Using car as generator for house power

Discussion in 'Gen 3 Prius Accessories and Modifications' started by ED9593, Oct 31, 2012.

  1. bisco

    bisco cookie crumbler

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    i think they are oob, too expensive. there are threads here iirc.
     
  2. MikeNinMass

    MikeNinMass Junior Member

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    Most of the posts about using a Prius as a backup home power supply are looking at it wrong and undersizing the capacity.

    First, limiting the output from the battery with a fuse rated for is less than the fuse that charges the battery (100 A from what I read) fails to take into account that the battery itself has an output capacity that is greater than the charging current. (Think along the lines of: you can't jump start an ICE-only car with a battery charger.)

    The extra current is useful for overcoming the startup loads of appliances with inducitve loads (including motors, fans, compressors, etc.), which are, as a rule of thumb, twice the normal operating load but only for a few seconds.

    So someone suggested putting an 80A fuse to the add-on inverter, which would mean the max output is 960 watts (if 100% efficient), so you have less than 500W for things with motors. One site, which lists appliance loads to estimate generator size, gives the following operating and startup wattage for several appliances (I think the list is old because the current average fridge is more like 750W, and microwave is 100W, but sump pumps and well pumps probably haven't changed much over the years)

    sump pump (1/3 hp): 800W operating / 1250W startup
    well pump (1/2 hp): 150W/1950W
    refrigerator: 500W/750W scaling this up: 750W/1125W
    kerosene heater: 500W/725W

    reference; Choosing a Generator: Which Size is Right? | HOECoop.org • Howell-Oregon Electric Cooperative

    So none of those appliances would work, nor would a 1000W microwave. (The list has other appliances, too.)

    If you are careful, and you plug only one of them in at a time (e.g., drain the basement, then get some water for coffee and a frozen meal from the fridge, then warm up the food and coffee in the microwave, re-cool the fridge, then warm up the house a little), you can safely run a bit over 1000W, steady-state operating. Then you'd need to double the capacity of the inverter (2000W) to handle the inductive (motor) loads.

    The standard battery is rated for 325 CCA, and a Optima Yellow Top is rated at 450CCA/575CA, So even the OEM battery can put out close to 4kW for a few seconds. And you can run over the operating current for a little while if you draw down the battery.

    If you keep the car in Ready mode and it shuts off every few minutes indicating it is keeping up with fully charging the battery, then you should be okay. Even better, keep the bluetooth OBD2 plugged in and monitor that voltage isn't dropping, and adjust your usage if needed.

    I've only needed to run my internet, laptop, and some lights for a few hours a couple of times, and everything worked fine. I'm mainly concerned about flooding in a bad storm, but I'm confident my Prius can handle it.
     
  3. MikeNinMass

    MikeNinMass Junior Member

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    oops, the heater would work with an 80A fuse...
     
  4. ChapmanF

    ChapmanF Senior Member

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    A common answer to the "needs X amps, except Y for short periods" is a slow-blowing fuse, which most of those available in high-amperage flavors in cars, like the MAXI style, sort of inherently are. (There are some very fast-blow styles for high-energy battery banks and such, but those are kind of a different beast.)
     
  5. bighammer

    bighammer Junior Member

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    The kits I've seen lately are just very small scale inverters with 12v input that wouldn't power much of anything. I thought there was a kit that tapped into the main battery(s). Basically a plug-in kit that can be reversed in power outages. It would be a lot nicer to have a Prius quietly idling in the garage instead of the drone of a 3600RPM generator.
     
  6. ChapmanF

    ChapmanF Senior Member

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    There was a company called Converdant that was importing some of those in various sizes, but they've exited that market. The smallest they used to carry was a 2 kVA made by AIMS, but the AIMS folks now say they haven't kept any drawings and don't even know how to support those models any more.

    Some years ago, hobbit posted a review of one of the larger models, only up to 3 kVA rather than two, but in a sort of comically oversized and ludicrously heavy steel box.
     
  7. Terrell

    Terrell Old-Timer

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    This week we installed solar on our house, which meant the grid power had to be turned off for a while. "Around four hours," the head guy said. "Less than that!" the electrician said. In fact, it was off for six hours. But I was prepared with my Prius, my 1kW inverter and extension cords. The Prius motor cycled on and off as needed, and it powered our phone system, alarm system, freezer full of food in the basement, computers (with modem and router), and a small LED lamp. The installers were very impressed that the Prius could do all that, and asked whether it was a dealer option, or did I install it myself? (Unfortunately, our refrigerator's startup kick is too much, so we just kept the door closed, and the small microwave I use for camping which runs fine on the Prius, didn't run with everything else on.) What a great car!
     
    jerrymildred, cwerdna and ASRDogman like this.
  8. cwerdna

    cwerdna Senior Member

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    I no longer have a Prius but I did use a Samlex PST-1000-12 PST w/my Chevy Bolt in READY mode to power a regular-sized fridge, some lights, laptop, NVR camera system on a UPS + AC adapters to keep my phones charged during the two PG&E "PSPS" I've experienced so far. Fortunately, that inverter can handle the startup draw of my fridge w/o issue.

    The tricky part is the terminals on the inverter and the flat lugs it comes with. I could find cables w/those lugs on them so I had to get a Batteries Plus location to crimp those onto the cables I had.
     
  9. johnnychimpo

    johnnychimpo Active Member

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    Looking to use the main ev battery with old server ups 240v can anyone point me to a how to.
     
  10. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I no longer own a Prius but there is an AC voltage between the battery power lines and the chassis which is used to identify a short to frame. There are non-trivial ground issues to address.

    Bob Wilson
     
  11. fuzzy1

    fuzzy1 Senior Member

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    I had understood it to be floating with respect to the chassis. And with DC ground fault detection, basically a current difference transformer to make sure the incoming and outgoing currents on the power wires are identical. If anything leaks and they don't match (within a certain very narrow tolerance), a relay inside the battery container opens up. But yes, this makes ground issues non-trivial.
     
  12. Maarten28

    Maarten28 Active Member

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    What is it exactly you want to do. Do you want to replace the UPS batteries with the EV battery? That is not trivial since normal UPS'es use 12V batteries (like car batteries) as power source. You would have to disassemble the EV battery and take out the right amount of modules to make 12V and hook that up to the UPS.

    Or do you want to use the whole EV battery to create the 240 V AC?
    If you have the battery still in the car, it is relatively easy: hook up an inverter to the 12V and make your 240V from there. But you need to have the car always on in order to recharge the EV battery.
    If it is without the car than there are a few problems: the voltage is somewhere between 180 and 260 V DC and you need to make 240 V AC from that. Charging the battery is done via MG1 which is run by the engine. In absence of that you need to create your own charging system.

    I would not bother with it. If you need a UPS, buy a UPS. If your UPS battery has gone dead, replace it with a suitable replacement.
     
  13. johnnychimpo

    johnnychimpo Active Member

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    IM not an electrical guy. what i understand is you want to use the car battery back to ensure you have plenty of power to run stuff. so the ups from a server room are normally 240 volt just like the cars hybrid system. All things bein equal I could use the built in safety electronics of the server UPS to safely use the engine to charge the battery back when it runs low as power is being drawn from the ups to power my home fridge tv microwave and tv (not all at the same time) but that is the Idea. is this doable or no? Im looking at a plug an play kind of deal, IM not looking to get deep into this else Im thinking of doubling up the 12 volt battery and using a 2000 watt power inverter. basically I want to have emergency power in an outage. basically tv microwave maybe fridge.
     
  14. fuzzy1

    fuzzy1 Senior Member

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    :eek: It looks like you are confusing DC and AC sides of this. And having unrealistic plug-and-play expectations. And for the alternate 12V solution, expecting more power than it is fused for.

    The 240V you refer to for server room UPS equipment is the AC side, and that is not at all like the Prius AC side. You simply will not be using the UPS to charge the batteries from the engine, you must stay with the Prius electrical system to do that. The UPS would be used only to produce the 120/240VAC output from the batteries.

    The immediate question here is, what is the UPS DC battery voltage? The DC side is what must be matched to the Prius battery pack.
     
  15. ChapmanF

    ChapmanF Senior Member

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    For the approach of connecting a high-input-voltage inverter to the traction battery, a lot of information can be found in this PriusChat Knowledge Base thread and the links out from it.

    In DC terms, it is floating. The isolation is tested by the battery ECU imposing a distinctive AC waveform and measuring how much of that can be seen with respect to body ground. That value can be seen in the Techstream data list as the amusingly-named "short wave" value: not a radio band where you can pick up distant broadcasts, but a roughly 5 kHz wave used for detecting shorts. :)

    Veteran member hobbit gave some details about the waveforms and related filtering and grounding issues.

    [​IMG]
     
  16. fuzzy1

    fuzzy1 Senior Member

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    I guess that's what I get for just sampling Hobbit's writings, not going through the whole encyclopedia.
     
  17. ChapmanF

    ChapmanF Senior Member

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    Weird-looking wave, should be somewhere on the bridge of a Klingon vessel.
     
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