My app "forgot" several times. I'm paranoid now and checking all settings every time I update the app or car software. I like the idea setting it up in the car if it's more reliable.
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Optimal Charging Amperage
- Thread starter SNYDERHAUS
- Start date
Falcon73
Member
I usually charge our BEVs at 25-30A or so, starting at 10pm for the lower rate.
I'm more concerned about the load on the circuit even though it should be able to handle 40A easily. It's 8ga wire on a 50A breaker but we had problems in the past on our old panel.
The run is at least 70' as well which is a concern. I'd feel more confident with 6ga wire, but it's not easy to replace it.
I'm more concerned about the load on the circuit even though it should be able to handle 40A easily. It's 8ga wire on a 50A breaker but we had problems in the past on our old panel.
The run is at least 70' as well which is a concern. I'd feel more confident with 6ga wire, but it's not easy to replace it.
I hope your 8 ga wire on a 50A breaker is not NM-B (in a plastic sheath vs individual wires in conduit or a metal clad), that's a 40A wire.
martinsfsu
Member
Lower amperage charging will have no effect on a battery that is designed to be charged x10+ faster at a supercharger, HOWEVER, it will protect your homes electric system. Regular and extended home charging can cause a lot of wear and tear on the circuit, wires, etc. My installer has noted seeing a lot of that a couple of years after install.
Then the panel, wiring was old and due to be replaced anyway. Service panels can wear out; even electrical meters can wear out or corrode given enough time (multiple decades). Properly sized and installed wiring for EV charging should last as long as any other home wiring. If not then the wiring was low quality or overloaded.
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One, minor redirect on "no reason to turn it down"... Some less common residential rate plans include a rateable demand charge that would incentivize lower charging rates. An edge case to be sure, but worth knowing the details of one's individual rate plan.
In my experience, having specifically opted into a time-of-use with demand charge plan (Dominion schedule 1S), the demand charges are only for on-peak times; off-peak has no demand charges. But yes, if your plan includes demand charges while you're charging, slowing it down will reduce those charges.
Yes, excellent point. In my part of TX, the retail sale of electricity is deregulated and a variety of plans and providers exist. A few years ago I unknowingly signed with a plan that had a fixed rate plus a rateable demand charge with no time of use exclusion. Shame on me for not reading the terms. I don't think Tesla had scheduled charging in firmware at the time (or I didn't use it) and I recall being surprised at my bill after a big concurrent peak. It's my, arguably uncommon experience there that prompted my post.
Just an added note to remind all that the energy loss equation has the amperage component SQUARED. Thus, you'll want high voltage and low current.
FWIW, I have found that if we charge our two MS's at higher amps (30 to 40 amps, IIRC, off of our NEMA 14-50 outlets) there is a noticeable voltage drop. Thus, we typically charge at 5, 10, or 15 amps overnight which keeps the voltage high/unchanged, all the wiring nice and cool, and is seemingly a comfortable trickle charge for the battery.
Wish Tesla would provide some insights on this for the technically curious.
FWIW, I have found that if we charge our two MS's at higher amps (30 to 40 amps, IIRC, off of our NEMA 14-50 outlets) there is a noticeable voltage drop. Thus, we typically charge at 5, 10, or 15 amps overnight which keeps the voltage high/unchanged, all the wiring nice and cool, and is seemingly a comfortable trickle charge for the battery.
Wish Tesla would provide some insights on this for the technically curious.
But isn't it best (ideal) to keep batteries at 50% SOC? If you slow charge you will spend more time closer to 50% than if you "less slow" charge and reach your set charge limit faster, keeping it there the whole night putting more stress on the battery.
It's a lot more complicated. My understanding from a cursory read through some Battery University articles is batteries degrade less at rest. Having it constantly charging or discharging could offset the whole 50% SOC theory. Also, having it charge longer puts more run time on the coolant pumps, computer, and charging circuit.
In the grand scheme of things, charging at 12 amps vs 48 amps AC isn't going to make any difference to battery longevity.
There is nothing about 240V Level 2 charging that puts "stress" on a tesla battery.
48 amps at 240 volts is the same as a 400v supercharger charging at ~29 amps (11.5 kW). The battery has no issue charging at 11.5 kW. Regen puts way more power into the battery.
Setting your car to be charged right before you leave is a good idea to reduce the time at a higher state of charge.
Setting your car to be charged right before you leave is a good idea to reduce the time at a higher state of charge.
I'm talking about SOC not ROC. For example if you set the limit at 90% then you will be sitting at 90%, which is more stressful than something closer to 50%, for a longer period of time if you charge faster.
If you use Scheduled Departure you can charge as fast as the circuit will support and minimize the time that the battery is at the upper end of the state of charge. Charging will always complete just prior to the time you start out on your commute.
As far as efficiency it has been stated that for Level 2 charging 240V/40A is the most efficient. Charging at 48A requires additional power to cool the charging system. Charging at less than 40A adds a bit of unnecessary overhead power usage due to the longer charging cycle.
What about the low end? You park in your garage at 10%. The scheduled departure doesn't charge until the next morning before you leave. So you minimize 90% but you maximize 10%. On the other hand if you slow charge overnight you average 50%.
Slower charging has been shown to be less efficient due to additional overhead losses by extending the charging period. I am unaware of any issue with the battery remaining at a low state of charge, i.e. 10% SOC for a short period or even remaining at a high state of charge for a short period.
If you want to minimize the amount of time that the battery state of charge is 90% or whatever you set as the daily upper charge limit then Scheduled Departure will do that regardless of the state of charge when you plug in. Schedule Departure will ensure that charging is completed by the time you normally leave. The battery state of charge will be at the upper limit you set for the shortest practical time.
There is no proof that any of this that you are talking about from a home user charging point of view (worrying about the car sitting at 10% for a few HOURS before it charges, vs a few days, weeks etc) will matter even enough to measure over a 4-5 year period.
It sounds like you fall in the camp of wanting to micro manage this to the Nth degree, and some people do that, but I personally dont think sitting at 10% for a few hours will matter, in the context of keeping the car awake longer by charging slower.
Keeping the car awake uses more power than letting it sleep, and charging slower will keep the car awake longer, using more energy (thus putting more "miles" on the battery).
There is no proof that any of this that you are talking about from a home user charging point of view (worrying about keeping the car awake longer for a few HOURS by slow charging, vs a few days, weeks etc) will matter even enough to measure over a 4-5 year period.
sleepydoc
Well-Known Member
You answered your question right in your post. The voltage drop is directly proportional to the current and the power loss is proportional to current squared. Doubling the current doubles the voltage drop. The degree depends on the house wiring as well as the charging cable.
Temperature is another factor. The resistance of copper increases about 5% per 10°C so power loss will increase as the cable heats up.
Finally, there will be some internal losses in the charging unit that will likely increase with current. I’ve never seen a teardown of an EV charging unit so I can’t comment on how significant those losses are.
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