1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Inverter-how much can it take?

Discussion in 'Gen 3 Prius Technical Discussion' started by prius121212, Nov 12, 2014.

  1. Tony D

    Tony D Active Member

    Joined:
    Aug 31, 2013
    468
    132
    0
    Location:
    Dublin, Ireland
    Vehicle:
    2008 Prius
    Model:
    N/A
    I'm not techy enough to chime in on the debate, but after discussing with a friend who is a Mechanic and happens to have a degree and masters in electrical engineering, said that it's not the best use of the car, especially due to the very large cost if your calculations were not right.

    What I can tell you is, I have this little Gas BBQ which is great for those trips where you can cook some tasty chicken, sausages, puddings, steak etc when needed ...... i love it and keep it in the boot / truck for most of the year irrespective of what the weather is like .... plus my 2 yr old love when we go on "picnics"!

    Calor Mini BBQ | Buy now from Calor Gas
     
  2. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

    Joined:
    Feb 14, 2010
    6,035
    3,854
    0
    Location:
    Rocky Mountains
    Vehicle:
    2006 Prius
    Model:
    Three
    This is very simple. The Prius can easily supply 1KW continuously from the 12v. Lots of people run their homes for days (continuous) off of the Prius. I have some thick 4awg wire connected right off of the inverter output and grounded to the inverter chassis connected to an anderson connector that mates to my 12v inverter. It has run my house a couple times during electrical upgrades.

    And 700W when used well, can be enough. But as a hot-plate or BBQ type thing, it can't be that useful... Seems much easier to just have a small tank of LP.
     
  3. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Regardless...
    Of whether Toyota chooses to use the term "alternator," or what any other self-appointed authority calls it, it's the word I chose to use in the post that ruffled all the feathers. Deal with it.

    And regardless of whether you are running your Prius as a power-plant and successfully powering your house, and have used it trouble free for years, I wouldn't do it. Deal with that too.

    Can we end it here? Thanks.

    Not to be deliberately disparaging, but someone with a masters degree in electrical engineering who is working as a mechanic isn't the best source of information in my opinion. I've known PhD's who drive cabs for a living and can barely tie their own shoes. If your friend was holding down a job as an engineer, I'd be more impressed.
     
    #23 GregP507, Nov 24, 2014
    Last edited by a moderator: Nov 24, 2014
  4. Tony D

    Tony D Active Member

    Joined:
    Aug 31, 2013
    468
    132
    0
    Location:
    Dublin, Ireland
    Vehicle:
    2008 Prius
    Model:
    N/A
    I wouldn't trust anyone else with my car, but that's my choice! He's been given a family business to run, so given the state of our economy here in Ireland, he faced a mediocre wage as an Engineer here in Ireland or run and grow a successful family business. I'm sure that he could earn a hell of alot more working as an engineer overseas, but due to ageing parents he made the choice to stay at home. He was a lecturer in Dublin City University so he is fairly clued in.

    He's built some very cool car projects including a Mk2 Jetta Coupe Syncro with a big Turbo 1.8T running 350+ bhp as well as a big turbo Audi S4 running over 450 bhp. In his case, he's a car fanatic who happens to have a Degree & Masters which he doesn't use.

    Everyones circumstances differ, so one has to be mindful of that too.

    I suppose alot of us here in Ireland are educated to a high level anyway, so a masters doesn't count for a huge pile these days

    • 48 per cent of Irish 25-34 year olds hold university-level qualifications (the highest rate in Europe and one of the highest in the OECD);
    • 95 per cent of Irish people graduate from secondary education (the highest in Europe);
    • 20 per cent of Irish people hold a Masters Degree (among the highest in Europe – average 13 per cent).
     
  5. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    That's why I was careful to say I wasn't being deliberately disparaging. I understand that every situation is different, but I'm being honest in saying that I feel an employed engineer has more credibility than an unemployed one. I've been unemployed myself, and even with a master's of science degree, some employers were reluctant to hire me until I had a bit more experience under my belt. It was not intended as a generalization, hence my prefacing remark.
     
    Tony D likes this.
  6. kbeck

    kbeck Active Member

    Joined:
    Feb 10, 2010
    420
    274
    0
    Location:
    Metuchen, NJ
    Vehicle:
    2010 Prius
    Model:
    III
    All right. I'm late to the party. And I do apologize for that.

    But a couple of things, then I'll go back to my usual cave.

    First, I am a working EE. Not an AC power guy, but, yeah, up to my elbows in various stuff, including DC power.

    Second: The common use of the term "alternator", as many have pointed out (and I agree) is that it's an Alternating Voltage Generator. Fine. That's not descriptive of the stuff-with-windings-all-over in the Prius because:
    1. Not only do they generate AC power, they also work as motors. So, if one wants to call them something like an Alternator, then one has to come up with a similar short-hand term for an AC Motor. Otherwise you've left out half the definition. Alternator/AC Motor? At that point one may as well punt and call them what Toyota does: Motor/Generators.
    2. The term Alternator came around, I think, because back in Ye Olde Days it wasn't uncommon to have DC generators in cars. If memory serves, Ye Olde '71 VW Bug that I used to run around in back in the day had a 12 V Generator. And brushes that had to be maintained and replaced over time as well. The term "Alternators" came up because "AC Generator" didn't have that nice "ring", it was a selling point, and the marketeers got involved. Alternators don't have brushes and are therefore more reliable.
    3. Besides, using the term "Alternator" for any AC Generator, in general, Seems Just Wrong. Is this what we'd call a 100 MW 3-phase generator buried in the guts of the local hydroelectric dam?
    4. Finally, the bit about burning out wires in the "Alternator" sure doesn't seem right. A quick check says that the traction motors in the Prius are good for 80 HP and the ICE is good for 98 HP. There's also a spec of 36 HP that can come from the battery which implies the power is coming from the battery through the various boost and switching transistors . The conversion to Watts is x 746 W/HP, so we have 26.9 kW coming down from the battery. Looking at the 12V battery end, that much power from the battery/(motor generators), at 12V, would be 2.23 kA. We don't get that much because the inverter is the limiting factor. But the implication is that even if one maxed out the inverter at it's 100A fuseable limit, sucking down 1200W, that would a factor of 22.4 less than what the batteries/motors handle when pushing the car forward. And one has to figure that Toyota put in some safety factors on the gauge of the wires in the motor/generators, meaning that that 22.4 ratio is conservative. Finally, just talking about currents flowing this way and that: In the case of max acceleration, where power is both coming out of the ICE gas engine and being sucked out of the battery, AC currents are being generated on the first motor/generator by taking power from the ICE. These are then rectified by the switching transistors on the first motor genertaor and put onto the DC bus which is also getting power dumped onto it from the battery through the boost transistors and such, all of which electric power is ending up on the second motor generator which cranks the energy into the driving wheels; so one gets 36 HP + 98 HP = 134 HP at the driving wheels, of which a maximum of 80 HP is flowing through the DC bus on its way to the second motor generator. That's 59.7 kW on that bus bar, with currents to match. Hence, the chances of a 1.2 kW load (and that's a max) on the battery circuit certainly isn't going to stress the motor/generators any. And, as I said, the limiting factor isn't the motor-generators/battery: It's the High Voltage to 12V converter itself that limits this kind of fun.
    Look: A couple of weeks ago I made a nice post but had a brain fart and said that the rear wheels on the Prius were the driving wheels. Um. Were you thinking of "normal" cars where putting a monster 12VDC to 120VAC converter on the 12V battery is a good way to burn out an alternator? If so, say so, and we'll all go on with our lives. :)

    KBeck.
     
    Patrick Wong and ftl like this.
  7. ftl

    ftl Explicator

    Joined:
    Jun 2, 2009
    1,812
    790
    0
    Location:
    Long Island NY
    Vehicle:
    2012 Prius c
    Model:
    Three
    Did you not understand a single thing that KBeck wrote?
     
  8. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Every word, but where in there did he point out that I was misrepresenting the facts?
     
  9. ftl

    ftl Explicator

    Joined:
    Jun 2, 2009
    1,812
    790
    0
    Location:
    Long Island NY
    Vehicle:
    2012 Prius c
    Model:
    Three
    You said, about taking a few hundred watts from the 12V circuit:
    "I'd be concerned about overheating the alternator by using it that way. It's not designed for continuous output as a power-plant. The circuitry may stand it, but the windings may overheat and burn off the lacquer insulation."

    KBeck said:
    "Finally, just talking about currents flowing this way and that: In the case of max acceleration, where power is both coming out of the ICE gas engine and being sucked out of the battery, AC currents are being generated on the first motor/generator by taking power from the ICE. These are then rectified by the switching transistors on the first motor generator and put onto the DC bus which is also getting power dumped onto it from the battery through the boost transistors and such, all of which electric power is ending up on the second motor generator which cranks the energy into the driving wheels; so one gets 36 HP + 98 HP = 134 HP at the driving wheels, of which a maximum of 80 HP is flowing through the DC bus on its way to the second motor generator. That's 59.7 kW on that bus bar, with currents to match. Hence, the chances of a 1.2 kW load (and that's a max) on the battery circuit certainly isn't going to stress the motor/generators any."

    In other words, the high voltage end of the Prius is routinely moving around tens of thousands of watts of electrical power, and all the equipment and control circuitry is designed to handle this. A load of a few hundred watts at the 12V end of the system isn't even a blip on the power handling capacity of MG1.
     
    Patrick Wong likes this.
  10. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Maybe he should write a letter to Toyota, explaining they should have nothing to worry about, standing behind their warranty when people tap into the system to use it as a stand-by generator for their house.

    I-wouldn't-do-it.
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    I agree with KBeck's main point which is that DC power taken from the DC/DC converter is not going to stress the motor generators. An abnormally high average current flow might stress the DC/DC converter. Any owner who adds an auxiliary system has to be aware of the high current loads and resultant I^2R power losses that will degrade efficiency of the system.
     
    ftl likes this.
  12. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    I never imagined anyone would be trying to run a large inverter off the puny 12V system. I assumed they were using the higher-power part of the hybrid system. I guess that was never very clear.
     
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Posts 1, 3, 6, 8 and 39 all are related to the concept of running a 12VDC to 110VAC inverter off the Prius 12V bus. This is a reasonable concept because you can use a two-foot length of cable run to the battery, minimizing I^2R losses. Then the 110VAC outlet runs through an extension cord to power those few items that need to run during your house power outage, such as your refrigerator and a few lights.
     
    ftl likes this.
  14. ftl

    ftl Explicator

    Joined:
    Jun 2, 2009
    1,812
    790
    0
    Location:
    Long Island NY
    Vehicle:
    2012 Prius c
    Model:
    Three
    My friend and fellow PriusChat member Richard Factor did extensive testing on the HV systems when he bought his first Prius, and eventually did exactly what you describe. I believe he was one of the first to tap the traction battery and use it to power the essential electrical appliances in his house, particularly the water pump and the freezer with the ice cream. Much more on his project here:
    PriUPS Site Navigation

    Since then other have done similar projects (including commercial suppliers), and Toyota has consumer-tested a line-voltage socket on some models in Japan. So the technology is quite feasible, and I expect we'll see more of it.
    Toyota Prius Backup Power – An Aftermarket Solution - The Green Optimistic
    Toyota Preparing Vehicle-to-Home Backup Power System - EVWORLD.COM
     
  15. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    I would love to do that myself, having a second way to tap all that reserve electrical power, but I have to follow my own advice. If it's not being used for the purpose for which it was designed, it's not worth the risks involved.

    It would be a much different story if I had more money to burn, or if I had perfect faith in the engineers who designed such a mod, but for now, I'll just stick to the original configuration.
     
  16. ftl

    ftl Explicator

    Joined:
    Jun 2, 2009
    1,812
    790
    0
    Location:
    Long Island NY
    Vehicle:
    2012 Prius c
    Model:
    Three
    I'd really like to see Toyota offer it as a reasonably-priced factory option on every Prius.
     
    bwilson4web likes this.
  17. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Another thing that prevents me from converting my Prius into a big standby power-plant is the fact that I don't need it. I have a portable generator that works great for all such purposes when I need it.

    How about using it to save money on the power bill? Nope, it doesn't work that way. Gasoline-generated electricity will always be more expensive than the powerline-electricity it replaces.
     
  18. ftl

    ftl Explicator

    Joined:
    Jun 2, 2009
    1,812
    790
    0
    Location:
    Long Island NY
    Vehicle:
    2012 Prius c
    Model:
    Three
    During Sandy two years ago I used my Prius c for 52 hours straight to run house essentials. With a portable generator I would have had to either keep several five-gallon cans of gas on hand, or try to get gas during the widespread power outage here on Long Island which also affected most gas stations. The few stations that had gas had hours-long lines. With the Prius suppling a fairly light load (heating system, internet connection, a few lights) I was able to keep the power on night and day and used very little gas.
     
    bwilson4web likes this.
  19. GregP507

    GregP507 Senior Member

    Joined:
    Apr 5, 2014
    3,002
    480
    0
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    These work fine for that purpose:
    6 Gallon Portable Fuel Tank - 5008623
     
  20. kbeck

    kbeck Active Member

    Joined:
    Feb 10, 2010
    420
    274
    0
    Location:
    Metuchen, NJ
    Vehicle:
    2010 Prius
    Model:
    III
    I wasn't trying to get your goat, honest. And I hate terminology wars, sorry I dug into that. (I've seen plenty of papers in the DSP technical literature where people simply talked past each other, each writer using different terminology for not-quite-the-same-thing, resulting in mass confusion.)

    It's one of those things. Half the fun of becoming any type of professional, be it candlemaker, barber, butcher, sailor, baker, EE, MD, electrician, lawyer is learning the specialized language of that profession. The profession, whatever profession it is, uses the specialized language in its precise definitions as a shorthand for complex concepts, and the parties in that profession have to use that specialized language in the same way, or they're in big trouble. And it's unfortunate that common English words get re-used to mean things that don't make sense to one party or another. (The definition of a line to a sailor on a three-masted vessel is precise and doesn't have much relationship to a line that an electrician uses.)

    So I apologize about having joined a terminology war, for pretty much no good reason. It doesn't move things forward that much.

    The real thing that got me going was about the 'overheating wires' comment.

    If one has a non-hybrid, standard car with the usual alternator-on-a-belt, drawing too much current from the 12V can definitely cause nasty burn-out of this and that. Police cars and other vehicles with extraordinary electric power consumption come with higher powered electric systems including bigger alternators and batteries for precisely that reason. So, if you had made that comment about a regular car, I'd be agreeing with you. But the comment wasn't about a regular car, it was about a Prius.

    Priuses have, relatively speaking, a motor/generator complex that's vastly more powerful than both the starter motors and alternators used on normal cars. They need that in order for the Prius to do its full-hybrid thing. The Prius also needs to have 12V to run the computers, radio, and car lights. So, since the car doesn't have a direct, motor-driven source of 12V, it has an inverter, instead, that takes in the 300V or so from the traction battery and converts it to 12V.

    Most people around here who are interested in using their Priuses as backup generators go the relatively simple way out: 12V to 120VAC inverters are commonly available in sizes up to 2 kW or so and aren't all that expensive. The limiting factor of how big an inverter one can hook to the 12V isn't how much power one can drag out of the motor/generators, it's how much power the 300V to 12V inverter can supply. Said inverter has a 100A fuse at 12V, which theoretically means one could get 1.2 kW. But it's never a good idea to push up against the limits, so a 1 kW intermittent load is about as much as one should really run. Hence, a 1 kW 12V->120VAC inverter is about as big a widget as one might place in the trunk, with big thick wires to the battery and an extension cord into the house. And, at those power levels, one is never going to overheat the motor/generators, although I'll take arguments about the long-term lifetime of the 300V->12V converter.

    1 kW is just about enough to run the 'fridge and a couple of lights. And, when one wants some hot water, one could disconnect the fridge and hook up the gas hot water heater instead.

    I have done some rough mumbling about how efficient this whole scheme is in terms of $/kW-hr. City power is cheapest, of course, but there's an argument that a gas-powered generator which uses gas even when it's not supplying power might not be as good as a Prius that only runs its engine intermittently, as needed, and in its efficient range at that.

    And now I promise I'll shut up.

    KBeck