Very frustrated with software limited charging

[spaceballs]

... This has something to do with the current limit from 40A to 30A when there are voltage fluctuations. ... As an engineer ...

Maybe shore power is not clean enough and is causing something on the UMC side to get into this condition?

 

[wk057]

Maybe shore power is not clean enough and is causing something on the UMC side to get into this condition?

The UMC is a mostly dumb appliance, it only changes the pilot signal amperage based on the resistor in the adapter attached. The car does the 40-30A change.

 

[spaceballs]

Well, it's supposed to trip.

Yep agreed, but you be surprised how many Don't when their post to. I've seen firetrucks come out to a lab because the wire in the wall was being overloaded and cooking, all due to bad breaker that failed (didn't trip).

However, my original point is that this still isn't the car's problem. If say after complaining, "Hey, Mr. Owner. I detected a voltage drop and am reducing current for your safety," I as the owner decide to tell the car, "You're an idiot, that was just my A/C kicking on, crank that **** back up."...... it should listen.

Ok say it's like qwk outlet at his work.. and in the wall is a bad connection causing the voltage drop.. say qwk then says override.. and breaker doesn't do it's job and then a fire happens... now exchange business with condo with sleeping baby in next door... well now you know how Tesla has to juggle these things.

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The UMC is a mostly dumb appliance, it only changes the pilot signal amperage based on the resistor in the adapter attached. The car does the 40-30A change.

When I say UMC side I mean anything past the relay in the UMC, i.e. Inlet of car, car onboard charger, etc..

 

[wk057]

Yep agreed, but you be surprised how many Don't when their post to. I've seen firetrucks come out to a lab because the wire in the wall was being overloaded and cooking, all due to bad breaker that failed (didn't trip).
Ok say it's like qwk outlet at his work.. and in the wall is a bad connection causing the voltage drop.. say qwk then says override.. and breaker doesn't do it's job and then a fire happens... now exchange business with condo with sleeping baby in next door... well now you know how Tesla has to juggle these things.

As tragic as your hypothetical sounds, objectively it's still not Tesla's problem. It's the fault of the breaker/wiring being bad, not the load on the receptacle.

When I say UMC side I mean anything past the relay in the UMC, i.e. Inlet of car, car onboard charger, etc..

That's the firmware making the decision, the complaint this entire thread is about.

 

[spaceballs]

... The latest FW causes the car to stop charging every 5 minutes, ...

In the future if I was really not wanting to upgrade my firmware I would disable car cellular.

 

[wk057]

In the future if I was really not wanting to upgrade my firmware I would disable car cellular.

While in for service:

I specifically requested that I NOT get updated to the new FW(I had 5.8 1.49.24), but got a call back saying it MUST and it WILL get upgraded, because it's a recall FW(any prior FW was recalled). After about 1+ hours on the phone arguing why I did not want ANY new FW, I gave in and that was that. The reason I didn't want new FW, was the charging current being backed off, starting with 5.8.4(there are a ton of threads here on that mess).

 

[spaceballs]

As tragic as your hypothetical sounds, objectively it's still not Tesla's problem. It's the fault of the breaker/wiring being bad, not the load on the receptacle.

OK say connecter at the inlet is loose and overheating.. and about to catch fire.. the car sees voltage drop... the car has to pick one.. 1. keep charging... 2. back down.
All you have to do is think of lawyers and then what parts are made by which company... sorry I can't make it any simpler than that for you.

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While in for service:

I understood while it was in service, he has no choose of the matter it's a safety issue.. if he has a problem then he should would work on why the car is backing down from 40A.

 

[wk057]

For anyone wondering, I'm particularly annoyed by this firmware-related change of the charge current because it has affected me on several occasions. I've put in the request that this be able to be overridden multiple times since, also.

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OK say connecter at the inlet is loose and overheating.. and about to catch fire.. the car sees voltage drop... the car pick one.. 1. keep charging... 2. back down.
All you have to do is think of lawyers and then what parts are made by which company... sorry I can't make it any simpler than that for you.

For the connector at the inlet to the car, the car knows the position of it. If it isn't seated properly it generally already knows this (orange ring) and reduces current or doesn't charge at all (red ring). If there is some mechanical issue in the inlet that is causing a bad connection while fully seated that's a whole other issue entirely and I'd fully expect Tesla to be held accountable regardless of if the car backed down the amperage or not.

So because Tesla might have screwed something up and there is a bad connection the could possibly result somewhere on the "UMC side" of things, the owner doesn't get to use the 10kW charger he paid for in false-detect (nearly all) situations?

If the bad connection is on the receptacle side... again, user error. The UMC or car didn't fail in this case. There is no NEC code that says the car/charge needs to perform this "safety" check, either.

 

[spaceballs]

... For the connector at the inlet to the car, the car knows the position of it. If it isn't seated properly it generally already knows this (orange ring) and reduces current or doesn't charge at all (red ring). If there is some mechanical issue in the inlet that is causing a bad connection while fully seated that's a whole other issue entirely and I'd fully expect Tesla to be held accountable regardless of if the car backed down the amperage or not. ...

A common failure on connectors dealing with high amperage is wear and dirt on the contacts themselves, how do you expect the car to detect when this happens? Only two things I can think of is heat and voltage drop. From common sense standpoint is to back down amps until voltage doesn't sag. Now like you and the OP states how much do you want it to back down from, that's the million dollar question, and only Tesla will get to decide from a safety standpoint. Personally I would have them error on the side of caution.

 

[wk057]

Don't get me wrong. There should certainly be some stupidity checks in the firmware with regard to this. For example, if when you start the charge, and the voltage drops proportional to the amperage ramp up and results in some ridiculous drop it should definitely dial back since obviously the car is the cause of the large sag.

It should also be able to easily detect full voltage drop outs on a sub-second level without much nuisance tripping, among other things like GFCI protection, possibly AFCI protection if the hardware can do this.

But when someone is consistently getting the same issue from a false-fault detection... an override button would be nice. Either that or they need to just not do it all together.

There is no other fault detection equipment that I'm aware of that reacts to voltage dips like the Model S does with recent firmware. The Model S charger is a 99% PF load that is awesomely steady. Any intermittent change in voltage is not the car's fault once charging is going. It will only be the result of other loads on the system, which aren't the car's problem. If Tesla expects every outlet to maintain a rock solid voltage at a steady high current they're crazy. With no changes in load in my house the voltage at the Model S dash can fluctuate 5% in either direction. This is from the street, nothing to do with anything going on in the house or with the car. Occasionally the car sees this as a concern and dials back the amperage...... and still the voltage fluctuation continues anyway. The dial down did nothing to help anyone here. My wiring is above that required for the HPWC, and the voltage drop between the HPWC and the service panel is virtually non-existent... yet the car sometimes thinks there is an issue. I find this annoying, but for someone needing to charge in a set time period on a daily basis (like qwk charging at his job) that 25% loss in power is not just something that you can just write off as nothing.

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A common failure on connectors dealing with for high amperage is wear and dirt on the contacts themselves, how do you expect the car to detect when this happens? Only two things I can think of is heat and voltage drop.

In this case the voltage drop would be immediate upon charge start, and would fall under the example I noted above. This doesn't appear to be the case with the OP. Definitely isn't the case with me with a brand new P85D and brand new HPWC that was just installed, either.

Edit: As an example, after my side-by-side efficiency test yesterday, the P85D and P85 were both charging at 80A from their HPWCs when we got home. Not a problem, I have 400A service here. Voltage sag at the panel, according to TED, was 1-2% off the service entrance conductors to the 200A panel the HPWCs are in.

Cars charged for a while (over an hour) without issue at 80A. The incoming voltage moved around a bit at the panel from the service side. A couple % up, and shortly back to where it was. Most likely a heavy load going offline elsewhere nearby, then coming back shortly. All of a sudden the P85D decided to drop to 60A. The P85 was still happy at 80A, though... yet the voltage at the dashes was the same.

I contacted Tesla about this because it's annoying. Had I actually needed to get a full charge in the expected amount of time for whatever reason, I would have been pissed. (In this case the P85 got to 90% charge ~45 minutes before the P85D, replacing nearly identical amounts of power).

 

[spaceballs]

... In this case the voltage drop would be immediate upon charge start, and would fall under the example I noted above. ...

That 100% false, i.e. contacts can start out just good enough but later one due to slow heat build up internally due to resistance, or external outside environment issue (i.e. sun hitting it) could cause it to happen at any time.. i.e. the voltage drop meeting the threshold where firmware thinks something is wrong.

... There is no other fault detection equipment that I'm aware of that reacts to voltage dips like the Model S does with recent firmware. ...

But in doing so covers (to me anyways) an additional safety feature I rather have present than not.

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... Cars charged for a while (over an hour) without issue at 80A. The incoming voltage moved around a bit at the panel from the service side. A couple % up, and shortly back to where it was. Most likely a heavy load going offline elsewhere nearby, then coming back shortly. All of a sudden the P85D decided to drop to 60A. The P85 was still happy at 80A, though... yet the voltage at the dashes was the same. ...

Maybe D has latest gen hardware/firmware charger and can better detect issues? Whatever the case, at least your contacting Tesla, if enough people complain maybe they will modify to not back off as much, or even just add in firmware code to creep amperage back up to the original preset if no more sag is present.

 

[hiroshiy]

qrk, I hope Tesla address the issue quickly and send you a temporary firmware and a new tested UMC. There will be debates as to where the source of the problem was, Tesla needs to make customer happy first.

That said I experienced similar dialing back from firmware 6.0 - I was charging at 80A with HPWC (in my case 200V) and even the voltage sags to 195V it was fine. Now with the 6.0 the current is dialed back to 17 all the time with around 198 or 197V...

 

[wk057]

A common failure on connectors dealing with high amperage is wear and dirt on the contacts themselves

In this case the voltage drop would be immediate upon charge start, and would fall under the example I noted above.

That 100% false, i.e. contacts can start out just good enough but later one due to slow heat build up internally due to resistance, or external outside environment issue (i.e. sun hitting it) could cause it to happen at any time.. i.e. the voltage drop meeting the threshold where firmware thinks something is wrong.

(Keeping this string of comments together for clarity)

Saying it is 100% false is in fact, false. Heat does cause resistance to increase, certainly. However, you were talking about "wear and dirt" in/on the contacts. Breaking that down, dirt is not going to be as conductive as the contacts, if at all, thus a loss of contact surface area, thus an immediately detectable increase in resistance (and voltage drop). Wear is the loss of part of the contact surface resulting in them not making contact to as much area as they had previously, resulting in a loss of surface area, and thus the same immediate increase in overall resistance (and voltage drop). Both situations covered by a voltage sense during the initial ramp up.

Now if while charging the contacts or other metal along the line (copper, silver, aluminum, whatever) increases in temperature, and increases the resistance, this is an entirely different scenario than "wear and dirt." The increased heat would exaggerate these issues, but the issue would be present all along anyway. So, my initial statement above is not "100% false" as it was meant to address the specific scenario mentioned in the first post quote above, not external or resistive heat build up after the initial charge ramp, which would, again, only exaggerate the preexisting issue anyway (which should have already been detected).

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Did some math here (pretty sure I've got this right), and I'll note that the voltage drop difference from temperature change in copper in pretty negligible at these currents anyway. At 40A in the UMC conductors, using 0C as a reference, increasing the temperature of the conductors by 100C (which I think would be pretty extreme) increases the voltage drop by 0.6%. There is pretty much no way the car is going to be able to distinguish this voltage drop from anything else on the line anyway, so the heat-based resistance increase isn't going to be detectable in the first place.

Edit: Going further on that, we'll assume a fault condition does present itself where say, 20% of the conductive material becomes unavailable for whatever reason (a gnome wedged itself in the contact lets say) long into a charge. If I did the math right (it is late, so possibly not), we're now looking at a voltage drop of just over 1% (about 2.6V) vs normal. Again, this is a pretty normal fluctuation for a grid connected outlet to have anyway. The car has no way to determine a fault vs normal voltage fluctuation.

Anyway, I'm done arguing this. You can go to bat for Tesla all you want on this for whatever reason. The fact is their algorithm has more false alarms than early generation AFCI breakers. Both situations are an annoyance, but an AFCI tripping when I use a table saw isn't going to leave me waiting an additional 2.5 hours to get somewhere. At least Tesla has the ability to fix their problem with new software that isn't so trigger happy. In the meantime, until they get it right, they need to let people who know what they're doing override the damn thing, at their own risk.

 

[Bet TSLA]

It's pretty clear that Tesla has already solved your problem, qwk. The HPWC is designed to work in challenging environments. For some reason you don't want to use it.

You are finding that over time Tesla has fine tuned the firmware to prevent damage and disasters. Apparently, given your history of melted cables, you are happy to operate close to the edge. Tesla, having to serve a large variety of customers, many of whom are ignorant and careless, has a responsibility to prevent problems. They are fulfilling their responsibility, which as a side effect is preventing you from doing what you like. Sorry, but they aren't going to change it back. Just get an HPWC and I bet your problems will go away.

Meanwhile, perhaps you can encourage the creation of some local HPWC installations by way of Tesla's destination charging program. That will make trips easier and faster for you. I bet you'll feel better too.

 

[spaceballs]

(Keeping this string of comments together for clarity)

Saying it is 100% false is in fact, false. Heat does cause resistance to increase, certainly. However, you were talking about "wear and dirt" in/on the contacts. Breaking that down, dirt is not going to be as conductive as the contacts, if at all, thus a loss of contact surface area, thus an immediately detectable increase in resistance (and voltage drop). Wear is the loss of part of the contact surface resulting in them not making contact to as much area as they had previously, resulting in a loss of surface area, and thus the same immediate increase in overall resistance (and voltage drop). Both situations covered by a voltage sense during the initial ramp up.

Now if while charging the contacts or other metal along the line (copper, silver, aluminum, whatever) increases in temperature, and increases the resistance, this is an entirely different scenario than "wear and dirt." The increased heat would exaggerate these issues, but the issue would be present all along anyway. So, my initial statement above is not "100% false" as it was meant to address the specific scenario mentioned in the first post quote above, not external or resistive heat build up after the initial charge ramp, which would, again, only exaggerate the preexisting issue anyway (which should have already been detected).

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Did some math here (pretty sure I've got this right), and I'll note that the voltage drop difference from temperature change in copper in pretty negligible at these currents anyway. At 40A in the UMC conductors, using 0C as a reference, increasing the temperature of the conductors by 100C (which I think would be pretty extreme) increases the voltage drop by 0.6%. There is pretty much no way the car is going to be able to distinguish this voltage drop from anything else on the line anyway, so the heat-base resistance increase isn't going to be detectable in the first place.

In a nut shell I'm saying you can't use the "Both situations covered by a voltage sense during the initial ramp up." Also your not following the end of the example, say the contractor did get hot enough to slowly deform the contacts. This could have a serious impact on over all surface area and quickly lead to dangerous resistance changes (what is the resistance of a small molten copper ball?). Another example that's non inlet wise is the cord insulator is failing in charge cord (cord getting crushed) and it starts to arc in the middle of a charge?, etc..

I think voltage sag should always be monitored and not just on the start of the inital ramp up.

 

[wk057]

In a nut shell I'm saying you can't use the "Both situations covered by a voltage sense during the initial ramp up." Also your not following the end of the example, say the contractor did get hot enough to slowly deform the contacts. This could have a serious impact on over all surface area and quickly lead to dangerous resistance changes (what is the resistance of a small molten copper ball?). Another example that's non inlet wise is the cord insulator is failing in charge cord (cord getting crushed) and it starts to arc in the middle of a charge?, etc..

I think voltage sag should always be monitored and not just on the start of the inital ramp up.

I'm just going to lol a bit at this one... the contacts in the charger cable and charge port are made of copper... which has a melting point of 1,085C (nearly 2000F)... if the contacts get deformed by heat I think you have some much more serious problems on your hands... like moving your car off of the surface of the sun. (And before anyone says anything about solder, keep in mind that Tesla uses ultrasonic welding for all of these parts, so, no solder to melt).

As for the plastic around the contacts, if this deforms under heat, you're already screwed anyway... but the plastic melting isn't going to cause a voltage change. Could cause a ground fault... maybe. The connectors themselves fit together pretty tightly, so even some play due to plastic becoming more malleable is probably not going to change things much with respect to voltage drop.

In the case of the cord insulation failing, someone cutting the cable, a cat chewing it, etc... this is the ground fault and arc fault detection and is an independent safety mechanism that has nothing to do with voltage drop. (GFCI works by detecting an imbalance of current to ground, AFCI detects arc faults via advanced logic to detect the arcing circuit, not voltage drop.)

Edit: Anyway, these scenarios don't seem to be what the whole voltage drop detection was intended to prevent anyway. It is intended, and was stated, that it detects substandard premises wiring and extension cords, both of which, again, are detectable on the initial ramp.

 

[spaceballs]

I'm just going to lol a bit at this one... the contacts in the charger cable and charge port are made of copper... which has a melting point of 1,085C (nearly 2000F)... if the contacts get deformed by heat I think you have some much more serious problems on your hands... like moving your car off of the surface of the sun. (And before anyone says anything about solder, keep in mind that Tesla uses ultrasonic welding for all of these parts, so, no solder to melt).

So you don't believe two copper contacts in a high amperage connector can never get into a case where they can melt and cause issues. Ok fair enough you win, I'll will ignore the my melted copper EV Anderson connector that I thew away from a current overload (I shorted one out with some ultracaps through it). btw there have been more than one EV DYI builds with connectors that have stayed withing it's rated power limits but due to resistance issues have melted (and it was after inital pre ramp). Can't find the orginal EV DYI post, but here something similar smaller scale Anderson Connector Meltdown - The GPSy EV Project Chief Delphi - Battery connector.....

In the case of the cord insulation failing, someone cutting the cable, a cat chewing it, etc... this is the ground fault and arc fault detection and is an independent safety mechanism that has nothing to do with voltage drop. (GFCI works by detecting an imbalance of current to ground, AFCI detects arc faults via advanced logic to detect the arcing circuit, not voltage drop.)

Say it wasn't the the ground wire that has the insulation fault, but the other two wires that start to arc. you hope in a short amount of time that the ground wire insulation will melt due to the arc heat and trigger the GFCI but that might take a second(s). So if you were the car for safety reasons do you just keep chugging along charging, or ramp down? I personally would at least have the car keep ramping it down till the point it disconnects the UMD relays.

I can make up more plausible scenarios, but I hope you see that having a safety circuit always monitoring for voltage sag makes for a safer design.

 

[wk057]

*sigh*

So you don't believe two copper contacts in a high amperage connector can never get into a case where they can melt and cause issues. Ok fair enough you win, I'll will ignore the my melted copper EV Anderson connector that I thew away from a current overload (I shorted one out with some ultracaps through it). btw there have been more than one EV DYI builds with connectors that have stayed withing it's rated power limits but due to resistance issues have melted (and it was after inital pre ramp).

An ultracap? Really? You're trying to compare a 40A/240V outlet protected with a 50A OCPD upstream, and at least one additional larger OCPD upstream, with the instantaneous unchecked power output of a charged ultracap? Talk about being out in left field... (Keep in mind I've already established that the reliability of the upstream OCPDs is not Tesla's problem, nor can their reliability be detected by voltage drop...)

You need currents in the order of kiloamps to do this type of damage...

As for the DIY EV builds, you're talking a whole different set of issues there that could have taken place, likely have little, if anything, to do with this particular issue with Tesla... and a failure analysis which will be left for another forum on DIY EVs. For the record, I've heard zero reports of a Tesla charge port inlet going up in flames...

Math to the rescue again... it would take ~500A for 10+ seconds to electrically melt the wiring in the UMC cable. It would take ~1500A for 10+ seconds to do the same to the wiring inside the car. Instant weld amperage for either is well over 15kA... well beyond what any OCPD would trip at, let alone that the supply wiring couldn't even provide that kind of current most likely. For fun, within reach of a decent ultra cap, though... and probably also possible from the DC side of the Model S battery.

I guess I have to get specific. Say it wasn't the the ground wire that has the insulation fault, but the other two wires start that start to arc. you hope in a short amount of time that the ground wire insulation will melt due to the arc heat and trigger the GFCI but that might take a second(s). So if you were the car for safety reasons do you just keep chugging along charging, or ramp down? I personally would at least have the car ramp it down.

What you describe is called an arc fault, and is prevented with an AFCI, as mentioned above. It has absolutely nothing to do with voltage sag. The AFCI monitors instantaneous current usage at a millisecond level and compares the patterns to lab produced arc faults, defines a probability that a similar condition is happening or not, and acts or doesn't act almost immediately. For what it's worth, as far as I know the Model S does NOT have any type of AFCI. The UMC and HPWC do have GFCIs however.

The lack of an AFCI doesn't justify the voltage drop reaction anyway. In the event of an arc fault, lowing the current isn't going to stop the arc. In fact, in this case lowering the amperage will increase the voltage and likely intensify the arc since an arc's ability to jump an air gap is directly proportional to voltage. Decrease amperage, which in turn increases line voltage, increase arcing

I can make up more plausible scenarios, but I hope you see that having a safety circuit always monitoring for voltage sag makes for a safer design.

You can make up thousands of scenarios. Until you find me a code reference in the NEC (or proposed addition, or similar safety code) that shows a safety method/device/procedure/etc for accurately detecting an actual real world fault condition based entirely by monitoring voltage sag, or some other actually plausible reason to cause false faults and inconvenience the majority of the time it triggers instead of actually preventing an unsafe condition... then I'm going to stick with this being a kludge of a solution to a mostly nonexistent problem.

Sorry, voltage drop is just NOT a reliable or useful method for detecting an unsafe situation. Voltage on home wiring can vary +/- 15V depending on neighborhood and local loads, at any time, without any unsafe practices or actual danger present. This is normal. Yet the Model S firmware will see some of these changes and just freak out.

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One of the only reasons I'm continuing to reply here is to make sure that no one reads this and thinks that Tesla's current drop based on voltage drop is going to in any way even remotely protect them from any of the scenario's you've brought up. *That* would be unsafe, and not combating such nonsense would feel negligent on my part. Proper wiring, receptacles, OCPDs, etc are what will actually protect the premises wiring.... not Tesla.

 

[spaceballs]

... Until you find me a code reference in the NEC (or proposed addition, or similar safety code) that shows a safety method/device/procedure/etc for accurately detecting an actual real world fault condition based entirely by monitoring voltage sag, or some other actually plausible reason to cause false faults and inconvenience the majority of the time it triggers instead of actually preventing an unsafe condition... then I'm going to stick with this being a kludge of a solution to a mostly nonexistent problem.

Sorry, voltage drop is just NOT a reliable or useful method for detecting an unsafe situation. Voltage on home wiring can vary +/- 15V depending on neighborhood and local loads, at any time, without any unsafe practices or actual danger present.

A Tesla roadster with 120v charger cable + 50 foot 14/3 gauge extension (which has max NEC limit rating of 15A). It's plugged into an 20amp socket. I start charging my roadster at 15A, at the end of the extension cable has two more outlets available. I connect up another device that uses 4 amps. Now I'm exceeding the NEC limit of the extension cord, BUT the Roadster will stop charging as soon as the 4 amp load is plugged in.

Now I can re-do the scenario that would fit the original poster but you can see how the voltage sag detection prevented the NEC Amp overlimit (prevent idiots from doing dumb things.) Sadly I accidentally did the above scenario, when I was testing extension cords out on my roadster.

Do i win a cookie?

 

[wk057]

A Tesla roadster with 120v charger cable + 50 foot 14/3 gauge extension (which has max NEC limit rating of 15A). It's plugged into an 20amp socket. I start charging my roadster at 15A, at the end of the extension cable has two more outlets available. I connect up another device that uses 4 amps. Now I'm exceeding the NEC limit of the extension cord, BUT the Roadster will stop charging preventing as soon as the 4 amp load is put on.

Now I can re-do the scenario that would fit the original poster but you can see how the voltage sag detection prevented the NEC Amp overlimit.

Do i win a cookie?

No cookie.

First, this isn't something the Roadster does that is covered by the NEC or any similar safety code. No plug and cord appliance (in this case, the Roadster) is expected to reduce it's current draw in response to voltage sag under any code, NEC or otherwise. On the contrary, most appliances *increase* their current draw in response to voltage drop to maintain their required power usage in watts.

Second, I'll point out that the negligence involved in the extension cord situation you describe STILL has nothing to do with the car... but anyway, the situation you describe at 19A would cause a voltage drop of about 6V on the 14 gauge extension cord. So the Roadster could eat 1,710 watts, the hypothetical exactly 4 amp load would get 456 watts, and the extension cord would be a resistive heater pulling 114 watts. 1,710 + 456 + 114 = 2,280 watts, or 19A @ 120V at the male end of the cord. The cord itself would eventually heat to about 68-72C at 30C ambient temp. Your Roadster annoyingly shutting your charge down in this situation hasn't actually saved anything, regardless of the operator stupidity in this scenario.

Also keep in mind that your hypothetical 4A load is likely drawing more than 4A depending on what it is. Unless it is something with a maximum amperage rating and not an actual wattage rating, it will draw the wattage it needs at an input voltage range. The chances of you actually staying under the 20A OCPD limit here with an extra 480W load (which would actually demand 4.2A at 114V) are slim since 20A breakers are not rated for continuous duty @ > 16A, the breaker will pop within about ~3-4 hours max under this load normally (even without the extra real world .2A).

(14 gauge wire is rated for 20A with 75C insulation. All of the 14 gauge extension cords I have use 90C insulation...)

Keep them coming. I'm having fun now. lol