Charging on 30A RV Outlet Question

[4tangledkites]

Last weekend I went camping. Purchased a good adapter (14-50 to TT30 rated for EVs) so I would take advantage of the 30A outlet. Charged the first night no issue. Charged some during the day no issue. Second night the breaker tripped at some point. Reset and charged again in the morning.

Yesterday it occurred to me, I never reduced the amperage limit in the truck like I should have. So was the R1T/mobile charger trying to pull 32A? And why didn't that blow the breaker sooner? Or did the mobile charger know I was only on 110V so all was good?

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[mikehmb]

A friend of mine had a 6-50 in his garage and was pulling >30 amps from it forever until it one day gave up.

Sometimes you just get lucky*.

* Luck is defined here as not burning your house down when the breaker hasn’t tripped as it should have.

 

[Cosmacelf]

Correct, you were probably drawing 32A. You should have dialed it down to 24A. Breakers aren’t digital devices, they usually trip based on heat build up. People are used to them tripping based on shorts, and in those cases, they trip right away, but for slightly above rated current, they can run for quite a while.

 

[Dark-Fx]

30A breaker might never trip at 32A continuous. It's within the normal operating specification of a lot of breakers. Of course you really don't want to do this because you are tempting fate with all of the wiring and adapters, and you're putting a lot of faith that the RV pedestal and system was wired well enough to support the overload.

 

[Zoidz]

A few unknowns here, but some (all?) EVSEs are "smart" and detect whether they are connected to 120v or 240v. I know for a fact that OpenEVSE does this.

Best practice would be to set the charge rate to 24A. It's entirely possible that it was trying to charge at 32A. It could have been something as subtle as higher ambient temperature differences that caused it to trip that one evening.

It's a common misperception that a breaker will trip at its rated current. They don't. Depending on many factors, they generally trip above their rated current. A 30A breaker might or might not trip at 32A or 35A, could take an hour to trip at 40A, etc. It depends on design, manufacturing tolerances, installation location, ambient temperature, etc. This is one reason that THxx type wire with higher temperature rating is preferable over "Romex" type wire. Less chance of insulation melting if a breaker does not trip.

 

[Dark-Fx]

A few unknowns here, but some (all?) EVSEs are "smart" and detect whether they are connected to 120v or 240v. I know for a fact that OpenEVSE does this

I know for a fact that if I tell my OpenEVSE it's a Level 2 charger, it doesn't matter what the input voltage actually is and it will still advertise whatever I have it set to current wise.

 

[brancky3]

A friend of mine had a 6-50 in his garage and was pulling >30 amps from it forever until it one day gave up.

Sometimes you just get lucky*.

* Luck is defined here as not burning your house down when the breaker hasn’t tripped as it should have.

Isn't 6-50 rated to 50 amps? Less than 40 should never have an issue.

 

[4tangledkites]

Thanks for the replies...learn something new everyday. I'll need to add a tag to the adapter so next time I don't forget to set the 24A limit in the truck!

 

[Zoidz]

I know for a fact that if I tell my OpenEVSE it's a Level 2 charger, it doesn't matter what the input voltage actually is and it will still advertise whatever I have it set to current wise.

My comment is based on this support article which implies that they detect voltage presence on L1 and L2 so that they can calculate power.

"OpenEVSE hardware does not currently measure voltage. The voltage used in energy calculations is assumed to be 120v for L1 and 240 for L2. This value can be changed with a RAPI command or updated real-time with a external source via MQTT."

 

[Dark-Fx]

My comment is based on this support article which implies that they detect voltage presence on L1 and L2 so that they can calculate power.

"OpenEVSE hardware does not currently measure voltage. The voltage used in energy calculations is assumed to be 120v for L1 and 240 for L2. This value can be changed with a RAPI command or updated real-time with a external source via MQTT."

I believe the energy estimation on my unit is essentially double what it should be with it configured this way. I haven't made any change to the voltage it uses for the calculation (and I wasn't even aware it could be changed, so thanks for pointing that out)

 

[mikehmb]

Isn't 6-50 rated to 50 amps? Less than 40 should never have an issue.

You’re correct - I’m not sure which plug he was using, but it was only rated at 30amp. 6-50 is definitely a 6-style 50a plug. I’m guessing it was a 6-30? Have to ask.

 

[Zoidz]

A friend of mine had a 6-50 in his garage and was pulling >30 amps from it forever until it one day gave up.

Sometimes you just get lucky*.

* Luck is defined here as not burning your house down when the breaker hasn’t tripped as it should have.

We obviously don't know what brand the 6-50 was, but this is an example of the reason for using Hubbell industrial quality receptacles over Amazon cheap stuff. The thought might be "Cheap stuff works fine for my dryer/appliance/welder/etc" but they are not drawing even close to rated current for many hours a day, every day or every few days like an EVSE.

 

[Cosmacelf]

Thanks for the replies...learn something new everyday. I'll need to add a tag to the adapter so next time I don't forget to set the 24A limit in the truck!

Yes indeed! I always tell people to tag their homemade adapters with maximum charge rates.

 

[Electrified Outdoors]

If you know the manufacturer of the breaker you can look up the trip curve charts. But yes a couple amps over may be able to go for a while without tripping. It should trip right away though if your over by 10 or 20 amps.

 

[Gateman]

maybe stating the obvious here. Many campsites have 50 amp service for the larger trailers. They cost more. Why not rent those spaces. That way you can fully charge in one night.

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