Use of Extension Cords

[sicki]

I am in the first week of ownership with my 2015 Spark EV. I have read the owners manual that states to NOT use extension cords to get from outlet to vehicle charging cord unit. I can think of several reasons why this may not be efficient. Are there reasons that it may harm the vehicle also?

Has anyone experimented with this?
Are there certain extension cords (12ft is all i need at work) that will not have a loss of power or harm vehicle.

Any help is greatly appreciated.

 

[sicki]

I did a search and found everything I need...sorry for being lazy and posting about a topic that has been discussed thoroughly...Thx in advance to all who post info on here...glad this forum exists!!!

Already stoked i havent seen a gas station all week..

Now I can tear apart my Tacoma and start building it up for the desert!

 

[oregonsparky]

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

 

[kevin]

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

 

[NORTON]

25 Ft. of 12 ga. wire in a wall is no different than a 25 Ft. 12 ga. extension cord, as long as the sockets and plugs are all in good condition.

An EVSE is only a smart/safe relay. It's either open or closed. It sends a pilot signal to the cars on board charger, limiting the max the car should draw.

The car's 'On Board Charger' controls the amount of power it will take from the grid. With the Spark EV its: 1kW or 1.4kW @ 120V or 3.3kW @ 240V.

 

[oregonsparky]

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

 

[MrDRMorgan]

I have a 25 ft., 12 ga extension cord connected on one end to a 20 amp wall outlet and the other end to the L1 EVSE supplied with the car. However, I only run at 8 amps and right now I am using it every night to help protect the HV battery from the cold weather. This is the least efficient of all of the charging options (60 - 65%). No problems so far.

My regular daily charging is done using a Bosch Power Max L2 EVSE charging at about 80 to 85% efficiency or at a nearby NRG eVgo DCFC.

 

[kevin]

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"...)
....

Jeff

I don't believe this would occur. The efficiency of the the charger is NOT reduced much by adding resistance in series with the AC supply.

Also the power cord will not be significantly reactive, the loop area will be small as the line and return are close together.

There is power lost within the extension cord which will cause it to heat up and at the lower power the losses due to fans pumps etc will be a larger proportion of the input power so the efficiency of the system will reduce, but the power dissipated in any individual component will be the same or less.

Since the current input to the charger is regulated that will tend to stay constant in spite of the voltage drop in the cable.

kevin

 

[kevin]

I have a 25 ft., 12 ga extension cord connected on one end to a 20 amp wall outlet and the other end to the L1 EVSE supplied with the car. However, I only run at 8 amps and right now I am using it every night to help protect the HV battery from the cold weather. This is the least efficient of all of the charging options (60 - 65%). No problems so far.
...

"(60 - 65%)"

That seems a bit pessimistic - I measured mine with 12Amps L1 charging and it was about 78%. (This is from AC input to power indicated on the energy display so it includes battery losses).

Using L2 charging I calculated 83% efficiency.

kevin

 

[MrDRMorgan]

I have a 25 ft., 12 ga extension cord connected on one end to a 20 amp wall outlet and the other end to the L1 EVSE supplied with the car. However, I only run at 8 amps and right now I am using it every night to help protect the HV battery from the cold weather. This is the least efficient of all of the charging options (60 - 65%). No problems so far.
...

"(60 - 65%)"

That seems a bit pessimistic - I measured mine with 12Amps L1 charging and it was about 78%. (This is from AC input to power indicated on the energy display so it includes battery losses).

Using L2 charging I calculated 83% efficiency.

kevin

I know it sounds low but the 60 to 65% efficiency number was derived from data taken daily during the month of July 2015. The actual power delivered into the L1 EVSE was taken using a Kill A Watt EZ power meter. The power meter was plugged directly into the wall socket (20 amp service) and the L1 EVSE was plugged directly into the power meter - no extension cord. The car was fully charged, driven for 40-50 miles and then fully recharged again.

At the end of the month I divided the total number of kWh the car's display showed the car used (139.5 kWh) by the number of kWh the power meter showed it took to fully recharge the car (214.9 kWh). The calculated efficiency for this 31-day, 759 mile test was 64.9% and all charging was done at the 8 amp charging rate. The 12 amp rate was about 5% better.

My calculated Bosch Power Pak L2 EVSE charging efficiency is very close to your 83% number: 80%

Test vehicle: New 2015 Spark EV 2LT with DCFC leased on 30 May 2015.

 

[NORTON]

I have a 25 ft., 12 ga extension cord connected on one end to a 20 amp wall outlet and the other end to the L1 EVSE supplied with the car. However, I only run at 8 amps and right now I am using it every night to help protect the HV battery from the cold weather. This is the least efficient of all of the charging options (60 - 65%). No problems so far....

This is my situation also. I want to measure: when plugged in at home and the 'Delayed Departure' is set so that the car does not start charging at home, will the battery's Thermal Management System (TMS) still draw current as needed to keep the battery at a 'happy temp' during these cold nights.
I mostly charge at free public L2 and DCFC. Cheap azz, I know....

My EVSE is an 'auto 120V or 240V unit. I normally run it at 240V, but to measure TMS usage I will plug it into 120V and run it through a 'Killawatt', a cheap kWh meter.

BTW: I'm using a 50 ft., 12 ga. extension cord, plugged into a new, dedicated 20A CB and outlet.
According to this 'Wire Gauge Calculator' it's OK at 12A on 120V. : http://www.csgnetwork.com/wiresizecalc.html
I have used this set up for 3 years now with a Volt and now with my Spark EV.

 

[oregonsparky]

I have also run a 12 gauge electrical cord - about 20 feet long before I got my car in the garage with the L2 going. I felt very safe in doing this - it was plugged into a brand new 20 amp plug that I had installed with 3 feet of wire from the plug to the breaker box - using 12 gauge wire.

When I say "long thin wire" - I mean a cheap extension cord that is 100 feet long (as an example). In my mind 10 or 12 gauge wire is not "thin" - 16 or 18 gauge is. I think the manual states no extension cords should be used because your average person doesn't know the difference - and might think that any old lamp cord will do - so they just say "don't use one" to cover their ass.

I think the two examples given here are fine - 25 feet or 50 feet of 12 gauge into a 20 amp plug close to your breaker box. I would feel safe doing this - and, as I said, I did it myself.

If you were plugging into a 15 amp receptacle in an older home 50 feet from your breaker box (might be 14 gauge wire) and you wanted to run 100 feet of 14 gauge cord - i would say "eh, I wouldn't if I were you..."

One thing that I didn't think about is that the motor for the compressor and all pumps for the coolants are electric motors and *are* reactive loads.

The only reason I am "beating a dead horse" here is that thinking about the "loads" as purely resistive when they are reactive - only thinking about the voltage drop in the wire implies that running longer runs of say, 14 or 16 gauge electrical cord has no risk other than fire in the cord due to resistive heating. People should be warned that you can damage the electric motors/pumps or the on board charger. (Do we really want to give advice that might damage someone's car?)

I have seen discussions on some forums that simply say "your charger might take longer to charge with a long extension cord due to the voltage drop but other than that - you are fine - just check to make sure the cord isn't getting hot" - it ain't that simple..

jeff

 

[NORTON]

...One thing that I didn't think about is that the motor for the compressor and all pumps for the coolants are electric motors and *are* reactive loads....
jeff

I think if you research this you'll see that that the AC compressor (used for Cabin Climate Control and battery TMS, when needed) runs from the HV DC and has it's own internal inverter for 3 phase AC. I hear it run up at different speeds as needed at a DCFC in the summer.
And I'm almost certain all the coolant pumps are plain 12 VDC.

This means the grid AC is only going to the On Board Charger.
And I know that regardless of what the car is doing at the moment the draw from the grid is rock steady at 1kW or 1.4kW @ 120V or 3.3kW @ 240V.
EDIT: except I've read the charge rate drops nearer to 100%.

 

[oregonsparky]

...One thing that I didn't think about is that the motor for the compressor and all pumps for the coolants are electric motors and *are* reactive loads....
jeff

I think if you research this you'll see that that the AC compressor (used for Cabin Climate Control and battery TMS, when needed) runs from the HV DC and has it's own internal inverter for 3 phase AC. I hear it run up at different speeds as needed at a DCFC in the summer.
And I'm almost certain all the coolant pumps are plain 12 VDC.

This means the grid AC is only going to the On Board Charger.
And I know that regardless of what the car is doing at the moment the draw from the grid is rock steady at 1kW or 1.4kW @ 120V or 3.3kW @ 240V.

Thanks for the clarification and the correction.

jeff

 

[kevin]

I know it sounds low but the 60 to 65% efficiency number was derived from data taken daily during the month of July 2015. The actual power delivered into the L1 EVSE was taken using a Kill A Watt EZ power meter. The power meter was plugged directly into the wall socket (20 amp service) and the L1 EVSE was plugged directly into the power meter - no extension cord. The car was fully charged, driven for 40-50 miles and then fully recharged again.

At the end of the month I divided the total number of kWh the car's display showed the car used (139.5 kWh) by the number of kWh the power meter showed it took to fully recharge the car (214.9 kWh). The calculated efficiency for this 31-day, 759 mile test was 64.9% and all charging was done at the 8 amp charging rate. The 12 amp rate was about 5% better.

My calculated Bosch Power Pak L2 EVSE charging efficiency is very close to your 83% number: 80%

I did my measurements in the same way for L1.

For L2 I used Chargepoint's numbers for energy input over a a year's worth of charging to get the 83% number (~150 charges).

I only had a half dozen charges for L1 so your numbers are almost certainly more accurate.

My car is a 2014 Spark EV - DCFC wasn't available when I got mine.

kevin