SAE J1772 EV charger checker

Sometimes chargepoints are wrongly commissioned, i.e. set for 63 amps, but fused for 40, which works mighty fine for all EVs, until a 43 kW capable Zoe comes along and trips the breaker.

In another case a driver in Belgium owning a new R240 and who has a single phase 32 amps chargepoint installed, the car consistently reports 20 amps max. He called the installer who insisted all was A-OK. So, the driver blamed the car. Renault couldn’t tell him if 32 A single phase is supported on the R240. However, they were nice enough to lend him a Q210 to try (and the Q210 supports the 32 A single phase configuration). Whoops, again 20 amps only.

CanZE of course reports this all, but to exclude any issue in the car, I build a little “amp checker” which reports the maximum current per lead the chargepoint communicates to the car. It’s a tiny, tiny little bugger. If you’re into some electronics fiddling and not afraid to try, here’s the instructable.

SAE J1772 EV charger checker

19 Comments on “SAE J1772 EV charger checker

    • That would not be any problem, except it being massive overkill 😉 Personally, but it’s really a matter of taste, I like these little buggers and for both you’d need some sort of programmer (a USB wired arduino for a bare chip, a USB-2-serial for a Pro-mini). If you’re interested, here’s a link to my ATtiny85 programmer.

      You might need to change a tiny bit to the processor’s register fiddling to enable the edge interrupts, but that can’t be a big deal.

      • Yes, I know that it would be overkill, but I bought a job lot of Pro-Minis for about £1 each. I used one for my version of your granny charger project.

        Sadly, my programming skills are not up to much, so I wouldn’t know where to start with ‘register fiddling’.

        • If you really building one, I’ll have a look in the data sheet of the 328 and compare with Attiny85, no worries

  1. About a week ago I found a nasty bug in the firmware and fixed it. If you started this project, please make sure you load the latest firmware from codebender.

    @Andy let me know if you’re planning to really build it and what pins you want to use (from a quick read I’d advice to use D8 = PB0 for input and D4 = PD4 for the LED, to keep it as close as possible to the original) Found the 328 interrupt stuff, and I think changes are minimal when using that pin layout.

    • @Jeroen, sorry for the late reply. Yes please, I would like to build one using a Pro-Mini. I don’t mind what pins are used, so I’m happy to go with your suggestion.

      • The LED pin is not very relevant. My suggestion would be to keep the LED on PB4 which is D12, unless you want to use the on board LED. In that case just use D13.

        The data in pin I’d keep on PB0, which is D8. Code changes are minor and I will update the source with some #ifdef stuff.

        • Done, you can pick up the source on codebender and change the lines where a reference to the 328 is made. Let me know if it works please Andy, I haven no chance to test it on a 328 anywhere soon.

  2. Thanks Jeroen. I won’t get chance to build it until next week. I’ll let you know how I get on. I’ll probably use the Pro-Mini’s own LED.

  3. I built it today and I can confirm that it works perfectly with an ATmega168 (5v, 16Mhz) Pro-Mini. I was a little concerned where it said “Careful, 8 MHz needed!” at the top of the listing, but it was no problem.

    I tested my home-made granny cable (12A) and my supplied home charger (30A).

    • Hehe, well, I will change that then. The ATtiny85 is default fused @ 1Mhz, therefor the warning. Precision is good at 8 MHz; 16 will NOT be a problem. Thanks for letting me know it works and enjoy the little bugger 🙂

  4. Have you tried it with a 3-phase charger? I wondered if it would indicate the total, or per phase current.

    Although my granny lead is set to 12A, my ZOE only seems to take 10A – perhaps this is because it’s an early model (October 2013).

    • It indicates in fact the copper diameter translated to amps. You need to multiply by 3 for 3 phases indeed! The car ony knows there are 3 phases because, well, it gets fed 3 phases. There is noting in the protocol.

      Does the bug tell you you 12A too? My commercial chargebox is set to 16, bug says 15, car takes 15-and-a-bit.

        • I’d think the only logical conclusion is then that the car takes less than it should, UNLESS the current that you report the car is taking is being calculated the RMS power divided by the voltage. The cos phi is a real thing at these lower rates.