Power tool cells

Discussion in 'Electric Propulsion' started by pictsidhe, Apr 1, 2019.

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  1. Jul 26, 2019 #21

    Armilite

    Armilite

    Armilite

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    To get 18650 Cell Price down to where it might be worth it if you Build your own Packs, you have to Buy 20,000 Bulk then you get them for $1 each. $5-$6 is the norm I found at the local Battery Stores. The Lazair was a Motor Glider Ultralight that flew on 18.8hp, the majority of Legal Part 103's need 25-35hp. For now, the FAA says Battery Weight is included in Total Airframe 254lb Weight. So till you figure out How much Weight you have to use for each Airframe, it's a moot point. Most of these Airframe Manufacturers haven't done any Test with these different Gas Engines.

    probably the Top (2) today, the Pheonix 103 with a Hirth F-23 (50hp)
    Weight: 78lbs, including reduction unit, full exhaust, and electric start or71lbs with recoil start reduction unit and full exhaust. 254lbs - 78lbs = 176lbs for Airframe.

    The Aerolite 103 just says Empty Weight (1) 235 lbs. 28 hp. - 50 hp. Doesn't Specify Weight with which Engine. The F-33 28hp. Weight: 35 lbs including exhaust sys. - 40 lbs W/re-drive - 45 lbs W/elec. start. 235 lbs - 45 lbs = 190 lbs for Airframe.

    So the most your going to have for Motor & Battery Packs is probably 78lbs. Which I doubt will give you even 1 hr of Flight.
     
  2. Aug 8, 2019 #22

    Scheny

    Scheny

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    I have constructed and built a small hybrid boat which is trailerable on the car roof and only weighs ~30 lbs (without battery). The battery was being built by EM3EV, a chinese company owned and run by someone from the US. Officially they focus on E-bikes, but they even build small series for electric cars and have really good quality and build state of the art.

    They have the best expertise in this field and they are proposing following four configurations (as of July 2019) for use in electric vehicles. Values are stating continuous and burst current:
    • Panasonic PF: 29/38A
    • Samsung 30Q: 38/55A
    • LG HG2: 44/55A
    • Samsung 35E: 25/34A
    These batteries vary slightly with current abaility and energy density. I have used the Samsung 35E.
     
  3. Aug 8, 2019 #23

    GeneG

    GeneG

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    Power tool batteries are normally between 1800 and 2200 mah. Panasonic and Samsung both offer cells rated at 3600 mah and are relatively high output.
    I would recommend buying these cells to increase the power available.
    Your choice of the Samsung 35e was wise as they are 3500 mah whereas the Panasonic choice is only 2900 mah.
     
  4. Aug 8, 2019 #24

    Hephaestus

    Hephaestus

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    Ebikes/scooters are a lovely source for parts for aircraft conversions. They're common as heck in Asia, massive production of parts aftermarket parts and replacements, and really well documented.

    While the packs amp ratings aren't high enough alone - take 2 packs in parallel - you double the amperage.

    2-3parallel and 2-3 in series would make a decent toy for playing in the local area.
     
  5. Aug 8, 2019 #25

    GeneG

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    Battery packs from wrecked Tesla's are available.
     
  6. Aug 8, 2019 #26

    Scheny

    Scheny

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    My (personal) opinion is, that Lithium batteries are not yet the best choice. It is very rare they burn, but if they do, not even a standard firewall will save you. Just look at the incident in Hungary, where the plane burned up before it could complete the traffic pattern it was in.

    I know the technology involved, because I worked 4 years with the project they derived it from as the safety engineer.
     
  7. Aug 8, 2019 #27

    pictsidhe

    pictsidhe

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    Call me paranoid...
     
  8. Aug 8, 2019 #28

    proppastie

    proppastie

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    using the existing hub/motor and controller?
     
  9. Aug 8, 2019 #29

    Hephaestus

    Hephaestus

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    Some of the crazier upgrade/conversion motors perhaps. If you checkout the ebike mods available in Korea/taiwan/China - they've got some insane options available to them. Friend brought back what looked like a cheap gio scooter from Hong Kong. It'll outrun a gsxr600 easily (for about 15minutes lol)

    Controller I wouldn't - none are really suited to flight use - low battery cutoff isn't going to ever go well in an aircraft. I'd rather risk destroying the battery than have it suddenly shut off myself... Ymmv
     
  10. Aug 8, 2019 #30

    GeneG

    GeneG

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    O.K. Reconditioned Nissan leaf batteries are about $2900, 30 KWH and weigh 648 pounds. Just right for LSA's.
     
  11. Aug 8, 2019 #31

    proppastie

    proppastie

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    So did you mean to say "lovely source for batteries"? What other parts, switches, fuse, ????
     
  12. Aug 8, 2019 #32

    Hephaestus

    Hephaestus

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    It all depends on your requirement what works for you... Some of those brushless motors are outrunners, some inrunners. That Little ebike I referenced had a chain drive with a motor similar to those 1/2hp motor you'd find in 80s appliances.

    But with the proliferation of them in Asia - it's definitely a place to look for parts that might suit you. Who knows half the controllers might be Arduino based and possible to adapt to our needs with a few code changes.
     
  13. Aug 9, 2019 #33

    pictsidhe

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    The problem with that is, most people won't junk the battery after using that -0.5% of available charge.
     
  14. Aug 9, 2019 #34

    Hephaestus

    Hephaestus

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    If the packs add up to 1200$ instead of 2900$ are they more or less likely to risk the hangar fire do you think?
     
  15. Aug 9, 2019 #35

    proppastie

    proppastie

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    just how often and why do these things catch on fire....can you measure something to know when there is a problem? How do the power tool/computer people get around the problem?
     
  16. Aug 9, 2019 #36

    pictsidhe

    pictsidhe

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    Hangar fire? I'd be more worried about an in flight fire. yes, that is quite possible after over discharge. There's actually very little charge left below minimum voltage, 0.5% is not a exageration, with a 20 minute flight time, that's 6 extra seconds of power. How much use it that likely to be?
    The power tool and computer people build the packs properly and use a full BMS. Emulate that, and also skipping additional aviation 'safety' features such as an extra 6 seconds of power before you go deadstick, and you should be pretty safe.
     
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  17. Aug 9, 2019 #37

    Scheny

    Scheny

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    You can do state of the art and be 99,999% safe, still there are some accidents as can be seen with the hungarian plane or all the burning Tesla's.

    Every battery has electrolytes with a diaphragm between them. If it gets punctured, the whole energy will be released at once, causing the fire. The thinner the diaphragm, the better the battery works in terms of energy density... Any imperfection will lead to a short current once in a while. This will only be obsolete as soon as "solid state" batteries are on the market.

    Lithium batteries like to be within a certain voltage range. If you are above --> poooff, if you are below, it will get damaged and then the next time --> poooff.

    State of the art means, that you use a balancer (called battery management system or BMS) which keeps every cell within this range during the charging process (keeping the voltages balanced). As this has no impact on parallel batteries, you will loose all parallel batteries if a single cell will fail and energy and voltage will decrease by this amount.

    In addition you will want to use cylindrical batteries, as they are contained in aluminum protective housing (like the 18650 series --> 18mm diameter, 65mm length). This is minimally more weight than "coffee bags" like used in model planes, but a single cell on fire will not let the surrounding cells catch fire too. Still, look at Tesla... Also have minimal spacing between the cells to let residual heat dissipate (otherwise Boeing 787). You can buy LEGO like spacers on AliExpress, they cost almost nothing. Last point, when soldering the batteries, the terminals can have intentional breaking points where you use narrow sections to act as melting fuses. This will take care if a single cell provides way too much current on its own (and is likely to blow soon).

    Feel free to ask meif you have questions, I did the electric car program for Volvo.
     
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  18. Aug 9, 2019 #38

    Scheny

    Scheny

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    If anyone looks for electric motors:

    First look at the Siemens motor, as it is the best on the market and has redundancy, but unfortunately it is in the 260kW range... Then look at Yuneec. They upscaled their model aircraft motors and are available in different sizes for real aircraft.

    At last, there is the UK company http://www.alienpowersystem.com which create systems up to 45kW. These motors are wayyy lighter than any scooter engine and already come with mounts to incorporate propellers (and have air cooling). In addition, their ESC's are programmable, so you can configure them to aircraft mode. This means you can either have a voltage constrained limp mode, or just ignore voltage drops (keep in mind you have to throw the battery away if you fly too long). There are also modes like prop brake if you want to use foldable propellers.

    So in case you want to create an utralight, give this british guys a call, they are very supportive.

    Anyway, I would not suggest to use any setup with less than two batteries in parallel (in case one dies or has serious voltage drop) and have them separated with diodes (to avoid current flowing into the broken one)!
     
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  19. Aug 9, 2019 #39

    pictsidhe

    pictsidhe

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    18650s should have spot welded connections. Soldering them is serious abuse.
     
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  20. Aug 9, 2019 #40

    Scheny

    Scheny

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    Bad translation, you are absolutely right. I meant spot welding.
     
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