I'm prepping for delivery day by getting a charging strategy ready for the Solterra and future cars completed. I figured I'd document for others. Some of this is unofficial so I listed the basis for those claims.
Prerequisites:
120V Charging:
What was missed? Anything incorrect? Let me know and I'll update.
Prerequisites:
- 80% Rule: The US electric standard is complex and for valid reasons a 50A breaker cannot supply 50A continuously. Rather it can supply 100A for a fraction of a second (motor starting), 60A for a few seconds. 55A for a minute, 50A for an hour and 40A continuously (made up numbers, but idea is directionally correct).
Since we plan to charge for hours on end, we must use the "continuous" rating of the circuit, which is the breaker size minus 20%. Voltage does not matter here. Thus the 80% rule means:
-- Breaker/wiring at 50A provides 40A usable
-- Breaker/wiring at 40A provides 32A usable
-- Breaker/wiring at 30A provides 24A usable
-- Breaker/wiring at 20A provides 16A usable
-- Breaker/wiring at 15A provides 12A usable
- Charger or EVSE? I'll use charger below, but technically they are Electric Vehicle Supply Equipment (EVSE).
- GFCI: should be added to all outlets (excludes hard-wired stations). They are expensive and hard to find right now (~$100). Codes changed on this ~5 years ago, so it's mandatory in some places, optional in others, and always a good idea. Most portable chargers do NOT have GFCI protection in them. Hard-wired stations typically do.
120V Charging:
- 15A Outlet: Included with the car is a 12A charger (EVSE) for common household 15A outlets. There is a feature in the manual to lower this down to 8A if needed (eg circuit shared with other items). Expect 2 miles added per hour at 8A. 3 miles added per hour at 12A. Slow, but if you are able to be plugging in constantly and only drive around town, this may get the job done.
Basis: Safe assumption based on marketing, prior cars from both Subaru/Toyota, and liability of including anything faster.
- 20A Outlet: Upgrade to 16A charger on a 20A outlet. This is where things get murky as various venders fudge things here, but at minimum the circuit should have a 20A breaker and 12 AWG wiring. Ideally it'd be a proper 20A receptacle and plug too, but many 16A ESVE are ignoring this part. Some, but not all, houses already have this wiring in place. Many business will too. If adding a 240V outlet is prohibitively expensive or this is an occasional use location (eg parent's house), look to see if using an existing 20A circuit is possible.
Basis: Manual states max charge rate is 16A and prior Toyota Prime hybrids with 6.6kW onboard charger work at 16A.
- 30A Travel Trailer Outlets: This was a disappointment as I have access to these plugs, but it appears the charger is limited to 16 amps per the manual at 110v. Others vendors (eg VW) have a similar ~16A limit. Tesla will charge using the full 24A (80%) at 110V. In this case, you could get a 30A to 20A adapter, and use your 12A or 16A charger per above. Using the supplied charger on the 30A > 20A adapter will still be limited to 12A.
- Car: can charge up to a maximum of 27.5 amps.
- Ideal Circuit: Hard-wire a charger to the wall or install a 14-50 NEMA outlet with 50A breaker (6AWG wire). Future-proof and no thinking required. This is the industry standard practice and should be done in 95% of cases if possible.
- Ideal Charger (EVSE): There are no 27.5A chargers. You can use higher-rated chargers (eg 32A/40A) but car will only pull it's maximum of 27.5A (6.6kW). The downside of going overly large (eg 48A) they will have bulkier (less flexible) cords and require 60A+ breakers and associated wiring. 32A EVSE is a good sweet spot of price/flexibility/etc. 40A works too. I'd stay ways from 48A+ chargers.
- Undersizing: Anything less than a 40A breaker + 8AWG wiring is undersizing and requires extra care. The problem is a problem is that the car needs to know it's attached to an undersized circuit otherwise it will try and pull 27.5A and trip breakers (or worse start a fire!). It's the job of the charger/EVSE to tell the car the maximum charge rate. Further challenging is the Solterra does not allow you to derate the current manually (unlike others eg Tesla). So if you plug into a 30A 240V circuit, which should only pull 24A using the 80% rule, the EVSE must properly tell it to pull 24A otherwise the car will attempt to pull the full 27.5A.
So in this case, first I'd suggest avoiding it all-together by installing an "ideal 50A circuit" above. If you do go this route, ensure you have an EVSE that is "programmable" in some manner so you can tell the EVSE (which tells the car) that the circuit can only safely hand 12A/16A/24A if you are on a 15A/20A/30A circuit.
- 100kW limit: Adequate, but not fast by today's standards.
- Real World Performance: Initial tests of BZ4X are showing that 100kW is optimistic. Charging rates while at a 0-50% state of charge in the battery is adequately fast to get you back on the road, but charging in the 60-100% range becomes painfully slow and should be avoided. Plan on only fast charging from 0-70% or so.
- Derate: Per the manual you can manually choose to DC fast charge at maximum of 50kW, 75kW or full 100kW (default). The only reason I can see using this is if you are at a DC charger at a shopping mall or restaurant and know you need 2 hours. Then the slower charge (50kW) is a bit easier on the pack's longevity. Even then it only makes sense if paying by the kWh. Some states by law require payment to be done by the minute, and thus going slower is costing more than you are benefiting.
If you must fast charge weekly, the Solterra is not a great choice compared to the competition. That said, most reading this will only fast charge at most 3 times a year, so what's an extra 3 hours over a year being slower does not really matter. The Solterra is not a regular road tripper compared to the competition. It's great for those that can charge at home nightly.
What was missed? Anything incorrect? Let me know and I'll update.
