Sudden HPWC problems: Does it "do" anything at the end of a charge cycle?

[MiddKid]

First, some background...Installed a HPWC last March when I took delivery of my MS. My house is newer construction with 200A service and most of our major appliances are gas. Our local utility does not have off-peak pricing. Due to all this, since the day we got the car we plug it in upon returning home and it charges at 80A. Zero problems. Even on a hot summer day with the AC running.

Fast forward 10 months to a few weeks ago.

January 27th I'm on treadmill, TV on, wife was working on a project in the kitchen, Model S charging...power goes off. I go out and our main breaker tripped. Important detail...the main whole-house breaker tripped...not the dedicated 100A breaker that the HPWC is on. It took about 4 minutes of flipping it on and off before it would turn back on. I guess it had to "cool" down. I figured that maybe we finally hit the 200A max (although in my head it made no sense) so I set the car to charge at 1am. All is good for the next week.

1:37am on February 2...power goes off. Obviously everyone was sleeping and the only thing that "on" was the Tesla. I realize at 2am and flip the main circuit back on at 2:10am. Main circuit tripped again at 3:05am. At this point I went into the Model S and changed it to charge at 60A. Works fine for a few days...

February 5...main circuit trips again. Same thing...takes 5 minutes or so for the main circuit to reset. Electrician scheduled to come out February 13. I set the car to charge at 40A. Charges fine for a few days...

Last night at 11:40pm...main circuit trips again this time with the car at 40A. ARG.

So...it can't be an overload problem since it has charged fine for 10 months at 80A and now it's tripping even at 40A. My theory is that the main breaker has "gone bad" but my electrician who is coming out on Friday is skeptical..."it's possible for a main breaker to go bad, but rare."

OK, here's the reason for the title of this post. In most of the scenarios above it tripped with less than 10 minutes of charging left. Last night it had 6 minutes of charging left. I'm assuming it's more about the heat/power build up over time (or something) and it trips at the end of the charge, but just wanted to make sure the unit itself doesn't actually "do" anything toward the end of charging that would cause this problem. I'm looking for help as obviously my electrician doesn't have years of HPWC experience!

Thanks for any thoughts!

 

[JackA]

Are you charging to 80% or "Range Charge?" It is my understanding that the last 20% of the charge is slower because it is somewhat like stuffing a sleeping bag into it's carrier. At first it is easy then as more bag is in the carrier it takes more effort to push the remainder in. I would recommend that you quiz the electrician on why the Main breaker is reacting before the 100A breaker. As you point out it could be the Main is defective. The HPWC is really just a connector between utility power and the car. The car does all the AC to DC inverting and has the charging logic. The HPWC also has two fuses in it that protect it, so while I am not an electrician it seems logical to me that if two circuit specific protective devices did not detect a problem on the 100A circuit the Main is the problem. Be sure to let us know the resolution.

 

[Lloyd]

Once a main breaker trips, it may not trip at the rated amout on subsequent trips. Replace the main breaker and you will be ok. IMO. Check torque of main lugs, and signs of heat there.

 

[MiddKid]

Thanks guys. I'm charging to 80%. The point about the first two protective devices not detecting the problem does seem to indicate our problem is the main breaker.

I'm hoping I can make it till Friday! I'll keep everyone posted.

 

[AmpedRealtor]

Sometimes it could be as simple as the breaker being a little loose or the screws not being tightened fully. My grid-tie solar array kept going down for a couple of weeks intermittently. No rhyme or reason. The solar guys came out and said it was a loose breaker. They tightened it up and everything has been fine.

 

[tom66]

I have seen this occur before. Was the breaker for that specific circuit. In your case, it's the main breaker.

These breakers are usually thermal devices. If they interrupt 100+A of current, the contacts can pit very easily which will cause them to heat up faster for any given current level. And they are not rated for many interrupt cycles before they are considered bad, especially not at 50% load.

 

[FlasherZ]

I concur it's likely to be a malfunctioning breaker (not unheard of), or loose lugs on the breaker that generate the heat required to trip the breaker.

Lugs on the main breaker are always live, so you must wear PPE or pull the meter to check/tighten them or replace the breaker. You should call an electrician to do so if you're not qualified.