Experiment EVSE X 4

Problem: Deploying an EVSE is expensive. Deploying several is very expensive and requires lots of electrical lines, panel space, etc...

Scenario: a place like LAX where lots of EVs park for an extended time. Let’s say we are going to install 16 30A J1772 EVSEs. That would take 16 EVSEs, 16 40A breakers, 16 Electrical runs, and 640A in the panel.

Experiment: 4 Open EVSE boards stacked… The latest boards have a communications bus I2c plus power pins on the top of each board. The boards are given a maximum group current to share, let’s say 60A on a 75A breaker. Each of the 4 hypothetical EVSEs are built to support up to 30A. So the minimum current for each EVSE is 15A. The EVSE stack communicates its status via the i2c bus. So if there is only 1 car actively charging it is offered 30A, 2 cars charging each gets 30A, 3 cars and each is offered 20A, and 4 would offer each the 15A minimum.

***The numbers can be changed to whatever… 2/4/8 EVSE stack… 16A/30A/75A EVSEs… 50/75/80/100A/more breaker. Lots of possibilities.

So now 16 EVSEs would require 4 breakers, 4 electrical runs, and 300A on the panel.


2011-12-16_18-19-47_762 by chris1howell, on Flickr

Thoughts…/?

From a user standpoint, I may care how long it will take to charge my car to a certain point. That could change drastically in this scenario depending on whether others hook up and what their car draws.

Otherwise, seems to be a good concept for making the EV charging infrastructure more feasible.

Anyone know if the J1772 protocol allows for the EVSE to change the available current (pilot duty cycle) while a charge is in progress? It might be necessary for the EVSE to interrupt the charge to change the available current. This could interact badly with set or overridden charge timers.

Yes J1772 allows for changing current...

"The EVSE may accept an external signal to vary the duty cycle for supply or premises power limitations. The EV/PHEV
vehicle shall use the duty cycle to control the on-board charger AC current drawn from the line."

The EV is allowed up to 5 seconds to respond.

In my experiment setup, the pilot starts at the minimum and works its way up. That way is an EV fails to respond at least it is stuck at the minimum.

Excellent idea. I would assume one tower with four J plugs to share a 30 or 40a circuit. Place the tower where four cars nose in together.

Yep 4 cars nose to nose and side to side... Quad EVSE at the X...


| | |
--X--
| | |


You could also do a stack of 8 with 4 20' cables and 4 30'. 8 EVSEs all at the big X and holders for each pair of the long cables at the little x...
Maybe a 100A breaker and a 10A minimum for each spot... With 8 spots what are the chances that all would be occupied and in use at the same time? I guess it depends on the location...


| | | | |
-x--X--x-
| | | | |

Interesting idea Chris, but I would assume the cost of a civil servant (or civil contractor) to install 16 individual units would be far far cheaper then the cost of a civil servant engineer to design and verify and approve something not UL approved, and then the additional cost of the installation.

LakeLeaf you are no fun :lol: ... My hypothetical Quad EVSE is now hypothetically UL listed :shock: ...

Problem solved.

:lol:

I thought that it was reported that:
The 2011 LEAF does not follow a changing Control Pilot's Max-Amps (but it should follow). Instead, it "reads" the Max-Amps only once, at the "start" of charging.

But, it is a nice current-sharing feature, Chris.
(Is it implemented in tour Open EVSE, or just an idea?)

Well, I think it is a great idea. It would certainly reduce costs. I suppose the only other way to do it would be to run much larger cables to the main EVSE box and have individual 30-amp breakers for each EVSE inside.

But being that the Leaf can currently only draw, what, about 16 amps or so? I don't think it is a problem.

I would say if this whole public charging thing ever takes off, something like this being manufactured is inevitable as it would reduce cost for a large installation.

Gary, I have implemented the i2c bus and the bus connections for 4 boards in hardware already. I have not written the code for the communication yet. There is a library for i2c communications already, so it will just be a few lines of code to send status.

Right now my priority has been getting the 12 Open EVSE boards finished, tested and shipped to those waiting. Maybe after the holidays I will play with this concept a bit more.

Chris

One idea is to start each car on a 30A pilot and then use a shunt to read the current actually consumed. If the car only draws 16A, the EVSE could drop the pilot signal down to 16A and have more in reserve to offer the next car.

Chris, great concept. I like the way you think. As others have noted, I'm not sure all cars will be compliant and follow pilot signal changes after charging commences. You might have to first as the charging cars to slow down when a new vehicle gets plugged in. If the charging cars respond you can then send the appropriate signal to the new car. If they don't slow down, the new car can only get what is remaining, which might be nothing until one of the other cars is done. Lots of options on how to perform this, you just need to be sure that it is clear to the users (and the owners).

I am thinking it should go the other way... Start out at the minimum current even if more is avaliable. Then ramp up, that way if a car does not comply with a changing pilot it is stuck at the low end and the other compliant cars get the extra...

This is a great idea for commercial applications. Maybe with a little tweak, it could serve a niche residential need too.

At least one EVSE manufacturer that I'm aware of is is marketing a line-sharing feature with their residential model. The idea is that you wouldn't have to install the EVSE on a dedicated circuit. If the EVSE senses other load on the circuit, it reduces its own load temporarily.

This is a little different, because in your idea, the EVSE is controlling all the load, and assumes it has access to 100% of the capacity. In this case, there would have to be a meter upstream of all loads.

richard said:

This is a great idea for commercial applications. Maybe with a little tweak, it could serve a niche residential need too. ...

Click to expand...

I've considered a second EV or PHEV in the family, and would love to have that sort of setup at home. It would allow me to install a dual 40a EVSE "cluster" on my existing 40a circuit and have confidence that both cars could charge at the highest rate possible.

or start low and ramp up until the voltage sags..

chris1howell said:

I am thinking it should go the other way... Start out at the minimum current even if more is avaliable. Then ramp up, that way if a car does not comply with a changing pilot it is stuck at the low end and the other compliant cars get the extra...

Click to expand...

Yep...that should do it.