Suitability of NEMA 14-50 for EV charging -- Child Safety & Thermal Cutoff

[wwhitney]

I was referring more to what carl said in post #19. These are certainly switching power supplies and not a simple rectifier that "chops off" half the wave so their Waveform will be complex.

But what is the relevance of the shape of the current waveform over one 60 Hz cycle of 16.7 ms?

Cheers, Wayne

 

[retirede]

But what is the relevance of the shape of the current waveform over one 60 Hz cycle of 16.7 ms?

Cheers, Wayne

IMO, not at all relevant to the subject at hand….installation of a safe branch circuit for an EVSE.

 

[electrofelon]

But what is the relevance of the shape of the current waveform over one 60 Hz cycle of 16.7 ms?

Cheers, Wayne

Post #15 claimed that these high frequency changes were hard on connections. I am skeptical, but I would like to see the scope of a typical charger to see what type of aberrations in the waveform we are even talking about.

 

[jaggedben]

A graph does not show the cyclic current. You will need a scope read out. I have included a link to an example I found on the web which is similar to what I have seen in the past.. I am working as a volunteer with the DOE on electrical charging infrastructure. I will see if they have an up-to-date read out.

https://imgur.com/a/L86amR9

What is the scale or units of the x axis in this graph?

 

[wwhitney]

Post #15 claimed that these high frequency changes

Interesting that you understood that when post #15 uses the word "cyclic" they mean high frequency cyclic (as demonstrated in post #19). That was not at all clear to me and would not be what I consider the common usage of that term to mean.

Cheers, Wayne

 

[wwhitney]

What is the scale or units of the x axis in this graph?

Evidently seconds. The entire graph is just one second.

If the scale were larger like minutes (but who gives minutes to 3 decimal places?) or hours, it would be a straight line.

Cheers, Wayne

 

[Carl_in_AZ]

I was referring more to what carl said in post #19. These are certainly switching power supplies and not a simple rectifier that "chops off" half the wave so their Waveform will be complex.

In the Phoenix Valley, a couple of AHJs are investigating the issues with electric dryer receptacle failures on EV chargers. It is not the amperage but the type of load. This was a similar issue I ran into in the early 80s working for Square D in upstate New York. Some of the non-hard wired-style EV chargers for their forklift trucks and parts mover at Kodak and RPD were powered off the OEM-non-approved supplied load centers. These breakers would trip even though the current was lower than its rating. Some of the breakers recorded over 160F. At first, they thought it was a bolt-on versus plug-in versus plug-on breaker issue. They replaced the OEMS load centers with Plug-on breakers in new panelboards, not load centers. Then the issue disappeared because there was spacing between adjoining breakers.. Kodak's standard was to use Bolt-on breakers only but OEMs supplied load centers that do not offer bolt-on breakers. They discovered they had more issues with not tightening the bolt-on breaker's screw down properly so they allowed plug-on only for cyclic loads in panelboards, switchgear, and busway taps. They would no longer allow load centers or plug-in breakers anywhere. Most of today's plug-in breakers have more contact surface area and better grip on the bus. Mobil Chemical (Foam) also ran into the same issue back then on occurrences in their Covington and Canandaigua facilities.

 

[electrofelon]

Interesting that you understood that when post #15 uses the word "cyclic" they mean high frequency cyclic (as demonstrated in post #19). That was not at all clear to me and would not be what I consider the common usage of that term to mean.

Cheers, Wayne

Well I read between the lines. I'm not sure "cyclic" is the correct word. I consider something like a dryer that cycles on and off to be "cyclic". I guess it's just my somewhat basic knowledge of switching power supplies in that you're not going to have a purely smooth sine wave, but also it's not just a simple rectifier that's just going to chop off half of the wave. I would assume these things are all power factor corrected and use inductors and capacitors etc to have a fairly smooth sinusoidal current waveform, but I don't know how smooth, hence I questioned wanting to see a scope of one.

 

[jaggedben]

I don't buy that a deformed 60hz waveform or low power factor needs a differently rated receptacle or breaker. RMS current is RMS current.

 

[jaggedben]

Evidently seconds. The entire graph is just one second.

If the scale were larger like minutes (but who gives minutes to 3 decimal places?) or hours, it would be a straight line.

Cheers, Wayne

Sorry, I meant the y axis. Oops.
I'm not at all sure what that graph is purporting to show.

 

[LarryFine]

RMS current is RMS current.

The high-frequency peaks may be much higher than sine-wave peaks.

 

[zbang]

How does that affect the actual heat produced? (I can't see that it does, that's why we use RMS values.)


BTW, last I'd heard the difference between a "load center" and a "panelboard" is how they're spelled. One could argue that "load centers" are cheaper but as far as the code is concerned they're panels all the same.

 

[brycenesbitt]

Does anyone have a graph of what the current
for a typical car charger looks like ?

Here's the view of two cars charging, with a current limit.
The bouncing around here is due to the current limit.
If it was just left you'd see charging start fast, then taper off as the battery gets full.

 

[brycenesbitt]

A car's on-board charger will generally have a maximum current of 27.5A, 30A, 32A, 40A, or 48A (other values are possible). Cheers, Wayne

I've seen some cars have step functions. But only the limit from the EVSE has a step function:
the car is free to ramp up or down charging rate in a smooth way (as when the battery starts to get full).

 

[brycenesbitt]

A graph does not show the cyclic current. You will need a scope read out.

Is all that switching noise why EVSEs and GFCI circuits don't get along?

 

[electrofelon]

Here's the view of two cars charging, with a current limit.
The bouncing around here is due to the current limit.
If it was just left you'd see charging start fast, then taper off as the battery gets full.

View attachment 2569975

Thanks. I was thinking on a smaller timescale though, like if that whole thing was one cycle.

 

[electrofelon]

Is all that switching noise why EVSEs and GFCI circuits don't get along?

Is it common for EVSE's to trip GFCI's? I don't recall hearing about that being an issue.

 

[brycenesbitt]

Is it common for EVSE's to trip GFCI's? I don't recall hearing about that being an issue.

Yep. And at the worst times of course (Murphy's Law -- or at least for the retelling).

 

[tortuga]

The problem with these melted outlets is they need to be treated like a proper fire incident and undergo a forensic investigation and they are not.
The photos from the reddit post do show a 6-50, that allegedly had a 30A EVSE.
It appeared to be #8 wire at best, probably copper NM we dont know the wire size or type for sure.

Besides the wire I would want to inspect the actual electric vehicle(s) that were using the charger and verify they obey the SAE control pilot ( 1khz sync) signal sent from the EVSE to the cars onboard charger. Also check if the EVSE is sending the correct sync signal.
I'd also look at any data stored in the cars charger and the EVSE and verify the charge time and amp draw are within spec.

I dont think a EVSE provides any supplementary overload protection, so the sync signal is its only overload protection.
If an EVSE is programed with a 30 amp sync signal and the car ignores the signal due to malfunction and pulls 48A instead of 30A, the residential 40A inverse time circuit breaker will never trip at 48A.

Sparkies and car owners can speculate all day long on what is causing an electrical incident, but without some science, proper investigation and good evidence (which the manufacturers and the insurance of this stuff will have to pony up for) you'll never know the real cause and the CMP/NHTSA wont budge.

 

[jaggedben]

... ....
If an EVSE is programed with a 30 amp sync signal and the car ignores the signal due to malfunction and pulls 48A instead of 30A, the residential 40A inverse time circuit breaker will never trip at 48A.
.....

I think it will trip, but likely not before the receptacle is damaged. Especially if the user resets the breaker and repeats the process.