RC India

Hey i know i am new to this forum and new to this community but has anyone tried using NiMH batteries instead of using Lipos. NiMH have a higher higher charge density than lipos and could single cell can easily provide 5A discharge current(voltage is low though).

Hi Jayant

Welcome to RCI.

Most nitro flyers use NiMH on their planes, LiPOs provide a higher discharge as compared to NiMH and have a better power to weight ratio as compared to NiMH...which is why they're preferred for electric setups. Also with most electric models, Kv is the equivocal of RPM on nitro. Kv bears a direct relationship to voltage, not current...

If the benefits (weight and discharge) of LiPo did not outrun NiMH for electric power, we'd still have NiMH in our cellphones ;)

thats exactly what i am asking

http://www.flipkart.com/sanyo-eneloop-hr-3uwxa-4tm-rechargeable-battery/p/itmdnfs4gvr3g65s?pid=ACCDNFS3WNUGGB32&cmpid=content_rechargeable-battery_8965229628_gmc_pla&tgi=sem,1,G,9226359,g,search,,24309680300,1o7,,,c,,,,,,,&gclid=CNipxPrsp7sCFYtV4godpU4AqA

2500mAh for 28gm

why aren't we using this one

later i will post a link that it really shows that it gives 2400mAh charge when discharged at 5A.

Lets say i use 8 of these in series then i have 9.6V 20Ah for 224gm

For a 1 kg plane you'd need about 100Wto fly decent, including the take off speed, aborted takeoffs etc, power surges..., factoring in motor and prop efficiency, you will need atleast 15-16A to fly on 12 v source to generate that power...this NiMH will not be able to provide that current...

Theoretically, most NiMH would overheat and gradually die at about 2C (5A in this case) ...although various manufacturers have different specs...

http://www.rcgroups.com/forums/showthread.php?t=1127160

(power to weight ratio)
the NiMH will do a 5.0A * 9.6  ~ 50W for 224 g
the lipo will do a 44A (2.2A LiPo on a 20C rating) * 11.1 ~  480W for 185g

http://www.hobbyking.com/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.html

Icing on the cake, NiMH need about 12 hours charge time for a decent charge..a 2200mah Lipo will take little less than 1 hour'

I haven't really tried NiMH for electrics, but feel free to do so, and post the results here for all and sundry :)

thats 50watts for 20Ah/5A=4hours

2.2Ah/44=0.05hours

i'm just trying to make a quadcopter with 1hr+ flytime

if yes never go for nimh

For a 1kg plane you need about 100W to fly, for a quad this, I presume, will be atleast 3-5 times higher (vertical take off and flight)! which means if your quad only had the battery, you'd still need way more than 70-80W just to pull up...quad builders will be able to help you better here in terms of the energy requirements...

that is why what i really want to know is that if i have 2 of those cells in series will i be able to draw 10A current from it(assuming each cell is capaable of giving 5A discharge current independently).

series does not add current, parallel does. Series will add the voltage.

The weight penalty and Discharge rate restricts their use in Air.
They aren't cheaper though. 2300Mah batteries are 270rs a pair. for 5 pair its 1350rs for just 12volt 2300Mah for just 2C?
though they are way too safe than Lipos.

Ashok.P

http://www.lygte-info.dk/info/indexBatteriesAndChargers%20UK.html

this is a pretty great site to analyze performance of different batteries