120v Mobile Charger reducing amps

[20221229 3RWD]

Sounds like voltage drop because of the telltale 8 amps. The car measures the voltage at first, before beginning charging, and then it will check how much it drops as it ramps up the current. If it sees drop more than a certain amount, then it will drop the current to 3/4 of what it was using. So that is what the 8 amps instead of 12 would show.

It's probably not just the heat sensor, because that almost always throws a visible error on the display.

A lot of builders put in those 120V outlets using the part on the back of the outlets called "stab-in". They are holes with little sharp teeth along the edges of the inside of the holes. You can strip the wire, and then just shove it in there, and the teeth scrape into the wire to kinda, sorta, make a weak connection. It's faster to get a bunch of outlets installed, but is generally crummy because those tiny teeth connections are a very small point of contact and are resistive, and after several years will usually stop working right.

So maybe pull that outlet and check. The outlets do still have the screw terminals on the side. So if it's using the stab-in holes, pull the wires out of that and wrap it around the screw on the side and tighten it up to make it a much better connection, and it won't have as much voltage drop, and that may fix that issue.

Or the wires may be loose at the other end where they are screwed into the breaker. Or, it may just be a really long run of the wire that is just going to have significant voltage drop regardless. That's not bad, but will keep dropping the current down to 8A. As @brkaus suggested, you might be able to turn the amps down to around 9 or 10 to start with, and that may keep it sustained without triggering that lowering.

Oh snap, all of that makes sense thanks. I understand and agree with the "stab-in" outlets. Coincidentally, I replaced this outlet a couple of years ago and upgraded it from a NEMA 5-15 to a NEMA 5-20 (no reason then, other than wanting a 20amp outlet consistent with a 20amp breaker).

I have no idea how long the wire run is, it's probably 30' at least from the breaker box on the south side of the garage to this north side outlet.

I will pull the outlet and check it for heat/smoke/fire and retighten the stuff. I didn't realize how sensitive the car/charger would be to voltage at level 1 charging?

 

[20221229 3RWD]

Since you have the graph, what did the voltage start at? I’m not sure if it samples enough to be useful.

Understood, see attached below.

 

[Rocky_H]

I didn't realize how sensitive the car/charger would be to voltage at level 1 charging?

It can sometimes be even more of a hassle from level 1, because of a couple of factors. Using an existing 120V outlet that is on a circuit with other things frequently means you really can't use 12A from it. The Nissan Leaf and some other brands of electric cars came with 8A as their default, because they expected people to generally just plug into whatever existing outlets were there.

And the other factor is just that each 120V phase can get pulled down from a heavy load turning on somewhere else in the house, and it sags for a few seconds, and that looks suspicious enough to the car to do that amp reduction out of an abundance of caution.

And you have the math factor that it looks like a bigger % drop. Let's say you have 6V drop on that phase. 6 out of 120 is a 5% drop. But if that 6V sag was one side of a 240V circuit, that's 6 out of 240, which is only 2.5% drop, so it won't seem as big to the car's detection.

 

[brkaus]

Oh snap, all of that makes sense thanks. I understand and agree with the "stab-in" outlets. Coincidentally, I replaced this outlet a couple of years ago and upgraded it from a NEMA 5-15 to a NEMA 5-20 (no reason then, other than wanting a 20amp outlet consistent with a 20amp breaker).

Does the wire size support 20a? You can also look at any outlets that maybe in between. If they are backstabbed for the through connection it could make it worse.

 

[mongo]

Sounds like voltage drop because of the telltale 8 amps. The car measures the voltage at first, before beginning charging, and then it will check how much it drops as it ramps up the current. If it sees drop more than a certain amount, then it will drop the current to 3/4 of what it was using. So that is what the 8 amps instead of 12 would show.

It's probably not just the heat sensor, because that almost always throws a visible error on the display.

A lot of builders put in those 120V outlets using the part on the back of the outlets called "stab-in". They are holes with little sharp teeth along the edges of the inside of the holes. You can strip the wire, and then just shove it in there, and the teeth scrape into the wire to kinda, sorta, make a weak connection. It's faster to get a bunch of outlets installed, but is generally crummy because those tiny teeth connections are a very small point of contact and are resistive, and after several years will usually stop working right.

So maybe pull that outlet and check. The outlets do still have the screw terminals on the side. So if it's using the stab-in holes, pull the wires out of that and wrap it around the screw on the side and tighten it up to make it a much better connection, and it won't have as much voltage drop, and that may fix that issue.

Or the wires may be loose at the other end where they are screwed into the breaker. Or, it may just be a really long run of the wire that is just going to have significant voltage drop regardless. That's not bad, but will keep dropping the current down to 8A. As @brkaus suggested, you might be able to turn the amps down to around 9 or 10 to start with, and that may keep it sustained without triggering that lowering.

3/4 of 12 is 9 though...
8 is 2/3 which could indicate a vehicle charger issue...

@20221229 3RWD have you AC charged at higher rates anywhere else?

 

[20221229 3RWD]

Does the wire size support 20a? You can also look at any outlets that maybe in between. If they are backstabbed for the through connection it could make it worse.

Understood, great suggestion. I will look at that today and revert.

 

[20221229 3RWD]

3/4 of 12 is 9 though...
8 is 2/3 which could indicate a vehicle charger issue...

@20221229 3RWD have you AC charged at higher rates anywhere else?

This was the first “at home” charge. All others have been superchargers (gen 2 or gen 3) and those appear to have been just fine. Maybe up to 150kw max, but certainly sustained charging from <10% to 100% no problem. So it doesn’t feel like a vehicle charging issue? I plan to have a NEMA 15-40 on a 50amp installed soon … will revert regarding level 2 charging then.

Thank you for taking the time to respond.

 

[mongo]

This was the first “at home” charge. All others have been superchargers (gen 2 or gen 3) and those appear to have been just fine. Maybe up to 150kw max, but certainly sustained charging from <10% to 100% no problem. So it doesn’t feel like a vehicle charging issue? I plan to have a NEMA 15-40 on a 50amp installed soon … will revert regarding level 2 charging then.

Thank you for taking the time to respond.

Supercharging bypasses the vehicle’s internal charger.
The on board one, I believe, uses three modules which split the power. If one had an issue that could drop charge current/ power by 1/3.
Testing with a higher AC charge connection would be informative, as would using different combinations of charge connector and outlet.

 

[20221229 3RWD]

Supercharging bypasses the vehicle’s internal charger.
The on board one, I believe, uses three modules which split the power. If one had an issue that could drop charge current/ power by 1/3.
Testing with a higher AC charge connection would be informative, as would using different combinations of charge connector and outlet.

Acknowledged, all makes sense. Let me test a different 110v socket and will revert when I test 240v socket. Agree, a few things to trouble shoot here.

 

[Rocky_H]

3/4 of 12 is 9 though...

Oh, good grief! Yep, that was quite a brain lapse. Messes up my theory.

8 is 2/3 which could indicate a vehicle charger issue...

The on board one, I believe, uses three modules which split the power. If one had an issue that could drop charge current/ power by 1/3.

But they don't just go by thirds regardless of what the amps are. Each board is a whole increment of 16A of charging, so the most frequent symptom happens to be people losing a board, and they can only use 32A now instead of their full 48A, which coincidentally happens to be losing 1/3 because one of the boards went out. But if they were only using 12A, they wouldn't lost one third of that. A single board can more than handle 12A, so it would be unaffected.

 

[mongo]

Oh, good grief! Yep, that was quite a brain lapse. Messes up my theory.


But they don't just go by thirds regardless of what the amps are. Each board is a whole increment of 16A of charging, so the most frequent symptom happens to be people losing a board, and they can only use 32A now instead of their full 48A, which coincidentally happens to be losing 1/3 because one of the boards went out. But if they were only using 12A, they wouldn't lost one third of that. A single board can more than handle 12A, so it would be unaffected.

That fallback mode makes a lot more sense, thanks!

 

[android04]

Oh, good grief! Yep, that was quite a brain lapse. Messes up my theory.


But they don't just go by thirds regardless of what the amps are. Each board is a whole increment of 16A of charging, so the most frequent symptom happens to be people losing a board, and they can only use 32A now instead of their full 48A, which coincidentally happens to be losing 1/3 because one of the boards went out. But if they were only using 12A, they wouldn't lost one third of that. A single board can more than handle 12A, so it would be unaffected.

I agree. I played around in Service Mode once to see how the car split the current between the 3 onboard charger phases, and it didn't just split everything in 3rds. I tested with a Wall Connector at 48A and results were as follows with different charge currents:

• 1-16A was all on 1 phase
• 17-32A was evenly split between 2 phases
• 33-48A was evenly split between 3 phases

Keep in mind Tesla can change the behavior through a software update and this was a few years ago.

 

[davewill]

I agree. I played around in Service Mode once to see how the car split the current between the 3 onboard charger phases, and it didn't just split everything in 3rds. I tested with a Wall Connector at 48A and results were as follows with different charge currents:

• 1-16A was all on 1 phase
• 17-32A was evenly split between 2 phases
• 33-48A was evenly split between 3 phases

Keep in mind Tesla can change the behavior through a software update and this was a few years ago.

My theory is that the phase boards are inefficient at lower amperages. This algorithm ensures that charging at any amperage between 8-48a, none of the phases will be run at less than 8 amps. Did you happen to notice whether the logic rotated the order in which the phases were used? Was 0-16 always on the same board and 17-32 on the same two boards?

 

[android04]

My theory is that the phase boards are inefficient at lower amperages. This algorithm ensures that charging at any amperage between 8-48a, none of the phases will be run at less than 8 amps. Did you happen to notice whether the logic rotated the order in which the phases were used? Was 0-16 always on the same board and 17-32 on the same two boards?

The computer does keep track of how many kWh have been charged by each phase, but I've mostly ever used 40-48 A charging and it divides that by the 3. I did briefly use the mobile charge connector that came with my car (that's limited to 32 A). I did not play with it enough and it has been a long enough time to be confident in the absolute behavior, but it did look like it tries to even out the lifetime kWh counter for each of the 3 phases. The following was what I observed:
Phase A - 6940 kWh lifetime
Phase B - 7220 kWh lifetime
Phase C - 7140 kWh lifetime

When I tested charging at 12A, it was all put on Phase A. When I tested charging at 24A, it was split evenly between Phase A and Phase C. When I tested charging at 34A, it was split evenly between all three.

 

[20221229 3RWD]

I continue to be surprised by the level 1 charging volatility at our house. It seems within the first 90 minutes the charger reduces from 12amp to 8amp fairly consistency.

I realize a lot of variables here (other items on the same circuit, wire connection between the breaker box and outlet, how well the outlet is wired etc …).

I had assumed level 1 would be consistent but slow. However, it seems very inconsistent.

Is this just our house, or typical for level 1?

Attaching most recent chart for context/review.

Thank you for all other input to this point.

Level 2 charger (well NEMA 15-40 plug) installed tomorrow.

 

[mongo]

I continue to be surprised by the level 1 charging volatility at our house. It seems within the first 90 minutes the charger reduces from 12amp to 8amp fairly consistency.

I realize a lot of variables here (other items on the same circuit, wire connection between the breaker box and outlet, how well the outlet is wired etc …).

I had assumed level 1 would be consistent but slow. However, it seems very inconsistent.

Is this just our house, or typical for level 1?

Attaching most recent chart for context/review.

Thank you for all other input to this point.

Level 2 charger (well NEMA 15-40 plug) installed tomorrow.

There have been people who has issues due to power company grid level issues.
The voltage step around 6:07 looks suspicious though. How much did it change for the 4 amp load change?

 

[davewill]

I continue to be surprised by the level 1 charging volatility at our house. It seems within the first 90 minutes the charger reduces from 12amp to 8amp fairly consistency.

I realize a lot of variables here (other items on the same circuit, wire connection between the breaker box and outlet, how well the outlet is wired etc …).

I had assumed level 1 would be consistent but slow. However, it seems very inconsistent.

Is this just our house, or typical for level 1?

Attaching most recent chart for context/review.

Thank you for all other input to this point.

Level 2 charger (well NEMA 15-40 plug) installed tomorrow.

I think it happens more often with L1 just because the circuits are usually not installed specifically for EV charging so they are rarely dedicated to the task, and 120v outlets are very rarely subjected to the stress that EV charging puts on them. I'm somewhat surprized they aren't more problematic than they are, truthfully. We probably have good building codes to thank for that.

 

[20221229 3RWD]

I think it happens more often with L1 just because the circuits are usually not installed specifically for EV charging so they are rarely dedicated to the task, and 120v outlets are very rarely subjected to the stress that EV charging puts on them. I'm somewhat surprized they aren't more problematic than they are, truthfully. We probably have good building codes to thank for that.

Nice, all good comments.

A NEMA 5-20 16amp plug arrived today, I will give it ago and see if it works better than the 12amp (NEMA 5-15). I am guessing it will also derate to 8amp?

 

[20221229 3RWD]

There have been people who has issues due to power company grid level issues.
The voltage step around 6:07 looks suspicious though. How much did it change for the 4 amp load change?

115v to 116v to 112v is all it seems?

 

[davewill]

Nice, all good comments.

A NEMA 5-20 16amp plug arrived today, I will give it ago and see if it works better than the 12amp (NEMA 5-15). I am guessing it will also derate to 8amp?

You intend to try to use 16a charging on an outlet that has been struggling to supply 12a? Doesn't sound like a good idea to me. If it were me, I'd instead be trying to discover if any of the wiring was bad, and exactly what other appliances might be on the same circuit. This is happening for a reason, and you should either stop using this outlet, or find out what the problem really is and fix it (or bite the bullet and put in a proper dedicated charging circuit).