Impact of high amp charging on Model 3 battery life

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garsh

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#61
From my understanding of NEC, a 50 amp circuit can provide 50 amps.
I believe the NEC says that _short duration_ loads (like compressor startup current) can go up to the limit, while _continuous_ loads should not exceed 80% of the breaker rating.
 
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#62
Correct, an EVSE is a continuous load and you must de-rate by 20%. 40A breaker -20% 32A load, 50A breaker, -20% 40A load, 60A breaker -20% 48A load. This de-rate allows for the wire and breaker to dissipate the heat that will build up over the hours of charging.

Today I charge a Mercedes B Class Electric Drive (B250E) @ 40A off a 50A breaker and not only does the charge cord get warm, the 6 gauge wire from the panel to the outlet does as well. 6 gauge wire is rated for 60 or 65 amps (I forget which) but even at 40A of load over a 2-3 hour continuous charge it heats up. Not to a dangerous or concerning level but enough that you can clearly see why this de-rating is a MUST.
 

Frank99

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#63
For continuous loads (longer than 3 hours), the NEC requires that the circuit (wires, breaker) be sized at 125% of the load (or, alternatively, the load can be 80% of the circuit rating).
Article 100: Continuous Load: A load where the maximum current is expected to continue for 3 hours or more.
210.19(A) ... Where a branch circuit supplies continuous loads...the minimum branch-circuit conductor size...shall have an allowable ampacity not less than...125 percent of the continuous load.
625.40 Rating. Electric vehicle supply equipment shall have sufficient rating to supply the load served. For the purposes of this article, electric vehicle charging loads shall be considered to be continuous loads.
 

Rusty

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#64
For continuous loads (longer than 3 hours), the NEC requires that the circuit (wires, breaker) be sized at 125% of the load (or, alternatively, the load can be 80% of the circuit rating).
Article 100: Continuous Load: A load where the maximum current is expected to continue for 3 hours or more.
210.19(A) ... Where a branch circuit supplies continuous loads...the minimum branch-circuit conductor size...shall have an allowable ampacity not less than...125 percent of the continuous load.
625.40 Rating. Electric vehicle supply equipment shall have sufficient rating to supply the load served. For the purposes of this article, electric vehicle charging loads shall be considered to be continuous loads.
Thanks for the info. Is a 50 amp plug ok continuously?

For continuous loads (longer than 3 hours), the NEC requires that the circuit (wires, breaker)be sized at 125%ofthe load (or, alternatively, theload can be 80% of the circuit rating).
 

Frank99

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#66
A 50 amp outlet is fine to pull 50 amps from..as long as you do it for less than three hours.
 

Sandy

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#67
I wired up my NEMA 14-50 outlets using 6 gauge wire. That should let me upgrade to a 60 amp breaker and a wall connector later if I decide I want to.
True. That’s why in my recent install I used 6/3 wire. Good in Canada for 150’ run on a 60 amp breaker. Anything longer requires an upgrade to 4/3. My run is 80’.
 

Insaneoctane

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#68
Did we ever get an answer about charging efficiency? I would like to charge my Model 3 using my HPWC at the most efficient current settings possible. It's wired up through a 60 amp breaker and set to 48 amps right now, but I could dial it down on the touchscreen. Question still remains, which setting is the most efficient?
 
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4701

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#69
Maximum charging speed is efficient. There are inefficiencies off-board the vehicle as well.
Depending on the wiring and connection quality between power meter and charger, YEMV (your efficiency may vary).
Thick conductors (not cable thickness) and excellent connections reduce inefficiencies that might increase with higher power.
Also breakers that have never tripped, are more efficient.
Charging at speeds at or above 3.3kW (16A) is recommended for minimal parasitic losses.
Also electrically, on board charger, as a device, should be operated at least on half-load (10kW charger at least at 5kW) for better results. Dual charger Tesla's might have exception here.
Li-ion battery coulombic efficiency is very high. Especially up to 90% state of charge. Keep it below that on daily basis anyway.
For best results, keep charging between 32-48A.
Verify that nowhere between power meter and the plug is there any meaningful warm/hot spots (Ir-camera or Ir-thermometer) during maximum charging speed.
 

Insaneoctane

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#70
My 6 gauge wire run from the HPWC to the panel installed 60A breaker is literally 30 inches. I will measure the temperature of the 1" conduit that houses the run, but how warm would you suggest is "meaningful"?
 
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4701

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#71
Don't worry about that last part (very short thick cable, meaningless voltage drop).
How about cable before breaker and power meter? What about that cross section. Also think about other devices under that cable (things that will run when you charge EV)

The most easiest way to measure losses is to measure voltage drop (under consistent load, for example max 48A).
Also measuring voltage drop right when charging beings (first 10 seconds) and an hour later. Will give you rough estimation how much things warm up (warm cable means more resistance).
Literally taking multimeter, measuring voltage between right after power meter and voltage right before it enters HPWC (while vehicle charging at maximum). Though you must know how to handle a 10$ multimeter.

10 degrees (absolute, C or K) would be acceptable, 20 degrees above ambient would count as not good. 30 is not ok to continue (hot to touch). Likely places to find this is wire under screw terminal and breaker/relay.
 

Idur

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#75
Really?

I happily use my free credit card sized multi-meter on 415V 3 phase ccts.

(I draw the line at 13/27KV stuff mind....)
I still think having a multimeter and knowing how to use it safely are two different things. Be safe. Electrocution kills.

Safe voltages are 24 V AC or 30 V DC. 415 V AC or 400 V AC like we have on the continent can be lethal. I think 240 V (or even 110 V) in the US should only be tested by people who know how to do it safely.
 
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#76
Safe voltages are 24 V AC or 30 V DC.
To be more exact, 30V AC and 60V DC are called safe limits though touching 100V DC is still damn safe if done with dry finger.
Up to 1000V is easy to learn/protect yourself with simple/cheap measures.
Multimeter itself is safe (if it is not cheap Chinese crap). Problems occurs near HV stuff.
Death doesn't require a multimeter - ignorance - that will do it.

Crash course for stuff up to 1000V - if you are not absolutely sure what are you doing, get appropriate HV gloves - this way it's hard to kill yourself by touching something though you can still break the multimeter so don't get an expensive one:D
 

JWardell

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#77
The quote is "any idiot" and that sets a low bar, for all you know they might touch the metal part of the leads. Just as you say, below 60V is safe. 100V with a dry finger requires knowledge and is already above that bar.
I know electricians here who have no problem wiring circuits live, they say they just get used to the sensation. But again, they are careful to only use one dry hand, they have some knowledge to do something potentially stupid :)
You and I of course have much more electrical knowledge than average and therefore are confident in working in situations up to 1000V, but you certainly can't expect everyone to be able to without knowledge.
The highest I've worked with is 277VAC and I am super careful...yet still had a spark and the brightness alone is enough to knock you off a ladder...spoken from experience :)