Interesting analysis - please keep it up with various continuous loads to try to hone in somewhat on the "parasitic" 12 volt loads. Using LeafSpy would help accuracy of the actual HV battery energy used. Some things to consider:woodgeek wrote:
I want to know my system efficiency, from traction battery kwh (estimated by drops to dash SOC) to kWh_AC output. When I do this, I appear to be getting numbers around 55% or so.
This figure assumes that the LEAF pack is 21 kWh total, and that kWh from the traction battery are approx:
(1) Energy_out_traction = 21 kWh * (\Delta SOC),
The formula neglects all onboard 12V loads when in 'ready to drive' (with all acc off, and the display at min brightness). Using the nominal eff of my inverter (80%), I conclude that either the onboard DC-DC converter is ~70% efficient, or onboard standby loads are like 150W or so, or some combination, like 90% onboard eff and 100W standby.
Does this make sense...if these numbers are typical, they DO somewhat limit the amount of useful energy that can be pulled from the LEAF. If I only want to take the traction battery down to 30% SOC (e.g. to drive to nearby DCFC to recharge) and my system eff is 55%, then I can only get 21*0.55*0.7 = 8 kWh_AC output energy.
This is of course enough to run my roughly 300W blackout loads for >24 hours, but it is a tad frustrating that I can't get more than 8-10 kWh out of a car with a nominal '24 kWh' battery. Its a classic case IMO of death by a thousand cuts....I lose 15% on true battery capacity, 20% in my inverter, 30% between standby and DC-DC losses, maybe I have 5-10% capacity loss....it all multiplies until I only get 1/3rd of the nominal energy (8 vs 24 kWh).
1. Inverters tend to become less efficient as the load is lowered (base-line wattage draw with no-loads). A good sine wave inverter likely has an efficiency curve (maybe from the manufacturer).
2. The DC/DC converter may have similar drop-offs in efficiency?? Someone with buck/boost circuitry would know? 70% seems quite low for any modern power conversion efficiency, but I don't really know where the Leaf's converter would operate.
3. (Low) 12 VDC systems tend to be somewhat inefficient by nature due to the high amperes and the resultant wiring/connector loses. Using 2 gauge (and well designed connectors) should be good for 1200 watts or so.
I am interested as I'd like to (eventually) tap into the HV battery directly using a high VDC inverter (UPS) to produce 240 VAC split phase. Understanding the "parasitic" loads of the Leaf and how they can be minimized is certainly of interest.