How to determine amp capacity of currently connected charge cable

neil1 · 3 February 2023 08:38

Hi All

I’m currently running FW openevse8.2.2_eu on my EVSE, as I’ve got a non tethered cable and I believe that this firmware has the option of reading the PP pin for the max current that the connected cable is capable of carrying enabled. I know that the cable that I have with me has a resistance of 683Ω between the PP pin and Earth, which should decode to a current of 20A.

Looking at the RAPI source code, I suspect that the value should be returned as part of hmaxamps, but when I run the query $GC, I get a value of 32A. I’m not sure if this is correct or not.

The question that I have is, How do I know what the amp limit of the cable is that is currently connected to the unit if if hmaxamps is not the correct query value?

Cheers

Robert.Wall · 3 February 2023 14:38

An electrical engineer’s reply, not an EV expert’s:

Can you see the bare conductor anywhere, and measure the diameter of a strand and count the number of strands? With that, you can calculate the cross-sectional area and look that up in the tables. You’ll need to know also they type of insulation, as that governs the maximum temperature the conductors can be allowed to reach. And it’s temperature which determines the maximum current.

glyn.hudson · 3 February 2023 15:11

If you’re using a non tethered cable you need to run emonevse.hex firmware which has PP_AUTO_AMPACITY enabled. This is what enables it to read the PP resistor which sets current capacity of the cable.

github.com

OpenEVSE/open_evse/blob/stable/platformio.ini#L104


      
          extends = env:openevse
          build_src_flags=
            ${common.eu_build_flags}
            -D 'VERSION="${common.version}.EU"'
          
          
# Non-tethered T2 EmonEVSE single-phase
          [env:emonevse]
          extends = env:openevse
          build_src_flags=
            ${common.eu_build_flags}
            -D PP_AUTO_AMPACITY
            -D 'VERSION="${common.version}.T2"'
          
          
# Non-tethered T2 EmonEVSE three-phase
          [env:emonevse_3ph]
          extends = env:openevse
          build_src_flags=
            ${common.eu_build_flags}
            -D PP_AUTO_AMPACITY
            -D THREEPHASE
            -D 'VERSION="${common.version}.3P"'

1500 Ω resistor – 13A cable
680 Ω resistor – 20A cable
220 Ω resistor – 32A cable
100 Ω resistor – 63A cable

Guillaume_S · 4 February 2023 08:27

@glyn.hudson , there’s a problem with current auto_ampacity implementation.
I’ve posted an issue here AutoSetCurrentCapacity() should set a max current capacity not actual charge current. · Issue #156 · lincomatic/open_evse · GitHub

If you can give a look. Thx

neil1 · 4 February 2023 20:52

@glyn.hudson if I was to install the version you suggest, is there a way for me to see the cable current limit, or is the bug stopping that?

jeremypoulter · 5 February 2023 07:32

You can use the $GC RAPI command to read the pilot value from the EVSE, when charging this will be set to the value of the cable.