WILL THIS LI-PO WORK

[ramstar]

i am going to convert my cub to a li-po and was wondering if the li-po out of my f-27c stryker would work? it is a 11.1v 12c 2200mah 3cell. if so, all i would have to do is change the leads over to deans and pull the jumper.

[mrmugen]

Yes it will work fine. See me post about modding the battery box to see one way of doing it. Kevin

[ramstar]

thanks Kevin, did you move your esc back a little to get enough room for the li-po?

[gazza1]

ive got a 3cell 2200mah battery but its 10c will 10c work?

[mrmugen]

ramstar- I made the hole that the esc wires run through and made it bigger and slid the esc in there. It gets nice and cool that way too. You can always use some velcro and stick it to the inside of the fuse (seating area). I did this to a few of them. Makes for easy checks and removal if needed.

gazza-2200mah is the same as saying 2.2amp. 10c is telling you how many times it's cell rating it can dump at once. So basically if it is 2.2 amp multiply that by 10 and you get 22amps. 22amps will be plenty to fly the cub on. I posted here somewhere about the stock SC amp draws on both 7-8 cell nimh's and 3s lipo's. Not sure where but it is here. I think the 3s was around 15 or 18amp. I could be wrong.

Kevin

[welshbloke]

Hi All,

Great forum!

I also would like to use a 11.1v 2200 mah 20C cell in my stock cub. Just wondering though if I would need to change the prop from the stock 10X8 with this set up?

Also, do I need to watch flight time or anything to avoid any damage?

Thanks in advance!

Rob

[flydiver]

This is from PZ:

[the jumper
is present the auto-cut is set at about 5.7 volts,
which works with 6- to 9-cell Ni-MH battery packs.
When the jumper is absent, the auto cut is set at
about 8.8 volts, which will function correctly with a
3S Li-Po Battery.]

IMO 8.8v is too low. 3.0v/cell is minimum, 3.3-3.5v/cell is optimal for modern batteries. This is for a LOADED battery-resting batteries will show a higher voltage. I'd recommend flying by time, and quitting when you still have 20% of your battery left. This translates to about (from another RC Group member work):
****
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Capacity below 3.7v "resting" is not usable for flying; it's where the battery voltage dump begins.
I have verified these results myself many times and simple fact is that the newer LiPolys do hold volts better under load so when a given LVC is reached they have even less capacity left in them.

For best life you should never use more than 80% capacity and resting / no load voltage should be a mininum of 3.7 per cell and 3.8 per cell is much better.

*****

You will not be able to do this without the right tools. Minimum is a voltmeter, better is a wattmeter (massively useful for figuring out lots of things), and best is a charger like the FMA Cellpro 4S (which I have touted in other threads). The 4S can give you % remaining after use and voltage of each cell.

If you've been ruining your lipos, they've been having a very short life, or puffing on you and you have not been aware of these precautions then that may be part of the reason.

Whether to prop down depends on your 'thumb'. If you merely use the extra power for occasional use and cruise a lot you may get by. If you 'throttle to the top' flying you'll fry something and should prop down to a GWS 10x6 HD or APCe 10x5.
The stock prop at full throttle is WAY over spec for the motor and electronics.
I know, I know, some of you out there are saying "works fine for me' but others are sagely nodding their heads after they burned something up. Some get lucky, some don't.

You can use a wattmeter to measure the output of this or any other system. Once you start modifying systems or putting together your own having and knowing how to use one becomes critical, at least I think so. It's one of my most frequently used tools.

fly

[welshbloke]

Thanks Fly, that's great information. I already have lipos and charger (1-5 Cell LiPo Charger with Balancer by E-flite ) as have been using them in my stock F27c. Although that charger doesnt seem as good as the FMA ones, it will give me the voltage of each cell.

I Will work on the battery box mod and give these cells a try! As soon as I have some results I will post here.