WARNING: Extension Cords

Right! Or, more formally, I=E/R.

If the load could command a certain wattage, then current would rise as voltage drops, but it can't. So that formula is P=Esquared/R. Either way, as resistance goes up, voltage drops and so does power.

 

Do note that with the widespread use of switch mode power supplies today, there are lots of loads that can command a certain wattage, or a certain current, regardless (almost) of the line resistance. These can make mincemeat of the old resistance rules, so some devices really do appear to have negative resistance, i.e. load current increases when input terminal voltage drops.

 

I haven't actually studied them much. I assume that's because of the feedback used to regulate them?

 

Correct.

You can design the controls in a switching power supply to regulate almost anything you want. Voltage is the most common but some regulate current and every battery charger does both depending on where you are in the charge cycle (current at the beginning, voltage at the end).

 

Good point. In California you are asked to charge at night because the grid is too weak.
Also, you are used to spending when you buy a new car, so cough up a few bucks for a “dedicated” extension cord.
BTW, is there such a thing as an in line thermal breaker, in stead of relying on the breaker in the box?

 

The Toyota charging cable has a temperature sensor in the plug (also linked in #23 above).

Commercially-available, in-line GFCI devices typically provide only ground-fault protection, not overcurrent protection (thermal, thermal-magnetic, electro-synthe-magnetic, or otherwise) but I suppose one could put a miniature circuit breaker or supplementary protector into a small enclosure with cable glands.

To be clear, I don’t recommend using extension cords for EV charging at all. (EV operation is fine, of course.)

 

Southwire E-238 Heavy Duty Power Station Cord reel, with 6 Grounded Outlets, 12/3 50-Foot Extension Cord, Built In 15-Amp Circuit Breaker, Green/Black https://a.co/d/j57pf8g