Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Help!! Charge amperage max drops from 80a to 32a

Lectric_Agent

2015 S85 AP1
May 25, 2019
99
46
Orange County
2015 MS 85 w/ dual chargers.
Gen 2 HPWC on 100amp sub panel, charger set to 80amps.

I remodeled a home and moved in 3mo ago. All new 200a panel and electrical. 100a sub panel run to garage and connected to HPWC 2 ft away.

I usually charge at 48a

A few weeks ago after being plugged in and not charging for at least 15-30min, the max charge rate drops to 32a or sometimes 54a. It doesn’t happen every time, but it’s happening more frequently and I’m guessing is dropped before and I never noticed.

When I unplug and plug back in, the max charge rate always goes back to 80a, and if i start charging immediately I can charge at any amps with no issues. Yesterday I charged at 80a for over an hour with no issues.

The charger, panel and sub panel breakers barely get warm. At 80a my voltage is around 228v

I have reset the MCU (replaced last year) multiple times, along the cycling the breaker and using the reset on the HPWC.

I am trying to figure out if it’s the HPWC gen 2 (less than 1yr old), the onboard car chargers, the charge port itself, or a glitch in the MCU 1 software

This forum has been extremely informative in the past. I tried searching for the issue and haven’t had any luck.

Any insight is very appreciated!!
 
Last edited:

whitex

Well-Known Member
Sep 30, 2015
6,453
7,643
Seattle area, WA
The car automatically drops amperage if it "thinks" there is a problem with the power supply. One of the problems it can detect would be higher than expected voltage drop when charging starts. What is the AWG of the wires from the 200A panel to subpanel and HPWC? Has your electrician checked that everything is securely connected (no loose connections, which sometimes can happen after the wire heats up and cools down a few times - but if you don't know how to do it safely, don't go tightening it yourself as most of the terminal screws are electrified and can kill you)? Something you could check is, what is the voltage when you first plug-in and how much does it drop when you draw 80A? Another possibility is something else is kicking in while your car is ramping up, but causing the car to think the voltage drop is car related, and therefore throttling the charge rate. Long time ago I had a brown out while I happen to be charging at 80A, which made my charge rate drop from 80A to 32A IIRC, re-plugging the car brought it back to 80A. I usually don't monitor the charge rate, I don't usually charge at 80A either (wife's side of the garage has the 80A capable charger, mine only has 40A), but in this case I was watching it as I needed a quick fill up before heading back out on the road. I also noticed the brownout as it happened because UPS'es at home kicked-in (beeped), but lights didn't go out completely.
 

David_Cary

Active Member
Dec 17, 2012
1,185
682
Cary, NC
Agree with above.
You can have any and all sorts of issues related to your house and the nearby electrical supply causing voltage dips that the car interprets is an issue.
Also - loose or small wires will cause an issue and maybe no where near where you can touch.
These things cause intermittent issues so are pretty hard to track down.
 

murphyS90D

Member
Jul 2, 2016
646
455
Horsham, PA
I have a 75 foot run from my panel to the HPWC. My voltage never drops that low. The run was done with 2 AWG wire.
Were copper ferrules put on the ends of the wires? It is extremely difficult to get all of the strands of wire captured by the clamps in the HPWC. A ferrule solves that problem.
 

EV-Fixme

Vendor
Oct 24, 2019
604
687
Orange County, CA
Hey since you're in OC, you can swing by our shop in Costa Mesa and plug into our to charger. We have a 48A charger so you can tell if your 2nd charger is working or not. Then you might be able to determine if it is your car or your charger that is having an issue. Let us know if you'd like to drop by and test.
 

Lectric_Agent

2015 S85 AP1
May 25, 2019
99
46
Orange County
Really appreciate all the responses!

Im actually not having an issue with the amps or speed dropping when charging. When I plug the car in during the day for a scheduled charge starting at 9pm, after the car has been sitting for a while sometimes the max rated amps drop. So for example the screen will show 32a as the max speed. As soon as I unplug and plug back in, the max amps are at 80 again.

Im not an electrician but I know electrical better than most amateurs, and I installed my HPWC at my last home myself with the guidance of an electrician friend. As far as the voltage drop, the voltage always drops more the higher the amperage, that being said it does seem to be low. I have about a 75ft run of 1awg copper to my sub panel as well, and at low charging amps the car detects 239v. Also, I used to live next to a hotel with a gen1 charger at 80a and i noticed the voltage was much lower, around 218v I believe

I am familiar with ferrules but the electricians i spoke with said they are unnecessary.

I have a torque driver that I specifically bought for installing the HPWC at my last home, I will go ahead and check everything, ive been meaning to do it anyways

I have a infared thermometer and have checked everything and im not finding any hotspots, and like I said the car/charger has never reduced the charge rate while charging, even with almost 2hrs at 80a.

After parking my car and plugging it in about 20min ago (not charging, scheduled for later), I went to check and the max amps showing on the screen was 32 again. Unplugged and plugged in and back to 80a.

Is it possible that there is a communication error between the car and charger? The amps are not dropping when its actually charging so that's why im thinking this is the case.
 

Lectric_Agent

2015 S85 AP1
May 25, 2019
99
46
Orange County
New development - my car has been sitting at 56a max charge rate for a while, and at 9pm the charging started. The car shows 48/80a charging (I have the charge speed set to 48a). So as soon as it started charging, it recognized that the max amps was 80.

In the past I tried manually starting the charge when the max charge is lower than 80a and it has never corrected and gone back up to 80 max.

Again, this is why im thinking its a communication error, so possibly the charge port or hpwc?
 

Snowstorm

Active Member
Dec 8, 2016
1,490
1,407
Ontario Canada
If it drops from 240v open circuit to 228v at 80A, then there seems to be a lot of drop. That can cause the car to think the wiring can’t handle the current and throttle back. Think of it this way, that’s 12V at 80A, so 100W of power dissipated as heat along the line.

If you live close to any old school 80A destination chargers go there and get it out to see if you see the same issue.
 
  • Like
Reactions: whitex

murphyS90D

Member
Jul 2, 2016
646
455
Horsham, PA
Charging will never go higher than the setting was at the start. If you want 80 you must set the car to 80 before you start. The car uses GPS to remember the charge setting for a specific location. If you set it to 32 in your garage it will revert to 32 the next time you arrive home no matter what it was before you arrived.
 
  • Like
Reactions: BrokerDon

Big Toys

Member
Jan 19, 2019
566
470
Florida
Also, if your charging area is hot, the charger itself may sense an overheat and limit amps to the car. It's an issue here in FL where the garage can get hot. Try putting a fan to the charger and see what happens.
 
Oct 10, 2019
263
122
So-Cal
The best way to check what the issue is, is to use a different charger. look on your MCU and find a destination charger that lists for like 15-19kW, that is the high amp ones. use a couple of them set to 80 amps and see what happens. if it works in the wild then its your HPWC issue, if it still goes down and has issues then its your car charger issues. At least that way you can get a proper diagnostic of which end of your charging spectrum you need to be messing with before you start fiddling with stuff.
 

BrokerDon

Active Member
Aug 23, 2014
1,399
1,289
Newport Coast, CA
Charging will never go higher than the setting was at the start. If you want 80 you must set the car to 80 before you start. The car uses GPS to remember the charge setting for a specific location. If you set it to 32 in your garage it will revert to 32 the next time you arrive home no matter what it was before you arrived.

I had this happen a couple of months ago after our MCU1 -> MCU2 upgrade in our 2015 P85D with Dual Chargers on our gen1 HPWC set to 80A max charge rate on a 100A breaker at our home (4 foot run from 200A main service panel with max gauge copper wire installed by a Tesla recommended licensed electrician). Charging on our 2015 P85D was set to 60A on MCU1 for 5 years... but "defaulted" to 32A after my MCU2 upgrade. Once I reset the "default" charge rate to 60A at this "location" my 32A charging "problem" disappeared

Glad to have you come by our Newport Coast home and plug in your Tesla to test at 80A... Just not between 2:00 PM and 9:00 PM when our SCE TOU-D-B-SDP kWh rates are crazy high. Our gen1 HPWC has a 24' cord which I can leave outside our garage door for "social distancing". Selection of cold Stone IPAs available upon request too. :D
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top