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How about a "Tesla Extension Cord Protocol" software feature?

wcalvin

Member
Apr 3, 2013
310
16
Seattle WA USA
I've been living for a few weeks with the equivalent of a very long thin extension cord: a 5 amp current draw will cause a 10V voltage drop, so 2 ohms line resistance. I'm only using a short extension cord so most of that is within the walls (as it were; actually an outlet at the far end of a parking lot with a long run of wire).

If you are set for the default 12A draw, the 24V drop will take the line voltage well below the 105-125VAC operating range. Charging stops. If I use 5 to 7A draws, it will stay stable overnight--all consistent with my 119VAC no-load supply staying above 105 at the car with the load. It doesn't kick out immediately at 104, but often does during the night. I am getting 1.5 m/h charging (at 20 hours per day, about 30 miles range).

I offer the following as a procedure for those inclined toward extension cords. But the whole thing could be implemented in Tesla's firmware when a 120VAC charging session was about to begin:


  1. Start charging at 5A setting (that's the minimum for some reason).
  2. Note the very first voltage display, when current still reads 0A, then note the V when current jumps to 5A. That's your voltage drop; divide by 5 to get the line resistance R.
  3. Increment load by 1A and note the reduced voltage.
  4. Repeat until V nears 105V.

A little mental arithmetic with Ohm's Law will get you there faster.
 
Last edited:

TexasEV

Well-Known Member
Jun 5, 2013
7,642
8,470
Austin, TX
I offer the following as a procedure for those inclined toward extension cords. But the whole thing could be implemented in Tesla's firmware when a 120VAC charging session was about to begin:.

Seems unlikely Tesla would do this as the owners manual says don't use extension cords :smile:
But that's good info to know.
 

AudubonB

One can NOT induce accuracy with precision!
Mar 24, 2013
8,029
26,331
I've been living for a few weeks with the equivalent of a very long thin extension cord

Guessing here: are you spending time in a winter cabin, or some other site with substandard power distribution? Or perhaps on a household generator system? You travails sound like everyday life in Bush Alaska, and I am more than a little worried I'm going to encounter similar problems when we get the Model S back home.

Before I put in our own system, we were connected to our local so-called utility (big generator behind the Lodge used to supply all of our community). Throughout any given day, voltages would vary between about 132V to 90V; Hz from 52 to 67; and they were always going out - rarely fewer than ten times per week and ofttimes 5X in a day. Try that on for size!
 

wcalvin

Member
Apr 3, 2013
310
16
Seattle WA USA
Brownouts are what need those voltage stabilizers. I am only talking about those long-run extension cords which drop the line voltage themselves. Most of the Model S's out there probably have an extension cord in the frunk; I am just offering a recipe for their use in temporary situations where trying to draw 12A yields a red ring.

Apropos warm wires concerns, a 7A draw through 2 ohms yields a 98 watt loss rate distributed along the wire.

Back home at the underground parking garage of my condo, I found that two 120v outlets would not support 12A charging, even with no extension cord. A third one works fine, even with the 100ft extension cord needed to bring it to my parking space.
 
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Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado
Before I put in our own system, we were connected to our local so-called utility (big generator behind the Lodge used to supply all of our community). Throughout any given day, voltages would vary between about 132V to 90V; Hz from 52 to 67; and they were always going out - rarely fewer than ten times per week and ofttimes 5X in a day. Try that on for size!

Wow! That's bad power even in a third world environment... Sounds like you now have a clean power system. Do you at least have a little Solar in it to make it really clean? :wink:

- - - Updated - - -

Brownouts are what need those voltage stabilizers. I am only talking about those long-run extension cords which drop the line voltage themselves. Most of the Model S's out there probably have an extension cord in the frunk; I am just offering a recipe for their use in temporary situations where trying to draw 12A yields a red ring..

Brownouts can be on a very local level (the end of your extension cord) or on a more macro level (city wide). If this problem goes on for a while, the solution is the same, something that will take in poorly regulated power and put out better regulated power.

I have a friend from South Korea. He told me his childhood story of poor power. His dad bought an autotransformer with a big knob. Everyone in the family took turns watching the voltmeter and adjusting the autotransformer to keep the house Voltage constant. The anti-brownout device that I cited is an example that does this automatically.

I agree that if it is just a short term issue, then use your method. If this is something that you encounter regularly (vacation home, etc) then the anti-brownout device may be a good investment. These devices will boost the Voltage on a long term basis.

Soak up those Joules...however you can... :wink:
 

AudubonB

One can NOT induce accuracy with precision!
Mar 24, 2013
8,029
26,331
Wow! That's bad power even in a third world environment... Sounds like you now have a clean power system. Do you at least have a little Solar in it to make it really clean? :wink:

Oh, given the niceties of Life In The Bush, on a good day we feel we're living in the third world. And I didn't mention how much we were charged for that juice.

Our own electricity, now, is 100% solar 90-95% of the time. As depicted here: Alternative Energy Powered - Page 12
My post is #113, I think. The linchpin in our system is not all the solar arrays - any number of this forum's members have larger set-ups - but the battery bank, which is 1100Ah @ 48V (not sure how you convert that into kWh). Weighs nine tons and cost as much as a Model S. As we have up to 22 guests each night - and very rarely fewer than 8 - we need real amounts of electricity all hours of the day and night.
 

wcalvin

Member
Apr 3, 2013
310
16
Seattle WA USA
UMC in-and-out, in-and-out

Coiling and uncoiling the UMC can get tiresome if you do it twice a day. But Tesla has provided (though not documented).
IMG_2630.JPG

Just use the storage bag to hold the unneeded lengths. When ready to leave, it is now easy to unplug twice and swing the bag into the trunk.

To keep the bag and most wires out of sight while charging unattended, tuck it under the rear bumper. Avoids trip hazard and lessens the chance of someone noticing it and trying to tamper.
IMG_2633.JPG
 

wcalvin

Member
Apr 3, 2013
310
16
Seattle WA USA
I offer the following as a procedure for those inclined toward extension cords. But the whole thing could be implemented in Tesla's firmware when a 120VAC charging session was about to begin:



  1. Start charging at 5A setting (that's the minimum for some reason).
  2. Note the very first voltage display, when current still reads 0A, then note the V when current jumps to 5A. That's your voltage drop; divide by 5 to get the line resistance R.
  3. Increment load by 1A and note the reduced voltage.
  4. Repeat until V nears 105V.
Apropos my #1 on extension cord strategy: They seem to have implemented this scheme in 5.9 firmware. Watch your dash display after connecting the UMC. It starts at 0A, showing 119V in my case. Then it starts ramping up the current and the voltage drops. When V=109, it stops incrementing current at, in my case, 10A. The 10V drop shows the source resistance (125ft extension cord plus what's in the walls) is one ohm.

In earlier firmware, it just kept increasing current and, when V<106v, it turned off. (The UMC operating range is 105-125.)
 
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Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado
I do not recommend coiling and/or enclosing the UMC, extension cords, or anything that generates heat while conducting electricity.

Hear, Hear!

HPWC, UMC, and extension cords will get much warmer when coiled because there is less total external area for heat dissipation.

If you have a nice coil of extra extension cord because you did not need it all, then at least scatter the loops apart and loosen the coil to increase the heat dissipation area!
 

paulkva

Member
Jul 22, 2013
703
235
Falls Church, VA
Hear, Hear!

HPWC, UMC, and extension cords will get much warmer when coiled because there is less total external area for heat dissipation.

If you have a nice coil of extra extension cord because you did not need it all, then at least scatter the loops apart and loosen the coil to increase the heat dissipation area!

Ahhh, this could explain my recent experience in Charlottesville; the hotel where I was staying ran a 120V extension cord for me from their wall to the parking lot. On day 1 it wasn't coiled up and I could charge at 7-8 amps. On day 2 it was coiled up (and slightly warmer outside) and it stopped charging even after dialing down to 6 amps. Fortunately I had enough power from other sources to get me back home. And yes, I'm going to write them to recommend they install a 14-50 outlet or HPWC closer to the parking spaces.
 

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