Testing 48A Charging on 40A Circuit

[mongo]

I have wondered about pulsing a charger. Just a totally random scenario, 40 amps for 1 minute, 50 amps for 30 seconds, repeat. 30 seconds is a lot shorter than 3 hours.....

I know it seems stupid to ponder, but I can imagine a scenario in the future when EV's make up over 50% of cars and renewables can generate over 100% of demand. If you''re looking at millions of cars charging just 5% faster, when the sun is blazing or the wind is blowing, it could real money and/or kWh being saved and/or not wasted.

Power into battery is linear with current, power into heat via wire resistance is quadratic with current, so the most efficient charge method is the highest safe steady state current level.
Example: If you boost the charge current 10%, the heat generated is 21% higher. To average to the same temperature (using thermal mass of wire/ specific heat ignoring increase heat transfer due to higher delta T), you have to produce 79% of the heat for an equivalent time, that means a reduction in charge rate to 89% (square root of 0.79). (0.89+1.1) / 2 = 1.10*0.79 = 99.4% effective charge rate compared to nominal.

 

[ewoodrick]

I'd just recommend going ahead and calling the fire department.
You seem to not be understanding what everyone is saying. The rating of circuits isn't based on the breaker flips, it's based upon when the wiring gets hot. But ignoring the rules, you are really attempting to create a fire. And it's not just the wire, it's the connection, the outlet, anda bunch of other little things that can create hotspots. A common situation of house fire is a perfectly specified circuit, but the plug may be old or the plug not in all the way, which ends up putting too much current through too little contact.

It will be way too easy for you to determine that 48A is safe, because it didn't trip the breaker and it didn't burn the house down.
What 2-3 years and in the middles of the night when you are asleep, maybe above the garage, one of the wires becomes too loose, because the heating cycles that you have made it go through has loosened the screw, it arcs for many minutes before it gets to something flammable and, the rest will be history.

If you want to play with this, do it in a safe, controlled environment, don't. do it in your house.

This is why you see so many people say not to do this yourself, even if you can do it. Remember, welders don't use this much current!!!

 

[mongo]

I'd just recommend going ahead and calling the fire department.
You seem to not be understanding what everyone is saying. The rating of circuits isn't based on the breaker flips, it's based upon when the wiring gets hot. But ignoring the rules, you are really attempting to create a fire. And it's not just the wire, it's the connection, the outlet, anda bunch of other little things that can create hotspots. A common situation of house fire is a perfectly specified circuit, but the plug may be old or the plug not in all the way, which ends up putting too much current through too little contact.

It will be way too easy for you to determine that 48A is safe, because it didn't trip the breaker and it didn't burn the house down.
What 2-3 years and in the middles of the night when you are asleep, maybe above the garage, one of the wires becomes too loose, because the heating cycles that you have made it go through has loosened the screw, it arcs for many minutes before it gets to something flammable and, the rest will be history.

If you want to play with this, do it in a safe, controlled environment, don't. do it in your house.

This is why you see so many people say not to do this yourself, even if you can do it. Remember, welders don't use this much current!!!

It was 48A on a 50 Amp circuit. The 40A in the title is due to OP's conflating continuous load rating with intermittent load rating.

 

[gavine]

It was 48A on a 50 Amp circuit. The 40A in the title is due to OP's conflating continuous load rating with intermittent load rating.

Correct. Breaker is 50A. And I’d like to reiterate that I don’t plan on charging at 48A ever again. It was a controlled test out of curiosity and not to see if I can do it when I charge for real. I was present the entire time and the breaker is in the garage.

Aren’t breakers designed to protect against overloading a circuit? We all know that our houses have several outlets on each breaker and you can easily overload a circuit by using too many outlets on the same breaker and that’s supposed to trip the breaker. That’s kind of what I was testing, only I was overloading (slightly) a circuit connected to an HPWC.

I didn’t expect this much flaming and I’m sorry if what I was doing wasn’t presented properly.

 

[Dr. J]

It was 48A on a 50 Amp circuit. The 40A in the title is due to OP's conflating continuous load rating with intermittent load rating.

But he is continuously loading 48A, correct? 8A more than recommended, right? Right?

 

[mongo]

But he is continuously loading 48A, correct? 8A more than recommended, right? Right?

Continuous (expected >3 hours) loads are multiplied by 125% for circuit loading calculations. This is a 50Amp circuit, so max continuous load is 40A. There is no problem loading this circuit to 50 Amps for 2 hours.

 

[mswlogo]

You started this test (which I don't have a problem with), but you left, are you nuts ?

 

[Dr. J]

You started this test (which I don't have a problem with), but you left, are you nuts ?

No, I think he hung around for a while, ended the test, then left. Each time.

 

[mongo]

Correct. Breaker is 50A. And I’d like to reiterate that I don’t plan on charging at 48A ever again. It was a controlled test out of curiosity and not to see if I can do it when I charge for real. I was present the entire time and the breaker is in the garage.

Aren’t breakers designed to protect against overloading a circuit? We all know that our houses have several outlets on each breaker and you can easily overload a circuit by using too many outlets on the same breaker and that’s supposed to trip the breaker. That’s kind of what I was testing, only I was overloading (slightly) a circuit connected to an HPWC.

I didn’t expect this much flaming and I’m sorry if what I was doing wasn’t presented properly.

You were fine, the problem is your title makes it seems like to were testing 48A on a 40A max circuit, not the 50A one you have. You could report your first post and request a title change to 50A circuit.

50 Amp breaker with 6 gauge copper can do 50A intermittent (less than 3 hours) or 40 A (x125% = 50) continuous. Breaker would protect the copper from overload, but 48A is not an overload and, being winter, the breaker will not trip at that level, nor will the wiring overheat.

 

[mswlogo]

No, I think he hung around for a while, ended the test, then left. Each time.

I guess I misread it. Thanks for the correction.

 

[Dr. J]

Correct. Breaker is 50A. And I’d like to reiterate that I don’t plan on charging at 48A ever again.

Like. But only that part.

 

[Dr. J]

I guess I misread it. Thanks for the correction.

I'm reading between the lines. He didn't specify, so I think you read it correctly.

 

[mongo]

I'm reading between the lines. He didn't specify, so I think you read it correctly.

@mswlogo
While not explicitly called out, leaving terminated the test, so either they set the charge lower, stopped the charge, or left in the car they were charging.

Both times, I had to leave before it tripped the breaker.

 

[mswlogo]

@mswlogo
While not explicitly called out, leaving terminated the test, so either they set the charge lower, stopped the charge, or left in the car they were charging.

Understood. My bad.

 

[gavine]

@mswlogo
While not explicitly called out, leaving terminated the test, so either they set the charge lower, stopped the charge, or left in the car they were charging.

Sorry. Yes, when I said I left, it was with the car which is why I terminated the tests early. I didn’t leave the house and continue the charging test.

I learned much more from this thread than I did from the actual test.

 

[gavine]

This video is appropriate for this thread -->

How a circuit breaker works in slow motion.

 

[nwdiver]

48A is not going to quickly trip a 50A breaker. It's below the breaker's rating.

Not quickly but it will probably trip after a few hours.

 

[mswlogo]

Not quickly but it will probably trip after a few hours.

It may or may not. I accidently set my wall connector wrong and had it set to pull 40A on a 40amp breaker.
It ran for hours fine. Breaker was warm.

 

[mongo]

Not quickly but it will probably trip after a few hours.

If it tripped with an ambient temp of less than 40C, that breaker would be failing CSA/ UL requirements.

 

[nwdiver]

If it tripped with an ambient temp of less than 40C, that breaker would be failing CSA/ UL requirements.

Hmmm... lots of failed breakers out there then. I've never met a breaker that could take >80% of its rating continuously overnight without tripping by morning.