CP not reaching -12V
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Hello, this project is amazing! I have tried multiple EVs, and it is working fine, but with a Skoda Plug-In, the car is throwing an error. The EVSE is at -9V State B.
I used an oscilloscope and the TL081CP is not reaching the low supply voltage. Instead of being at -12V it is at around -10.7V. Everything else looks fine, the rise and fall time is under 2us and the PWM frequency is at 1kHz. Maybe it is because of the TL081 not being a rail-to-rail OpAmp (it is a genuine one).
I have read the EN61851-1:2011 standard and the only value that is not within the tolerances is the negative voltage.
Any clue about what the problem may be?
Hi,
I am study SAE J1772-2010, there is section about pilot line voltage ranges:
Earlier, when I connected the oscilloscope, I did not reach -11.4V but only -11.2V
I tested charging on three different EVs (Skoda, VW, BMW), so I didn't think much more about it...
I have a few questions:
- Which negative voltage supply of TL081CP?
- Do you have a TVS diode at CP out? If so, I would try to measure it without it.
- Which board schematic do you have? ESP32DevkitC, ESP32 S2 DA or custom?
I definitely agree with that, a rail-to-rail OpAmp could improve the output CP voltage. But I couldn't find any in my local store...
I am reading at the input supply a -12,5V on the TL081 (pin 4 VEE).
I tried reading with and without the TVS diode and the difference is negligible still above the +-0.6 tolerances and the car won't charge. I am not understanding where the problem may be, the only thing that is not within specs is the negative voltage of the PWM.
I used the schematic from ESP32 S2 DA.
I will try using a voltage comparator like the LM311 it should have a faster response time and the output should reach the supply voltage both on the negative and positive rails. I don't know any OpAmp that meets all the requirments of the protocol...
Where are you measuring voltage? On CP or OpAmp pin (before or after 1k resistor) ?
When you charging EV which works charging, what is negative voltage?
When set EVSE to disabled state, CP should be -12V, what is voltage on CP without car.
I am measuring on CP after the 1k resistor.
The negative voltage works in -10.7V for all the EVs I have tested except for the Skoda Plug-In.
The voltage is the same -10.7V that was the reason that made me think that it could be because of the TL081
I still couldn't configure the CP (Control Pilot) and my measurement values are like this, in real measurements they are like this.
I have studied many projects, I have read about SAE J1772, and I have built the recommended circuit, but unfortunately it didn't work. Where am I making the mistake?
I have tried with a TL072 and now it is working. I used only 1 of the 2 OpAmp channels. The rise and fall time is bellow the 2us and the negative voltage is on the -12V rail.
Good job, now changing Skoda plug-in?
Yes! Thanks for your help and congratulations on this amazing project.