I am measuring kWh outside the car at the breaker box using Sitesage. The other issues are constants, or at least one of the things I'm interested in exploring.
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nwdiver
Well-Known Member
I apologize if this has been asked... how many feet from breaker box to HWPC and what wire gauge?
There are really two parts to this question...
- Losses in the charging
- Losses in the wiring
The second part is simple Math. I²R= Line loss. You generate 16x as much heat at 80amps as you do at 20. So depending on line resistance 80amps could be worse than 20 due to line losses even if the car charges much more efficiently at 80 vs 20. I have ~70' of #2 Aluminum wire feeding my HPWC so I lose 280w to heat charging at 80amps vs 18w at 20amps. That doesn't count my service drop with is >200' but I don't pay for that. :tongue:
So a 3 hour charge session would cost me 840wh at 80amps vs a 12 hour 20 amp session costing 216wh.
You need to find the 'break even' point where increased efficiency of charging makes up for increased line losses. These will be different for everyone.
http://www.powerstream.com/Wire_Size.htm
The fastest way to calculate line losses from this site is to enter your wire data, find your voltage drop then use this equation
Power = Charging current x Voltage drop
In this case 'Power' is heat generated in the line...
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Yes, it's further upthread, but my installation is ~30' of #3 copper. As you can see from the data above, so far there has been no significant difference between settings at 20-80 amps.
nwdiver
Well-Known Member
Ah... yeah your line resistance is ~70% less than mine. I would have liked to have copper but it would have cost another ~$300.
All,
I have added a bunch of charts to the wiki at the top of the thread.
Observations:
- We're currently at 17 samples -- still a small number, but find that the average kWh per Ideal Mile is starting to converge around .287 for all tested charging rates. The differences are statistically insignificant on their own, and are probably within the measurement variance of my equipment.
I'm still trying to figure out the best way to update this thread now that TMC has changed the editing rules. I may give the Blog type a try, but for now, the second message in this thread has the current updates.
I have added a bunch of charts to the wiki at the top of the thread.
Observations:
- We're currently at 17 samples -- still a small number, but find that the average kWh per Ideal Mile is starting to converge around .287 for all tested charging rates. The differences are statistically insignificant on their own, and are probably within the measurement variance of my equipment.
I'm still trying to figure out the best way to update this thread now that TMC has changed the editing rules. I may give the Blog type a try, but for now, the second message in this thread has the current updates.
