There is a way to double your charge rate when you have 120V supplies (either through TT-30s or regular household 120V plugs). If you can find two receptacles that are fed from the two different 120V legs of the breaker box, then you could combine the 120V hots to make a 240V output at whatever amperage rating is for the plug (de-rated 24A for TT-30 and 12A for 5-15 and 16A for 5-20). This would double your charge rate for 120V sources.
HOWEVER, making such an adapter is NOT straightforward and REQUIRES the use of relays for shock safety. You might think it would just be a matter of connecting hots from each plug into a receptacle, BUT THIS WILL RESULT IN AN IMMEDIATE SHOCK HAZARD WHEN CONNECTED TO MOST VEHICLES. The EVSE will complete a circuit and when you go to unplug one of the two 120V plugs from the wall, the PLUG will have 120V on it from the other plug that is still plugged into the wall. Obviously PLUGS should never have electricity on them unless safely plugged into a receptacle, so this is a major safety hazard.
There is one more caveat about using these devices. They will not work when plugged into GFCI protected outlets. They only work with non-GFCI receptacles and each receptacle must be located on a different phase of the electrical supply (it can take some hunting to find two such receptacles in a house).
Coming soon, I'll post information on how to build one of these combiners, but for now, see the sidebar to purchase one.
Quick 220 Systems makes devices that allow you to safely combine 120V outlets to make a 240V outlet.
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