Charging from 14-50 at 50A?

[bluetinc]

Hi all,

I'm working on some trip planning and I'm curious about squeezing a little more out of charging at a 14-50 outlet. From what I have read, as long as you are charging for under 3 hours, the NEC doesn't consider you a continuous load, and drawing up to 100% of the breaker rating is permissible (vs. an 80% limit of rating for continuous loads). This seems to imply that I could bump my charging rate up from 40A to 50A at RV parks etc. if I am just stopping in for a couple hour charge.

So, code books aside, I wanted to find out if others have done or do this and how well it has worked?

Thanks!

Peter

 

[donauker]

Hi all,

I'm working on some trip planning and I'm curious about squeezing a little more out of charging at a 14-50 outlet. From what I have read, as long as you are charging for under 3 hours, the NEC doesn't consider you a continuous load, and drawing up to 100% of the breaker rating is permissible (vs. an 80% limit of rating for continuous loads). This seems to imply that I could bump my charging rate up from 40A to 50A at RV parks etc. if I am just stopping in for a couple hour charge.

So, code books aside, I wanted to find out if others have done or do this and how well it has worked?

Thanks!

Peter

I have successfully pushed new breakers to 100% without a problem, but many campground breakers are weathered and also worn from being used as switches. I have had several campground 50 amp breakers that tripped occasionally at 40 amps and there was even one that wouldn't reliably handle 32 amps.

 

[doug]

Probably not that big of a deal if you're there to watch it or are using something like OVMS/Tattler to alert you if the breaker trips.

What charge connector are you using? Are you able to hack the pilot signal?

 

[bluetinc]

Doug,

Unfortunately this is all in my mind so far.. I'm planning on picking up my S in October out on the west coast, and doing a fun road trip back home (MD) (read 4500 miles). I've been refining my trip plan, and time needed to charge each day (especially for the mid day charges) and I'm trying to figure out if pulling the full 50A is realistic to include in my plan.

Peter

 

[doug]

Oh? I thought you were talking about the Roadster since this thread is in the Roadster forum. If you're talking about using the Model S, you are unlikely to be able to get more than 40A from UMC that comes with your Model S. Also I don't think you'll be able to convince the Model S to ignore the pilot signal and pull 50A instead of 40A.

You'd need a custom NEMA 14-50 EVSE where you can manually set the pilot signal. You can probably buy or make one that goes 14-50 to J1772, and then use the J1772 adapter that Tesla has promised to provide.

 

[Doug_G]

NEC says "continuous" is > 3 hours? I don't really understand that. I'm sure the temperature of the components after 100 hours will be no different than after 3 hours.

 

[bluetinc]

Doug,

I figured that any real world experiences with this would only be over here with Roadster owners, and all I would get in the S forum would be guesses.

I'll have to look into the max on the UMC for the S, and overriding the Pilot signal. As you suggest going through the J1772 adapter may be necessary. I guess the other option would be to kludge an adapter that goes from 14-50 to the HPWC, and then to the S...

I thought that somewhere along the way, but quite some time ago, I had seen a screen in the Roadster (or maybe an S prototype) that allowed someone to override the default current limits when charging. Perhaps I didn't understand quite what I was seeing?

Doug_G, I don't know why they chose 3 rather than 1 or two...

Peter

 

[donauker]

Peter,

You can only override the pilot signal with a lower value. You would need a charge connector that provided a higher current pilot signal such as a DIY unit or a HPWC with a 14-50 plug.

Don

 

[vfx]

Another "Can I make it"? topic. Maybe it needs a section?

 

[TEG]

Along with worn breakers, I have heard that many NEMA14-50s at campgrounds have physically worn sockets that can overheat just due to marginal connection between the plug and socket. So, campgrounds are probably one of the worst places to try pushing max current through the connector. Are you going to sit and watch it the whole time to make sure nothing melts or catches fire? Some (but not all) EVSEs include temp sensors in the 14-50 plug to detect high temps and reduce the level if that happens.


Slightly related:
Why Did My R.V. Adapter Plug Melt? My 125V 30A to 125V 15A got very hot. : Electrical Online
Milbank RV 50amp receptacles melting

 

[bluetinc]

TEG,

Worn sockets are a good thing to keep in mind. Hmmm sitting and watching it the whole time, I don't think I'll sign up for that. I'll probably check what the unloaded voltage is at the receptacle, check it again under load to verify that I'm not seeing undo losses under load (from poor wiring or from worn contacts), and maybe I'll check the receptacle for a temperature rise over the first few minutes. Adding a thermal cutout on an adapter is a very good idea, I'll keep that in mind if I make my own adapter.

Donauker, what type of setup did you use to push that draw up to 100%?


Peter

 

[TEG]

...Adding a thermal cutout on an adapter is a very good idea, I'll keep that in mind if I make my own adapter...

See this:
http://www.teslamotorsclub.com/attachment.php?attachmentid=468&d=1257844780

...
Each Plug Adapter, except the 120V Plug Adapter, also contains a thermal switch that shorts
this signal out when hot, to indicate a fault. The thermal switch is glued with epoxy to the inside
of the plastic plug housing.
...
During charging, the Charger monitors the temperature sensor in its Plug Adapter, and
stops generating a square wave if the Plug Adapter is too hot. (The Plug Adapter and the
receptacle will overheat if the receptacle is dirty, damaged, or worn out – not entirely
uncommon for receptacles in public locations.) In this state, the Charger blinks all its
lights quickly. It will continue to do so until the Plug Adapter cools off and the Charger is
reset (by unplugging the Charger from the receptacle, and then plugging it in again)...
...
;*********************************************************************************
;* 40-amp charging loop *
;* *
;* Test for 40-amp charging and temperature okay. *
;* Create 1 KHz Control Pilot (CP) signal if so. *
;* High Time: nominally 667 uSec, and between 660 uSec and 795 uSec *
;* Frequency: nominally 1000 Hz, between 995 Hz and 1005 Hz *
;* 40-amp charging is indicated by a diode from the DIODE line to ground, such *
;* that the DIODE line cannot go higher than 0.7V, but can go to -12V. *
;* *
;* Hot will be indicated by NEG_DIODE becoming 1 while DIODE = 0. *
...

 

[bluetinc]

TEG,

Thanks for the great document link. It has some great tidbits in there and it has all the info I need to spin a quick design of my own if it turns out I need to, which it seems I may.

Peter

 

[doug]

I think these days you can get a low cost pilot signal generator.

 

[hcsharp]

I have a DIY UMC that allows me to manually set the current. I tested 48A on a brand new 50A breaker and the breaker got warm but never hot. I also tested 60A on a 60A breaker with the same result but it got a little warmer. In both cases I stayed near the car and the breaker to monitor everything for safety since I was so close to the limits. The 14-50 plugs also warmed up a bit but not like the breaker. In both cases the breakers reached their terminal temperature within about 30-40 minutes so I'm curious how they came up with 3hrs in the NEC. Also Scott451 used to charge his car at 48A most of the time from a NEMA 14-50.

BTW, what section of the NEC is that in?

Check out the OpenEVSE project for a circuit that you could easily modify with push-buttons to manually set the charge current.

 

[TEG]

BTW, what section of the NEC is that in?

http://www.wsdot.wa.gov/NR/rdonlyres/B2644606-5850-40DC-B9C1-4B97453D56A1/0/ServiceCabinetandTransformerBreakerSizing1082004.pdf

...Continuous Load –A load where the maximum current is expected to continue for 3 hours or more.( NEC 2002 -Article 100 )...

 

[TEG]

http://www.sea.siemens.com/us/SiteCollectionDocuments/LVTB-RCIRB-0711(lo-res).pdf

...The 80 percent reference is derived from the NEC’s required load calculation in Section 210.20(A) which states in part:
“Where a branch circuit supplies continuous loads or any combination of continuous and non-continuous loads, the rating of the overcurrent device shall not be less than the non-continuous load plus 125 percent of the continuous load...

...The 80 percent is simply the inverse of the 125 percent of continuous load requirement and is a common “derating” factor. Sizing circuit breakers based on an 80 percent “derating” assumes that all the connected design loads are continuous...

...It is up to the engineer to calculate the design loading of the overcurrent device based on the profile of its load, which is often a combination of continuous and noncontinuous loads. It is also up to the engineer to carefully determine which loads are continuous and account for the 25 percent margin required.
Continuous load, as defined in NEC article 100, is “a load where the maximum current is expected to continue for 3 hours or more”...

 

[donauker]

TEG,

Worn sockets are a good thing to keep in mind. Hmmm sitting and watching it the whole time, I don't think I'll sign up for that. I'll probably check what the unloaded voltage is at the receptacle, check it again under load to verify that I'm not seeing undo losses under load (from poor wiring or from worn contacts), and maybe I'll check the receptacle for a temperature rise over the first few minutes. Adding a thermal cutout on an adapter is a very good idea, I'll keep that in mind if I make my own adapter.

Donauker, what type of setup did you use to push that draw up to 100%?


Peter

I definitely agree with TEG that you need to watch for worn sockets!

I have in the past used a HPC with a 14-50 plug to charge at 48 amps on a 50 amp circuit, this was only done while personally monitoring the charge.

More recently using my RFMC which is limited to 40 amps in combination with the Tesla Tattler to set the car charge rate to any value up to this limit, I have pushed 30 and 40 amp circuits up to their respective limits. This unit does have thermal fuses in the plug to automatically stop the charge if the plug were to over heat from a worn socket. Although I have run into worn breakers that would not even handle the normal 80% load, I have not yet had a socket that caused an over temp problem.