Varistors are more for surge suppression and momentary voltage spikes. If you apply 240V across a 150V varistor it will fail open in a rather incendiary fashion. In other words, the magic smoke found inside all electronics that make them work would leak out rendering it inoperable. Also I doubt very highly it would trip the 40A breaker on my 240V outlet.spirilis wrote:I think a 150V varistor would preclude its use at 240V as it should short circuit the input, tripping the breaker and overheating the input wiring.
Unless it blows "open" instead, rendering itself useless right away while the remainder of the EVSE functions OK. That would be a technical design fault since its safety function is useless but who knows. I should pop open the case on my CMax EVSE at some point and snoop.
Tomorrow I plan on modifying mine to make it dual voltage. Although I'm going to "cheat" a little and I'm sure UL would not approve! I'm separating the voltage going thru the relays and out to the car from the voltage supplied to the circuit board. The cheating part is I am going to use the ground as a neutral for the power supplying the circuit board. This is highly improper from an electrical wiring standpoint but it will work relatively safely.
This is possible because a 240V circuit isn't really a 240V circuit it is two 120V circuits. If you're not familiar with how household wiring works here's a readers digest explanation. A typical 120V circuit has 3 wires, a NEUTRAL, HOT, and GROUND (GND). A typical 240V circuit like my NEMA 6-50 outlet also has 3 wires, HOT, HOT, and GND. Some like a NEMA 14-50 outlet have a 4th wire which is a NEUTRAL. Each HOT is still only 120V. The trick to getting 240V from this is that between the two HOTs the AC sine waves are 180 degrees out of phase. What this means is that when one HOT is at +120V the other HOT is at -120V and measured between them you get 240V.
I have only used the OEM EVSE once and that was just to see if it worked. The only use I have for it is as a backup to my L2 EVSE should it ever fail. This would be bad since my FFE is my only car and there is no reasonable other way to charge my car but at home. If I can make the OEM EVSE into a 12A L2 it will be much more useful as a backup. I'll take pictures and post an explanation if anyone wants to copy and make their non-240V OEM EVSE more useful as a L1/L2 EVSE.