Extension Cord?

Here’s another question, and some experience behind it. Again, the car is a 2013 smart electric coupe.

The car comes with a charger that plugs into a normal 110 volt household receptacle. There is one in the in-house garage. The user’s manual says that there should be nothing else on the circuit. There isn’t. According to the breaker in the junction box the circuit is rated at 15 amps. So far so good. However the cord on the charger is not long enough to let me park where I want in the garage and charge the car. In fact to do so would be very inconvenient.

The manual states clearly that using an extension cord is a no-no. I tried it anyway with an old but heavy duty extension cord. The plug got kind of warm, and the car stopped charging. The charger must be smart, because nothing was damaged. I then bit the bullet and parked the car next to the outlet (after moving a lot of stuff around). No problem, charged as expected.

Then, looking through the car’s menus, I found that I could limit the amps that the charger would draw from the default of “MAX” to 12 or 8 amps. I tried it at 12 amps, and there was no problem using the extension cord.

Then I bought a new extension cord rated at 15 amps (same as the circuit I’m plugging it in to) and with 12 gauge wire (heaviest you can get). I have charged the car with the setting at 12 amps and “MAX” amps. No problems and nothing getting even slightly warm. I throttled it back to 12 amps just to be on the safe side anyway. Given the miles we drive in a day it will have plenty of time to charge overnight at that setting.

Does anyone have any thoughts on/experience with all of this? Before you answer, let me say that one thing I will not do, at least at this juncture, is rewire the garage for this purpose. The junction box is at exactly the opposite corner of the building from where I want the charger. This would not be cheap. If we really get into electric vehicles (I’ve only had this thing 3 days) then we might do it really right and run a 220 line all the way over and get a faster charger. But that will be after we have the car a while, see how it does in a New England Winter, and if it fits our lifestyle as well as I think it will.

After doing some more research, getting some knowledgeable consulting, and a bit more playing around with it, I have answered my own question. So never mind.

An extension cord is not dangerous if the current it will carry is the same as or more than the circuit behind the wall outlet. In my case the wall outlet is on a 15 amp circuit supplied by 14 gauge wire. The extension cord is rated also at 15 amps and uses 12 gauge wire. In the gauge system, a smaller number means bigger wire. So the extension cord specs actually exceed those of the base circuit. So there’s no possibility of hazard. However, since the run from the junction (fuse) box in the house to the outlet is around 35 feet, and the extension cord is 25 feet, there is some loss of potential due to the increased distance. While not dangerous, this does increase charging time, quite a bit actually.

Reading more in the manual for the charger itself I learned that the charger is smart enough to detect a problem with the incoming power supply, and will shut itself off and a light that is normally green will flash red. In all of my experiments, this never happened. I also noticed that when using a 110-120 volt source, the charger is programed to never draw more than 12 amps. So setting the car to not draw more than 12 amps was not needed, and I set it back up to “MAX” so that it can use public charging stations effectively, as they are all 240 volt units and charge about twice as fast.

Maybe all this will help some other pilgrim. All of this applies to North America only, by the way.

I suspect that the warning (multiple warnings!) against using an extension cord is to cover the manufacturer in case someone uses a lamp cord weight extension cord like we would use in the house. That would be a fire hazard, as the plug and outlet would get very hot.