How I built my 3-phase Open EVSE

Ever since I posted on my blog that I built my own Open EVSE for my future Tesla Model S I’m getting a lot of e-mails from people asking how I build it.

A couple of notes to everybody who wants to build one:

I’m using a Open EVSE board with a modified firmware
I modified the firmware so that with the Advanced Power Supply it will switch to level 2 charging when it senses 230V on L1.

The source code can be found on my Github account.

I also have two compiled versions (with LCD support) available (both from 01-09-2012):

You can program the EVSE using ‘avrdude’ and the right programmer.

The relais I’m using is a 40A 4p
I’m using a Hager ESL440S relais.

This relais has 4 poles and works on 12V AC or DC.

There is a second relais which switches on my main relais
The main relais (Hager ESL440S) works on 12V DC, but pulls about 1000mA to switch on.

That is a bit to much for the Open EVSE board, so I had to buy a 12V DC transformer and a second smaller relais. When Open EVSE board switches on the small relais, it switches on the main relais by using the external 12V transformer.

If you go to page 8 of the PDF I wrote you can see these components.

In the casing where the Open EVSE board is you can see the small relais on the left.

The external 12V DC power supply is in the distribution panel on the right and is on the left of the main relais. You can see the green and red LED on it.

I limited my EVSE to 30A
I limited the pilot signal to 30A. 32A would stress some fuses in the distribution panel in my house, since that 32A relais also provides power to the TL-lights in my shed. So I turned the EVSE down to 30A instead of 32A. Technically I could use 32A, but 30A was a safe bet in this case.

1-phase of 3-phase doesn’t matter
The EVSE itself doesn’t know anything about 1-phase or 3-phase. When a car connects and talks to the EVSE it requests power, when all the criteria match the EVSE turns on the relais.

The car then senses 3-phases and will use them if the charger supports it. The EVSE has nothing to do with that.

To conclude:

  • Read the PDF I wrote.
  • For the EVSE 3-phase or 1-phase doesn’t matter. It just switches on a relais.
  • Read the Open EVSE website about J1772, programming, etc, etc

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Wido den Hollander

I am the CTO at PCextreme B.V. and i will keep this blog just to post some interesting information about my daily work on Linux (and other) systems.