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Cooperating group of OpenEVSE chargers

I would be interested in comments and suggestions regarding an installation of three EV chargers which cooperate to manage the combined primary load.

Here's the background. I live in a cooperative housing group that has three Nissan Leaf owners. The first owner installed a standard Nissan/Aerovironment outdoor level 2 charger on the wall of a common building, adjacent to our parking area. I am the 2nd owner; I joined the community last October and have been sharing the charger cord with owner #1. Leaf owner #3 has been charging off-site for the moment but we are looking for a longer-term solution.

We think the best approach is to install three charging outlets on the building where we now have one. However we are limited by the service capacity of the building, which is 200a, and the subpanel which feeds the existing charger, which is protected at 100a. The building contains a wood shop, also powered through the 100a subpanel, which gets occasional usage including some substantial power tools (table saw, air compressor, etc.).

My thought is to install OpenEVSE chargers and use the remote API to control maximum charging current (pilot duty cycle). When several cars are charging simultaneously, I would dial back the charge current. I would also install a separate AC current sensor on the subpanel feeder, which would tell me when other loads (e.g. air compressor) kick in; if necessary I would dial back the charge current to maintain a safe load on the panel. I intend to use a Raspberry Pi to do the control logic. It would also monitor kWhr usage for cost allocation.

This should use our capacity pretty efficiently and I expect that we could expand this to another few chargers before having to upgrade our service or subpanel.

We are a small trusting group so I am not particularly worried about people intentionally "stealing" power from each other. If we need more control I would go for a web-based login (typically via smartphone).



The contractor used in the Wattzilla UL EVSE kit has a 240V DC coil and an interface board to rectify and control the AC input.

Which sw82 version do you have? Specifically, which coil voltage and spring strength? Is the c3 able to reliably charge the coil to close the contactor? I didn't think they were designed to output the wattage needed for the coil (roughly 15watts)

Project update: First EVSE module is assembled and working on a bench test. Need to move forward on the load management system now.

We've got a design based on an EVSE module that an electrician will be able to install and wire. In this case the modules will be in an indoor equipment box and we will run thru conduit to exterior charging cords.

We are designing around the Wattzilla module because we need it all code-legal inspected etc, but it should work with standard OpenEVSEv4 as well.

Anybody else interested in using this design?


Chris, I think you've seen the 4-charger condo proposal. I figure the field evaluated customized system is very likely a win on cost and definitely a win on flexibility.

In order to avoid a field evaluation you would have to use a UL listed charging station like the Wattzilla Uno (Shipping is free in the OpenEVSE Store during April). It may be less costly to use the Uno without field evaluation than to build with OpenEVSE or use the UL Wattzilla components.

City inspector says the installation will need a 3rd party field evaluation, even though the components are UL recognized. This service is available from a lot of vendors; I'm finding out what it costs.

I am speculating how large the market might be for this sort of customized load-managed multi-charger systems.

FYI I have started a conversation about this project with the city electrical inspector here in Seattle.

Chris, would you be willing to serve as a reference? If you have private contact info for that you can drop me a line via gmail at cfharr.

Frank already sent me your requirements for review. The Wattzilla UL parts are available in the OpenEVSE store.

I am moving forward with this condo multi-charger project. For insurance reasons, we want to go by the book on electrical code, so we are looking at the Wattzilla UL listed version of OpenEVSE.

I am thinking of a car identification feature which would simplify usage tracking, I'll put it in another thread.

I think it is a good plan. Here is something very similar on a larger scale.

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