30 Amp vs 40 Amp Charging

[kalel14]

Right now I'm charging the FFE on the charger that came with the car. An electrician says that the way things are wired in the house, I can change breakers and install a 30 amp wall charger. If I want to put in a 40 amp charger, the investment would be higher with running heavier duty wiring and other upgrades.

So what's the marginal benefit of 40 vs. 30? There's a huge time savings from what I'm doing now to the 30 amp. How much will a 40 amp improve on the 30?

Thanks!

 

[jmueller065]

None: The FFE won't charge at 40amps, at most it does is about 28 amps (6.6kW).

 

[Pearl]

Right now I'm charging the FFE on the charger that came with the car. An electrician says that the way things are wired in the house, I can change breakers and install a 30 amp wall charger. If I want to put in a 40 amp charger, the investment would be higher with running heavier duty wiring and other upgrades.

So what's the marginal benefit of 40 vs. 30? There's a huge time savings from what I'm doing now to the 30 amp. How much will a 40 amp improve on the 30?

Thanks!

Not sure I understand "the way things are wired in the house", if you're aware that "the investment would be higher with running heavier duty wiring". It sounds like the way things are wired is, "they're not".

If you want to future proof your home, running a higher power circuit will allow you to at the least just upgrade the EVSE to something over the 6.6kW that the Ford Focus need. A NEMA 14-50 will give you nearly 10kW, enough to add 30 miles per hour to a Tesla Model S, and potential future EVs will need more power at home.

 

[kalel14]

None: The FFE won't charge at 40amps, at most it does is about 28 amps (6.6kW).

That's what I needed to know. Thanks!

 

[TomEV]

You should go ahead and install the 50 amp circuit breaker and wiring. It's not that much more expensive. As for level 2 charging, the speed of charging is much better. Well worth it. I got a plug in version of the EVSE. No problem so far.

https://store.clippercreek.com/index.php?route=product/product&product_id=67&search=hcs-40

 

[WattsUp]

You should go ahead and install the 50 amp circuit breaker and wiring. It's not that much more expensive.

I agree.

The FFE is not likely to be your last EV. And, when you get that next EV that can charge at a higher rate, you'll be glad to have a 50-amp circuit installed.

 

[amped]

You should go ahead and install the 50 amp circuit breaker and wiring. It's not that much more expensive.

I agree.

The FFE is not likely to be your last EV. And, when you get that next EV that can charge at a higher rate, you'll be glad to have a 50-amp circuit installed.

The extra expense will depend greatly upon your particular circumstances. If you have a house of recent vintage with higher amp service than most households really need and your service entrance is in your garage, then the cost differential will be minimal. If you have to upgrade your service to fit the extra 50 amp circuit and you have to route it 50' from a service entrance on the opposite side of the house (instead of e.g. routing a smaller circuit from a conveniently located sub panel that already has enough spare capacity) the extra costs could be considerable.

...bit of a contrarian view here...

Also, consider that the extra utility of 40 amp charging vs 32 amp charging is not really going to be that great for most people most of the time. Sure, you could charge your future EV 25% faster but 240v/32 amps would still be able to dump ~6.1 kW (7.68 kW from the grid X ~80% charging efficiency) into the battery. That's going to be ~25-30 miles of range added per hour of charging (assuming it's not an electric Hummer) or ~300-360 miles for a 12h overnight charge. How many people will need to replenish 300 miles while they sleep? Where the extra amps might help are in situations where you have limited range left and need a quick range boost to, e.g., enable running a bunch of errands after dinner. In that case you would get an extra 6-8 miles per hour of charging. However, future EVs will have more and more range, making the above scenario increasingly less common. There would also be extra stress on the local grid infrastructure from these hours long high amperage loads. Why tax the grid more than necessary with all these future EV owners charging away at 50+ amps when they don't really need to? Public DC fast charging / supercharging infrastructure (MUCH faster than any feasible residential EVSE) should also more readily available in the future.

OTOH, I suppose multi-EV households with long commutes would require a LOT of power dedicated to charging. Possibly a multi-head EVSE sitting on a 50+ amp circuit or multiple EVSEs on several lower amp circuits. It's not clear to me what would be a better form of future-proofing: a single high amp circuit or two lower amp circuits?

 

[cpwl]

There are plenty of good comments here regarding charging capacity and future-proofing your home EV charging infrastructure. Only you can decide what works for your situation and gives you the flexibility you need and can foresee needing. However a word of electrical installation caution here. Whatever you chose to do remember that charging an EV is a continuous load since it will draw a rated and almost unchanging current for in excess of 30 minutes. As such in almost all North American jurisdictions the electrical codes require that continuous loads do not exceed 80% of the breaker capacity. So if you want to install a 30 amp EVSE you must size the breaker and wiring for 30 amps/.8 =37.5amps. The nearest readily available size breaker to that is 40 amps. If you install a NEMA 14-50 plug you should limit your EVSE to charging at no more than 40 amps. Drawing 50 amps continuously would nominally require a 62.5 amp breaker so call it a 60 amp circuit. But that breaker exceeds the NEMA 14-50 capacity so it wold be an illegal and unsafe arrangement. Even if you were willing ignore the code and limit your EVSE to 50 amps on a 60 amp circuit you would be pushing the NEMA 14-50 to its limits for an extended period – not recommended and not safe.

In my case I have a 40 amp circuit for my 30 amp L2 J1772 EVSE to charge Montgomery and a 100 Amp circuit to charge my Tesla MS at 80 amps from a Tesla HPWC (twin chargers fitted so 58 miles of range per hour of charging). Typically that load only happens at night so the only other loads are HVAC and refrigeration so my 200 amp home service is well capable of supporting the concurrent demand. I would not charge both cars at the rated charging capacity in the daytime when other significant loads (oven, clothes dryer workshop tools etc.,) could also be running.


Thanks and Cheers

Carl

 

[kalel14]

Good info! Thanks.