later it's an easy switch, and you should have good thermals/safety/performance for now.

Personally I like running at 40amps on a plugged in Grizzl-e using a 14-50 plug. My plug is locked and and I don't use it for anything else, but I have the option of easily moving my Grizzl-e if I have to, or plugging in my mobile EVSE if the Grizzl-e is not working. (Which, while they were switching over their software, happened for me).

 

[khbkhb]

Obviously all our situations are different. We had ample panel capacity, so we put in two circuits, one to hardware a wallbox and one a NEMA 14-50. The latter in case we get a second EV or the wallbox needs servicing.

When we needed to replace our driveway (40+ year old concrete, badly done to start with)we borrowed our neighbors' driveway ... and ran a 100 ft NEMA 14-50 extension to our outlet (and used the mobile charger). So in retrospect, I'm glad we sprang for the outlet.

Note that the wallbox can communicate with its peers, so you can run multiple on a single circuit and they can adjust the amps up or down based on the individual car draws.

Usually, the speed of charge doesn't greatly matter to us; but the extra 20% speed is worth having in one's back pocket ;>

 

[ZuleMME]

I bought a Neocharge to use to intelligently "split" my 50a 14-50 outlet between my OpenEVSE (primary) and my wife's future car, a Tesla. It'll be able to allow both to pull 20A at the same time and/or if one wants more it'll switch off the secondary while the primary runs and then turn back on the other when the power is available. Figured that was about the best scenario.

 

[entenna]

I am getting two Wallbox Plus (48A) installed; one outside garage and one inside. They each have their own 60A dedicated circuit and are hardwired. One of the chargers is set to 48A while the other charger is hooked up to an energy monitor so that it adjusts the max current automatically instead of throttling its current based on a worst-case load analysis.

 

[RetiredDP]

I considered 48 amp vs 40 amp, and went with 40. I use an Alpha EVSE, with a 40 amp max output, and have NEVER felt the need for more speed in a charge. I'm wired with a 14-50 outlet, so if my Alpha ever dies, I can just unplug it and plug the Mach-E's remote charger INTO THE SAME OUTLET. Why complicate life with a hard-wired charger, when it's not needed? A 48 amp EVSE can only deliver 43 amps into the Mach-E, so there is NOT a 20% improvement in charge speed...you just get a 9.3% speed improvement. And if the 48 amper ever fails (all EVSE's will do that, eventually), I can't just buy another and plug it in...I'd have to hire a pro electrician to re-hardwire in a replacement, with no ability to use the Ford Mobile Charger (14-50 plug-in connector) in the meantime. And have you ever tried to book a pro electrician? They are usually booked-up for 1-3 weeks in the future.

 

[Oldbutalive]

I recently purchased a ChargePoint Home Flex with a NEMA 6-50 plug at list price. NEMA 14-50 model is out of stock in most places, delayed shipping and costing more.

Anyway, I'm torn between hardwire install with 240V/48A supply/60A Breaker (estimated range per hour of 36 miles) and plug-install with 240V/40A supply/50A Breaker (estimated range per hour of 30 miles). Would appreciate hearing from owners who have one of the 40A or 48A setups (doesn't have to be a ChargePoint EVSE) with their pros and cons. My chosen electrician has quoted $150 difference between hardwire and plug install; not enough to sway me one way or another; wire-run of 35 feet from breaker panel. I plan to carry the Ford-supplied EVSE w/cables in my frunk as I know the NEMA 14-50 plug is more prevalent across the country.

Thanks for any input you provide!

My Hard-wire install was $250 including the wire and 60AMP Breaker.
BUT is this the last/only EV in your future? My wife will want her own as her 2019 Lexus ES300H has 40K+. Today still skeptical. Than Tomorrow will come some DAY and having quicker power will allow flexibility

 

[bcb]

I did hardwire with 60 amp. Not that I need it today but add in another EV it’s possible that would need a little fast to swich over before bedtime

Yep, same here and will likely get another EV someday, (right now 2nd car is
a prius plugin). I would hardwire it, don't use that other plug, you will regret it.
Also there should NOT be a price difference.

 

[entenna]

Yep, same here and will likely get another EV someday, (right now 2nd car is
a prius plugin). I would hardwire it, don't use that other plug, you will regret it.
Also there should NOT be a price difference.

from what I was told, hardwire should be cheaper since you are saving ~$150 on the receptacle, enclosure, GFCI

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