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Marktm
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Sun Oct 09, 2016 2:08 pm

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).


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:

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.
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

BrockWI
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Sun Oct 09, 2016 2:16 pm

Another issue is the car itself takes 500+ watts just sitting there turned on in ready mode, so that is a large load on the HV battery as well.
3 kw solar pv - XW6048 - 8 L16's
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2003 VW TDI 170k miles - 52 mpg lifetime
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woodgeek
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Mon Oct 10, 2016 4:57 am

Ran an overnight (11 hour) test with the car in 'ready to drive' mode with no accs on, min display brightness, and no external loads attached. Car ran down 6%, from 100% to 94% SOC (I don't have leafspy). I think the rate was uneven (e.g. charging the 12V batt, etc), as the car still read 100% several hours in, but it is what it is, an estimate. I'm assuming an 80% eff on my inverter....youtubers doing tests report slightly higher values.

The data suggest a 112W standby consumption on-board. Factoring that into my earlier inverter test, I get an 78% eff. estimated for the onboard DC-DC unit.

The calculated breakdown is thus:

Output, AC: 485W
Loss, inverter: 125W
Loss, 2AWG cabling: 12W
Standby, onboard: 112W
Loss, DC-DC onboard: 170W

Total power out from traction battery: 900W, delivered as 120VAC 485W, system efficiency = 54%

While somewhat disappointing, the inverter approach in this thread is simple, safe and cheap to set up, and will provide useful backup during a 1 day or shorter power outage for me.

This analysis, of course, assumed I have 21 kWh capacity at 100% SOC. If we assume I have lost 10% (worst case IMO), then the car only used 810 W from traction, the standby was only 100W, and the DC-DC loss was just 90W.

This makes the

DC-DC inverter eff: (810-90-100)/710 = 87%
Overall system eff: 485/810 = 60%

I think these figures, taking into account the battery depletion in my vehicle, are more likely to be accurate....most DC-DC converters run about 90% eff.

gonefishin
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Tue Oct 18, 2016 11:09 am

What is this Phil's Law about not connecting anything to the negative terminal of the battery? That negative terminal is connected to the chassis, so why is it any different to connect there?

Did anyone else notice that the kit mentioned in this thread http://www.evextend.com/Nissan-Leaf-Inverter-Kit.php plugs directly into the negative terminal? I would think they'd be out of business if this was destroying Leafs.

arnis
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Tue Oct 18, 2016 12:52 pm

gonefishin wrote:What is this Phil's Law about not connecting anything to the negative terminal of the battery? That negative terminal is connected to the chassis, so why is it any different to connect there?

Did anyone else notice that the kit mentioned in this thread http://www.evextend.com/Nissan-Leaf-Inverter-Kit.php plugs directly into the negative terminal? I would think they'd be out of business if this was destroying Leafs.


Just at the negative terminal there is a current measuring device. Leaf is using that to estimate what DC-DC converter should do.
I'm also interested now. Either it won't notice the draw immediately and let the voltage drop A LOT or will not act appropriately. There are some other variables that are offtopic for this thread.
It is easy to use any other negative connection near battery.

If somebody has blackout system could he/she report: will Leaf keep voltage at 13V or 14.4V if it finds out a huge load? Will it switch
from 14.4V to 13V right after switching the vehicle to READY mode even if there is a load due to 12V-120V inverter.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

GerryAZ
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Wed Oct 19, 2016 9:34 pm

If you connect directly to the negative battery terminal, the DC-DC converter will see the inverter current as 12V battery charging current (will look like discharged battery) and maintain about 14V output trying to charge the "low" battery. This would be a good way to equalize charge the battery (or toast it if you leave it on too long).

Gerry
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015

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Marktm
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Thu Oct 20, 2016 5:50 am

Not to change the subject, but I remember a recent bench test of the DC/DC converter that was posted on this forum. It was a fairly elaborate set up that had a converter on the bench and all the CAN bus (EV CAN?) signals identified with relays that energized the converter.

Can anyone find that post (had a couple of videos also).

Thanks
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

91040
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Thu Oct 20, 2016 7:03 am

Check out FalconFour's first post on Why the Leaf 12V Battery Behaviors thread.

viewtopic.php?f=30&t=22752
1st Capacity Bar loss 30k mi 16.25mo 2nd- 49k mi 25.5mo 51.5Ah
3rd- 73k mi 36.5mo 46.9Ah 71% SOH 50.9Hx 4th- 86.5k mi 43mo 42.61Ah 64% SOH 43.79Hx
5th- 101k mi 50.5mo 38.38Ah 58% SOH 37.02Hx Replaced Battery 9/28/15 104.2k mi 36.13Ah

RockyNv
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Fri Oct 21, 2016 8:03 pm

I didn't back track through all of this however aren't countries like Norway and Denmark doing this as SOP with their EV Chargers in some locations? I recall watching a video covering how they even have solar charging stations for fleets of electric rental cars that when they are not being used feed power back into the grid during peak hours. I believe this was via the DC charge port.

I did do a quick spot check and did see a number of posts about soldering verses crimping and such. My Dad was a Wire Chief for the Americal's HQ Division out in the South Pacific during the late 1930's to mid 1940's when he was not being deployed as a Ranger and Jungle/Island Raider. He taught us to use Western Union splices when joining two cables together. If the splice came under tension even if the solder melted it will not come apart unless you exceed the strength of the wire itself. Simple explanation is to tie the wires together in a square knot soldering the knot for a better connection in wet or corrosive conditions wrapping in butyl rubber and vulcanizing when done.

I still have Dads original TE-33 Kit that was issued to him.

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Marktm
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Re: Using the Leaf for power in a Blackout: MY "Leaf to Home"

Sat Oct 22, 2016 5:40 am

91040 wrote:Check out FalconFour's first post on Why the Leaf 12V Battery Behaviors thread.

viewtopic.php?f=30&t=22752


That's it - thanks
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

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