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

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

http://www.mynissanleaf.com/viewtopic.php?f=30&t=22752
 
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.
 
arnis said:
gonefishin said:
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.

Under load, my DC-DC was putting out a very steady voltage at 1200, 500 and 0W_ac output, over the course of several hours. IIRC, it was 13.8V at the LEAF.
 
Had a short outage this AM, and used the LEAF system to backfeed my house for an hour. All 240V breakers off. 100-500W. No issues.

FYI: Backfeed was done with appropriate interlock in place, if you don't know how to do this safely, don't.
 
woodgeek said:
Under load, my DC-DC was putting out a very steady voltage at 1200, 500 and 0W_ac output, over the course of several hours. IIRC, it was 13.8V at the LEAF.

And you have your negative lead connected right to the battery terminal?

Interesting. 13.8V is not known on Leaf. So lets suppose Leaf is not connected to anything. As soon as you switch it on, at what voltage
does it hold the 12V system? 13.8V? Do you use voltmeter on the terminals or any other integrated voltmeter somewhere inside inverter?
 
Some time ago we were notified by our Utility that our neighborhood would be turned off overnight for some maintenance. I sleep with a c-PAP machine to breath at night so I used a small inverter from Harbor Freight plugged into the car, then extension cord from car and garage down hall to bedroom. I slept well, thank you. With the Leaf in Ready mode, and no adjustments for display lights, I used it overnight. The next morning all was well, the inverter worked great, and displayed GOM went down very little. I do not remember, but it was almost nothing, maybe one or two miles range loss. Sorry to not have a better or more accurate reporting, but did not write it down, I just remember it was almost nothing.

Hope this helps.
 
arnis said:
woodgeek said:
Under load, my DC-DC was putting out a very steady voltage at 1200, 500 and 0W_ac output, over the course of several hours. IIRC, it was 13.8V at the LEAF.

And you have your negative lead connected right to the battery terminal?

Interesting. 13.8V is not known on Leaf. So lets suppose Leaf is not connected to anything. As soon as you switch it on, at what voltage
does it hold the 12V system? 13.8V? Do you use voltmeter on the terminals or any other integrated voltmeter somewhere inside inverter?

I did the neg connection by clamping directly to the drive unit...pos to the battery clamp.

Upon reflection, I think it was 12.8, but def v steady. That's 12.8 across the 12V battery. At 1200W_ac output, and 140A_dc, the drop on my 2 AWG leads was over half a volt (more like 12.2-12.3 at the inverter). It was similar across the battery at different loads, including no (external) load.
 
woodgeek said:
arnis said:
woodgeek said:
Under load, my DC-DC was putting out a very steady voltage at 1200, 500 and 0W_ac output, over the course of several hours. IIRC, it was 13.8V at the LEAF.

And you have your negative lead connected right to the battery terminal?

Interesting. 13.8V is not known on Leaf. So lets suppose Leaf is not connected to anything. As soon as you switch it on, at what voltage
does it hold the 12V system? 13.8V? Do you use voltmeter on the terminals or any other integrated voltmeter somewhere inside inverter?

I did the neg connection by clamping directly to the drive unit...pos to the battery clamp.

Upon reflection, I think it was 12.8, but def v steady. That's 12.8 across the 12V battery. At 1200W_ac output, and 140A_dc, the drop on my 2 AWG leads was over half a volt (more like 12.2-12.3 at the inverter). It was similar across the battery at different loads, including no (external) load.

That seems really reasonable. 13.0V is everywhere if there is no massive load. But if there is 140A current running from DC-DC convert to battery terminal, there is definitely voltage drop across that positive cable as well. Therefore battery terminals could be at 12.8V.
Could we trick DC-DC device to supply 14.4V. This should drop amps (10%?). Therefore some gain in efficiency.
 
Had a derecho come through here last week, and it made a couple hundred small outages in my and neighboring towns. We had a transformer explode, so we were out for 18 hours or so.

The LEAF-inverter system ran our fridge, (LED) lights, wifi and personal electronics just fine, and we depleted the dash SOC by 30%.

Most important for the wife....it can (just) run our Nespresso pod machine. :roll:
 
LeftieBiker said:
10 amps at 12 volts, IIRC, which is 120 watts.

I see "10 Amps" in the Owner Guide, but the 2013 Service Manual says it comes from a dedicated 20A fuse #21.
 
Just wanted to say thanks for the idea in this thread, with a 2000w (240v) inverter my leaf now makes very passable coffee at our hillclimb venues.

the inverter can potentially draw 200a @12v but the coffee machine only needs 1600w I guess it's only drawing 160A.

awesome idea thanks guys

https://youtu.be/XydY1J6CNc8
 
I've gotten a 300 watt unit for smaller loads. The unit has a "chassis ground" separate from the negative 12v input. I don't understand this. What would be the point of putting 120V AC onto the vehicle chassis? That doesn't even seem to be an effective ground and I'd really worry about frying the vehicle electronics.
 
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