15 amps Vs. 30

[Jae001]

Does anyone know if you use more electricity charging at 15 amps for say 4 hours vs. 30 amps for 2 hours? Obviously 30 amps charges quicker but does it use more electricity over a shorter period of time? I can't seemed to find an answer to this on the Internet. I would like to upgrade my house wiring to support higher amperage charging but speed is not really an issue but the cost of electricity is. Any help would be appreciated. Thanks.

 

[ralph142]

watt hours are amps * volts per hour. so 15 amps @120v = 1800 watts x 4 hours = 7200 wh, 30 x 120 = 3600 x 2 = 7200. so no, if the voltage is the same.

 

[Jae001]

watt hours are amps * volts per hour. so 15 amps @120v = 1800 watts x 4 hours = 7200 wh, 30 x 120 = 3600 x 2 = 7200. so no, if the voltage is the same.

Thanks. The voltage would be 220 for both but I assume the formula is the same?

 

[jmaddr]

Same watts as @ralph142 mentions.
The only difference, and I can't quantify this...is I've also read some literature that 240V may be slightly more "efficient" than 120V. Is that an 88% efficiency vs 96%? I couldn't say. Maybe someone here with the more knowledge of the voltage transformer in the MS can comment.

 

[ralph142]

Same watts as @ralph142 mentions.
The only difference, and I can't quantify this...is I've also read some literature that 240V may be slightly more "efficient" than 120V. Is that an 88% efficiency vs 96%? I couldn't say. Maybe someone here with the more knowledge of the voltage transformer in the MS can comment.

yep, there is about 200-300 watts / hour or so used by the car for running the electronics, so slower charging is less efficient, and, of course if the plug is a 15 amp plug, the car will only pull 80% of the amps, so delivered to the battery it would be:
12 amps x 240 v x 4 hours - (4 x 300w ) =10320 wh,
vs a 30 amp plug:
24 amps x 240 volts x 2 hours - (2 x 300 watts) = 10920 wh,
but I was trying to keep it simpler.

same amount of power consumed, but more delivered to the battery at 30 amps for a shorter period. thats approximate, somebody with more detailed knowledge can clean up the rough edges.

 

[Jae001]

OK, I found the dumbed down explanation for efficiency (120 vs 240)

The main losses come from resistance. A higher voltage means that a lower current is required to transmit the same amount of power. Over long wires, this means lower losses. This is actually the main reason why power lines are run a much much higher voltage, and then stepped down when they get to your home. This also means that less copper is needed in the wires in your home.

 

[ewoodrick]

At home your voltage should be 120/240. Most houses are wired with Line1 to neutral and Line 2 to Neutral, each at 120V, for 240V total.

There is a small overhead that the car uses, so there is slight efficiencies in charging at 240V. But easiest to just assume that they are equal. Not going to make a realistic difference.

 

[murphyS90D]

120 volts AC has to be converted to DC and then multiplied up to more than 400 volts DC to charge the battery.
There are losses in that multiplication.
The same happens with 240 volts AC but only half of the multiplication is needed so 240 volts AC is more efficient than 120 volts AC.
If the house is wired properly resistance in the wires is very low. When drawing 80 amps at 240 volts through a 75 foot run of 2 gauge wire the voltage drop due to wire resistance is 2 volts in my house. That is a 0.83% drop.

 

[D.E.]

There is an efficiency of charging. The car has overhead so with 120V, it charges at about 4 miles of range per hour of charge. With 240V, much more of the juice ends up in the battery, if my memory is correct it’s about 13 miles of range per hour with a 30A 240V. There is a step up in efficiency each time you go up in amperage so you’ll spend less on electricity if you put in a 240V 50A plug than if you rely on 120V current. You shouldn’t allow the car to pull the maximum current anyway, an electrician should explain it but if it’s a 50A circuit, it shouldn’t be expected to deliver all the 50A.

Anyway, your electrically cheapest option is to install the largest supply current circuit. Or you could put in solar panels. That’s an expensive way to get free power.

 

[Jae001]

Thank you guys for all the great comments! Tesla solar system is being installed in a few weeks then we are talking free power to charge all I want. Electricity rates in Southern California are out of control. My last power bill was $550 for one month (power only).

 

[quickstrike12]

I think solar is the way to go for sure.
I want to justify and get solar. I just can’t make the math work when I’m only paying 7.9¢ Per kw. Would take me forever to recover that.

 

[azjohn]

I think solar is the way to go for sure.
I want to justify and get solar. I just can’t make the math work when I’m only paying 7.9¢ Per kw. Would take me forever to recover that.

I saw a recent YouTube video on this subject and somebody who had solar after 1 year crunched numbers and figured on if nothing changes it would take about 40 years to justify investing in solar. They lived in Colorado and owned a Tesla

 

[Jae001]

I saw a recent YouTube video on this subject and somebody who had solar after 1 year crunched numbers and figured on if nothing changes it would take about 40 years to justify investing in solar. They lived in Colorado and owned a Tesla

It all depends on where you live and the electricity rates. Here in Los Angeles you pay between 0.17-.0.31 per kW. Totally out of control!! Here solar makes sense especially with all the sun we get. Remember Tesla now rents (subscription) solar so there is no upfront costs (providing you have a 200 amp panel and a good roof). No long term contracts or a credit check. It is a no brainer.

 

[murphyS90D]

Adding solar to a house is an improvement to the house. You get the cost back if/when you sell the house. Do you expect to see a break even point if you add a room or a pool to a house? I installed solar in September of 2013. So far my panels have generated 71,800 kWh.
That's 71,800 kWh I didn't have to buy from the power company.

 

[quickstrike12]

Adding solar to a house is an improvement to the house. You get the cost back if/when you sell the house. Do you expect to see a break even point if you add a room or a pool to a house? I installed solar in September of 2013. So far my panels have generated 71,800 kWh.
That's 71,800 kWh I didn't have to buy from the power company.

No I don’t expect a break even point for a pool or additional room. I DO however expect to use them and enjoy them as an additional feature of my home. Solar is not something I get to use and get a difference from. It is just a “different” source of my energy needs. I choose the cheaper of my options. The same as I change electric companies when one raises rates higher than the other.
In Texas selling your home with solar may or may not provide the buyer with incentive. It’s not so cut and dry here due to the low cost of energy and some would say unsightly look and extra Maint they may incur from solar.
believe me I want it and am very pro solar as a resource but trying to justify it, I just don’t think it makes sense for me yet.

 

[Big Toys]

Does anyone know if you use more electricity charging at 15 amps for say 4 hours vs. 30 amps for 2 hours? Obviously 30 amps charges quicker but does it use more electricity over a shorter period of time? I can't seemed to find an answer to this on the Internet. I would like to upgrade my house wiring to support higher amperage charging but speed is not really an issue but the cost of electricity is. Any help would be appreciated. Thanks.

Keeping it in layman's terms:

"More electricity" is not the right question. Higher amps and voltage delivers more "power" in a shorter period of time, but your batteries will only hold the amount of "power" it is designed for, much like filling a gas tank with the handle half or fully squeezed. Unless you have a cost differential (night time cheaper), the time and cost it takes to charge is dependent on how much "power" you deliver (per hour). That's why higher amps will charge faster than lower amps. If you are installing from scratch, pay for the thicker wire needed to deliver 30 Amps at 220 V. Your electricity bill will be the same, and charge at night if you have price differential.

 

[Big Toys]

No I don’t expect a break even point for a pool or additional room. I DO however expect to use them and enjoy them as an additional feature of my home. Solar is not something I get to use and get a difference from. It is just a “different” source of my energy needs. I choose the cheaper of my options. The same as I change electric companies when one raises rates higher than the other.
In Texas selling your home with solar may or may not provide the buyer with incentive. It’s not so cut and dry here due to the low cost of energy and some would say unsightly look and extra Maint they may incur from solar.
believe me I want it and am very pro solar as a resource but trying to justify it, I just don’t think it makes sense for me yet.

Same here in Florida. I'd love to go solar. Upfront costs are supposed to be lower than even a few years ago, but it never seemed to improve. It also makes no financial sense as I probably will never see the ROI in my lifetime with the relatively cheap price of electricity here, and I still have a quite a bit to go.

 

[D.E.]

I saw a recent YouTube video on this subject and somebody who had solar after 1 year crunched numbers and figured on if nothing changes it would take about 40 years to justify investing in solar. They lived in Colorado and owned a Tesla

I may do solar even if not justified by the payback period. I’d just feel better knowing my electricity use was provided by solar so not contributing to warming the Earth.

 

[D.E.]

Keeping it in layman's terms:

"More electricity" is not the right question. Higher amps and voltage delivers more "power" in a shorter period of time, but your batteries will only hold the amount of "power" it is designed for, much like filling a gas tank with the handle half or fully squeezed. Unless you have a cost differential (night time cheaper), the time and cost it takes to charge is dependent on how much "power" you deliver (per hour). That's why higher amps will charge faster than lower amps. If you are installing from scratch, pay for the thicker wire needed to deliver 30 Amps at 220 V. Your electricity bill will be the same, and charge at night if you have price differential.

I don’t think that is right. It uses more total kilowatt hours to recharge the Tesla at 120V than it does charging at 240V. It’ll charge at 120V but there is more electricity used due to the lower charging efficiency.

 

[AndrewTX]

I think solar is the way to go for sure.
I want to justify and get solar. I just can’t make the math work when I’m only paying 7.9¢ Per kw. Would take me forever to recover that.

Are you finding that rate for a renewable energy source? I've not seen one that low which isn't almost 100% gas/coal generated.

No I don’t expect a break even point for a pool or additional room. I DO however expect to use them and enjoy them as an additional feature of my home. Solar is not something I get to use and get a difference from. It is just a “different” source of my energy needs. I choose the cheaper of my options. The same as I change electric companies when one raises rates higher than the other.
In Texas selling your home with solar may or may not provide the buyer with incentive. It’s not so cut and dry here due to the low cost of energy and some would say unsightly look and extra Maint they may incur from solar.
believe me I want it and am very pro solar as a resource but trying to justify it, I just don’t think it makes sense for me yet.

You're probably right if this is a 100% financial decision for you. Buying a Tesla probably wasn't a sound decision financially, either.