Powering a 1700W microwave using a Nissan Leaf

Thread Starter

LMF5000

Joined Oct 25, 2017
130
I'd like to use my leaf as a backup emergency power source instead of my generator since it's silent, odourless, cheaper and more convenient. As the leaf doesn't have a 240V outlet like some newer EVs, and since 240V converters that are powered directly from the 400V traction battery via the CHAdeMO port are prohibitively expensive and not easy to buy, the most feasible way to take power from the leaf seems to be via the 12V battery, which is charged from the 400V traction battery by an onboard DC-DC converter that's rumored to have a maximum external load capacity of 1500W (2000W max output minus 500W of the car's own internal 12V loads).

I plan to use a large (100Ah) battery as a buffer between the leaf and the inverter. So the power flow would be something like this:
Leaf's onboard 12V battery -> Jump leads -> 100Ah buffer battery -> 5000W inverter -> house

Is there a way I can configure this circuit to limit the draw on the leaf's DC-DC converter to only 1500W (about 135A)? The only house load that will actually go over this figure is the microwave (1700W at the plug) but that only works for 30 seconds at a time. I'm hoping that the jump leads will have enough resistance such that the buffer battery and leaf battery will supply at least 200W to the inverter while the microwave is running (meaning only 1500W from the DC-DC converter), but I'm open to any suggestions regarding the whole idea. The top priority is to protect the leaf's DC-DC converter from overload or electrical noise since it's expensive and labour-intensive to replace.

On a related note, my spouse has a second Leaf. Is there a way to parallel them safely so each Leaf only delivers about half the load? I'm not sure whether simply connecting the jump leads across the internal 12V batteries would cause unintended large current flows between that could damage the converters.
 

crutschow

Joined Mar 14, 2008
34,280
power from the leaf seems to be via the 12V battery, which is charged from the 400V traction battery by an onboard DC-DC converter that's rumored to have a maximum external load capacity of 1500W
I would not rely upon a rumor to think it's okay to draw such a heavy load from the Leaf's inverter.
As you noted, it's expensive to replace.

You do realize you will be drawing 125A @ 12V from the Leaf?
 
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Thread Starter

LMF5000

Joined Oct 25, 2017
130
I would not rely upon a rumor to think it's okay to draw such a heavy load from the Leaf's inverter.
As you noted, it's expensive to replace.

You do realize you will be drawing 125A @ 12V from the Leaf?
A few leaf users have posted evidence of them running 1500W appliances on the leaf's 12V system. It's a rumor because it's not an official spec from Nissan. I realize the currents involved, I mentioned 135A in my original post. It's not too different to a car alternator (some of which can supply 160A), only the leaf electronics are water-cooled so less risk of thermal damage compared to loading an alternator with an idling engine.
 

jlm1948

Joined May 19, 2014
18
That's an interesting concept.
I have no doubt connecting two cars in parallels is not an issue. I say that because I had an issue with a stuck parking brake on my Soul EV. The only way to unstuck it was to jump a massive booster-charger.
Regarding the 135A, they will be shared between the car's battery and the external one, how well depends on the jump cable resistance. Anyway, can these batteries withstand intermittent operation at about 100% of nominal? I tend to answer yes, since on a combustion engine, the starter draws more than 100%, and sometimes for quite a long time, as can be heard in winter times.
How long the battery will survive is an issue, though.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
130
That's an interesting concept.
I have no doubt connecting two cars in parallels is not an issue. I say that because I had an issue with a stuck parking brake on my Soul EV. The only way to unstuck it was to jump a massive booster-charger.
Regarding the 135A, they will be shared between the car's battery and the external one, how well depends on the jump cable resistance. Anyway, can these batteries withstand intermittent operation at about 100% of nominal? I tend to answer yes, since on a combustion engine, the starter draws more than 100%, and sometimes for quite a long time, as can be heard in winter times.
How long the battery will survive is an issue, though.
So you paralleled two EVs while they were both in "ready to drive" mode? That's a useful data point to have. It means both DC/DC converters were active and they didn't kill each other.

I'm hoping the bulk of the current comes from the DC-DC converter. Since that tries to keep an output voltage of 13.4V or more, then the leaf's internal 12V battery won't be discharging (assuming terminal voltage never falls below 12.7V, which is the resting voltage of a fully charged 12V lead-acid battery).

The buffer battery is another matter since its terminal voltage depends on the current and the resistance of the jump leads. I'm not overly concerned about my buffer battery, it's a 100Ah AGM starting battery from a conventional Diesel car, it got too old to start the car reliably, but it still has a good 70Ah of real-world capacity left. I'm sure 135A is easily doable for it - its starting current is rated for 680 or 800A DIN (can't remember right now) and the microwave will only run for 30 seconds at a time or so.
 

lyleleverich

Joined Apr 2, 2019
35
A few leaf users have posted evidence of them running 1500W appliances on the leaf's 12V system. It's a rumor because it's not an official spec from Nissan. I realize the currents involved, I mentioned 135A in my original post. It's not too different to a car alternator (some of which can supply 160A), only the leaf electronics are water-cooled so less risk of thermal damage compared to loading an alternator with an idling engine.
Is the water cooling running when you do this, or just with the car in drive?
 

wayneh

Joined Sep 9, 2010
17,496
One approach to current limiting is to run all current through a (very) low resistance shunt, measure the voltage across that shunt, use a comparator to decide if the measured voltage is exceeding a target, and trip a relay to break the circuit if it is. A circuit breaker, basically. Of course you can also measure current with a Hall effect sensor to avoid invading the circuit with the shunt.

The trickier part would be to take any action other than shutting down. Circuit breakers obviously don't do that, and "dimming" any circuit risks damage to the devices on that circuit.

I could envision a priority tree, where power is disabled one device/circuit at a time until the total current is no longer a problem. You could even automate it to reset (turn back on) circuits if the current draw has come back down to a safe level.

It'd be simpler to get a lower wattage microwave.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
130
One approach to current limiting is to run all current through a (very) low resistance shunt, measure the voltage across that shunt, use a comparator to decide if the measured voltage is exceeding a target, and trip a relay to break the circuit if it is. A circuit breaker, basically. Of course you can also measure current with a Hall effect sensor to avoid invading the circuit with the shunt.

The trickier part would be to take any action other than shutting down. Circuit breakers obviously don't do that, and "dimming" any circuit risks damage to the devices on that circuit.

I could envision a priority tree, where power is disabled one device/circuit at a time until the total current is no longer a problem. You could even automate it to reset (turn back on) circuits if the current draw has come back down to a safe level.

It'd be simpler to get a lower wattage microwave.
Thanks for being one of the first actual solutions so far!

This approach would actually be very easy without building the circuit myself, I can buy a generic DC circuit breaker on aliexpress for $20 that will trip at a predifined current (they make common ones for 100A, 150A and less common ones for 125A). I could put that between the car and the buffer battery. The problem with that is that once overloaded, all the load will fall on the buffer battery.

The behaviour I prefer is for the dc/dc converter to supply all the power up to its limit, and for the excess to be supplied from the battery.

Hopefully the jump leads will act as a low-ohm resistor and achieve some of that. The buffer battery's voltage will be 12.6V with no load. The DC/DC converter output from the Leaf is 13.2V. We basically have to drop 13.2-12.6 = 0.6V at 125A for the voltage to drop so much at the buffer battery that it starts being discharged. Which means a target resistance for the jump leads of V/I = 0.6/125 = 0.0048 ohms.

A quick search tells me jumper cable has a resistance of 53 millohm per meter, and my set of cables are about 1.5m long, so it seems their resistance is about 10x higher than needed. Once we factor contact resistance from the crocodile clips the scenario gets a little worse. On the other hand, the leaf's DC/DC converter dynamically adjusts voltage and can go over 14V under some conditions. So I think the best strategy is to build the circuit and test it by sweeping output power and measuring voltages across the buffer battery and the leaf's internal 12V battery. Then I can see at what point the buffer starts being discharged and build heavier-gauge "jumper cables" (this time with bolted terminal ends) if needed.
 

MisterBill2

Joined Jan 23, 2018
18,167
"Jumper Cable" covers a huge spectrum of capabilities. I have a 24 foot set made with #6 wire that is easily good for 100 amps to crank a cold engine for a few seconds to start it. I have a set to give to whoever is in need that is made with what looks like number 12 stranded wire. It would be OK for boosting a low battery for a few minutes to get enough charge to crank an engine.
The big voltage drop with "good" jumper cables is the connection between the clips and the battery terminals. That is often an unknown variable.
 

jkenny

Joined Aug 15, 2009
6
I wonder if there's a large enough current equivalent of a PTC resettable fuse. They're lossy, and generally only good for lower current loads, but they do have very nice characteristics of being passive and having a "soft" failure (protecting the source until the overload is removed/current drops). I found this one for 21A, but you would need to parallel around 5 of them which gets expensive, and parallel fuses don't necessarily trip in expected ways: https://www.digikey.com/en/products/detail/littelfuse-inc/BD540-30/3516283

I'm currently doing similar using the DC-DC converter on my Prius in the case of extended power outages; I live in an area with somewhat unreliable power, especially during winter and windy days. The battery charges at up to 70A from the DC-DC converter, but I've replaced the existing small lead-acid with a custom 105AH LFP pack which can output 105A to a 1500W inverter. Mostly just need to run the refrigerator and some network gear off it (~300W).

Would also highly suggest instead of using "jumper cables" to fashion a proper Anderson connector in parallel to the car's battery. They're good quality connectors, I've got one on my car that is rated for 175A. Jumper cables are sketchy at best, the clamp connection isn't great and varies a lot, and causes a lot more risk of slipping and shorting something out against the frame.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
130
I wonder if there's a large enough current equivalent of a PTC resettable fuse. They're lossy, and generally only good for lower current loads, but they do have very nice characteristics of being passive and having a "soft" failure (protecting the source until the overload is removed/current drops). I found this one for 21A, but you would need to parallel around 5 of them which gets expensive, and parallel fuses don't necessarily trip in expected ways: https://www.digikey.com/en/products/detail/littelfuse-inc/BD540-30/3516283

I'm currently doing similar using the DC-DC converter on my Prius in the case of extended power outages; I live in an area with somewhat unreliable power, especially during winter and windy days. The battery charges at up to 70A from the DC-DC converter, but I've replaced the existing small lead-acid with a custom 105AH LFP pack which can output 105A to a 1500W inverter. Mostly just need to run the refrigerator and some network gear off it (~300W).

Would also highly suggest instead of using "jumper cables" to fashion a proper Anderson connector in parallel to the car's battery. They're good quality connectors, I've got one on my car that is rated for 175A. Jumper cables are sketchy at best, the clamp connection isn't great and varies a lot, and causes a lot more risk of slipping and shorting something out against the frame.
Thanks for the suggestions. You're right, PTC fuses are a tad pricey, though it seems par for the course at this point. The cabling and ancillary things are ending up costing close to as much as the actual power electronics. Anderson connectors sound interesting. I might make proper bolted terminals for this setup (the kind with hydraulically crimped ends) for the remaining connections. We'll see when the inverter gets here and I can do some voltage and current tests :)
 

JoeyD1968

Joined Feb 17, 2023
2
I've been using an 1100w inverter run off the 12v in my 2019 SV Plus (with a downgraded 40kWh HV battery) for about a year. Ordinarily, I run a power strip with a reset/off switch into the cablin, and then use that for phone/laptop charging, and to run AC far infrared heating film, which comes in 26-27w sections x 5-8, so it runs about >250w. On a rare occasion, I'll boil water in an electric kettle or use a 1000w hot plate. I once used an energy-saver air fryer. I've never had a problem with anyone of these. I haven't tried a microwave. But I found this in the manual:

"Operating a Microwave oven with Your Power Inverter The power rating used with microwave ovens is the "cooking power" which means the power being "delivered" to the food being cooked. The actual operating power rating is listed on the back of the microwave. If the operating power cannot be found on the back of the microwave, check the owner's manual or contact the manufacturer."

I attached the manual as a PDF, if anyone is interested.

My plan is a little more ambitious than the OP. I am going to get a larger inverter and use it as a secondary circuit at home with power from public chargers. I would like to see how much I can avoid using the grid and paying my utility company.

However, even with nothing plugged in, or nothing other than the power strip, if I don't drive/turn on the Leaf for more than 24 hours, my 12V gets fully drained and I have to jump it. I can leave my car parked and locked, in drive mode, with the EBrake engaged (to keep the daytime running lights from coming on), and that keeps the 12V charged by keeping the DC-DC converter topping it off. If I leave it long enough, obviously, it will drain the traction battery low enough that it will stop maintaining the 12V. i don't know how long that would take. It hasn't happened yet. But it's certainly something I need to figure out before making this move.

Is there any harm in leaving the car in drive mode for extended periods, like 24-48 hours? And would there be any harm in using an inverter on a daily basis in that state? Or, Any suggestions for how I can keep the DC-DC Converter active when Lulu (that's my Leaf's name) is powered down?

Perhaps I should post this on its own, but because the OP is pondering something similar, it seems to belong.
 

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Thread Starter

LMF5000

Joined Oct 25, 2017
130
OP Here :). Since my last post the inverter has arrived and I've done some tests. My microwave is rated at 1100W of cooking power, but actually draws 1700W from the wall (measured with a wattmeter).

I tried powering the contraption with the leaf using a buffer battery as I described earlier in the thread, but my el cheapo jump leads let me down. They look thick from the outside, but it's actually a thin copper wire inside with a very thick layer of plastic insulation. Also the ends were crimped by folding the copper back onto the plastic and squeezing that - plastic and all! That means a good 0.3 ohms of resistance per cable. Long story short, I wasn't able to draw more than half an amp from the Leaf via the jump leads. I'm now looking for either better quality jump leads or some high-current cables which I can bolt to the leaf's terminals.

I did test my inverter (a "5000W" pure sine model from AliExpress, with a continuous rating of 2500W) on my microwave. As power source I used an old AGM 100Ah starting battery that got too weak to start the car. It was able to keep the microwave barely running for 30 seconds. By "barely running" I mean the voltage dropped enough that the microwave's light dimmed and the fan and turntable ran a little slower than usual, but it did heat up a cup of water so we'll call it a success for now. For anyone wondering, on all cheap inverters I've ever used, the output voltage tends to drop a little when the input voltage drops. The microwave put a load of about 140A on the battery (measured with clamp meter), so with my tired old battery the terminal voltage was barely above 10.5V for the duration. Hence I'm guessing output voltage drooped to around 210V or so.
 

MisterBill2

Joined Jan 23, 2018
18,167
It is difficult to imagine a more complex manner to get free electricity, nor one more costly, if the "public chargers" that are not the Pay As You Go variety. And as the goal is to avoid paying for power via a rather tedious theft scheme, the various injuries to the vehicle shall await the TS discovery.
 

JoeyD1968

Joined Feb 17, 2023
2
It is difficult to imagine a more complex manner to get free electricity, nor one more costly, if the "public chargers" that are not the Pay As You Go variety. And as the goal is to avoid paying for power via a rather tedious theft scheme, the various injuries to the vehicle shall await the TS discovery.
I'm sorry, i missed the theft part. And what does "TS" mean?
 

MisterBill2

Joined Jan 23, 2018
18,167
In this forum, AAC, "TS" is short for "thread Starter", also sometimes called "OP", for Original Poster. My apology for being a bit lay there. That comes from not noting who started the thread.
 

MisterBill2

Joined Jan 23, 2018
18,167
In this forum, AAC, "TS" is short for "thread Starter", also sometimes called "OP", for Original Poster. My apology for being a bit lay there. That comes from not noting who started the thread.
It seems that there are at least two different threads have become a bit tangled, although it may just be me.
 
I'm a certified mechanic.

Don't. You'll void any warrantee on the car. You possibly endanger drivers on the road.

You will stress your alternator.

"asian sub compact" are not designed for "alternator upgrades" like a Dodge Charger is.

A general guide is: cigarette lighters often fail - so much so mfg stopped offering them. Cell phone chargers are hard on batteries and cause failures, actually. Sure it works. But they only put in "enough overhead" to cover what the car needs. Put on chargers: and it tends to cause early battery and even alternator failure.

If there "isn't enough room" for allot of cell phone charging - then there definitely isn't enough room to be running "a microwave".

Unless Nissan releases a flier saying "1,700W radios work great with our sub-compact model's electrical system" DON'T.

YET ANOTHER ISSUE IS THE ENGINE / PASSENGER WIRE HARNESSES.

They are doublessly not designed for 1,700W. You'll cause a fire. You might cause an accident by partly melting a harness that later fails at highway speeds.

All I can say is: stay away from the car.
 
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