Ran into this same thing with the Roadster charger at the Tesla store at Santana Row today. Didn't really need the extra 10A because we were stopping for a while, but I was a little surprised.
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pilotSteve
Active Member
I am still running 4.3 firmware and happily charging at 79A (55 mph) every night. No warnings appear and no problems of any kind. The cable from my HPWC is a bit warm but no more than the UMC at 40A. I am 100% happy with this setup and love the fast charge speed.
Following advice on this thread I did buy two spare fuses (just in case since I only have HPWC or 110V). Also my unit was installed by a trusted electrician who spent some time making sure all connections were torqued properly, etc. and that the 100A breaker was firmly placed in the breaker box.
Maybe just good luck but I don't understand what Tesla is concerned about. Maybe there are differences in software in the HPWC that is the "early" version? Mine was received and installed on March 2nd.
Following advice on this thread I did buy two spare fuses (just in case since I only have HPWC or 110V). Also my unit was installed by a trusted electrician who spent some time making sure all connections were torqued properly, etc. and that the 100A breaker was firmly placed in the breaker box.
Maybe just good luck but I don't understand what Tesla is concerned about. Maybe there are differences in software in the HPWC that is the "early" version? Mine was received and installed on March 2nd.
Where would the loose connection potentially be? If it's inside the HPWC plug, I guess there's no point in calling my electrician, right? I need to have Tesla look at it? Or are you saying it could be a loose connection somewhere else? I can tell you that it's the plug that is burning hot, and the wire for about 6" behind the plug. The rest of the cable is fine.
Sounds like a bad crimp inside the plug. Tell Tesla and they should replace it.
Because the HPWC uses the J1772 protocol, the car cannot tell the difference between the two. So to protect HPWC owners, the limitation is applied. It'll be fixed when Tesla publishes fixes to HPWC's.
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If your handle that plugs into the car is getting extremely hot, you have a loose connection between the car and the Tesla connector (a/k/a "coupling means"). The electrician won't help you here, it's Tesla service.
Why would voltage matter? The car should still pull the same amount of current...
Anyway - heat buildup under continuous loads is why circuits are de-rated by 20%. But still, things really shouldn't be getting hot... Breakers can definitely heat up over time under load, but as long as it doesn't trip it should be OK. Still a good idea to make sure that the lugs on the breaker are secure (turn off the power first!).
It's not about current, it's about power (aka Watts). To get watts, you multiply current times voltage. So, 30A at 204V delivers 6120 watts. 30A at 240V delivers 7200 watts or 17.6% more power. A watt hour is 1 watt delivered for 1 hour. In a battery it is a measure of how much power the battery can store. This is a simplistic description but it get's the general idea across. The more power through a conductor, the higher the temperature.
Hey PhilBa,
You are close, but that's not quite it. It's the resistance drop across the conductor or connector that yields a voltage drop. It's that voltage that then is multiplied times the current to figure out the power being generated in that wire or connector. That means in this case the voltage drop is not affected by the initial voltage being either 204V or 240V, the drop through the connector and/or the wire is only going to be related to the current.
Peter
You are close, but that's not quite it. It's the resistance drop across the conductor or connector that yields a voltage drop. It's that voltage that then is multiplied times the current to figure out the power being generated in that wire or connector. That means in this case the voltage drop is not affected by the initial voltage being either 204V or 240V, the drop through the connector and/or the wire is only going to be related to the current.
Peter
True but I was answering the question why voltage matters. You see it all the time - people don't understand that it's power into the car and power is the product of V and I.
As to why the cord heats up, I seriously doubt that it's the voltage drop but rather an incomplete connection. Less conducting contact area means higher resistance and thus more dissipation. I'd bet the heat in the cord is from conduction.
As to why the cord heats up, I seriously doubt that it's the voltage drop but rather an incomplete connection. Less conducting contact area means higher resistance and thus more dissipation. I'd bet the heat in the cord is from conduction.
To the question before us - yes, my cord gets fairly warm. It is a design choice -- the HPWC uses #6 wire rated at 105 degC insulation, which can carry up to 85 amps. Thicker wire would be harder to handle and store. Unless it's too hot to touch and becomes a safety issue for a contact burn, you shouldn't have to worry about the electrical safety.
Heat dissipation across a resistor is measured as power, but the V in P=IV is the voltage *drop* across a resistor, not the potential offered. So it doesn't matter whether it's 240V or 250V or 208V. As a result, the heat dissipated by a conductor varies with the square of the current (combine P=IV and V=IR and you get P=I^2*R). So the heat dissipation in the cable is 78% more with 80A over 60A.
If this were a DC circuit, the 25 ft of #6 used in the HPWC would dissipate 128 watts (2 conductors * (80A^2) * .01 ohms). AC introduces some complexity because of the reactive load of the battery chargers and such. Let's just say 100 watts of heat -- that's not insignificant.
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As I mention above, the voltage supplied to the car does not matter here, because power dissipated is the voltage drop across a resistor, not the voltage supplied. A given length of wire will dissipate the same amount of heat by a current-controlled circuit, whether it's supplied at 5v, 50v, 500v, or 5 kV.
Heat dissipation across a resistor is measured as power, but the V in P=IV is the voltage *drop* across a resistor, not the potential offered. So it doesn't matter whether it's 240V or 250V or 208V. As a result, the heat dissipated by a conductor varies with the square of the current (combine P=IV and V=IR and you get P=I^2*R). So the heat dissipation in the cable is 78% more with 80A over 60A.
If this were a DC circuit, the 25 ft of #6 used in the HPWC would dissipate 128 watts (2 conductors * (80A^2) * .01 ohms). AC introduces some complexity because of the reactive load of the battery chargers and such. Let's just say 100 watts of heat -- that's not insignificant.
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As I mention above, the voltage supplied to the car does not matter here, because power dissipated is the voltage drop across a resistor, not the voltage supplied. A given length of wire will dissipate the same amount of heat by a current-controlled circuit, whether it's supplied at 5v, 50v, 500v, or 5 kV.
Yes, but he is getting heat at the breaker, along the conduit feeding the HPWC, and at the DC cord, and that should not be getting "hot" . Warm I understand.
I believe he should check the wiring and make sure that he has #3 minimum to feed the HPWC at full power with a 100 amp breaker, as the conduit should not be generating heat.
I still don't see how that's relevant to the issue at hand unless you are measuring the difference in voltage/current at the car and the voltage at your main service breaker and thus measuring the amount of power being disappated between the car and main service breaker.
I seriously doubt that resistive dissipation in the cable is the culprit here.
I work with electronics a lot and frequently hear people say HOT when they mean WARM. The key question - what is the temperature. People will feel 120F and call that hot when it is likely to be within spec. Heat will conduct pretty far in heavy wires like #6 or larger so it's best to understand where it's coming from. I doubt the breaker itself is the cause.
I still think incomplete connection is the most likely culprit. Either not enough contact area or improperly torqued bolt. Though, if the cord is coiled up tightly, that could be a reason as well.
I work with electronics a lot and frequently hear people say HOT when they mean WARM. The key question - what is the temperature. People will feel 120F and call that hot when it is likely to be within spec. Heat will conduct pretty far in heavy wires like #6 or larger so it's best to understand where it's coming from. I doubt the breaker itself is the cause.
I still think incomplete connection is the most likely culprit. Either not enough contact area or improperly torqued bolt. Though, if the cord is coiled up tightly, that could be a reason as well.
Al Sherman
It's about THIS car.
Sorry guys. I must have lost track.
Where do we stand now on 80 amp charging? I have the latest version of 4.5. Am I still limited to 60amps? If not, can I charge at 80 without getting new fuses? I would prefer not to blow the HPWC fuses. Was it strictly a firmware fix, or do I need the new fuses also?
Where do we stand now on 80 amp charging? I have the latest version of 4.5. Am I still limited to 60amps? If not, can I charge at 80 without getting new fuses? I would prefer not to blow the HPWC fuses. Was it strictly a firmware fix, or do I need the new fuses also?
FW4.5 here, i charged at 80A for a while and it was fine.
THEN I charged at 80A on a really hot day, and after a while,everything **** the bed. Tesla replaced the fuses with the OLDER style - new ones not yet available.
In short; Don't charge at 80A unless you have the new style HPWC or fuses.
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