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Hi there,

I found little information about this topic on internet (actually none on MDX although some on Prius) so I figured I'd start a thread to share my experience as well as getting feedback from you guys.

I bought my MDX Hybrid a little over a year ago, and loved it. In fact I loved it so much I bought another, albeit regular MDX, for my wife.

A few weeks ago there was a wicked storm and we lost power for more than 2 days. I happened to have a 300W inverter so I plugged it into the cigarette lighter and it powered up our WiFi router and kid's TV, plus some lights, effortlessly. That got me thinking, why not use my hybrid as an emergency generator? Being an electric engineer by training, I had a vague idea that hybrid had a generator instead of alternator.

After the storm I started researching in earnest. I found stories about Prius owners powering their houses in storms, and a NY Times story called it V2G (Vehicle to Grid). I could attest to many of the benefits mentioned in the stories. It's super quiet. My neighbor across the street 100 yards from us had a gas-powered generator that we could hear with windows closed, yet our hybrid barely made a whisper from our own backyard. The engine only comes on when it needs to like only a hybrid could do. Not to mention the convenience and low cost.

The only question that stumped me was exactly how much power (watts, or amps) I could draw. The whole car industry was hush hush about it and the last paragraph of the NY Times story might have explained why. A spokesman from - none other - Honda didn't like the idea and suggested to buy a generator, which Honda happened to have a decent lineup.

Apparently adventurous Prius owners took to themselves to solve the mystery. While most people limited the power to around 1KW and the NY Times story claimed at least 3KW was available, this dedicated researcher dug deeper and believed there should be 5~6KW. Accidentally I took a similar approach to do my research before I saw his work. Like him I started with information I had. I knew the three electric motors totaled to around 90KW, so it seemed reasonable to assume the generator had the capacity of that range. The DC-to-DC Converter would be the bottleneck. I found the main fuse in the engine compartment to be 200A (and regular MDX is 150A). Although I couldn't figure out if that was the converter fuse or out of the 12V battery, I thought anything lower than that would sure be safe.

So I had an inlet box and interlock switch installed on my house for the prospect power generator. I chose 30A wire and inlet box for up to 7.5KW. Then I bought a 4KW continuous / 16KW peak pure sine split phase power inverter for $289 plus taxes from eBay. There were other more expensive choices, but this worked perfectly for me. I chose 4KW even though I didn't expect to draw that much power because it costed only $70 more than the 2KW one, and so I'd have more head room if I wanted to go higher.
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And a clamp meter, a twist lock connector for 120/240VAC, 1/0 AWG battery cables with connectors, and a series of 100A, 150A, 200A, and 300A in-line circuit breakers from Amazon.

Hooking up the battery cables was fairly easy and the rest of my experiment went like this:

I first tried the 100A breaker and a hair dryer for load. The breaker would trip when it was around 60 amps. Hooking up to the house had similar results. I decided the breaker was faulty and 100A was too low for me anyway.

I switched to the 150A breaker and it worked well. Using hair dryer I managed to go up to 148A and stayed there until I went one notch higher.
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Satisfied, I hooked up to the house and started a 3-hour test run. I increased the load gradually by turning on more breakers, and eventually stayed at around 1KW with all what I considered essentials (lots of lights, refrigerator, furnace blower, WiFi router, TVs, stereo blasting music, etc.), and was able to also handle range hood and garage door, each costed about 200W, until I decided to run dish washer at the end.
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During the 3 hours both the car and the inverter seemed to work effortlessly. The inverter occasionally turned on the fan but stayed cool to the touch. The 12V battery was cool initially for a long while, only got warm from the engine when it ran more often. The engine came on occasionally like I saw before, only this time I clocked how long it ran and how often. When there was no load, it ran 75s every 12 minutes, and at about 1KW load, it ran 75s every 270s. So the load made a difference, which makes sense. It came on when the battery gauge got to certain level, which also proved the 12v was charged by the main battery.

I also measured the battery voltage from beginning to end. It started around 12.46v, and stayed around 12.4v 'til the end. My conclusion from that was, the engine/DC-to-DC converter was able to keep up by running only 75/270 of the time. In other words, if the engine were to run continuously, it should output about 3.6KW. It might even be able to go higher if the engine could throttle. A few factors might change that equation though. First, the converter might overheat if run continuously, which I thought was unlikely since it's liquid cooled. Second, the 12V battery might not be able to handle the higher amps output, again unlikely since in that scenario the current would be directly drawn from the converter instead.

That's where I am now. I'm hesitating to continue with higher amp since I don't want to risk anything more than I had to, and 1.8KW seemed plenty enough for me.

So what do you guys think?

Oh something I thought interesting I saw. At the beginning of the 3-hour, I saw the 12V battery being charged by the main battery when the engine was off (because the voltage I measured was 14.4v), but afterwards it would not seem so when the engine was off (voltage measured at 12.4v). I don't know what to make of that. It seems to be drawing current because the battery gauge was going down slowly. So perhaps it's charging at a lower voltage when engine was off?
 

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I read every word and am impressed with your skills and lack of risk aversion.

For your household to operate on 1.2kW @115 (120?)v, needing only ~10.5a, how did you account for FLA vs your LRA calculation? Everything steady state? Refrigerator? Or just buy a Honda 1000w portable generator...and not worry...
 

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I read every word and am impressed with your skills and lack of risk aversion.

For your household to operate on 1.2kW @115 (120?)v, needing only ~10.5a, how did you account for FLA vs your LRA calculation? Everything steady state? Refrigerator? Or just buy a Honda 1000w portable generator...and not worry...
Thanks for reading my rambling and sharing your thoughts:) I did take a bit of a risk but was far from being reckless. I think I know why you thought so though. I should have mentioned most of my amps were on DV 12V. I did have photos of the 150A breaker on the positive terminal, and the clamp meter on the thick battery cable. So 12v x 150a = 1.8KW. My inverter was 110/220vac split phase, so that translates to ~8A on the AC end. I had purposely installed a 15A breaker in my house panel in case the DC breaker failed I'd still be limited to only 3.3KW. Other than these, I was careful to first test with a hair dryer, then on the house, gradually increasing the load in both cases, and monitoring what I thought could be problems. My big assumption was the converter had to have some sort of mechanism to protect from being overdrawn. So what could happen was the battery couldn't be charged fast enough, resulting in a depleted battery, which was a risk I could take. Another worse scenario was the battery couldn't handle that much output and would overheat and explode. Unlikely because I knew Prius 12V batteries were smaller, and mine was rated CCA 620A, which meant it could output 620A for 30 seconds for cranking. I kept monitoring that nonetheless in the 3-hour run. For all I could tell, it went really well.

FLA and LRA, if they're what I think they are, were exactly one of the reasons I did my test. Unfortunately my clamp meter does averaging so it couldn't measure instant current. I had read somewhere the starting current of a motor is typically twice as much as the running one. For example my fridge was rated 5A @ 120VAC. So it'd be 10A, or 1.2KW. In 3 hours I'd think it had started and stopped multiple times, and was fine. I purposely tested garage door and hood range because both had motors, Both had steady draw of 200W, so I'm guessing it'd be 400W starting. Both worked fine although I didn't start them at the same time.

Why not buy a generator? Are you kidding me:) Besides the thrill of finding the secret power of my beloved car and answering the question that had been bugging me for weeks, many practical benefits that led me to actually believe hybrid generator beats others of similar power:
  1. Convenience. I don't need to store and maintain a generator, keep running to gas station to refill in the midst of a storm. Prius could run for a week on 1KW load with half tank of gas. With a 17-gal tank I'd think MDX would run at least that long.
  2. Noise like I mentioned before.
  3. Efficiency. This is the only option I'm aware of (other than those whole house standby generators that cost the price of a small car) that's capable of starting/stopping engine based on load.
  4. Clean power. Inverters are all electronic and can produce consistent output. Mine was a pure sine wave the same as utility power. Generators more or less get affected by mechanics of inter-combustion engine. Some good ones manage to have low THD, but to get pure sine wave you'll need to go with more expensive inverter generator.
  5. Most lower powered generators, like the 1000W Honda you mentioned, or the higher powered eu2200i, are not split phase 120/240vac, therefore can't directly plug into the panel and power the house. You need to run an extension cord to plug in few appliances.
  6. Cost. There are generators that can generate clean power and have split phase but they're more expensive.
The only drawback that I could see is the power limit. It won't be able to reach 7.5KW that I'd need to run AC. Fortunate for me my wife doesn't worry about AC in summer as much as heat in winter, which it did power the furnace very nicely.
 

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Wow! Admire your enthusiasm and yeah, the fearless and incredibly thorough approach.. :)
thinking about a hybrid myself, good to know there's an 'unspoken' bonus :D
 

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Yes - impressive and very interesting. We've had more, longer power outages in the past 2 years than during the previous 20+ years and a handful of neighbors have installed generators. Never dawned on me that I already have one sitting in the driveway. Thanks for posting this.
 

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For regular power outages, you may want to shop around more for a whole house system. Makes life a lot easier.


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For regular power outages, you may want to shop around more for a whole house system. Makes life a lot easier.


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Yeah I'd thought about that, but couldn't justify the cost. Probably for those who have multiple outages a year. Here it's about once a year occurrence, more in winter than summer.
 

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For those of you who find this information helpful - thank you. I was also hoping to seek out those who had also tried to share their experience so I could learn as well.

For those who're thinking to try, here is a bit of more information that might be helpful:
  1. The battery cable with connectors I picked from Amazon was 3 feet thick 1/0 AWG capable of 600 amps, oversized to be safe, and costed $37.42 plus taxes. It came with long thinner ground wire that was just right to be bolted to the chassis.
  2. I happened to have a PVC board that's about the right size to bolt the inverter on. I let it sit on a chair next to the car, as far as the 3-foot cable would allow to stay away from the heat and vibration of the engine. There will need to be some protection from the elements, or at minimum I need to flip the PVC board to use it as a shield.
  3. All these plus 25-foot generator cable cost about $400 plus taxes.
 

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If you hook up a generator for outages, please ensure you isolate yourself from the grid. Even if it’s your MDX! Back-feeding is a thing that could injure utility workers or anyone coming across a downed power line.
 

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If you hook up a generator for outages, please ensure you isolate yourself from the grid. Even if it’s your MDX! Back-feeding is a thing that could injure utility workers or anyone coming across a downed power line.
Yes absolutely! I had the house wired up to the code including an interlocking switch exactly matching my panel, which was part of my test run. I feel I'm ready for the next storm:)
 

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according to the honda/acura press release the battery pack under the car is 1.3kwh and the voltage for all cells combined is about 260V in battery pack. Nice thing is the generator unit rather than an alternator to help generate power more efficiently from gas engine.

In all honesty, with the inverter and everything you've gotten, look into solar for your home! Buy the panels and DIY install them for huge savings. Never have to worry about outages and you can build you own battery wall.
 

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according to the honda/acura press release the battery pack under the car is 1.3kwh and the voltage for all cells combined is about 260V in battery pack. Nice thing is the generator unit rather than an alternator to help generate power more efficiently from gas engine.

In all honesty, with the inverter and everything you've gotten, look into solar for your home! Buy the panels and DIY install them for huge savings. Never have to worry about outages and you can build you own battery wall.
Yeah I noticed the 1.3kwh and thought it's odd. Prius has a much bigger battery pack instead. Do you think this means its generator is more powerful than Prius's (since it would need to output more in real-time) or less?

Emm I didn't think of solar. Would it be able supply enough to power the house in an outage and for how long?
 

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As long as the sun was shining bright....as I type, listening to the rain beating on my house (the outer bands of Laura have arrived).

Depends whether you have a battery and what kind. Otherwise ask California if it’s possible they’ve relied on solar to support the grid just a touch too much...
 

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Yeah I noticed the 1.3kwh and thought it's odd. Prius has a much bigger battery pack instead. Do you think this means its generator is more powerful than Prius's (since it would need to output more in real-time) or less?

Emm I didn't think of solar. Would it be able supply enough to power the house in an outage and for how long?
I don't believe the generator is as powerful as the prius as the battery pack is smaller and MDX battery is mainly used for rear SH-AWD motors when wheel slip is detected or AWD is needed so pretty rarely.

Folks in FL have about 20-30 panels and can power a whole home + A/C and washer/drier with negative bills in cooler months because of net metering. Some guy in my neighborhood built his own battery wall with a variety of Li-Ion Batteries and hooked it up to his inverter system so the power auto charges the grid when batteries are full.
 
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