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solentlife
Extreme 3D
Joined: 30 Dec 2010
Posts: 872
Location: Latvia / UK
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 Posted: Thu Dec 08, 2011 3:17 am
Post subject: LiPo C rating / mA size and outputs .... |
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As many here know from Off-Topic RC threads - I fly fixed wing as well. One in particular is the 50mm EDF T-45, a US version of the BAe Hawk Trainer from UK ....
The video shows it to be fast ... and judging by various info from others posts on other forums etc. - faster than other owners same models !
So once I received the extra LiPo's I ordered to fly this and other models I have - I did a comparison test via Wattmeter and full throttle. Now I think I know why my EDF was faster than many others ..............
LiPo + results :
LiPo used in Video .. 1800mAh, 3S, 25C = 18A / 210W
Recc'd LiPo 800mAh, 3S, 20C = 16A / 170W ... a significant drop of nearly 20% power ... this is pack usually quoted as used by others.
Intended LiPo to balance out wheels fitted etc. 1300mAh, 3S, 25C = 16A / 170W at first but when cycle charged gave 18A / 220W falling of quickly to 16A / 170W
Just to see what could be achieved - I fitted one of my 450 LiPo's 2280mAh, 3S, 35C = 21A / 240W ... had to call that one of quick before ESC gave out.
The 800 LiPo's have much thinner power leads, about half the diam of the 1300 and higher leads ....
I thought it might be interesting to others about the difference the C rating seems to make ...
I have to admit a touch of suprise, as I'm used to motors / batterys etc. taking what they need from a battery and putting out what they are designed / set for ... not like this where extra C capability is actually giving more power ......
I realise that a LOW C rating will be an issue as then amps cannot be supplied as demanded ...
Posted on this section as really it applies to any LiPo range as I see it ...
_________________
If you don't crash - you ain't flying !
Fast learning to be 450 Heli Repair specialist !
Have : 2ch Bumblebee,
Co-Ax Syma S006 Alloy Shark
2x Clone 450 SE V2
+ fixed wing stuff ...
Returning to RC after 20 odd yrs away .. Ex Display flyer. |
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tombo242
Extreme 3D
Joined: 04 Nov 2008
Posts: 3633
Location: Santo Estêvão, East Algarve, Portugal. 76, but still feels 18.
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Posted: Thu Dec 08, 2011 7:42 am
Post subject: Re: LiPo C rating / mA size and outputs .... |
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| solentlife wrote: | I have to admit a touch of suprise, as I'm used to motors / batterys etc. taking what they need from a battery and putting out what they are designed / set for ... not like this where extra C capability is actually giving more power ......
I realise that a LOW C rating will be an issue as then amps cannot be supplied as demanded ... |
That is just what happens Solentlife, difference is when due to internal/circuit resistance the ESC cannot supply the motor with the power it requires.
As an experiment I tried extended leads to check the hovering power requirement of a heli. It would only just get off the ground and no way could get out of ground effect. Removed the electrical test gear and the flight returned to normal. Seems to me that all the connectors, connecting wires and their lengths/widths are of vital importance with the high currents that we use in our electric models. Any circuit resistance must be kept to an absolute minimum.
Tom.
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solentlife
Extreme 3D
Joined: 30 Dec 2010
Posts: 872
Location: Latvia / UK
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Posted: Thu Dec 08, 2011 7:57 pm
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What I'd like to do is now use thicker leads on my Lipo's .... so current carrying is maximised and voltage drop is minimised ... but like many - I don't like idea of opening up a pack ! Especially when it's new even if it only cost about $6 from HK.
_________________
If you don't crash - you ain't flying !
Fast learning to be 450 Heli Repair specialist !
Have : 2ch Bumblebee,
Co-Ax Syma S006 Alloy Shark
2x Clone 450 SE V2
+ fixed wing stuff ...
Returning to RC after 20 odd yrs away .. Ex Display flyer. |
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solentlife
Extreme 3D
Joined: 30 Dec 2010
Posts: 872
Location: Latvia / UK
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Posted: Sat Dec 10, 2011 1:52 am
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I know this is not Helis but as its LiPo then I think it useful subject ....
My EDF is 3S 20C rated and above posts indicate my test findings ... I want to go 4S ...
So lets move to next stage ...........
My EDF is rated for 3S lipo - but many are putting 4S in them. having seen that a higher C rated 3S is best to get the magic 200W needed for exhilarating flight ......... what C rating to head for on 4S.
Technically ... 11.1 up to 14.8 = 33.3% increase in motive force (volts).
Motor is 4200KV .... so 3S is = 46620rpm no load, 4S = 62160rpm no load.
Can I play numbers to arrive at desired amps to give similar 210W as I get with prime 3S ?
Ohms law ... 210w = volts 11.1 x amps .... which calcs out to 18.9A ... close to test results.
So taking 210w again and now using 14.8v = 14.2A
I am going to assume that a 20C 4S pack will work better than a 3S 20C pack ? If so then pricing is attractive, pack size is smaller ... I can afford to up the mA from 800 to maybe 1000 or more and fit the space I have.
Need others thoughts / ideas / findings on this ......
_________________
If you don't crash - you ain't flying !
Fast learning to be 450 Heli Repair specialist !
Have : 2ch Bumblebee,
Co-Ax Syma S006 Alloy Shark
2x Clone 450 SE V2
+ fixed wing stuff ...
Returning to RC after 20 odd yrs away .. Ex Display flyer. |
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tombo242
Extreme 3D
Joined: 04 Nov 2008
Posts: 3633
Location: Santo Estêvão, East Algarve, Portugal. 76, but still feels 18.
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Posted: Sat Dec 10, 2011 8:37 am
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Difficult to fault what you say here Solentlife. Sounds good to me.
My only concern is that some ESCs on 4 cell (or more) batteries require a BEC/power pack to drive servos and Rx. You might need to consider that if your ESC has a 3 cell BEC limit.
Tom.
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solentlife
Extreme 3D
Joined: 30 Dec 2010
Posts: 872
Location: Latvia / UK
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Posted: Sat Dec 10, 2011 7:48 pm
Post subject: |
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| tombo242 wrote: | Difficult to fault what you say here Solentlife. Sounds good to me.
My only concern is that some ESCs on 4 cell (or more) batteries require a BEC/power pack to drive servos and Rx. You might need to consider that if your ESC has a 3 cell BEC limit.
Tom. |
I have a separate UBEC in the box (5A jobbie) just in case ...
With regard to the T45 that it's about - others have fitted 4S with no other mod - so I hope all works ok ..
Weather is howling gale and freezing rain here at moment ...
_________________
If you don't crash - you ain't flying !
Fast learning to be 450 Heli Repair specialist !
Have : 2ch Bumblebee,
Co-Ax Syma S006 Alloy Shark
2x Clone 450 SE V2
+ fixed wing stuff ...
Returning to RC after 20 odd yrs away .. Ex Display flyer. |
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tombo242
Extreme 3D
Joined: 04 Nov 2008
Posts: 3633
Location: Santo Estêvão, East Algarve, Portugal. 76, but still feels 18.
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Posted: Sun Dec 11, 2011 1:23 am
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I had a feeling that you might be prepared there Solentlife. 
Tom.
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