Titanium48
Posts: 148
Joined: Thu Jan 31, 2019 7:33 am
Delivery Date: 25 Jan 2019
Location: Edmonton, AB

Boost mode for EVSE?

Wed Nov 20, 2019 2:19 pm

Since an EVSE is considered a continuous load, electrical code compliance limits it to 80% of the nominal rating of the branch circuit it is connected to. The definition of "continuous" appears to be three hours or more, so it should be acceptable to build an EVSE that will feed the car 100% of the nominal branch circuit rating if it automatically shuts down after three hours. An EVSE with such a "boost mode" could be useful for EV owners whose charging capabilities are limited by wiring that is cost-prohibitive to upgrade. For example, an EVSE for a 20 A circuit could have a normal mode where it would limit current to 16 A, and a boost mode where it would supply 20 A but automatically shut down after 3 hours. Normal mode would be used for usual overnight charging, while boost mode would be useful to get as much charge as possible in a short time, such as if you want to go out in the evening after the drive home from work has drained the battery.
Has this ever been implemented?
2016 SL

jjeff
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Leaf Number: 422121
Location: MSP MN

Re: Boost mode for EVSE?

Wed Nov 20, 2019 4:14 pm

They don't make a EVSE with such a mode nor do I see they ever will but I do it all the time. My EVSE has a 20a and 30a setting and when I need to I use the 20a setting(actually pulls 19a which is good) and of course 30a is limited to 27.5a by the Leaf.
Note while you can generally pull full load amps for a short period of time after about a half-hour things will get very warm, things like the breaker(you can actually feel it) and even the blades of the plug, I'm sure the socket is very warm also but you can't really feel that. You also need to know your outlets and wiring are up to snuff, a weak or old outlet and things could go from very warm to HOT which is NOT good. You can't really feel things like wiring, especially behind the wall but you might be able to feel it near the breaker panel, warm is OK but NOT HOT.
If you want to play around with maxing your circuit I'd suggest an EVSE like Juicebox that lets you set the current draw down to the amp, start at 80% and gradually start increasing your draw by an amp, then keep a close on eye on things by feeling the plug and wiring if you can, also feel the breaker. Again warm is ok but not hot. Once you find a good max setting you'll have to manually stop charging, automating it would be rather complicated and again your not going to find an EVSE that does it automatically.
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henrydehoja
Posts: 91
Joined: Sun Sep 16, 2018 6:40 pm
Delivery Date: 12 Sep 2018
Leaf Number: 317129
Location: Metro Boston, MA

Re: Boost mode for EVSE?

Wed Nov 20, 2019 5:04 pm

In my experience, I have seen a 20A breaker trip within seconds of running around 18A equipment load connected to its circuit. A high current draw will heat the breaker and cause it to trip. I expect that higher rated breakers will trip too when they are loaded close to their rating.

The heat build-up is greater when the breaker is in an enclosure or exposed to warmer ambient temperatures. And, don't forget about the heat build-up of the circuit's cables behind walls or within conduits/boxes/receptacles. The purpose of a breaker is to protect the cable, so the heat of both need to be considered.

The electric codes (NFPA and CSA) are setup for safety reasons under various conditions. Just because something may work under some conditions, even though it violates the code, that does not mean that it should be done.
2018 Nissan Leaf S w/QC
Placed in action: 9/2018

nlspace
Posts: 269
Joined: Mon Jun 05, 2017 10:21 pm
Delivery Date: 06 Jun 2017

Re: Boost mode for EVSE?

Wed Nov 20, 2019 6:16 pm

The wires inside the EV_SE can get quite hot and crispy, as seen in a FLiR image here:

http://fsamw.myevblog.com/i-miev-techni ... terminals/

Oilpan4
Posts: 1809
Joined: Wed Jan 09, 2019 10:51 pm
Delivery Date: 10 May 2018
Leaf Number: 004270

Re: Boost mode for EVSE?

Wed Nov 20, 2019 7:17 pm

According to NEC the term "continuous load" is fairly ambiguous.
It could mean anything from 20 minutes to 3 hours.
For example a clothes dryer is considered a continuous load even though I have never seen one with a timer that goes longer than 90 minutes and the heater element cycles on and off. Based on observations it is definitely not a continuous load, but NEC defines it as continuous.

A 20amp breaker that trips at 18 amps is worn or defective and needs to be replaced.
A good 20 amp breaker, for example a square d QO should be able to hold a 22 amp load just about indefinitely then trip from over heating at 25 amps any where between 50 seconds and about 8 minutes.
It's called a trip curve.

If you run a wire at its max amp rating it will start to overheat well before 3 hours.

NEC always figures worst case scenario. In this case using NEC logic the worst case scenario would be "what if the timer failed and it stays running at 20 amps"?
Then what if someone plugs this evse into a nearly dead tesla and it runs a 20 amps for 20 hours on a 12ga circuit?

NEC has a section dedicated to wiring in evse units, article 625. I suggest everyone adhere to it.
"THE ABOVE POST CONTAINS MISLEADING AND INACCURATE INFORMATION. PLEASE CONSIDER IT OPINION, NOT FACT". -someone who I offended and is unable to produce the facts in question.

henrydehoja
Posts: 91
Joined: Sun Sep 16, 2018 6:40 pm
Delivery Date: 12 Sep 2018
Leaf Number: 317129
Location: Metro Boston, MA

Re: Boost mode for EVSE?

Wed Nov 20, 2019 8:55 pm

Oilpan4 wrote:
Wed Nov 20, 2019 7:17 pm
A 20amp breaker that trips at 18 amps is worn or defective and needs to be replaced.

A good 20 amp breaker, for example a square d QO should be able to hold a 22 amp load just about indefinitely then trip from over heating at 25 amps any where between 50 seconds and about 8 minutes.
It's called a trip curve.
I agree on the worn breaker. I expect that most people's homes have old/aged breakers in their power panels, so there is a good chance that they are not operating under like-new conditions.

I have seen some Square D model QO series breaker time-current trip curves:
https://download.schneider-electric.com ... _Ref=910-3
Like most overcurrent protective devices, a breaker has a trip curve with a band (i.e., lower curve and upper curve), which is the ideal curve +/- margin for temperature and other deviations. The breaker may trip anywhere within this band. Based on the lower band (lower part of the curve) for a 20A QO series breaker, the breaker may start to trip with 20A (1.0 multiple) load after approx 600 s (10 min). The higher the current, the sooner the breaker will start to trip, so with a 25A (1.25 multiple) load, the lower band shows that this breaker may start to trip sooner, after approx 60 s (1 minute).
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Placed in action: 9/2018

smkettner
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Location: Orange County, CA

Re: Boost mode for EVSE?

Wed Nov 20, 2019 10:09 pm

If it will shut down in 3 hours you are only gaining 36 minutes, but it shuts down. Leave it at normal and let it sit another 36 minutes or even longer.

The additional power is too small to gain advantage in all but the most narrow of circumstances.
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Nubo
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Re: Boost mode for EVSE?

Wed Nov 20, 2019 11:19 pm

smkettner wrote:
Wed Nov 20, 2019 10:09 pm
If it will shut down in 3 hours you are only gaining 36 minutes, but it shuts down. Leave it at normal and let it sit another 36 minutes or even longer.

The additional power is too small to gain advantage in all but the most narrow of circumstances.
I agree. Charge rate is one of those things where it takes more than a nominal increase to make a noticeable difference.
I noticed you're still working with polymers.

LeftieBiker
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Re: Boost mode for EVSE?

Thu Nov 21, 2019 12:45 am

It makes more sense, if possible, to reconfigure an existing 120 volt 20A circuit as a 240 volt 16A EVSE circuit with no Neutral. That gives about 4x the charge rate.
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Oilpan4
Posts: 1809
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Leaf Number: 004270

Re: Boost mode for EVSE?

Thu Nov 21, 2019 1:25 am

Going from the oem Panasonic 120v 12amp granny charger configuration to modded 240 12 amp was night and day difference.
Almost 20 hours to go from lbw to full, ain't not body got time for that. Cutting 20 hours down to 8 or 9 was a game changer.
Then going from my modded 240v 12 amp granny charger to a 240v 16 amp duosida was a nice improvement too.
Then their's the chademo, 395v at 20 amps is almost twice as nice for about 6x the cost of the duosida.
"THE ABOVE POST CONTAINS MISLEADING AND INACCURATE INFORMATION. PLEASE CONSIDER IT OPINION, NOT FACT". -someone who I offended and is unable to produce the facts in question.

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