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How much current (kW) is your house using while charging?

Jimat

Member
Jun 21, 2014
98
14
Burra NSW
I've got a question for you guys. I've recently installed a solar system that collects up to 5kw during peak sunshine.

How would I know what Amp to set the car to, to make sure the car is getting charged by the solar array and not pulling from the grid?
A 5kw array should produce about 5kw when in full sun in ideal conditions but the output will almost always be less than that. So just set the charge current at about 20A (4600w) and most of your PV output will go to the car.
 

RichardMcN

Member
Mar 12, 2016
620
486
Sydney
I've got a question for you guys. I've recently installed a solar system that collects up to 5kw during peak sunshine.

How would I know what Amp to set the car to, to make sure the car is getting charged by the solar array and not pulling from the grid?

20A x 240V = 4800W = 4.8kW so maybe try 20 amps and see how you go (single phase).

or if you are on 3 phase ...

7A x 240V x 3 phases = 5040W = 5.04kW or maybe a bit less to allow for your fridge!
 
Last edited:

meloccom

Moderator Aus/NZ
Feb 11, 2008
2,331
1,224
Sydney Australia
I have a 3.6Kw Solar and Powerwall, and a 3 phase wall connector. By trial and error I discovered that if I charge at about 5 amps 3 phase that maxes out the output 3600W capacity of the system and the Powerwall will take up any slack if the sun goes behind a cloud.
I have no idea how the calculations work. :oops:
 

RichardMcN

Member
Mar 12, 2016
620
486
Sydney
I have a 3.6Kw Solar and Powerwall, and a 3 phase wall connector. By trial and error I discovered that if I charge at about 5 amps 3 phase that maxes out the output 3600W capacity of the system and the Powerwall will take up any slack if the sun goes behind a cloud.
I have no idea how the calculations work. :oops:

5A x 240V x 3ph = 3600W Almost suspiciously exact !
 

RC CAR

Member
Oct 28, 2016
6
0
Maylands
20A x 240V = 4800W = 4.8kW so maybe try 20 amps and see how you go (single phase).

or if you are on 3 phase ...

7A x 240V x 3 phases = 5040W = 5.04kW or maybe a bit less to allow for your fridge!

Thanks for the info.
My house is on 3 phase and looking on the inverter, it's pulling an easy 5kw during sunshine without clouds (it's a 6.5kw array with a 5kw inverter). So from your line above, 7A seems to be the right amount to set it to .. thanks.
 

Mark E

Member
Jun 27, 2012
860
176
Sydney NSW
I've got a question for you guys. I've recently installed a solar system that collects up to 5kw during peak sunshine.

How would I know what Amp to set the car to, to make sure the car is getting charged by the solar array and not pulling from the grid?
I assume that you mean you have a 5kW inverter and panels. Just because it *can* produce 5kW doesn't mean that it will all the time - it ramps up to the peak and then back down again. You'd need to know how much your house is drawing at the time as well as how much the system is generating.

Power = Volts x Amps, so 5000W = 240 x Amps. therefore 5000W = 20.8A.
Assuming you have a normal house and nothing much else is drawing power then you are probably using around 5-600W constantly with standby currents, wifi routers etc so about 18-19A would be the max around peak generating time.

If you don't have it already, get a system to monitor and log the output from your solar system and you will get a better idea of how it generates power. This is a pic of the output from my 3.3kW system today.
today's generation.jpg
 

RC CAR

Member
Oct 28, 2016
6
0
Maylands
I assume that you mean you have a 5kW inverter and panels. Just because it *can* produce 5kW doesn't mean that it will all the time - it ramps up to the peak and then back down again. You'd need to know how much your house is drawing at the time as well as how much the system is generating.

Power = Volts x Amps, so 5000W = 240 x Amps. therefore 5000W = 20.8A.
Assuming you have a normal house and nothing much else is drawing power then you are probably using around 5-600W constantly with standby currents, wifi routers etc so about 18-19A would be the max around peak generating time.

If you don't have it already, get a system to monitor and log the output from your solar system and you will get a better idea of how it generates power. This is a pic of the output from my 3.3kW system today.
View attachment 200952

Thanks for that. There's 6.5kw of panels and a 5kw inverter so when there's no cloud it operates at 5kw most of the time.

From one of the above quotes, my house is 3 phase so I will need to divide that number by 3 and set the Amp to about 7. Does 3 phase @ 7 Amps charge the same rate as 21 Amps single phase?
 

seclinton

Member
May 25, 2015
387
270
Newark, CA
I have a Sieman's adjustable EVSE, and just 100A service at my house (until we upgrade in a few years to 200A), so I use the old dryer circuit (30A) breaker, which then I turn down to 75% (22A = 233V*22= 5.1kW) on the Sieman's which keeps it from tripping the breaker.

Now for my dirty little secret and go ahead and call it risky/dangerous. I dialed the unit back up to 100% which gives me the option up to 30A on a 30A breaker. WTF? I've tried this just a few times

So I set the limit at 28A on the Tesla, and it regulats the EVSE at 233V/28A = ~6.5kW? Did I calculate correctly?

None, the cable, plug, EVSE, breaker ever feel even warm if it let it charge overnight. And no, I am not sure why I get voltage as high as 233V.


This is my Solar monitor and the spikes are a combo of car charging and probably running the stove/oven at the same time sometimes
 

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Mark E

Member
Jun 27, 2012
860
176
Sydney NSW
Thanks for that. There's 6.5kw of panels and a 5kw inverter so when there's no cloud it operates at 5kw most of the time.

From one of the above quotes, my house is 3 phase so I will need to divide that number by 3 and set the Amp to about 7. Does 3 phase @ 7 Amps charge the same rate as 21 Amps single phase?

I have 4kW of panels on a 3.3kW inverter... You still get the bell curve shaped output. Also bear in mind that a cloud coming past can put a huge dent in the output for the duration.
 

RichardMcN

Member
Mar 12, 2016
620
486
Sydney
I have a Sieman's adjustable EVSE, and just 100A service at my house (until we upgrade in a few years to 200A), so I use the old dryer circuit (30A) breaker, which then I turn down to 75% (22A = 233V*22= 5.1kW) on the Sieman's which keeps it from tripping the breaker.

Now for my dirty little secret and go ahead and call it risky/dangerous. I dialed the unit back up to 100% which gives me the option up to 30A on a 30A breaker. WTF? I've tried this just a few times

So I set the limit at 28A on the Tesla, and it regulats the EVSE at 233V/28A = ~6.5kW? Did I calculate correctly?

None, the cable, plug, EVSE, breaker ever feel even warm if it let it charge overnight. And no, I am not sure why I get voltage as high as 233V.


This is my Solar monitor and the spikes are a combo of car charging and probably running the stove/oven at the same time sometimes
Drawing 30A on a 30A breaker does not sound risky, but I've heard of an 80% rule in the US where you should not draw more than 80% for a continuous load.

Is going over 80% the risky secret?
 

360C

Member
Aug 5, 2015
87
33
Melbourne Australia
I upgraded my system in preparation for the arrival of my Model X. We will then be running 2 Tesla's and the house and be "off grid" most of the year. The system is now 20kw of solar with 48 kw of battery storage.

I have both a 3 phase and a single phase charger at home and have been playing around with both at different times of the day to see how and when I can charge the car purely off solar generated power. I charge the car daily so generally charge required is 20kw or less. I can use the single phase pretty much any time and it won't exceed the systems capacity.
The 3 phase is a bit trickier. As you can see from the attached graph (consumption top, generation bottom), the energy used including the house requirements is about 25kw. So you are always going to be using a combination of direct solar generation, stored energy and grid power when system capacity is exceeded. So if using the 3 phase I have to check what the solar is generating and what the battery capacity is at the time. At this time of year in Melbourne I can charge on 3 phase from about 11am to 5pm without drawing from the grid on most days. Single phase draws about 8kw so I can use that at any time.

As an aside, if you have 2 or more chargers in your house you can plug both cars in to charge at the same time without tripping the house main fuse. The chargers are "smart" and will load share to the appropriate levels.
 

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joninmelbourne

Solid Black S60 new face
Jun 29, 2016
146
25
Melbourne
2.52kw on my 10 amp plug. Have not installed the Tesla wall charger yet as waiting to see what the AGL $1 a day all you can charge deal needs. 10 amp seems fine for me at moment. Guess one day will need to do a long trip straight after another long trip making the walk charger necessary.
 

garyjac

Member
Jan 14, 2016
485
145
Brisbane, Queensland
Yes, that's good reasoning. I installed a 3-phase plug for quicker charging (dual chargers) in case, as I do from time to time have to make an ad hoc 200 - 250 km trip on short notice.
 

seclinton

Member
May 25, 2015
387
270
Newark, CA
Drawing 30A on a 30A breaker does not sound risky, but I've heard of an 80% rule in the US where you should not draw more than 80% for a continuous load.

Is going over 80% the risky secret?
yes I think so, but i assume it's just a safety factor and best practice to follow those guidelines
 

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