Anyone Still Experiencing Charge Current Limiting (40A->30A)?

[FlasherZ]

Just as an example of what can trigger this - I was charging my car on a 14-50 at a 200A service shop where I was the only load beyond a refrigerator. The car normally charges just fine at 40A, but then my son started to play with the lights in the office - a single 8-bulb 432W T5 fixture that has a known "iffy" ballast in it. The reactive currents and surges created by flipping it on and off caused the car to back down to 30A.

Now, there's no way for the car to tell that it's my son flipping a light switch... it just sees a voltage disruption that could be indicative of a problem, and is erring on the safe side.

 

[scaesare]

Just as an example of what can trigger this - I was charging my car on a 14-50 at a 200A service shop where I was the only load beyond a refrigerator. The car normally charges just fine at 40A, but then my son started to play with the lights in the office - a single 8-bulb 432W T5 fixture that has a known "iffy" ballast in it. The reactive currents and surges created by flipping it on and off caused the car to back down to 30A.

Now, there's no way for the car to tell that it's my son flipping a light switch... it just sees a voltage disruption that could be indicative of a problem, and is erring on the safe side.

Yeah, clearly there's something that's causing it to trip over the threshold. I wonder how much hysteresis there is in the detection algorithm... I'd hope that something momentary wouldn't do it... but who knows.

I also wonder how close 5% is to the lower threshold.

 

[David99]

Just as an example of what can trigger this - I was charging my car on a 14-50 at a 200A service shop where I was the only load beyond a refrigerator. The car normally charges just fine at 40A, but then my son started to play with the lights in the office - a single 8-bulb 432W T5 fixture that has a known "iffy" ballast in it. The reactive currents and surges created by flipping it on and off caused the car to back down to 30A.

Now, there's no way for the car to tell that it's my son flipping a light switch... it just sees a voltage disruption that could be indicative of a problem, and is erring on the safe side.

With the latest firmware the car will adjust up to 40 Amp again. I have seen it happen a few times on my car lately. I have no idea what triggers it to go up and down. It used to never adjust up again, but after the latest update it now will.

 

[supratachophobia]

This is something I have been working with service on ever since I purchased the car. About one in every 10 charges, the amperage will drop to 30 from 40 and in about the half of those cases, you can't manually turn it back up to 40 without unplugging and re-plugging the car back in. They've swapped onboard chargers twice and replaced the charging port. I am currently on a loaner UMC which they wanted me to try, but as I just informed them, ever since I switched to scheduled charging, the amperage drop has not happened. They want me to try the scheduled charging for a little longer before going back to instant charging with the loaner UMC to see if the drop happens again. It should be noted that VisibleTesla does record the amperage drops very nicely so you can go back and see when the 30amp drops happens. Again, to my knowledge from those logs, it has not happened on scheduled chargers.

I will say that I have a very strong 240v service @ 200amps. Electrician and utility both did not find anything wrong with the wiring or the service. I do run multiple servers in our data center which pull quite a bit of power, but those are going 24x7. But with the comment someone made about a light-switch affecting the charge, it really could be anything used daily that triggers it; ie. dishwasher, washers, dryer, furnace, etc.

As far as real world affects, it becomes a problem when you are expecting a certain charge level when you go out in the morning and it isn't finished. As with most on here, we know the worst thing we can do to the battery is leaving it at higher SOC for extended periods of time. And adjusting the charge schedule to be earlier, would mean that would be the case in the majority of instances.

I wish there was a more definitive answer for this because it looks like I'm not the only one experiencing the trouble. And I feel for the services center because they keep "asking corporate" or "contacting the engineering team" and there doesn't seem to be any useful help on those fronts (as evidenced by my 3rd onboard charger). I only had a pre-v6 release for about 2 weeks of ownership. Yet, I did not experience the amperage drop at that time when statistically I should have seen it at least 2-3 times.

 

[DavidM]

UPDATE - After Tesla Service replaced my master charger, I had two error-free charging sessions, so I thought my problems were resolved. But then, the errors returned. The car backs off from 40A to 30A about 3 out 4 charging sessions. I've been closely monitoring the voltage and my voltage is typically in the 248V - 253V range. The power company insists that up to 252V is considered normal (+/-5% of 240V). Whenever the voltage is at or above 249V, the car kicks the amps down to 30A within 10 min. So Tesla's tolerances ARE NOT in line with the power company's tolerances. It's possible that Tesla thinks that the (continuous) wattage is too much for the skinny cable on the UMC to handle at 250V & 40A (10,000 watts)? Or maybe too much for the charger to handle, since it's designed for 9.6kW not 10.0kW?

 

[mibaro2]

I had my charging sessions drop to 30amp after the last update. Last week, I decided to unplug the UMC from the 14-50 outlet, hold the reset button for 10 seconds, and reconnect the UMC.
So far, a week later, I am charging consistently at 40amp without it dropping to 30amp.
Has anyone else tried resetting the UMC to solve this problem? And was it successful for you?

 

[scaesare]

I've been closely monitoring the voltage and my voltage is typically in the 248V - 253V range. The power company insists that up to 252V is considered normal (+/-5% of 240V). Whenever the voltage is at or above 249V, the car kicks the amps down to 30A within 10 min.

I suspect none of this is related to in-car hardware failure, but rather the algorithm implemented in a firmware change after a garage fire apparently caused by faulty premise wiring.

I don't think starting voltage will cause the current reduction (although I've seen reports of too high a line voltage preventing the car from starting to charge all together). rather, I think is the total drop over the session. I don't know if the algorithm evaluates that delta in voltage as a straight number, or a percentage.

In any case, my line voltage will start somewhere in the 244 range, and drop to about 232 or so... so a delta of about 12 volts, or ~5%. It would be nice to know what the threshold is... as I assume I'm right on the edge, as I get current reduction every few weeks...

 

[FlasherZ]

In any case, my line voltage will start somewhere in the 244 range, and drop to about 232 or so... so a delta of about 12 volts, or ~5%. It would be nice to know what the threshold is... as I assume I'm right on the edge, as I get current reduction every few weeks...

Based on the data we have seen from reports, we can assume the algorithm looks for 2 things:

1. The initial voltage drop as current is applied - the "extension cord detection" algorithm that would indicate a high-resistance problem in wiring, or an overloaded transformer, on initial ramp-up. This one's easy to spot - as the current ramps up, the voltage drops too much and holds steady at that dropped voltage. In these cases, it's likely you'll see current downshifting nearly every time. It can be caused by low starting voltage (in some cases, the power company can fix this by adjusting the transformer voltage), undersized wire, long wiring runs, etc. It's usually pretty easy to track this down because you can take voltage readings at various points in the service and determine where the voltage drop is coming from.

2. An arc-fault detection algorithm - the "voltage disturbance" detection. This is the one that is likely affecting most people who see more "random" patterns in downshifting and is the hardest one to track down. It is harder to detect because you need equipment with sufficient measurement capabilities to capture sub-second variations in voltage (the car's volts/amps read-out will not show you this, nor will your run-of-the-mill voltmeter). This can caused by a loose wiring connection (an actual arcing problem), a misbehaving appliance (bad motor start capacitor, bad ballast, etc. that can draw a lot of current or send a voltage surge via reactive current), or even a bad charger in the car.

 

[DriverOne]

I get the drop from 40A->30A annoyingly frequently. It seems to correlate somewhat with temperature - cold nights do not normally cause a drop to 30A. Sep/Oct/Nov last year about 1 drop every 6 days. December and January, no drops at all. Now in February it has dropped twice again.

I checked my eGauge and don't see the AC or heating coming on in sync with the Tesla drops. My UMC has been replaced; made no difference.

I've seen it happen on both daytime (unscheduled) and nighttime (scheduled) charging. :-(

 

[qwk]

UPDATE - After Tesla Service replaced my master charger, I had two error-free charging sessions, so I thought my problems were resolved. But then, the errors returned. The car backs off from 40A to 30A about 3 out 4 charging sessions. I've been closely monitoring the voltage and my voltage is typically in the 248V - 253V range. The power company insists that up to 252V is considered normal (+/-5% of 240V). Whenever the voltage is at or above 249V, the car kicks the amps down to 30A within 10 min. So Tesla's tolerances ARE NOT in line with the power company's tolerances. It's possible that Tesla thinks that the (continuous) wattage is too much for the skinny cable on the UMC to handle at 250V & 40A (10,000 watts)? Or maybe too much for the charger to handle, since it's designed for 9.6kW not 10.0kW?

The charger can handle the full 10kW(or at least it used to with previous firmwares). If you plug it into Voltage over 250, it lowers the amperage so that it doesn't ever exceed 10kW total. Your scenario sounds like it's all firmware related.

 

[svp6]

I charged this morning at a public charger. Car dropped to 30A - did not come back to 40 when I plugged in at home. I had to manually reset to 40, so far so good. Perhaps in the new firmware the 40 Amp limit is no longer the default.

 

[FlasherZ]

I charged this morning at a public charger. Car dropped to 30A - did not come back to 40 when I plugged in at home. I had to manually reset to 40, so far so good. Perhaps in the new firmware the 40 Amp limit is no longer the default.

The default has not changed. However, what can happen is that you plug in at a lesser-capable charger, then click the arrow to move the current down, then click the arrow to move it back up and it will remember that current as the max current for future sessions. Set it at 40 or 80 (depending on your car's configuration) *before* you plug in, and that will be your default.

 

[supratachophobia]

I get the drop from 40A->30A annoyingly frequently. It seems to correlate somewhat with temperature - cold nights do not normally cause a drop to 30A. Sep/Oct/Nov last year about 1 drop every 6 days. December and January, no drops at all. Now in February it has dropped twice again.

I checked my eGauge and don't see the AC or heating coming on in sync with the Tesla drops. My UMC has been replaced; made no difference.

I've seen it happen on both daytime (unscheduled) and nighttime (scheduled) charging. :-(

Another update after 1 year. Amperage drop still happens under scheduled charging, without a doubt, the colder weather seems to make it happen way more, like, 4/7 times.

 

[svp6]

The default has not changed. However, what can happen is that you plug in at a lesser-capable charger, then click the arrow to move the current down, then click the arrow to move it back up and it will remember that current as the max current for future sessions. Set it at 40 or 80 (depending on your car's configuration) *before* you plug in, and that will be your default.

I did not change manually the amperage at the public charger, car adjusted that on its own. When returning home it stayed at the lower 30A. My guess is that if for any particular reason the amperage goes down, in the current software you have to manually reset.

 

[youlikeadajuice]

Another update after 1 year. Amperage drop still happens under scheduled charging, without a doubt, the colder weather seems to make it happen way more, like, 4/7 times.

I have the opposite happen, no problems in the winter but summertime it always drops to 30A. I always chalked it up to everyone on the same transformer using their air conditioning and it was causing a large electrical draw. Perhaps everyone on yours has electric heat?

 

[FlasherZ]

I did not change manually the amperage at the public charger, car adjusted that on its own. When returning home it stayed at the lower 30A. My guess is that if for any particular reason the amperage goes down, in the current software you have to manually reset.

If you can reproduce it, that would be wonderful.

I've done extensive testing with this. The behavior hasn't changed - as long as you don't touch the charging current setting, if the car reduces its current it will return the next time you plug it in. You can see the default charge current for your current location by bringing up the "charging" screen (lightning bolt on the touchscreen) BEFORE plugging in.

- - - Updated - - -

I have the opposite happen, no problems in the winter but summertime it always drops to 30A. I always chalked it up to everyone on the same transformer using their air conditioning and it was causing a large electrical draw. Perhaps everyone on yours has electric heat?

Forced air furnace with a bad start capacitor on the blower motor will do this.

 

[ken830]

My car is still reducing charge current to 30A. Rarely, it will recover back up to 40A later in the session. Sometimes, it'll stay at 30A for the remainder of the session, but will be at 40A at the next session. But most of the time, it'll trigger a "charging problem" message, finish charging, and be stuck at 30A as if someone had manually adjusted it down for that location.

It's annoying because I have a dedicated meter, breaker, and circuit for the car alone. And it's brand new put in by a trusted professional electrician (my father) and even inspected by my local Tesla service center's preferred electrician. My on-board charger was also replaced once, but the problem remains. I monitor the voltage on the line, and it's always a solid 247V.

 

[FlasherZ]

All of those things that you are doing are good, but it's not capturing all of the things that trigger the Tesla's backing down. See my FAQ (in my signature) for more information. It could be that your transformer is a bit overloaded. Even though you have a dedicated meter and service disconnect for the EV, it still shares the transformer and misbehaving loads can still cause problems.

 

[ken830]

All of those things that you are doing are good, but it's not capturing all of the things that trigger the Tesla's backing down. See my FAQ (in my signature) for more information. It could be that your transformer is a bit overloaded. Even though you have a dedicated meter and service disconnect for the EV, it still shares the transformer and misbehaving loads can still cause problems.

Thanks, but none of the suggestions in your sig link really helped me. I already had two professional electricians inspect everything. The circuit breaker is about 6 inches from the power-pole drop. The NEMA 14-50 is 2 inches from the breaker box. 6 guage wires. Everything is brand new. Only one breaker and one outlet to one car. Voltage sags don't seem to be a problem as I'm consistently seeing 245-247 volts. We have 200A service to the house, 100A circuit to the house, and 100A circuit to the car. UMC and adapter has been replaced twice. The on-board charger was replaced too. And when I had the traction pack failed, I used a loaner pack for a few months. Nothing changed the behavior. Tesla can't diagnose the car because they don't have a way to charge at 240V/40A. They have 3-phase service, so they only have 208V/40A, which is only about 8 kW.

 

[jerry33]

Thanks, but none of the suggestions in your sig link really helped me. I already had two professional electricians inspect everything. The circuit breaker is about 6 inches from the power-pole drop. The NEMA 14-50 is 2 inches from the breaker box. 6 guage wires. Everything is brand new. Only one breaker and one outlet to one car. Voltage sags don't seem to be a problem as I'm consistently seeing 245-247 volts. We have 200A service to the house, 100A circuit to the house, and 100A circuit to the car. UMC and adapter has been replaced twice. The on-board charger was replaced too. And when I had the traction pack failed, I used a loaner pack for a few months. Nothing changed the behavior. Tesla can't diagnose the car because they don't have a way to charge at 240V/40A. They have 3-phase service, so they only have 208V/40A, which is only about 8 kW.

Try finding a nearby Tesla owner who doesn't have a problem and have them charge their car at your house with their UMC, and your car at their house, and see if the safety reduction kicks in.