VERY LIGHT BATTERIES

Discussion in 'General Experimental Aviation Questions' started by oldcrow, Jan 16, 2020.

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  1. Jan 16, 2020 #1

    oldcrow

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  2. Jan 16, 2020 #2

    TFF

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    I run the lithium iron in my RC radios. They have a lot of pluses. A friend is putting one in his RV8 as a main battery. They are lite. Not as fire prone. Still they are three times heavier than lipoly batteries. But those can burn good.
     
  3. Jan 16, 2020 #3

    bmcj

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    For what use? There are different types of batteries. Some have high cranking amps for running things like starters, but can’t support prolonged extended discharge capability for steady state use. Others, like cart and scooter batteries don’t have the cranking amps needed for a starter, but have a long, flat-voltage discharge rate so that they provide moderate but even motive force over a long duration. According to the name in your link, I think those in your link are the latter.
     
  4. Jan 16, 2020 #4

    Aerowerx

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    If I did my math right, you would need 70 of their YTX25HL-BS to get 40 hp for 1 hour.

    That would weigh 347.2 pounds.
     
  5. Jan 16, 2020 #5

    Victor Bravo

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    Sorry, thread drift, but has anyone on this forum done the real math on a turbine-generator or turbine-alternator as a power source for an electric motor? When you add up the weights, power conversion losses, wire losses, fuel weight, etc.... is it competitive with the Li-Ion battery?

    I'm not talking about any significant size battery in the middle of it as a buffer or emergency energy backup. I'm talking about straight conversion of jet fuel to spin a gen. or alt. which then puts wattage directly to a motor.
     
  6. Jan 16, 2020 #6

    BJC

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    Small turbine-generators are not very efficient. The sizes that might be used in a small airplane are not justified on an energy efficiency basis for electric energy generation. They are useful for stand alone power generation when used in combined cycle applications, for emergency back-up power generation, or where installing incremental grid infrastructure is prohibitively expensive.

    Current efficiency data is hard to find, but the statements above are based on the testing of actual equipment some years ago plus a quick review of one of the primary manufacturer’s current literature.


    BJC
     
  7. Jan 16, 2020 #7

    Aerowerx

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    Isn't that the same thing as using a gas generator to charge your electric car?

    Why not just put a prop on the turbine shaft and eliminate all the extra weight?
     
  8. Jan 16, 2020 #8

    12notes

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    The batteries on the linked website have CCA ratings between 330-540A, so they should start reasonable engines.

    There are LiPO4 batteries like this one if you need to start a big engine:
    https://www.ebay.com/itm/Lithium-Au...art-Batteries-LiFePo4-CCA-1200A-/112412257060
     
  9. Jan 16, 2020 #9

    radfordc

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    One application would be if you wanted to use the turbine generator to power multiple electric motors. Like the NASA X-57 concept aircraft

     
  10. Jan 16, 2020 #10

    radfordc

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    I've been using an EarthX LiPoFe battery to start the Rotax 503 in my Eindecker for several years with good results. This battery includes a BMS (battery management system) that lets you safely use the Rotax's electric charging system. https://earthxbatteries.com/about-us
     
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  11. Jan 16, 2020 #11

    bmcj

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    We don’t need no stinkin’ turbojet... where is Nikola Tesla when you really need him?

    Along the same line of thought, Nikola Tesla advocated for AC power and Thomas Edison advocates for DC power. Shouldn’t Elon’s electric car line be called the ‘Edison’?
     
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  12. Jan 16, 2020 #12

    BBerson

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    I think the three phase brushless motor is more like an alternating current motor than direct current.
    The controller converts DC into timed pulses to the motor. But Edison invented some batteries.
    Musk didn't pick the name Tesla. He bought the existing company. So.....
     
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  13. Jan 17, 2020 #13

    Aerowerx

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    AIN'T NO SUCH THING AS A DC MOTOR!!!

    All rotating motors are AC. There has to be something that converts a DC power source to AC to feed the actual motor itself. This would include brushes and commutators, and, as in the so-called brushless DC motors, an electronic circuit.
     
  14. Jan 17, 2020 #14

    BBerson

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    But isn't alternating current a bit different than chopped direct current?
     
  15. Jan 17, 2020 #15

    Aerowerx

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    "Alternating Current" is considered as a sine wave.

    "Chopped direct current" consists of a bunch of square waves, which is a since wave with a whole bunch of harmonic sine waves along with it. And in many cases if you low pass filter the "chopped direct current" you will get a sine wave.

    As far as the motor is concerned they are the same, but some motors do not like all the harmonics.
     
  16. Jan 17, 2020 #16

    pfarber

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    There are quite a few REPUTABLE (not ebay) lithium batter sellers out there. Do you think you will get warranty service from 'Chinaseller2020'?

    https://earthxbatteries.com/shop/etx900

    You do not need 1200CCA for an engine to start.
     
  17. Jan 17, 2020 #17

    Aerowerx

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    Well, maybe for one of those huge stacked radial engines. Think DC-6 or Lockheed Constellation.
     
  18. Jan 17, 2020 #18

    TFF

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    The high cca helps when it gets cold. Amps drop off with temp. The earthex users in winter will hit the starter a couple of times to raise the temps internally. That’s what a couple of guys do with their 540 powered biplanes.
    I believe the industry calls the brushless motors three phase DC. No ramp in the wave. Power and off. DC input with computer controlled switching.
     
  19. Jan 17, 2020 #19

    12notes

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    I was not making a specific purchasing suggestion, that was merely the first link in Google for that specific search term, to show that "There are LiFePO4 batteries like this one if you need to start a big engine".

    You don't need 1200CCA to start a VW,O-200, or IO-540, which are reasonable engines. 1200CCA is needed for larger ones, which is why I specified "big engines".

    EarthX are nice batteries, but for my personal project, I can get the battery specs I need for less than half the cost from the scooter company originally linked, and even cheaper from China. I will gladly give up the warranty on an industrial product if it is cheaper to buy two and keep one on the shelf than it is to buy one with a warranty.
     
  20. Jan 17, 2020 #20

    pfarber

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    Not sure what your special project is, but LiFePo4 batteries have some pretty stringent charging requirements... something I don't see on the scooter batteries (any sort of monitoring or charge control) whereas the EarthX has an integrated charger that you simply hook up to the alternator. maybe scooters have separate controllers?

    And what experimentals have 'big radials'? Everyone runs off into the weeds trying to sound smart.
     

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