5 ms·

Are you an EE with a specialty in power electronics? Cause that seems insane to me, inductive loads will cause a voltage spike (flyback) when disconnected, whic

Are you an EE with a specialty in power electronics? Cause that seems insane to me, inductive loads will cause a voltage spike (flyback) when disconnected, which will exceed that easily. That is why there is generally a reverse diode across the contacts, which I didn't see in the diagram. Granted the article notes it appears to be largely a resistive load, but I would want data sheets on the car/charging requirements, not measurements, to ensure this is true 100% of the time. Maybe the car has an AC compressor or a pump to cool the battery during charging, which draws directly from the charger when plugged in. You might not see that doing a few random measurements because it turns on only after some time or if someone is sitting in the car.

ferongr 3y ago
>Maybe the car has an AC compressor or a pump to cool the battery during charging, which draws directly from the charger when plugged in No it doesn't. A/C compressors in EVs are 3 phase AC powered by an inverter supplied by the traction battery. The contactors in an EVSE open and close at practically zero current, the OBC ramps the current up or down accordingly. And as another sibling comment noted, the OBCs are PFC corrected and act as a largely resistive load.
sokoloff 3y ago
No, but I'm a mechanical engineer who's taken a subset of my uni's EE curriculum, done a fair amount of hobby electronics, read a lot about the SAE J1772 charging standard that applies here, and disassembled two commercial EVSEs (all in contemplation of building my own EVSE, which I haven't pulled the trigger on yet). It turns out that the engineers who designed J1772 thought a fair amount about how to handle the connect/disconnect concerns that you raise (via the pilot signals and proximity microswitch) and they didn't just leave it to EVSE designers to YOLO it. > I would want data sheets on the car/charging requirements, not measurements, to ensure this is true 100% of the time The "datasheet" that you want is the J1772 standard. There are many free summaries of it, including https://openev.freshdesk.com/support/solutions/articles/6000052074-basics-of-sae-j1772 https://openev.freshdesk.com/support/solutions/articles/6000... Scroll all the way to the bottom and read the section on "Proximity" to understand how the relays are not disconnected while large currents are flowing.

ferongr 3y ago

>Maybe the car has an AC compressor or a pump to cool the battery during charging, which draws directly from the charger when plugged in No it doesn't. A/C compressors in EVs are 3 phase AC powered by an inverter supplied by the traction battery. The contactors in an EVSE open and close at practically zero current, the OBC ramps the current up or down accordingly. And as another sibling comment noted, the OBCs are PFC corrected and act as a largely resistive load.

sokoloff 3y ago

No, but I'm a mechanical engineer who's taken a subset of my uni's EE curriculum, done a fair amount of hobby electronics, read a lot about the SAE J1772 charging standard that applies here, and disassembled two commercial EVSEs (all in contemplation of building my own EVSE, which I haven't pulled the trigger on yet). It turns out that the engineers who designed J1772 thought a fair amount about how to handle the connect/disconnect concerns that you raise (via the pilot signals and proximity microswitch) and they didn't just leave it to EVSE designers to YOLO it. > I would want data sheets on the car/charging requirements, not measurements, to ensure this is true 100% of the time The "datasheet" that you want is the J1772 standard. There are many free summaries of it, including https://openev.freshdesk.com/support/solutions/articles/6000052074-basics-of-sae-j1772 https://openev.freshdesk.com/support/solutions/articles/6000... Scroll all the way to the bottom and read the section on "Proximity" to understand how the relays are not disconnected while large currents are flowing.