kevin said:
oregonsparky said:
Most of the discussions here related to running extension cords consider the load to be 'purely resistive". The load being the charger in the car... So this leads most to talk about voltage drop and heat in wires due to their resistance, etc. ohms law, kirchoffs voltage law, etc.
But it isn't "purely resistive" so one can't think about it completely in these simple terms. It is "reactive". Which means a thing called 'power factor' comes into play.
I studied "power" taking electrical engineering 30+ years ago. So I have forgotten much in this area - so any budding electrical engineers are welcome to correct me... With a purely resistive load - the current and voltage waveforms are sinusoidal and line up perfectly. With a reactive load there is a lag and they don't "line up". This is represented as power factor and some of the magnitude is "real" and some "imaginary", etc. When this happens the current can go "way up' on the load... This may easily fry the on board charger.
My understanding of it, I see it as a domino effect if you run a long extension cord.
- long thin wire increases resistance
- increase in resistance (and maybe accompanying volt drop) throws off power factor to a point where the on-board charger can't correct for it (it surely has power factor correction.)
- Power factor change means the charger itself actually starts pulling *alot* more current...
- Charger "smokes" due to excessive current....
It is not at all intuitive - but add a long and thin extension cord and the on board charger will 'fry itself". And they are not cheap...
jeff
" - Charger "smokes" due to excessive current...."
I can't see any way that would occur and I think it is not something to worry about.
The main problems is loss of power and heating of the extension cord.
kevin
Kevin -
I did say it wasn't intuitive. Didn't I?
Think of it this way - if you add a long and cheap extension cord it not only reduces power to the charger - because of power dropped in the wire - it also makes the charger inefficient. When it is inefficient - then it produces less work for the amount of energy coming into it. Conservation of energy means that wattage that is not used for "work" goes somewhere..... heat... So, like I said, it isn't intuitive - but run a long extension cord to your charger that is too small and the thing that catches on fire isn't the extension cord - it might be the charger itself... (less likely because we have a water cooled charger - but you can still "kill it"...)
This is also true if you use a cheap generator - it will produce quite a few harmonics in those voltage and current waveforms that it is putting out for you. These harmonics create inefficiencies in the on board charger. So energy going in does not equal work performed - the difference being *heat*. This is a good reason why the manual says not to feed the car with a gas generator.
I learned this lesson when I was working framing apartment buildings in the 1970s in the seattle area. Late 70s the economy was "on fire" and apartments were flying up - they couldn't hire enough rough carpenters - so guys would show up with zero experience with a brand new skilsaw and 200 feet of 16 gauge electrical cord. the cord didn't get hot and catch fire... The saw would sound funny and would be dead by the end of the day - the windings in the saw would burn up.
We would run 300 feet of cord when we had to - but it would be 10/3 for the majority of the run... Never lost a saw...
Later, when I was studying electrical engineering at Washington State University I had this great professor - Professor Baker - bless his soul. He would say - "this is how it works" describing magnetic fields building and rotating - charge, current & voltage relationships - electric motors and generators of all kinds - it was the most wonderful learning experience in my life. After explaining "how things worked" - he would say "okay, now that we understand it - let's talk about the math for this...". It was awesome.
I asked professor baker about my experiences of watching saws fail when I was a framer - and he explained to me why the saw burned up - the power factor degrading - the inefficiency building - the current - the heat.... I wish he were here to repeat it to us - as my memory is fading...
Believe me when I say you don't fully understand what is going on with this situation - and what you don't know could hurt you....
To both you and Norton - read these pages on wikipedia related to "power factor" and different types of power - it took me some time to understand terms like "real power", "reactive power", "imaginary power, etc (and I have forgotten most of it!).. I would hope you will come away saying "this might be a little more complex than I was thinking..."
https://en.wikipedia.org/wiki/Power_factor
https://en.wikipedia.org/wiki/AC_power#Active.2C_reactive.2C_and_apparent_power
I am not saying I know this stuff and you don't. But I think I can say that I do remember enough to "know what I don't know" - and that is enough to say to myself - be careful and don't run a cheap, long extension cord to the new electric car - it won't hurt the electicral cord - it could really f*ck up the car... I think a new charger is like $2500...
Jeff