## EVSE source current

pgrovetom
Posts: 75
Joined: Wed Jun 23, 2010 12:29 pm

### EVSE source current

I was looking over the J1772 standard I found at:

http://wenku.baidu.com/view/8d35b7d0496 ... 747b5.html

and it turns out the pilot signal from the EVSE to the EV charger tells the charger how much current it may try to draw. The pilot tone of 1KHz besides defining the coupler state also has a duty cycle which defines the EVSE current capacity.

Up to about 85A, the formula is %duty cycle x .6 = capacity in Amps.

So if the 1KHz pilot tone has a 20% duty cycle ( 20% on and 80% off ), it means the EV charger may draw 12A. If the EVSE was plugged into a 15A circuit ( or didn't know ), it would tell the EV charger to only draw 12A. That keeps the load current at the NEC 80% level.

On the other hand if someone installed the Level 1 EVSE with a dedicated 20A circuit, the EVSE should have the feature of sending the pilot tone at 26.67% which says the charger may draw 16A or 80% of the 20A circuit. The same would be true for the Level 2 where a 32A EVSE circuit would send a 53.3% duty cycle,while a 50A circuit could draw 40A = 80% which would be indicated with a 40/.6= 66.7% duty cycle.

So why is this important? It means the SAE standard allows both 15A and 20A Level 1 circuits and additional currents above the 32A from the AV EVSE. That means if you wanted to wait and use the Level 1 charger until the prices came down on the Level 2, you could buy a level 1 that had this feature and reduce your charging time by roughly the current ratio if you had a dedicated 20A circuit. Forgetting charger and battery losses for the moment, a 24KWHr battery requires 120V x 12A = 1440VA = 16.67 hours to charge.

Also ignoring the inefficiency in charging for the moment, 120V x 16A = 1920VA = 12.5 hours to charge. That's the difference between overnight and being short of overnight when one takes inefficiencies into account.

Hopefully someone will come out with a Level 1 EVSE that allows this feature so it's practical to wait for a cost effective Level 2 EVSE to arrive as volumes and competition arise. There are many companies designing EVSEs so it shouldn't take long before one can buy it yourself and install it yourself or hire and electrician to do it and not have to be forced to go with AV.
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AndyH
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Location: San Antonio

### Re: EVSE source current

Congrats for catching up!

This from June 19th...
http://www.mynissanleaf.com/viewtopic.php?p=7751#p7751

I have a copy of the J1772 recommended practice from Jan 2010. I haven't yet played with any hardware designed to use this standard, so cannot say how EVSE manufacturers are actually using the info in the J1772 doc.

According to the document, the Control Pilot signal performs multiple functions. It allows the EVSE to properly detect that a vehicle is connected. The EV receives a signal that the EVSE is ready to supply energy. The EVSE is notified if the charge area needs ventilation. Finally, the EVSE signals the EV, by modulating the pilot duty cycle, to communicate the maximum available continuous current capacity.

5.3.5.1 IF the EV/PHEV reads a duty cycle of 3-7%, the EV/PHEV shall interpret this as a valid digital communications command.

5.3.5.2 IF the EV/PHEV reads a duty cycle between 8% and less than 10%, the EV/PHEV should interpret this as a valid 10% duty cycle.

5.3.5.3 IF the EV reads a duty cycle less than or equal to 85.0% the EV/PHEV should base the current on the Amps = (% duty cycle) * 0.6 formula.

5.3.5.4 If the EV reads a duty cycle greater than 85.0%, the EV/PHEV should base the current on the Amps = (% duty cycle - 64) * 2.5 formula.

5.3.5.5 IF the EV reads a duty cycle of 97%, it is recommended the EV/PHEV consider this as a valid 96% duty cycle.

AndyH
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Location: San Antonio

### Re: EVSE source current

Discussion of 120V L1 charging options:
http://www.mynissanleaf.com/viewtopic.php?f=9&t=647

J1772 L3 update and info on L2:
http://www.mynissanleaf.com/viewtopic.php?f=9&t=640

AndyH
Posts: 6388
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Location: San Antonio

### Re: EVSE source current

pgrovetom wrote:I was looking over the J1772 standard I found at:

http://wenku.baidu.com/view/8d35b7d0496 ... 747b5.html
The on-line copy appears to be missing plenty of pages - are you seeing all 51 pages?. It also appears to be a copy of an electronic copy of the spec. I have a hard-copy from the SAE and it's black and white.

pgrovetom
Posts: 75
Joined: Wed Jun 23, 2010 12:29 pm

### Re: EVSE source current

The on-line copy appears to be missing plenty of pages - are you seeing all 51 pages?. It also appears to be a copy of an electronic copy of the spec. I have a hard-copy from the SAE and it's black and white.
I was able to see all 51 pages but it was slow loading. Since the regular copy is over \$50, I just tried to find a reference online. If I decide to build one, I'll probably buy my own copy. I'm trying to find a supplier for the Yazaki connector itself. I see Amphenol makes it and Northwire ( http://www.northwire.com/PDF/NW_EVCable_SS10.pdf) will build you a cable and I found a Chinese supplier. It looks like building a Level 2 EVSE wouldn't be all that hard if I can find a robust cabled J1772 coupler/receptacle. The 240V path GFCI and relays can be easily purchased and a few \$ microcontroller and a little software could do all the control work monitoring and pilot generation.
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garygid
Posts: 12469
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### Re: EVSE source current

Thanks for the info.

NorthWire appears to offer cable, but not the connectors or "handles". Did I miss something?

Amphenol connector ... can you provide a link to the J1772 part(s)? Thanks.

Please keep us posted on any other sources you might find.
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AndyH
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Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

### Re: EVSE source current

pgrovetom wrote:I was able to see all 51 pages but it was slow loading. Since the regular copy is over \$50, I just tried to find a reference online. If I decide to build one, I'll probably buy my own copy. I'm trying to find a supplier for the Yazaki connector itself.
You're right - very slow! Nice find, though - thanks! I bought a hardcopy from the SAE - the softcopy looks great. I'll check on prices - it might be easier to mod a commercial L1 instead of starting from scratch.

Andy

planet4ever
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### Re: EVSE source current

So, as you guys now agree, the EVSE tells the charger what it can pull but it is the charger itself that actually controls how much it does pull. So far as I know, the SAE standard doesn't force the charger to pull the maximum the EVSE allows. Is it trivial for the charger to provide both 12A and 16A charging? If not, what are the chances that passing the 16A signal from the EVSE will make any difference at all in how fast you charge from 120v?
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garygid
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### Re: EVSE source current

The standards have the EVSE "tell" the car the MAXIMUM current "available".

The charger in the car decides how much current to draw, depending upon its own design, limitations, and the stage of charging the battery.

The AV Level 2 (240v) EVSE, wired to a 40-amp dedicated breaker, should "tell" the car "32 amps MAX". The "rollout" LEAF will probably use a maximum of 15 amps (maybe 16).

The "upgraded" charger might use up to 30 or 32 amps, for substantially faster charging.

The "included" Level 1 (120v) EVSE will probably "tell" the car "12 amps MAX".
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AndyH
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Joined: Fri Apr 23, 2010 3:43 pm
Location: San Antonio

### Re: EVSE source current

planet4ever wrote:So, as you guys now agree, the EVSE tells the charger what it can pull but it is the charger itself that actually controls how much it does pull. So far as I know, the SAE standard doesn't force the charger to pull the maximum the EVSE allows. Is it trivial for the charger to provide both 12A and 16A charging? If not, what are the chances that passing the 16A signal from the EVSE will make any difference at all in how fast you charge from 120v?
I think you've got it, planet. The EVSE tells the car how much current is available - it tells the car how large a 'pipe' it's connected to. The J1772 spec also defines what the charger should do with the information. If 12A is the max, the charger must turn itself down so it draws 12A or less.

The J1772 standard also allows for the EVSE to receive info from the power grid and the EVSE can adjust the 'max power available' signal on the fly. This isn't implemented in EVSE yet - that's likely part of the data comms work being done in other SAE standards. So today - the EVSE will be wired and manually set to report a maximum available current. In future, the EVSE will be able to receive 'throttle' info from the grid and in turn signal the car to reduce the power draw or pause charging if necessary to keep the power grid healthy.

Andy