Hello everyone, I want to set up charging in my apartment's garage from a regular 110V outlet. When I connect directly to the outlet (without using an extension cord), I get 110V and 12 Amps. However, when I use an extension cord, the current strength drops to 8 Amps. I can't charge without the extension cord because it blocks access for my neighbors. So, I decided that the extension cord would solve my problem. I bought a 150-foot extension cord with the following specifications: 15A, 1875W, 125V, 12AWG. Is there any way I can get 12 Amps, and what do I need to do for that?
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The current strength decreases when I use an extension cord.
- Thread starter tihaleks@gmail
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You may have a voltage drop problem in using a 150 ft extension cord with only 12ga wire. This adds 300 ft of wire to whatever the wire length is from the breaker panel to the building outlet. 300 ft of wire, at 12 amps, has almost 15V drop. It's likely that the Tesla mobile connector senses the voltage and reduces current to keep the voltage above a threshold level. At 8 amps, the voltage drop is 9.5 V.
It's also possible that the temperature sensor in the mobile connectors plug has sensed a high temperature where it is plugged into the extension cord outlet and has scaled back the charging current to prevent a fire.
Using a shorter extension cord and/or larger gauge wire may increase the charging current. However, using an extension cord with a mobile connector is a fire hazard as the temperature sensor at the mobile connector plug is not at the building outlet. Cheap outlets, and those that have not been installed using best practices, can overheat when drawing high currents for long charging sessions.
It's also possible that the temperature sensor in the mobile connectors plug has sensed a high temperature where it is plugged into the extension cord outlet and has scaled back the charging current to prevent a fire.
Using a shorter extension cord and/or larger gauge wire may increase the charging current. However, using an extension cord with a mobile connector is a fire hazard as the temperature sensor at the mobile connector plug is not at the building outlet. Cheap outlets, and those that have not been installed using best practices, can overheat when drawing high currents for long charging sessions.
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rhumbliner
Member
It’s almost certainly caused by the length of the extension cord and that fact that it is only 12AWG. It would be pricey but you could try a 10AWG extension cord from Amazon: 10 AWG Extension Cord and see if that works any better.
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Adding length to a wire increases the resistance, which is why both the length of the run and the wire gauge matters. I use a 10 gauge generator extension cord on a dedicated 20 amp circuit. Buy one only long enough to properly reach, and avoid anything made in China.
That outlet needs to be on a dedicated circuit. There should be no other loads on that circuit as you're pulling the maximum current on a continuous basis.
That outlet needs to be on a dedicated circuit. There should be no other loads on that circuit as you're pulling the maximum current on a continuous basis.
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Resistance increases from extra wire length and thin wire gauge, and you have both of those going on here. If it were only 15 or 20 feet, it probably wouldn't impact it much, but yours is much longer than that. As others mentioned, 10 gauge wire and shorter length should help this.
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10gauge 100' extension cord form Uline worked well for me-no hot end pieces nor voltage lost but not cheap
Heavy Duty Extension Cord - 100', 10 Gauge, 15 Amp S-23548 - Uline
I'm sure there are others brands
Heavy Duty Extension Cord - 100', 10 Gauge, 15 Amp S-23548 - Uline
I'm sure there are others brands
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fiveangle
Member
For those searching in the future, you can calculate the extension cord size in AWG for charging using this web app:
www.inchcalculator.com
For extension cord, you double the wire length (because 150x2 or 300 feet in the OPs case) and set the acceptable voltage drop to 5%. For OPs use, if he needed a 150' extension, the calculator indicates you would need a 9AWG cord. As 10AWG is the maximum AWG you can typically find at most hardware stores, you would need to drop to a maximum of 100' of 10AWG to safety charge at 12A continuous.
It's always best to use the shortest cord possible (ideally none, if possible, but you gotta do what you gotta do
Wire Size Calculator
Calculate the wire size needed for a circuit given the voltage and current rating required. Plus, calculate the size of a wire gauge in AWG.
For extension cord, you double the wire length (because 150x2 or 300 feet in the OPs case) and set the acceptable voltage drop to 5%. For OPs use, if he needed a 150' extension, the calculator indicates you would need a 9AWG cord. As 10AWG is the maximum AWG you can typically find at most hardware stores, you would need to drop to a maximum of 100' of 10AWG to safety charge at 12A continuous.
It's always best to use the shortest cord possible (ideally none, if possible, but you gotta do what you gotta do
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Clearly, 10 gauge or 12 gauge are best, however, for shorter runs and convenient carry, I carry one of these in my frunk for those rare times it's needed:
or
www.acehardware.com
Since it has 3 outlets at different distances along the cord I can use the shortest length needed. Going more than 25 feet should be avoided in general however, if one's permanent location requires it, that definitely calls for a heavy 10 or 12 gauge cord which I don't care to carry with me,
Woods 25 ft. 14/3 Multi-Outlet (3) Garden Outdoor Medium-Duty Extension Cord, Green 3030 - The Home Depot
Woods 3030 14/3 Cord Runner Multi-Outlet Extension Cord with Spaced Plugs, 25 ft. These in-line extension cords have 3 evenly-spaced outlets instead of just one at the end and each outlet has a power indicator to let you know when the power is on. The heavy-duty STW cords are durable and outdoor...
www.homedepot.com
Ace Outdoor 25 ft. L Green Triple Outlet Cord 14/3 STW - Ace Hardware
Find the EXT CORD 25' 3OUTLT GRND at Ace.
www.acehardware.com
Since it has 3 outlets at different distances along the cord I can use the shortest length needed. Going more than 25 feet should be avoided in general however, if one's permanent location requires it, that definitely calls for a heavy 10 or 12 gauge cord which I don't care to carry with me,
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Personally I would never use a 14 gauge cord for EV charging.Clearly, 10 gauge or 12 gauge are best, however, for shorter runs and convenient carry, I carry one of these in my frunk for those rare times it's needed:
orWoods 25 ft. 14/3 Multi-Outlet (3) Garden Outdoor Medium-Duty Extension Cord, Green 3030 - The Home Depot
Woods 3030 14/3 Cord Runner Multi-Outlet Extension Cord with Spaced Plugs, 25 ft. These in-line extension cords have 3 evenly-spaced outlets instead of just one at the end and each outlet has a power indicator to let you know when the power is on. The heavy-duty STW cords are durable and outdoor...www.homedepot.com
Ace Outdoor 25 ft. L Green Triple Outlet Cord 14/3 STW - Ace Hardware
Find the EXT CORD 25' 3OUTLT GRND at Ace.
Since it has 3 outlets at different distances along the cord I can use the shortest length needed. Going more than 25 feet should be avoided in general however, if one's permanent location requires it, that definitely calls for a heavy 10 or 12 gauge cord which I don't care to carry with me,
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Eric33432
Member
Don' think you need to double the length when using this calculatorFor those searching in the future, you can calculate the extension cord size in AWG for charging using this web app:
Wire Size Calculator
Calculate the wire size needed for a circuit given the voltage and current rating required. Plus, calculate the size of a wire gauge in AWG.
For extension cord, you double the wire length (because 150x2 or 300 feet in the OPs case) and set the acceptable voltage drop to 5%. For OPs use, if he needed a 150' extension, the calculator indicates you would need a 9AWG cord. As 10AWG is the maximum AWG you can typically find at most hardware stores, you would need to drop to a maximum of 100' of 10AWG to safety charge at 12A continuous.
It's always best to use the shortest cord possible (ideally none, if possible, but you gotta do what you gotta do
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I understand and appreciate this prudence, however, 14 gauge is rated for 15 amps (NFPA ratings). The Model 3, Y, and Roadster (all I can quickly verify right now) default to 12 amps when charging on 120v. Therefore, 14 gauge it is technically sufficient (it even has 20% extra margin) to charge. Using the 25 ft cord that I recommend and, even better, using the shortest length possible, made possible by the inter-spaced outlets along this particular cord, is still fine by pretty much any measure.
This is especially useful when overnight parking in extreme cold weather when it generally won't allow you to charge much but it will keep the battery warm to facilitate Supercharging or reduced range when departing.
Please don't let Perfect become the enemy of Good Enough.
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You're giving partial information. You're being too general when you just say "when charging on 120V". The reason why people are cautioning against that is that 120V can be at various amp levels. So if people have the 5-15 adapter and the 5-20 adapter, they would have to be careful, as the 14 gauge cord is appropriate for one but not the other.
So by recommending 12 gauge as a minimum, the one cord could cover both cases.
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There's no doubt that a 12 gauge wire will work in all cases. Its just bulkier, more expensive, and harder to find that 14 gauge ones that will work just fine.
One cannot plug a 5-20 adapter into a 5-15 outlet anyway. The 5-20 adapter has one blade vertical and the other horizontal so it won't fit in most extension cords, including the one I called out, that only have 2 parallel vertical blade sockets.
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