Successful Clarity Back-up Power

Discussion in 'Clarity' started by M.M., Nov 2, 2019.

  1. M.M.

    M.M. Active Member

    I originally joined this forum because I was trying to learn details of the Clarity's 12V system to figure out how to execute a plan to use the vehicle as an emergency back-up power source for some house loads during a blackout.

    Well, the recent public safety power shutoffs in California finally had me running a real-world test on what I assembled.

    I was using a somewhat oversized Samlex 1500W pure-sine inverter with 2/0 cables that I screwed on to the extra-long 12V battery posts; the post for the power cable on the positive terminal and the battery clamp on the negative terminal, each with an appropriate nut. It looked a little kludgy, and I couldn't get all the threads on the nut down onto the bolt, but was a solid enough connection, and when I spot checked repeatedly the points of contact weren't even warm to the touch at the relatively low loads I had it under.

    I did shut it down when I went to bed, though, partly to conserve power and partly because I wasn't comfortable enough with the setup to leave it running without a bit of monitoring. I'd hate to wake up to an exploded battery or stolen car.

    I could have fed the battery cables through the grille on the front, but I just let the hood down gently and it wasn't putting any pressure on them. I ran the cables under my garage door so I could put the inverter inside out of the weather and also somewhere it wouldn't burn down my car or house if it blew up or something.

    I have a manual transfer panel for circuits that have my fridge, TV, and some lights that I normally use with a large UPS, and I made up a cable to connect the hardwired output on the inverter to that transfer panel. I used hardwired instead of plug so I could ground the inverter but use the house's existing neutral bond instead of creating a parallel ground path.

    I turned off everything in the car I could--interior lights, headlights, climate, infotainment screen--and dimmed the dash all the way to minimize parasitic use by the car.

    Worked better than I expected it to, if anything. Ran the fridge and living room lights for many hours without issue. Keeping an eye on the app's battery state of charge report, I calculated about 3% of the battery pack per hour of fridge and lights. Would have been faster of course had I been watching TV much, but still probably on the order of 7-8% per hour or so.

    I didn't run the battery down to the point the ICE kicked in, but per previous experiments I did it will cycle on at 1% and charge to 4%, so it would have been running for probably a few minutes about once an hour. Not the best way to treat the main battery pack, but wouldn't have broken anything to be sure.

    The inverter I bought never even got warm on the loads I was giving it, and the fans never turned on, so it was completely silent even in the garage. The car likewise was silent unless you got very close, at which point I could hear what I assume was the internal cooling system running just a bit. Battery voltage at the terminals was between 14.6V and 14.5V every time I checked, and with the fat cables I had there was maybe a 0.05V drop at the inverter terminals.

    I also figured out that using the Secure Power outlet on my SMA PV inverter, which will generate up to 2000W AC directly from the panels on the roof, that I could charge the car with the 120V trunk charger and still have enough left over for the refrigerator during the day, and could put enough back in to the car to replace what I used at night as long as the weather was good.

    Only two downsides to the whole setup:
    1. You can't lock the dang car! Because the key fob was not in the car, it refused to lock. No one in my neighborhood is likely to try to steal it (and you'd have to unhook the battery cables first), and I don't have anything of value in the car, but still it was pretty annoying.
    2. The way the 12V system is set up there's no good place to connect the cables without cutting into something or removing the existing terminals.
    For future use I'm considering making a short cable with one of those winch-power-style quick-connect connectors and an inline fuse, attaching it under the posts where the power system is connected to the battery, and just leaving the connector under the hood for quick connect when necessary. Only downside is that I'd probably want to take it off before service so some mechanic didn't mark "unauthorized modification" or something and screw up the warranty, and the positive connection point is really buried so it'll be hard to squeeze a lug in there without having to damage the plastic shield.

    All in all, though, highly successful, and I'm now confident that I can at minimum keep some lights on, the food, cold, and a computer running indefinitely in case of disaster.
  2. Claire Green

    Claire Green Member

    I'm really interested in this set up but was never sure what size inverter I need to run the refrigerator in my house. I don't have the manual transfer like you do but my only objective is to keep the refrigerator running so I can just use an extension cord from the inverter to the ref. So are you saying that a 1500 watt inverter is big enough to run a full size refrigerator?
  3. That is pure genius.

    The only parts I didn’t follow are the ICE cycling on at 1% and charging to 4%, and I believe you meant to say that you can’t lock the car because the key fob was “in” the car. I lock mine every day with the key fob out of the car.
    Last edited: Nov 2, 2019
  4. Sandroad

    Sandroad Well-Known Member Subscriber

    Great report.
    My full size Kenmore fridge uses 500 watts when running. It takes a bit more when starting up and I like to oversize inverters somewhat. So for fridge, I would use a 1000 watt inverter.
  5. Sandroad

    Sandroad Well-Known Member Subscriber

    Thanks for posting the info, @M.M. I do recommend attaching an Andersen connector to the 12v battery and your inverter because that will greatly reduce resistance and potential connections problems. In addition, I recommend keeping the battery to inverter cord as short as possible. If you were to run that inverter near its maximum output you’d be pulling over 100 amps from the battery and that’s not trivial!
  6. jorgie393

    jorgie393 Active Member

    Thank for all this! Question: what power state did you leave the car in? Full on (“ready to drive”), or Accessory?

    Also, re locking the car: I wonder if the physical key (hidden in the fob) would have worked .

    Sent from my iPhone using Inside EVs
  7. Robert_Alabama

    Robert_Alabama Well-Known Member

    We had a small upright chest freezer that would run fine on a 750W inverter (1500W peak) with the Chevrolet Volt. I'd guess that a 1000W (2000W peak) should run most upright refrigerator freezers as well. It's all about the starting current for the compressor. I always listen to the compressor start to make sure it doesn't sound like it is struggling during the start. You don't want to burn up a compressor by using too light an inverter. I never went to the trouble to set up any kind of transfer to use existing house wiring, just used extension cords. It is nice to hear that someone has used their Clarity for this without any issues.
  8. Bruce J Deeter

    Bruce J Deeter New Member

    That is a very clever idea, kudos.
  9. M.M.

    M.M. Active Member

    Yeah, the transfer switch is obviously not necessary, just a convenience; an extension cord will work fine in a pinch. I would strongly recommend running some kind of a ground wire from a pipe or existing outlet to the inverter case for safety, however.

    As far as sizing, it depends entirely on the particular fridge you have, but I would guess 1000W.

    Mine is a large, recent, efficient Frigidaire, which unlike older models runs constantly instead of cycling, so it only draws about 60W except during startup and defrost. Defrost is about 600W. So a 750W inverter would have been sufficient for my fridge, and 1000W would have been plenty for the fridge, some lights, and a computer. I got 1500W mostly as a just-in-case. I would guess broadly speaking that a decent quality 1000W inverter will be sufficient for just about any refrigerator, taking into account that most inverters are designed to supply significantly more than their rated output for a few seconds to start a power tool or other motor. Cheap inverters, however, often can't supply as much as their nameplate, or give the peak output as the nameplate rating, so I do not recommend cheap on the inverter. Likewise pure sine vs. "modified sine"; that might run a drill or a laptop power brick without burning anything up, but you're just asking for a broken compressor.

    1% to 4%: If I'm remembering correctly (I posted a thread with some experiments a while ago), if the main battery pack runs down to 1% state of charge (as reported by the Honda app), the car will turn on the gasoline engine and run it to charge the battery until it reaches 4% then turn off the engine. So if my loads are pulling about 3% of the battery per hour, the ICE will come on about once an hour and run for something like 5 minutes.

    Key fob in versus out of the car: No, I meant out. If the fob is out of the car and it's off, of course you can lock it. If the key fob is in the car and the car is on, you can also lock it (at least from the inside; never tried with a second remote). But if you turn the car on, leave it on, get out with the fob, and try to lock the doors, the car knows the fob is not inside and refuses to lock. I'm not entirely sure why this is, to be honest, but I guess it's to discourage leaving the car running or something.

    It's also possible that it had to do with having the hood unlatched; the car does seem to know the state of the hood, so that might have been the reason; I didn't test.

    I know from past tests that if the fob is not in the car you can drive it as long as it was on to start with, so had someone disconnected the cables and gotten in, they could have driven off, although once they turned the car off it would then of course refuse to start.
    Yeah, I parked very close to the garage to keep the cables under 6' long, but in the end it comes down to voltage drop, and with 2/0 copper 100A would have been a trivial 0.1V; even the inverter specs list 2/0 for good up to short-peak load (250A) with NEC-appropriate <2% voltage drop for up to 10'. I could easily have run the load I was dealing with on 2ga without issue, as long as I didn't load up the inverter, and really (since the DC-DC converter holds the battery at 14.5V rather than it being just a battery loaded down to <12V, you would have to use flagrantly unsafe cables to get voltage drop bad enough to shut the inverter down on undervolt.

    I left it in full-on; you have to. Accessory mode, like in all vehicles, turns off the DC-DC converter, so I would have been running things off of just the 12V lead-acid battery, which obviously would run down quickly. Accessory mode also shuts itself off after a while, if I remember correctly. I thought that it might turn itself off after a while in Park (like the later Volts, to keep your garage from filling with CO if you forget to turn the car off), in which case I'd have put it in neutral and left the parking brake on, but it stayed on for ~8 hours without issue

    I didn't try that, but I believe that only mechanically locks the door you put it in, so it wouldn't have worked on the passenger doors.
  10. Groves Cooke

    Groves Cooke Active Member

    "I didn't try that, but I believe that only mechanically locks the door you put it in, so it wouldn't have worked on the passenger doors."

    Maybe try locking the passenger doors from the inside and then locking the driver door with the mechanical key.

    This has been an interesting discussion. I live on rural property with a well the well itself needs about 3000 1W on startup so this would not work very weell for me and I have a 7500 W generator for rare power outages.
  11. Sandroad

    Sandroad Well-Known Member Subscriber

    And your well pump may be 240V?
  12. Mowcowbell

    Mowcowbell Active Member

    I went with a pure dino solution. Bought a 7500watt dual fuel generator from Tractor Supply for $800, had an electrician install a 10 circuit transfer switch for $300 labor and $400 in parts. Power goes out, I can run on gasoline or propane indefinitely. Runs everything in my home that isn't 240v.
    Last edited: Nov 2, 2019
  13. Yes, with the power on and key fob outside there seems to be no way to lock the car.

    You have made this work with a 1500 watt inverter. We probably have 15kwh available from the HV battery. The limiting factor would be the amount of power available to the 12v LA battery from the lithium battery. This would dictate the size of the inverter which could safely be used to extract the energy from the lithium bank. Perhaps a 1000w-1500w is as large as one should go.
    That should be sufficient to operate a residential refrigerator.

    Our solution for powering the well pump and holding tank pump was a solar array, lead acid battery bank and 2 inverters to provide 240v.
  14. M.M.

    M.M. Active Member

    Someone on this forum determined the capacity of the DC-DC converter, I don't remember the exact number but I believe it's 1600W. You can of course draw more than that for a short time (it'll just draw down the lead-acid battery), and people go on road trips with the headlights, car computing, power steering, stereo, heated seats, and fan blower all running for long periods of time, so clearly the DC-DC converter must be designed to run at a pretty high capacity without issue for extended periods. But I basically figure that for thermal reasons it's probably a good idea not to load it constantly to more than maybe 50% capacity, so I would be wary of putting more than an 800W load on it, personally. Probably fine, especially if the weather is cool, but just to be careful. That's why I picked a 1500W inverter.

    Which is more than enough to run even an old-style residential fridge.
    This is obviously the simplest and cheapest option for someone in your situation, although in my fairly isolated area we have the interesting problem of fuel being hard to find or outright unavailable during a widespread blackout, and particularly in a major disaster (earthquake).

    There were I think four gas stations in the county open during the recent blackouts, and they ran out of fuel pretty quickly. But after a major earthquake we can expect to be without power, natural gas, or any source of liquid fuel for probably two weeks, and the only way into or out of the county will be air or sea.

    Planning for this situation, being able to run some lights, computing, and refrigeration off of my Clarity, then charge up what I drained during the day off of my PV array's backup outlet, will be extremely valuable if/when that happens (as is the ability to produce transportation fuel from the PV array in the same way, if I need to drive somewhere).
    Sandroad likes this.
  15. Sandroad

    Sandroad Well-Known Member Subscriber

    Thanks again for sharing your expertise and ideas. You’ve obviously thought this through and have the knowledge to do it safely. If I didn’t already have an off-grid solar system that can supply what a need, I’d be on this right away!
  16. MrFixit

    MrFixit Well-Known Member

    Maybe I missed this, but if you were in HV mode, could you do this at whatever SOC that you desired? ie: if you were worried about operating between 1% and 4% for a 'long' duration, could you use HV and operate between 51% and 54% [and still only have the ICE run for a few minutes every hour]?
    Or, would the engine cycle much more often in order to hold a tighter window of SOC?
    Last edited: Nov 3, 2019
  17. Mowcowbell

    Mowcowbell Active Member

    No gasoline at any stations? No problem. That's the beauty of a dual fuel generator. Propane has no expiration date and won't get old. Large propane cylinder will supply enough fuel for a week of use.

    Electricity here is very reliable and only goes out for a day or two if we have a major tornado breakout or freak icestorm. I typically have enough gas and propane on hand to run for a few days, no more.
  18. M.M.

    M.M. Active Member

    Good question, and I have not tested it. I would think it would do something along those lines, though. Cycling around 50% SOC rather than 0% SOC would be a little more gentle on the pack, although in the grand scheme of things it's negligible unless you did this for a very long period of time.

    Peripherally, I've noticed that the ICE turns on sometimes when I'm just sitting there listening to the radio or something, but not every time. I haven't noticed it recently, so maybe they fixed it in the software updates the dealer installed a while ago, although it was not mentioned. I was kind of expecting it to randomly turn on while running the inverter, but it didn't.

    Propane is at a substantial advantage to gasoline, and is a good long-term fuel storage solution for most people, like yourself. In my area, looking at the catastrophe-recovery use case, propane would rapidly become unavailable, too, so unless I had one of those huge 100gal tanks installed and kept it full I would probably have the same problem with a fossil-fueled generator. I'd also frankly be worried about the valve on the tank breaking in a 9.0 earthquake, in which case the fuel storage would become more of a hazard than a benefit.

    If my house is a pile of rubble I can't use the PV, either, but if the building is even partly intact I have enough tools and electrical skills to patch up some wires and get it running, and all I need is the inverter and cables to get some power out of the car.
    Last edited: Nov 3, 2019
  19. jdonalds

    jdonalds Well-Known Member

    This is roughly the plan I have too. I'm waiting for the electrician to call to get this started. I learned propane tanks can be filled even when the source of the propane does not have electric power. I like the idea of using propane that can be stored indefinitely. I only need about 3,500 watts. I don't want to oversize which would use more fuel.

    All I want to do is power the refrigerator (surge 1,200w), a few lights, the garage door opener, and perhaps a one room electric 1500w space heater if the temperature drops too far.

    I'm reading this thread because someone mentioned you're not supposed to charge a plug-in car with a generator. Does anyone know if Honda has that restriction? The power should be clean coming out of an inverter/generator. I doubt if I'd try to charge the car with a generator but I'd just like to know if it is acceptable. Should be able to fully charge a Clarity in about 4-5 hours depending on the size of the generator.

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