[Canberrauav] GEB Battery testing results

Jack Pittar jpittar at bigpond.net.au
Thu Feb 5 09:51:10 EST 2015


That's right, its kind a like Ohm's law. The well known equation is Power = Voltage x Current.
Let's take the case where each battery supplies 6 amps at 12 volts.
In the series case, Power = 24volts  X 6amps = 144 watts.
In the parallel case, Power = 12volts X 12amps = 144watts.
Therefore, the increase in flight time Chris sees must come purely from the slower motor with a larger propeller.
Right now, we are concentrating on the batteries. Experience shows that we should change only one thing at a time.
Playing with different motors and propellers, or even the number of motors and propellers, is definitely a worthwhile avenue to persue, but I suggest we don't go down it right now.
Jack.


 -----Original Message-----
From: Chris Wilson [mailto:chris.wilson at hobbyking.com]
Sent: Thursday, 5 February 2015 12:34 AM
To: Lloyd Breckenridge
Cc: Warren Eather; Jack Pittar; andrew at tridgell.net; canberrauav at canberrauav.com
Subject: Re: [Canberrauav] GEB Battery testing results


  Hi James you're absolutely correct high-voltage Multirotors when built to spin big props slowly suffer from stability problems. But in reality instead of building and 8S system for Max efficiency it only needs to be built to reduce the current demand to meet the high density batteries basically the increased flight time doesn't come from increased efficient, But from the ability to use the higher density batteries this way you don't give up stability still utilizing smaller 13 inch props versus slower 15 inch props at an 8S HV system. Now definitely if you built an efficient ate a system and used high density batteries of course the pay off would even be greater but realistically you can already achieve over an hour with off-the-shelf components and maintain stability.

  On Wednesday, February 4, 2015, Chris Wilson <chris.wilson at hobbyking.com> wrote:

    You're confusing watts consumed and current it's kind a like Ohm's law but instead of resistance watts . If there's a set amount of power or watts being needed to spin a prop there's a relationship between voltage and amperage to achieve that by increasing one the other will decrease for the same watts being used in this case increasing voltage decreases amperage.so all we are really doing is shifting the power system to match the batteries constraints the cells don't care about voltage but have a limitation on amperage therefore increase voltage to decrease amperage to match the cells ability.but we need to match the motor because if we just arbitrarily increased voltage without lowering the motors KV we will just simply spin the motor faster actually consuming more watts.. If you go to Hobby King.com and do a search for the 3508 multistar elite and watch the related video I cover some of the theory behind it. The cells will totally work for the application you just need to increase voltage and lower amperage you will need a new motor.

    On Wednesday, February 4, 2015, Lloyd Breckenridge <lloydb at iinet.net.au> wrote:

      The whole point here is to reduce the current through these batteries and maintain the same power.
      The only way to do that is increase the voltage.

      Lloyd Breckenridge

      From: Warren Eather 
      Sent: Wednesday, February 04, 2015 11:14 PM
      To: 'Lloyd Breckenridge' ; 'Jack Pittar' ; 'Chris Wilson' ; andrew at tridgell.net 
      Cc: canberrauav at canberrauav.com 
      Subject: RE: [Canberrauav] GEB Battery testing results

      I’m with Jack on this one.

      -Waz



      From: Canberrauav [mailto:canberrauav-bounces at canberrauav.org.au] On Behalf Of Lloyd Breckenridge
      Sent: Wednesday, 4 February 2015 10:24 PM
      To: Jack Pittar; Chris Wilson; andrew at tridgell.net
      Cc: canberrauav at canberrauav.com
      Subject: Re: [Canberrauav] GEB Battery testing results



      Hi Jack

      Due to the higher voltage your get more power for the same current.



      Lloyd Breckenridge







      From: Jack Pittar 

      Sent: Wednesday, February 04, 2015 10:37 PM

      To: Chris Wilson ; andrew at tridgell.net 

      Cc: canberrauav at canberrauav.com 

      Subject: Re: [Canberrauav] GEB Battery testing results



      I don't understand --- surely if you put the two batteries in parallel, or if you put them in series, you would get the same current draw PER BATTERY.

      With the batteries in parallel, you do not have to find new motors and controllers to work with the higher voltages, and you can still revert to using a single LiPo for shorter test flights.


       -----Original Message-----
      From: Canberrauav [mailto:canberrauav-bounces at canberrauav.org.au]On Behalf Of Chris Wilson
      Sent: Wednesday, 4 February 2015 9:26 PM
      To: andrew at tridgell.net
      Cc: canberrauav at canberrauav.com
      Subject: Re: [Canberrauav] GEB Battery testing results

        Sorry meant 13 not 18 inch prop, LOL

        On Wednesday, February 4, 2015, Chris Wilson <chris.wilson at hobbyking.com> wrote:

          Yeah at first when testing these batteries with standard rules of thumb LVC, we were actually pretty disappointed, but after consulting with the cell manufacture and getting more data these particular cells can safely be discharged to 3 volts per cell no problem..so once we re-did our tests to the new lower cut off, found the batteries to be slightly better than spec surprisingly. I've got some fancy dancy charts from our battery analyzer I can post if you guys want, but definitely the key was a 1.5 C or lower discharge. The whole idea of this battery was to try and get conventional multirotors in the air for an hour or better without the need of a sliderule an engineering team behind you, LOL basically take a vantage of these batteries. How we devised to do it and deal with the C rating was simply not increase efficiency but decrease amp draw demand. Meaning high-voltage..the higher the voltage the lower the amperage for the same power being produced, lots of people assume higher voltage equals higher efficiency and if engineered probably could but we found issues with motor design and magnetic saturation etc the higher the voltage got. We were able to design some 8S motors that are not necessarily more efficient then a 4S motor just looking at Grams versus watts efficiency, they where on par and still over 10 g/w so decent enough, however because the amp draw was lower this is where the magic happens!!! the higher density batteries GEB or Panasonic cells for the same given weight are now well within C range of the total draw and can be used safely. Take our  3508 multi star elite endurance motor it has a 268 KV and can swing an 18 inch prop producing 1600g of thrust at only 2.7 A or a 15 inch prop at 6s for sub 4 amps..The key to utilizing these batteries and leveraging their higher capacity comes down to matching a power system, figure out prop speed max prop dis and thrust required and I can have a motor built and wound in 6s and 8s kvs and then draw would probably be in the 1C rating. It would be interesting to see what could be devised on fixed wing. On multirotors we've achieved well over an hour flights utilizing standard 680 hex frames 13 inch props and just 8s set ups. 

          On Wednesday, February 4, 2015, Andrew Tridgell <javascript:_e(%7B%7D,'cvml','andrew at tridgell.net');> wrote:

            Hi Chris,

            Thanks for chiming in!

            > We have a ultra capacity battery line coming out soon based on the GEB
            > cells, from speaking with the factory and our test found these batteries
            > have a lower cutoff voltage than standard LiPo's and using the new spec can
            > achieve spec capacity at 1.5c We geared the line for HV multi rotor setup
            > 8~10s that pull minimal amps, well with in the batterys C rating. What
            > voltage are you terminating your test?

            As James said we terminated at 12.5V loaded voltage on a 4S 12Ah pack
            (2x4S 6Ah in parallel). The load at 12.5V was around 19A. So that is
            3.13V per cell at around 1.5C load.

            The unloaded voltage at that level of charge was about 14.7V (around
            3.7V/cell).

            What loaded cutoff voltage would you recommend for these cells to give
            us about 10 to 15% remaining capacity to bring the plane home?

            The other issue we noticed is that because the voltage drops so much the
            usual Ah rules of thumb get pretty bad, as the current draw to keep the
            plane in the air kept rising. So you really need to talk about Wh not
            Ah, and the usual autopilot failsafe code based on Ah consumed is
            perhaps not the best approach. Have you thought about that at all?

            Ideally we'd have an equation modelling the behaviour of the battery
            under different loads, so we can properly calculate the amount of
            capacity remaining for failsafe handling.

            Cheers, Tridge



          -- 

          Chris Wilson
          Products Specialist

          Hextronik Limited
          Address: Rm K1, 9/F. MG Tower, 133 Hoi Bun Road, Kwun Tong, Hong Kong.
          地址: 九龍觀塘海濱道133號萬兆豐中心20樓A1室
          Phone: (852) 3125 1900 ext. 181
          Skype: javascript:_e(%7B%7D,'cvml','Products03 at hextronik.com');





        -- 

        Chris Wilson
        Products Specialist

        Hextronik Limited
        Address: Rm K1, 9/F. MG Tower, 133 Hoi Bun Road, Kwun Tong, Hong Kong.
        地址: 九龍觀塘海濱道133號萬兆豐中心20樓A1室
        Phone: (852) 3125 1900 ext. 181
        Skype: Products03 at hextronik.com





    -- 

    Chris Wilson
    Products Specialist

    Hextronik Limited
    Address: Rm K1, 9/F. MG Tower, 133 Hoi Bun Road, Kwun Tong, Hong Kong.
    地址: 九龍觀塘海濱道133號萬兆豐中心20樓A1室
    Phone: (852) 3125 1900 ext. 181
    Skype: Products03 at hextronik.com





  -- 

  Chris Wilson
  Products Specialist

  Hextronik Limited
  Address: Rm K1, 9/F. MG Tower, 133 Hoi Bun Road, Kwun Tong, Hong Kong.
  地址: 九龍觀塘海濱道133號萬兆豐中心20樓A1室
  Phone: (852) 3125 1900 ext. 181
  Skype: Products03 at hextronik.com


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