pgrovetom
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 1:53 pm

http://www.sfenvironment.org/downloads/library/SFCCC/ABC%27s%20of%20Battery%20Charging.pdf

http://www.mag.maricopa.gov/pdf/cms.resource/EVC_2009-12-10_Electric-Vehicles-and-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.
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AndyH
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 2:00 pm

pgrovetom wrote: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.


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%20PCS-15%20Brochure.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.


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:

AndyH
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 2:11 pm

pgrovetom wrote:http://www.sfenvironment.org/downloads/library/SFCCC/ABC%27s%20of%20Battery%20Charging.pdf

http://www.mag.maricopa.gov/pdf/cms.resource/EVC_2009-12-10_Electric-Vehicles-and-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.


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 wrote: 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.


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. ;)

pgrovetom
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 2:16 pm

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


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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pgrovetom
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 3:12 pm

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
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pgrovetom
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Re: Level 2 Charger Confusion

Sun Jul 11, 2010 4:16 pm

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. ;)


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.
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AndyH
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Re: Level 2 Charger Confusion

Mon Jul 12, 2010 6:14 pm

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


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


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 wrote: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?


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


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.
[/quote]

Ok...we got there! Continued here:
http://www.mynissanleaf.com/viewtopic.php?f=9&t=750

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