Shopping for an inverter: 12 VDC vs. 240 VDC

Discussion in 'Gen 4 Prius Technical Discussion' started by Smaug1, Sep 13, 2018.

  1. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    Hi all. I'm shopping for an inverter for my Prius, and am on the fence on which to get. I'm an electrical engineer, but I figure someone has already researched this and if so, it would save me some time.

    Is the 12V battery big enough to power a 1500 W inverter at full load?

    I just realized my automotive knowledge from the past doesn't necessarily apply for a Prius, since it doesn't need a bunch of cold cranking amps from the 12 V battery to start it. I haven't yet looked up the specs of the 12 V battery. I found a nice UL Listed 2 kW inverter at homedepot.com for about $160. Thinking about it 2 kW @ 12 VDC = 167 A draw. It should yield about 14 A out @ 120 VAC, which is about the equivalent of a typical branch circuit in the home.

    Thinking about it, 167 A draw from the 12 V battery is probably too much.

    A 1500 W inverter would draw about 125 A. Also probably too much.

    1000 W inverter would be more like 83 A, which might be in the "reasonable" ballpark, depending on how beefy the 12 V battery is.

    In any case, it may be a higher load than the battery sees in normal use and toast the car's 12 V battery. (or at least accelerate it wearing out...)

    *************

    The other option, using the traction battery, is better electrically. Higher source voltage = higher efficiency, (around 97%!) and the resulting input current would be a lot lower too. 2 kW @ 240 VDC is only 8.3 A. However, a good sinusoidal, UL Listed 2 kW inverter runs $700. It would also require a wiring custom harness, which will cost some bucks too: a DC fuse, fuseholder, appropriate heat-shrink tubing, welding cable, Andersen PowerPole connectors... This will probably add up to another $100 at least.

    So we're talking in the neighborhood of $800 for this path, though it would be more useful in a power outage situation. It could run a fridge, modem and WiFi router, etc.

    A Google search sent me to some older threads, where someone had considered it, but it was obviously for a different Prius and all the pix were missing.
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Active Member

    Joined:
    May 12, 2018
    457
    393
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    It's a lot of amps for the battery to handle. It will do it, briefly.

    The real concern: what can the DC-DC converter actually supply? It normally replenishes the 12v battery from the high voltage system, but I don't know what continuous rate it can handle.

    I really doubt it'll keep up with an 80-100A draw on the 12v side.

    I looked into this shortly after we got our Prius, and quickly determined that it works great for small inverters for small needs, but it costs more than it is worth to scale it up for whole-house backup power. $800 goes a long way to getting a decent genny & interfacing it with your home panel.
     
    DLC82SV, krmcg and Smaug1 like this.
  3. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    3,713
    4,745
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    There was a thread with extensive discussion - someone wanting to run some Medical gear while camping - you might find it in a search.

    EDIT - also someone wanting to run a security camera 24/7.
     
    DLC82SV likes this.
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    5,708
    3,439
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    It won't be coming from the 12 V battery, because of course you won't be using it except when the car is in READY, and the power will be coming from the DC/DC converter. Per lots of past discussions here, the 83 A is probably a good limit for what you can expect to siphon off from the converter (which has generally been rated somewhere in the 100 to 120 amp ballpark depending on generation) while still leaving some to run the rest of the car. That's assuming you don't have the other heavy loads simultaneously on, like lights, defogger, supplemental heat elements, etc.

    I don't know about Gen 4, but in the first 3 generations anyway, the DC/DC converter has an output signal called IDH. It asserts this signal when it is near overloaded. In the stock configuration, the only thing it's used by is the ECU controlling the heat, which will shed the supplemental heat elements if they are on and the converter asserts that signal. If you are going to add any load up around 83 amps, you might consider tapping that signal and monitoring it somehow, either for some automatic load shedding or just for a red LED or buzzer for your own information.

    *************

    Where did you find one? I haven't looked in a while. An outfit called ConVerdant used to offer some for Prii, but they seemed to go away.

    -Chap
     
  5. padroo

    padroo Senior Member

    Joined:
    Jan 11, 2008
    1,744
    1,511
    8
    Location:
    Chesterton, Indiana Another third world country.
    Vehicle:
    2016 Prius
    Model:
    Four
    If I needed the kind of information you want I would contact professor John Kelly at Weber University.


    John Kelly
     
    DLC82SV likes this.
  6. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    3,713
    4,745
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    Now that I read your question in more depth - I see that it's to run a house.

    Check out PriusChat threads - I typed in "house power" and came up with quite a few - mostly old:

    upload_2018-9-14_11-35-52.png
     
    DLC82SV likes this.
  7. Elektroingenieur

    Elektroingenieur Senior Member

    Joined:
    Jan 8, 2017
    770
    1,145
    9
    Location:
    California
    Vehicle:
    2016 Prius
    Model:
    Three Touring
    These previous postings might be informative, if not helpful—I have no recommendations:

    Prius Whole house Converdant Inverter | PriusChat
    Prius Whole house Converdant Inverter | Page 2 | PriusChat

    Please explain 12V system to me--how to keep battery charged while using accessories? | PriusChat
    Please explain 12V system to me--how to keep battery charged while using accessories? | Page 2 | PriusChat
    For fourth-generation cars, it’s listed in the Repair Manual as a Data List item (“PTC Heater Activate Permission Status/Prohibition Signal(IDH)”), but the separate wire appears to have been removed.
     
    alanclarkeau likes this.
  8. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    It takes some searching, but I found some.

    This company seems to make them, but they don't list their options, they want the customer to specify what he wants. So I requested a quote from them.
    DC-AC Sine Wave Inverters with High Input Voltage Deliver 100VA - ABSOPULSE Electronics Ltd

    For 12 V, UL Listed ones, I found a few candidates:
    Eaton 1800W
    PowerDrive 1000 W (not sinusoidal output, but inexpensive)
    PowerDrive 2000 W

    I just looked again, and the one I thought was perfect (traction battery voltage) was a grid-tied inverter; won't work for our application.
     
    DLC82SV likes this.
  9. DLC82SV

    DLC82SV Member

    Joined:
    Jul 16, 2018
    165
    73
    0
    Location:
    81212
    Vehicle:
    2008 Prius
    Model:
    ----USA----
    Professor Kelley is a Genius!

    Posted via the PriusChat mobile app.
     
  10. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Active Member

    Joined:
    May 12, 2018
    457
    393
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    Just to offer it- We've been using inverters from Exeltech of Fort Worth TX. Outstanding quality and support. Extremely clean power, good manners in bad conditions too- clean cutoff & de-bounce lock, no brownouts or weird behavior. I haven't asked them about the possibility of a high voltage DC input version, but they have previously been open to custom variations. They would be my go-to.

    We've had one of their 12V 1kW models for nearly 20 years, and more recently I installed the 24V XPX 2kW model as the primary power for the beach cottage.

    My primary home is rural enough that I need 240VAC for water pumping, so my own storm outage solution needs to account for that. That's a lot of why I'm biased towards using a generator instead. Currently getting by with a 4kW jobsite rig, though it probably ought to be a 7kW. Next time.
     
    DLC82SV likes this.
  11. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    What I was thinking, Leadfoot, was that the Prius engine and electric system is probably a LOT more fuel efficient than a purpose-built generator that is reasonably affordable. One account I found somewhere had one guy using his Prius with a 1600 W inverter on the 12 V battery for a 3-4 days and used half a tank of gas, (~ 5 gal.) while his neighbor with a little Honda stand-alone generator went through at least 5 gal. per day.

    Add to that the challenge of keeping fresh gas handy for the stand-alone generator, compared to almost certainly having fresh gas in the Prius. Going to a natural gas generator would be even more involved and expensive.

    I guess I'm thinking mostly of having juice to run the refrigerator and gas furnace controller. I think a basic 1 kW (continuous) modified sine inverter would probably do it. If not, then certainly a (proper) sine inverter in the 1 - 1.5 kW range.

    It's starting to seem like getting a high voltage inverter to use the traction battery will have enough challenges that it won't be worth it for my limited use. Better to just hobble by with a lower power low voltage one.
     
    #11 Smaug1, Sep 14, 2018
    Last edited: Sep 14, 2018
    DLC82SV likes this.
  12. DLC82SV

    DLC82SV Member

    Joined:
    Jul 16, 2018
    165
    73
    0
    Location:
    81212
    Vehicle:
    2008 Prius
    Model:
    ----USA----
    Pure Sine?

    Posted via the PriusChat mobile app.
     
  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Active Member

    Joined:
    May 12, 2018
    457
    393
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    Those are all great advantages. You're right, the Toyota will burn less fuel, it'll burn it with lower emissions and less noise. From that angle the Prius is a great way to get your emergency power.

    The downside for me is the adaptation cost. My emergency power needs would mean a > $3000 inverter system, or a $750 generator. (and I already have the genny)

    On days like today, the generator really wins because I'm home and my wife has the car on a business trip 150 miles away. Factor that in.

    IF you can power enough of your home on a 1kW rig, I say go for it.
     
    Smaug1 likes this.
  14. Fester

    Fester Active Member

    Joined:
    Mar 29, 2010
    146
    154
    0
    Location:
    Ohio
    Vehicle:
    2017 Prius
    Model:
    Two
    I'd be concerned about unintended adverse consequences on the Prius's electrical system with this arrangement. Perhaps a battery/inverter system might be more suitable for a power standby system. Mine is Solar/Battery system, around 1800 watts solar, 3kw Prosine inverter/charger, 4 Trojan 6v flooded cells, in a 24 volt system.
     
  15. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    Yes, of course a dedicated system would be better. But also a lot more expensive. It's not really comparable to a 1 kW 12V inverter.

    I guess it could almost be comparable to a higher power one off of the traction battery...
     
  16. Fester

    Fester Active Member

    Joined:
    Mar 29, 2010
    146
    154
    0
    Location:
    Ohio
    Vehicle:
    2017 Prius
    Model:
    Two
    That is possible provided there is no inadvertent damage to the Prius's electrical system, if there is however, your warranty would not apply; which could turn into a very expensive proposition. You's also have to add a step down converter, as most inverters are 12, 24, or 48vdc inputs.
     
  17. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Active Member

    Joined:
    May 12, 2018
    457
    393
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    The whole point is to avoid that intermediate step-down because it is too restrictive. Granted, there aren't many high voltage DC inverters on the market, but there are some. Somebody has previously made a business of modifying commercially available inverters to work with the exact voltage the prius traction battery provides. I understand they're no longer in business, but the point is it's been done, and it can be done again.

    One quick google turned this up. Looks like it could work unmodified.
     
    fuzzy1 and DLC82SV like this.
  18. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    Well, there are a lot, but most of them are grid-tied ones designed to work with solar arrays.

    What we'd need is a high voltage one that is NOT grid-tied.

    The grid-tied ones have to be able to synchronize with the waveforms they see on the grid, and a whole lot of other things. There are a lot of safety requirements in the grid-tied ones that we don't need or want to pay for. (UL 1741 standard for the US)
     
  19. Smaug1

    Smaug1 Member

    Joined:
    Jul 31, 2018
    123
    84
    0
    Location:
    Chicago suburbs
    Vehicle:
    2018 Prius
    Model:
    Two
    That one you linked to seems to have a HUGE input voltage range: nominally 192 VDC, but the max DC voltage is 480!

    I was looking for one that is UL Listed; that one isn't, but they do claim compliance to some European standards instead, 3rd party by TÜV/SÜD.

    It also says it can be either on-grid or off-grid.

    ****

    I'm thinking more about the traction battery, and wiring in at the battery (or just after a battery fuse) vs. after a relay. I'm betting that the battery stats are being monitored constantly by a controller somewhere, and if the traction battery is being drained while the car is in 'P', it will assume a fault and tell the relay to open.

    There seem to be 4 main options here:

    1. If 1 kW is enough, use the DC-DC converter output and it can be inexpensive. (~$150 for modified sine, ~$500 for sine) A sine one could run a fridge and a furnace controller, for example.

    2. If 1 kW is NOT enough, find a "unicorn" inverter and use the traction battery. This will be invasive and would require some dedicated wiring, and more shock risk. (these inverters seem to be well over $500)

    3. Leave the car alone and buy a traditional gas generator, and commit to taking care of it and maintaining a fresh fuel supply. (The highly-rated 2200 W Honda sells for $1k on Amazon)

    4. Build one's own battery/solar/inverter set-up. This is big bucks.
     
  20. sam spade 2

    sam spade 2 Active Member

    Joined:
    Mar 31, 2018
    584
    312
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    This.
    And.....if you can fuel the gen with natural gas or propane it becomes really easy.