DC -> AC inverter, UPS questions/discussion

Discussion in 'Fred's House of Pancakes' started by cwerdna, Jul 5, 2012.

  1. edthefox5

    edthefox5 Senior Member

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    Your scaring me Bob:

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  2. bwilson4web

    bwilson4web i3 and Prime

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    Sorry, fixed.

    Bob Wilson
     
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  3. SeattleKen

    SeattleKen New Member

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    El Dobro suggested that I repost my message (in the Gen III Technical Forum) here. Thanks El Dobro!

    I'm a relatively new 2012 Prius owner who was motivated to buy a Prius, in no small part, by the Prius's ability to serve as an UPS and generator in a jam. I've got a 1000w Xantrex Pure Sine Wave inverter and have all the 2ga cables ready to go. Then, an ugly thought occurred to me--- if I run down the 12v auxiliary battery (after some time powering a few appliances during a blackout) and the DC converter is working hard to recharge the battery, I might still blow the 100a DC/DC converter fuse if I have a sudden increase in load (e.g. the compressor in my refrigerator turns on).

    After thinking about it for awhile, I think the weak link is the puny 12v battery in the Prius. It doesn't have much capacity (so will be low more often) and doesn't have much power for intermittent high loads (i.e. little "crank power"). A better option might be to use a battery isolator in the line into the existing 12v battery and then have a much bigger battery serve the inverter.

    I've created some circuit diagrams of what I'm getting at. If the battery is bigger, it might lessen the chance that of a sudden load on the converter-- both because there will be fewer "low charge" periods and because there's more residual amps in a bigger battery.I've heard the idea of using a battery isolator bantered around on the forum before, but haven't found any specifics.A few questions
    1. Is this a viable idea and will it lessen the chances of blowing out my 100A fuse?
    2. Having never used a battery isolator before, is this the way to wire it?
    3. If I keep the leads to the isolator really short, do I have to fuse it?
    4. I'm thinking about the Optima D51 Yellow battery for this application because its specs seem close to the Prius existing battery-- except that it has a lot more cranking power and a lot more amp hours, of course. Is that the right way to go?
    5. I'm assuming that a 100A battery isolator is optimal, but what do I know?
    [​IMG]
     
  4. SeattleKen

    SeattleKen New Member

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    Inverter Update:

    BTW, I just connected my inverter (Xantrex ProWattSW 1000) straight to the battery terminals of the 12v auxiliary battery and ran my big kitchen refrigerator and a few lights off of it. Worked flawlessly! Prius cycled as necessary (kept it in "Ready" and "Park").

    I was really surprised, actually, about how low the load of my refrigerator was. It's a Kenmore side-by-side that's about 5 years old. When idling, it drew less than 70w of electricity and, when the compressor kicked on, it only drew about 250-300watts maximum. I used a Kill-A-Watt powerstrip (PS-10) which measures the total load of up to 10 items plugged into the strip (also useful for this application).

    Here's a description of my setup. I mounted the inverter on a 11" x 17" piece of plywood (thank you, Home Depot) and used some 2ga cables (a pack of 2 x 6' jumper cables was enough for the project) and some battery jumper clamps (both from Amazon) to connect it up. I also mounted a 60a ANL fuse (very conservative-- recommended elsewhere to protect the 100a DC-DC converter fuse in the Prius). I had to cut a bunch of the cables and reconnected them with compression ring connectors (search for "Accel eyelet battery terminal" in Amazon). Home Depot also sells 3/8" electrical cable clamps that works great with the 2ga cables-- that keeps everything nice and tidy. The whole thing fits perfectly in a Seahorse SE710 waterproof case (just like a Pelican), along with the kill-a-watt power strip. A total emergency package just ready for the next blackout.
     
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  5. alsteckprius

    alsteckprius Junior Member

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    Hi Ken. Well, after losing power on 3 separate occasions in the last 5 days (thanks, Sandy), I've finally decided to make the leap and get my 2010 hooked up as an emergency generator. I liked your idea of supplementing the Prius 12V. bat with a heavy duty deep cycle bat. Couldn't you just hook up the deep-cycle in parallel to the stock bat, and then to the inverter? A fuse would be a great idea. Could it go into the positive line between the two batteries? What do you think? Keep in mind, I know about as much about electricity as I do about brain surgery.
     
  6. bwilson4web

    bwilson4web i3 and Prime

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    I'd like to volunteer some design tradeoffs:
    • no space and extra weight of second battery - there is not really a place to put a second battery and the extra weight is unwelcome. Rather, I suggest replacing the existing OEM battery with one that has a high crank rating (for surge loads) and deep discharge capabilities (not really used.) In normal operation, the Prius is providing the power for the inverter and the battery is an energy buffer.
    • fuse vs fusible link vs circuit breaker - I plan to replace the 140A, fusible link in the cable assembly that attaches to the B+ with my 120A 12v circuit breaker. This provides a margin so the engine compartment, 120A fusible link from the DC-to-DC converter is somewhat protected. However, I need to make some voltage drop measurements before I make this mod.
    Although I agree that more inverter power could be gotten if it were tapped to the 'jumper post' under the hood in the primary fuse box, I am not going that way:
    • battery 'buffer' capacity is lost - the long cable run to the 12V battery in the rear reduces its ability to respond instantly to surge loads. This puts the 120A fusible link from the inverter at risk.
    • unable to operate while driving - I use the inverter to drive low power loads on long distances such as laptops and cell phone recharger. In fact, any 110VAC load could be driven . . . (espresso ?)
    GOOD LUCK and work safe!

    Bob Wilson
     
  7. This aspect of installing a larger 12V in parallel with what is in place was discussed in detail in the Gen 2 archives. In a actual situation the deep cycle (I think that is what was used) would have to be reconnected. As I remember, it worked fine. All this discussion is inspiring me to go buy a brand new 2000W inverter on sale for $80. Of course I do not need it, BUT, that's exactly when one should buy and prepare, when you don't need it. Anyway it might be Fun.
     
  8. To: Bob Wilson. I have come across a 2000 Watt inverter for sale and am thinking of going over and looking at it tomorrow. Normally, people have been mentioning 1KW TO 1.5KW devices. Do you think that the 12V can drive the inverter OK. I don't know what the parameters might be.....TY
     
  9. wjtracy

    wjtracy Senior Member

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    We need some kind of list of options:
    Getting power from Prius (Most simple to more complex):

    DIY Options
    Option-1: Small inverters (<200 Watt) that plug into cig lighters are common for all cars
    Option-2: Medium size inverter (1000-1500 Watts) attached via cables to 12v battery of Prius
    Option-3: Larger size inverter attached to 12-v battery with extra 12v battery added for peak load
    (need some how-tos on this)

    Advanced DIY Options: (Don't try this at home)
    Option-4: Larger size inverter attached to Traction battery

    Toyota Options (P2H) coming for PiP? (available in Japan soon)

    For me I think Option-2 is OK
     
  10. I agree, I am not sure how it may hurt to use a slightly larger inverter. I think it is something like burning a 60W.....100W....to a 1000W light bulb. Eventually you blow the light bulb OR the generating system, ie: the Prius. But I am sure there are some reasonable parameters.
     
  11. Where is NOVA?"..............scotia?
     
  12. wjtracy

    wjtracy Senior Member

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    Do you have NOCA (northern CA)? well we have NOVA (northern VA)

    Bunch of threads going on this, but if you take too much power apparently you risk blowing 100A fuse in Prius that disables vehicle and would need to take to dealer for fixing
     
  13. Ah so deska. Not that I know, however I don't know much, and less each day.
     
  14. Bob is a EE, I believe and has done extensive testing with batteries so I will await his reply.
     
  15. Time to go beddybye.
     
  16. bwilson4web

    bwilson4web i3 and Prime

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    Let's go down the list of electrical power sources that can drive a 110 VAC inverter:
    • 120W - cigarette lighter, just enough for laptop, small lights, works when driving and parked.
    • 1000W - power tapped at 12V battery terminals, enough for fridge, TV, lights, 1 hp motor.
    • 3000W - power tapped at the 202V traction battery, runs a house.
    If you are not technical, the small inverter provides essentially 'camping at home.' Buy it, test with the car, and store under a seat. Tapping the traction battery provides the greatest amount of power but is also the most technically challenging. The web page is unavailable but Richard is also in the Sandy area and the ISP and communications may be 'offline.' My experience has been with the NHW11(2001-03) and ZVW30 (2010-current).

    This sketch is the NHW11, 12V power bus configuration:
    [​IMG]
    The ZVW30 has a similar configuration using 140 A fusible link at the battery and 120 A at the "HVC" power inverter. The NHW11 120 A fusible link is in the red-plastic housing that connects to the battery B+ terminal:
    [​IMG]
    Here you see the two, 4 gauge cables connected directly to the 12 V battery terminals. The end of the B+ cable was first wrapped in electrician's tape so it would not short to the car frame and like an arc welder, burn holes. However, this is not recommended because the B+ cable still has to be connected to the inverter.

    A better approach when working with the 12 V battery, disconnect the ground and keep it off:
    [​IMG]
    This means with the car off, you can freely work with the B+ cable and there is no risk of sparks and arcs.

    Once everything is mechanically mounted and cables secured, the ground can be connected:
    [​IMG]
    In this case, the inverter mount folds down to improve cooling under load. These inverters are typically running 85-90% efficient which means 100-150 W of heat. Make sure your inverter mount lets the hot air escape and cold air come in.

    Inverter Technical Stuff
    • operating power - the sustained load. The minimum should be 1 kW but can be larger if you have a battery with a significant, cold cranking capacity. The battery can provide 10s of seconds of power handle motor startup loads.
    • 12 V cables - WalMart and auto stores sell them with properly swaged terminals. Although 6 gauge can work, 4 gauge cables run cooler with less power loss. Mount the inverter to use the shortest possible cable. They also sell terminals so the cables can be cut to fit . . . less is more.
    • surge power - typically this is just under a second, 30-40 cycles. Meant to deal with inrush, this is not a realistic motor startup.
    • in-rush - many electronic devices have a serious in-rush current that can sometimes be seen as a small arc when first plugged into the wall outlet. This can trip the inverter, low-voltage protection and go into a slow-speed oscillation. Plug these loads in first and then the rest.
    I am in the process of installing a 1.5 kW / 3.0 kW surge, sine-wave inverter in my wife's 2010 Prius. A work in progress, I'm learning lessons in this new installation such as Anderson connectors waste a lot of energy and the characteristics of a 120 A, 12 V circuit breaker.

    With 1.2 kW, space heater load on the AC inverter, the OEM battery started providing the extra current. It had been floating around 13.8 VDC but soon dropped to 13.1, 13.0, 12.9 . . . and the current into the inverter increased to maintain the 1.2 kW output load. Eventually the current draw reached 120 A and it tripped. This took just under a minute so I was able to watch and take measurements.

    I am replacing the OEM battery with an Odyssey PC925 to maximize the surge capability for startup loads. I'm also trying to figure out what to do about the 140 A, fusible link. I want to 'protect' the inverter 120 A fusible link.

    Since I know the Prius can provide 80 A @13.8 V, I will get an 80 A, 12 V circuit breaker. If (when) an overload drains the 12V battery that it starts drawing 80 A from the inverter, the circuit breaker will trip protecting the car, power inverter.

    Bob Wilson
     
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  17. That is inclusive, Thanks much Bob.
     
  18. cwerdna

    cwerdna Senior Member

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    I think the page that Bob's referring to is PriUPS-getting electricity FROM your hybrid vehicle, which was down for days and now has apparently gone back up. The archive via Internet Archive: Digital Library of Free Books, Movies, Music & Wayback Machine was not giving me very useful results while PriUPS was down.

    As for operating power, do you mean maximum load instead of minimum?
     
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  19. MJFrog

    MJFrog Active Member

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    I'm not sure why it hasn't been suggested yet, but in order to buffer the 'inrush' surge of your fridge or furnace motors starting up, why not try this: Hook up one or two of those UPS battery systems you already have your PC(s) connected to, to the extension cord coming off the inverter into the house. Then plug-in the fridge or furnace to those. The power surge will be soaked up by the UPS while the inverter will keep the UPS systems charged.

    Obviously, there's still a limit to how far you can run your extension cord and how much power you can pull, but it should save your Prius fuse from blowing.
     
  20. bwilson4web

    bwilson4web i3 and Prime

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    Thanks,
    I'll go back and edit it but with these bullets:
    • safest is under or 1 kW sustained
    • over 1 kW up to 1.5 kW needs higher CCA battery and overload circuit breaker
    I'll have to think about how to edit this so for now, I'll modify the original to something like:

    "easiest 1 kW or less"

    Then I'll add the 'Super Bob' as some sort of footnote or addendum.

    Bob Wilson
     
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