C rating does make a difference

[solentlife]

As many here know I fly fixed wing as well as heli's. 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 ...

[Richard]

Yeap, nice bit of work there.

When the first lipos started reaching C ratings of 20+ advice then was you may need prop down or risk burning your motor/ESC out

[solentlife]

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 ......