Level 2 Charger Confusion

Perhaps others can benefit from my PV experience, and even give me some suggestions on adding EV support:

I had a meter wired directly to a 150 amp "main" breaker in the immediately adjacent (connected) 150-amp rated breaker panel.

I was told that SDG&E requires trenching, conduit (24" deep), and new feed wires (to replace the 32-year old "buried" service feed wires) if ANY service panel "upgrade" is done.

I was adding 7050 watts (SunnyBoy 7000 inverter, max just over 29 amps of AC) of Solar Generation required adding a 40-amp dual breaker for the PV "feed-in".

I was told (apparently incorrectly) that I would have to reduce the size of the main feed breaker by 40 amps to avoid the theoretical possibility of over-driving the 150-amp buss. So, we replaced the 150-amp main breaker with a 110-amp breaker, and added the 40-amp "PV" braker, thereby avoiding the expensive panel upgrade and trenching.

Apparently the "correct" buss loading calculation for PV feeds is: one is allowed to "over-rate" a panel by 20% when adding a PV feed-in. So, my 150 amp panel should have been treated like a 180-amp panel. Then, adding the 40-amp breaker would have only required reducing the main breaker from 150 to 140 amps. But, a 140-amp breaker seems very difficult to find. I suppose that a case could be made that the PV "feed" could never exceed 30 amps, and using the original 150-amp breaker should be OK, but I doubt that an inspector would go for that argumenr, because of the 40-amp PV breaker.

Now, faced with an almost full breaker panel, and wanting to add a dual 40-amp breaker (or two, the second for a future 2nd PHEV) for EV charging (and possibly one or two dedicated 20-amp breakers for Level 1 EV charging).

Since it is a GE panel that already uses "narrow" breakers, I cannot gain space by replacing pairs of 15 (or pairs of 20) amp breakers with the 2-in-1 type breakers, to free up a few slots. I will have to open it up to see if any of the remaining (two single and one double) knockouts will take breakers. I think the PV electrician said that some contact "tabs" were either missing or broken, and the associated spaces could not be used.

So, I might need to add a subpanel on the inside of the garage wall (right in back of the main panel that is IN the wall, facing outwards).

Perhaps I could then move some of the existing loads to the sub-panel and have the new EV-charging breakers conveniently located (within line-of-sight of the future EVSE) in the interior sub-panel.

When one has PV generation, a two-meter solution does not allow running both meters "backward". So, it would seem that some one-meter solution (Tariff) would be "best", even "required" to offset both the house consumption and the EV charging.

Further complication: If one has EV-TOU metering, the generation will all be in the daytime, in the high-rate or mid-rate time slots. There, I over-generate at least 9 months of the year, and A/C usage spikes usage in at least August and September so that there is perhaps 300 to 600 kWh net usage in those months. But, for the year, there is net generation. The night-charging time slot will never get any generation, so it would always show net usage (EV charging), perhaps of 200 to 600 kWh a month. Within one month's billing, does the over-geberation in the daytime time slots offset the net usage in the night slot? If it does, is it kWh for hWh, or datyime power rate offsetting nightime total (power plus distribution) billing?

Thanks for any help.

garygid said:

Further complication: If one has EV-TOU metering, the generation will all be in the daytime, in the high-rate or mid-rate time slots. There, I over-generate at least 9 months of the year, and A/C usage spikes usage in at least August and September so that there is perhaps 300 to 600 kWh net usage in those months. But, for the year, there is net generation. The night-charging time slot will never get any generation, so it would always show net usage (EV charging), perhaps of 200 to 600 kWh a month. Within one month's billing, does the over-geberation in the daytime time slots offset the net usage in the night slot? If it does, is it kWh for hWh, or datyime power rate offsetting nightime total (power plus distribution) billing?

Thanks for any help.

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I think we all need that kind of help from the math whizzes amongst us - to try and figure out how what we have to buy at the TOU super off-peak and off-peak rates is affected by the surpluses we generate at TOU peak rates.

garygid said:

Further complication: If one has EV-TOU metering, the generation will all be in the daytime, in the high-rate or mid-rate time slots. There, I over-generate at least 9 months of the year, and A/C usage spikes usage in at least August and September so that there is perhaps 300 to 600 kWh net usage in those months. But, for the year, there is net generation. The night-charging time slot will never get any generation, so it would always show net usage (EV charging), perhaps of 200 to 600 kWh a month. Within one month's billing, does the over-geberation in the daytime time slots offset the net usage in the night slot? If it does, is it kWh for hWh, or datyime power rate offsetting nightime total (power plus distribution) billing?

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This sounds like something best discussed on the SDG&E thread. I can say that for PG&E we are assigned one tier for the month based on our total usage (night +/- day), but PG&E doesn't break out distribution separately, so SDG&E calculations are going to be different.

It does sound like you may have a similar sub panel need to mine, so I hope pgrovetom can provide some wisdom here.

I've just done some figures in the Edison area. Don't blast me for incorrect conclusions...I am NOT a math whizz by any stretch of the imagination. But I'll take constructive commentary on-board!

http://www.mynissanleaf.com/viewtopic.php?f=25&t=666&p=10304#p10304

But, since it can be plugged in anywhere - people are going to do just that. L-1 EVSE needs to handle that, right ...

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Yes that is true and it will usually just work. With 16A as the specified maximum for Level 1, a real charger probably won't pull the maximum. That means it probably won't even pop a 15A breaker unless its got some other significant load on it. The building department, if one actually applies for a permit, would require a dedicated 20A circuit since 16A x 1.25 = 19A which is pushing even a 20 circuit close to the edge. That being said, the NEC and code requirements are very conservative so what is required and what will happen in the real world are different. I suspect someone who just plugs into an outlet in their garage will probably get a 20A circuit and it probably won't have anything else on it since its a garage. If they are unlucky enough to be charging and plug an electric drill into the same circuit, then it could pop the breaker. When that happens, you will know it as the drill will stop, then you just check it out, reset the breaker and put the Level 1 charger on an outlet where non of the other outlets get used typically and it will never be a problem.

It interesting they chose 16A given 15A and 20A are the standard breakers and circuits. They probably took the 20A, subtracted 1A for other loads and new 1.25 x 16 = 19 + 1 = 20A. So its probably built into their 16A choice so it typically just works in most outlets without popping the breaker. So yes it will only be an issue if one chooses to get a permit. I presume if one signs that waiver, Nissan will just give you the Level 1 chord and it will become the users problem.

16x1.25=20 in my "calculator" (not the "magic 19" you "found"). And that's the proper limit (16A) to be pulled per NEC625 (80% of breaker rating for continuous loads). Unfortunately L1 EVSE will probably only pull 12A (assuming a 12x1.25=15A breaker).

(5/4 = inverse of 4/5, or 1.25 = inverse or 0.8)

http://www.sfenvironment.org/downloads/library/SFCCC/ABC's of Battery Charging.pdf

http://www.mag.maricopa.gov/pdf/cms...-the-National-Electric-Code-Handout_69446.pdf

This does bring up an interesting point. The Level 1 EVSE itself does not have any mechanism to limit current nor know whether its plugged into a 15A or 20A outlet. The charger inside the EV will decide how much current it wants to draw. The EV will know whether its a Level 1 or Level 2 EVSE but not what the circuit capacity actually is. Its a shame not to have the EV programmable such that it could be configured for 80% of 15A or 20A so it charges as fast as practical given the charging source circuit. Both 120V and 240V can have different source circuits if they are hardwired. 120V @ 15A x .8 = 12A is the safest route but also the slowest charge. Does the Leaf provide any kind of charge current programmability?

Its too bad the EVSE can't communicate to the EV, its source current capacity, if it knows. If its hardwired it could let the EV know for Level 1 or Level 2 and if it doesn't know, the EV falls back to the minimums of 12A for 120V and 32A for Level 2. It would be simple to implement in the pilot pin interlock mechanism. Moving from 12A to 16A for Level 1 which is by far the most common available, would make a significant difference. It could make the difference between squeezing in a charge overnight at 12 1/2 versus 16 2/3 hours roughly ignoring losses.

pgrovetom said:

Yes that is true and it will usually just work. With 16A as the specified maximum for Level 1, a real charger probably won't pull the maximum. That means it probably won't even pop a 15A breaker unless its got some other significant load on it. The building department, if one actually applies for a permit, would require a dedicated 20A circuit since 16A x 1.25 = 19A which is pushing even a 20 circuit close to the edge.

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Your probable erroneous assumption is that the fielded L1 units will draw the 16A max. While we don't yet have details for the device that will ship with the LEAF, we do have details of this device from Clipper Creek: http://www.clippercreek.net/images/ClipperCreek PCS-15 Brochure.pdf

Service Entrance:
120 V – 15 Amp, single phase, 2-wire, with ground
...
Compatibility
The PCS-15 is designed to the latest standards, making it
compatible with vehicles from the major automobile manufacturers.

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With a 120V 15A service entrance requirement, this means 12A MAX to the car.

We can make this harder than it has to be if we choose... I don't choose. :lol:

pgrovetom said:

http://www.sfenvironment.org/downloads/library/SFCCC/ABC's of Battery Charging.pdf

http://www.mag.maricopa.gov/pdf/cms...-the-National-Electric-Code-Handout_69446.pdf

This does bring up an interesting point. The Level 1 EVSE itself does not have any mechanism to limit current nor know whether its plugged into a 15A or 20A outlet. The charger inside the EV will decide how much current it wants to draw. The EV will know whether its a Level 1 or Level 2 EVSE but not what the circuit capacity actually is.

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This is incorrect. One of the primary functions of the pilot signal is to allow the EVSE to communicate the max current available to the car's systems.

pgrovetom said:

Its a shame not to have the EV programmable such that it could be configured for 80% of 15A or 20A so it charges as fast as practical given the charging source circuit.

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The car doesn't have to worry about 'thinking about' 80% because that's already solved upstream when the EVSE is installed and configured. The car can concentrate on the only thing that it needs to know - how much power can I draw from the line I'm connected to right now.

The current J1772 system allows charging from a 120V 20A circuit. Available current is communicated by the pilot signal. While the commercial EVSE might be factory configured to report a max available 12A, there's nothing stopping someone from creating a L1 EVSE that's built for and communicates 16A available. The perceived limitation is NOT a Leaf 'limitation'.

Build your own or communicate with an existing L1 EVSE manufacturer and ask for a new product. It'll probably fast-track the process if you want to help them pay for part of development and UL evaluation.

With a 120V 15A service entrance requirement, this means 12A MAX to the car.

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The flaw here is the charger in the car decides how much current to draw, not the EVSE. The EVSE is really just an extension chord with GFI protection but no mechanism to limit current. Does the EVSE have some mechanism to communicate to the charger? Without some kind of simple communication, the EV must assume 12A. My later point is that is a shame since 16A would make Level 1 almost usable. Certainly if you visited some place without an EVSE, it would be nice to push it to 16A as one could almost charge overnight at 16A.

We can make this harder than it has to be if we choose... I don't choose

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Its not about being easy, hard or harder - its just curiosity about possibilities.

Turns out the J1772 standard has a mechanism built into the pilot signal so the EVSE can tell the EV charger it's current capacity. The EVSE sends a 1KHz tone to the EV where the duty cycle defines its current capacity. There is a Figure 7 showing the relationship between duty cycle and current.

The source current in Amps = %duty cycle x .6 (up to just over 80A)

So a duty cycle of 20% = 12A and

a duty cycle of 26.67% = 16A and so forth.

So an EVSE can have a feature that allows the installer to define a 15A or 20A circuit and the EVSE will generate the appropriate duty cycle of its 1KHz pilot tone.

So that allows Level 2 to do the same thing. A 53.3% duty cycle = 32A etc..

see: J1772 @ http://wenku.baidu.com/view/10b7d51755270722192ef7b6.html

Build your own or communicate with an existing L1 EVSE manufacturer and ask for a new product. It'll probably fast-track the process if you want to help them pay for part of development and UL evaluation.

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The more I look into it, the easier it looks to build my own. I'm exploring getting a J1772 EVSE side coupler and building my own just as a project. Functionally its the coupler, the chord and a box with 40A GFI's, disconnect relays and a small micro-controller, power supply and a few analog circuits for signal conditioning. Its not very complex.

A Level 1 EVSE with the 15/20A circuit feature might be a worthy product. I'm considering it.

pgrovetom said:

With a 120V 15A service entrance requirement, this means 12A MAX to the car.

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The flaw here is the charger in the car decides how much current to draw, not the EVSE.

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Nope. The EVSE is configured during installation (if L2) and likely from the factory (if L1) with the max current available from the AC supply to which it's connected. It uses the 'max current' info to set the proper duty cycle on the pilot signal.

pgrovetom said:

The EVSE is really just an extension chord with GFI protection but no mechanism to limit current. Does the EVSE have some mechanism to communicate to the charger?

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The EVSE communicates with the charger and/or the car's systems via the pilot signal and via the voltage it's feeding to the charger.

pgrovetom said:

Without some kind of simple communication, the EV must assume 12A.

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No. The minimum allowable current allowed is zero. If the pilot duty cycle does not fall into either the 5% signal that digital data comms are present, or into the 10-97% range to report an allowable current, then the car is required to acknowledge an error condition and NOT CHARGE.
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Ok...we got there! Continued here:
http://www.mynissanleaf.com/viewtopic.php?f=9&t=750