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HPWC: 40 amp with pigtail vs 48 amp hardwired

zmarty

Member
Jun 25, 2017
220
655
Kirkland, WA
I currently have a NEMA 14-50 in the garage and I am buying a HPWC.

I have two choices:
- 40 amp charging: Keep the NEMA 14-50 and add connect the HPWC to it through a pigtail.
- 48 amp charging: Replace the 50 amp circuit breaker with a 60 amp one, then hardwire the HPWC and get rid of the NEMA 14-50.

Which one would you choose and why? Also, what's the difference in range per hour between 40 amp and 48 amp?
 

RedMS

Member
Dec 5, 2017
355
373
USA
If you are using the UMC provided with the model 3, it’s only capable of charging at 32 amp anyway so that is where you are presently limited. The M3LR is capable of charging up to 48 amp but you will have to install a HPWC for that on a 60 amp breaker like you said. Now if you are holding out for the M3SR, those are capped at 32 amp max charge rate.

The charge rate between 40 and 48 amp is only a few mph, but more noticeable between the 32 amp you get now and 48 amp you can have with the HPWC. It just depends wether you need a faster charge rate. Either other will recharge the battery overnight.
 
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goto10

Member
Mar 6, 2018
182
240
Provo, UT
48 amps is roughly 44 miles/hour, 40 amps would be about 37 miles/hour. I personally would try to get 48 amps because charging at a higher rate is a bit more efficient and a bit better for the battery. You may have to replace the wiring as well as the breaker though. It's unlikely you already have the correct gauge of wire for a 60amp circuit if it was originally wired as a 50 amp circuit.
 
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goto10

Member
Mar 6, 2018
182
240
Provo, UT
Technically, depending on who you ask, adding a pigtail to the HPWC is not allowed.
Tesla recommends against it because they are concerned that you'll yank it out and expose the bare wires. This can be mitigated with a proper strain relief. I don't believe it's against code to add a pigtail though. I always advocate wiring directly regardless. I just like the clean look. :)
 
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ewoodrick

Well-Known Member
Apr 13, 2018
5,285
3,735
Buford, GA
"More" isn't necessarily needed.
How much charging are you going to actually need? I highly suspect that 40A charging is going to be a lot more than you really need, unless you drive a LOT of miles each day.
I saw a question the other day from a gentleman thinking about whether he should rewire his dryer port or what.
Then he mentioned that he drove 15 miles per day. At that point, just use the 120V plug and be happy!
 

TexasEV

Well-Known Member
Jun 5, 2013
7,650
8,482
Austin, TX
The car will completely charge overnight. Does it matter at what time during the night the charging is finished? Not for most people. If your driving pattern is such that you come home with an almost empty battery and have to go out on a long trip within a few hours, then yes, faster charging may be helpful for you. For most people 32A charging at home is sufficient.
 
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dc81

Member
Jul 14, 2017
65
58
TX
What's the cost difference? 20% faster charging and cleaner install is probably worth at least 100 bucks to me.
 

run-the-joules

Turgid Member
Aug 13, 2017
3,785
6,868
SF Bay
I'm using a pigtailed HPWC on a 50a breaker and the speed is plenty for me, there's no realistic situation where I'll get home with a super low battery and need to drive a long distance again sooner than I could charge.

Very happy with it and glad I did it, now I can leave the UMC in the frunk with the snow chains and the inflation kit.
 
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dc81

Member
Jul 14, 2017
65
58
TX
I did not know this. Home come it's better for the battery to charge at a higher rate (48 amp vs 40 amp)?

When charging, some of the energy is used to power the car including heating/cooling the battery and a little to transmissions loss. I would ballpark about 1kWh is not going into the battery depending on the temperature and other things. So 40/48Amps is really charging the battery at ~36/44 Amps. Thus 44/48 is slightly more efficient than 36/40.
 
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goto10

Member
Mar 6, 2018
182
240
Provo, UT
I did not know this. Home come it's better for the battery to charge at a higher rate (48 amp vs 40 amp)?
When the battery is charged the anode and cathode are reactive with the electrolyte. As long as charging/discharging is occurring that interface remains reactive. However when the battery is idle a byproduct of that reaction is a non-reactive film that prevents further breakdown of the electrolyte. Because of this it's better if the charge can be completed quickly so that the battery spends less time in this unprotected reactive state.

The benefit of 48amps vs 40amps is probably not significant but all things being equal I'm going to provide the optimal environment that I'm able to provide.

This video describes it well:
 
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goto10

Member
Mar 6, 2018
182
240
Provo, UT
The efficiency difference is also surfaced in Tesla's estimate of charge time for their UMC. The 15A (draws 12A) 120V adapter is rated for 3 mph. The 30A (draws 24A) 240V adapter provides 22 mph. The 50A (draws 32A) 240V adapter is rated for 30mph.

If you break those numbers down, you can see how efficiency improves as the charge rate increases.

12A * 120V = 1.4kW / 3 = 480 Wh/mile
24A * 240V = 5.8kW / 22 = 261 Wh/mile
32A * 240V = 7.7kW / 30 = 256 Wh/mile

Again the difference between 48 and 40 will be incremental, but it will be a bit more efficient.
 
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mongo

Well-Known Member
May 3, 2017
13,290
40,616
Michigan
I currently have a NEMA 14-50 in the garage and I am buying a HPWC.

I have two choices:
- 40 amp charging: Keep the NEMA 14-50 and add connect the HPWC to it through a pigtail.
- 48 amp charging: Replace the 50 amp circuit breaker with a 60 amp one, then hardwire the HPWC and get rid of the NEMA 14-50.

Which one would you choose and why? Also, what's the difference in range per hour between 40 amp and 48 amp?

Does the existing wire support 60 Amps? Or are you replacing that also?
You could also hardwire the HPWC and stay at 50 Amp breaker/ 40A charge rate.
 

zmarty

Member
Jun 25, 2017
220
655
Kirkland, WA
Does the existing wire support 60 Amps? Or are you replacing that also?

Replacing it. The cable will need to go to the other side of the garage, since Tesla decided to put the charging port in the back-left side of the car. My Leaf is more convenient because the port is in the nose. I don't want to back in into the garage every day since I am bad at it.
 
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Darmie

Super Member
Supporting Member
Jan 13, 2016
2,001
1,286
Clear Lake TX.
4a bit better for the battery. .
Yes. We all want to protect our battery but I haven't seen this. Now i feel really screwed charging at the apartment at 110v.
apartment.JPG
 

goto10

Member
Mar 6, 2018
182
240
Provo, UT
Now i feel really screwed charging at the apartment at 110v.

I wouldn't fret too much over it. It's just one factor to consider when you have a choice between options. My brother-in-law charges his P100D on 120V only because that's his only practical option and he's not getting significant degradation. I'm charging at 24A 240V right now because that's the best I can get in my current house, but in the new home we're building I'll have a 60A circuit put in for the wall connector.

Tesla engineers their batteries to provide acceptable performance in a wide variety of circumstances.
 

brkaus

Well-Known Member
Jul 8, 2014
8,021
6,507
Austin, TX
Replacing it. The cable will need to go to the other side of the garage, since Tesla decided to put the charging port in the back-left side of the car. My Leaf is more convenient because the port is in the nose. I don't want to back in into the garage every day since I am bad at it.
I back into my garage. Only way car fits.

I still have the HPWC by the garage door.

The cord reaches all the way around from the front passenger side.
 
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