picassolsus

I may be way off here and totally missing something critical like not enough mAh or something of that sort but, is there any particular reason why two 3.7v Lithium Ion cell phone batteries wired in series (for 7.4v) would not work to power something like a Blade CX? I ask because I have TONS of 3.7v cell phone li-on batteries lying around from a previous job. I could recharge them in the phones they came out of.

Would they not provide enough juice for lift or run time? just curious if anyone has tried this. I'm certain I'm missing something here. Thanks.

Derek

Coyote64

I would definitly think that the current demand on them would toast them or at least drop the voltage down that much in an effort to work.

Charge time would be much longer if this was feesable also

picassolsus

Yeah, see that's the end of it I'm kinda clueless on. The mAh on the Motorola BT60 battery I have several of is 1000mAh, 3.7v. How does this differ from a stock Blade CX battery which is just two LiPo's in series at 7.4v 850mAh (I'm guessing those numbers are right?).

Where is the show stopper so to speak?

Coyote64

If your running in series which obviously you will the max the two can dump between them is the same so 1000 mha seems fine

By your figures this might indeed be feesable

But having said that if its that obvious and feesable then why havent any manufactorers noticed and taken the market, after all a lighter battery is the holy grail

picassolsus

Exactly...that's why I'm figuring I've missed something here. I'm going to give it a shot tonight anyway with a couple of these BT60's Motorola batteries I've got. I'm just going to do a half throttle (about the point where I hover) and time it. If it's at least 5 minutes then as far as I'm concerned it's worth it....strictly considering it's $0 cost since I already have the batteries. We'll see I guess! I'll post back with the results. If anyone has any additional input on the subject feel free to chime in. Thanks.

Derek

gnd2

The voltage of two in series would be fine. The capacity sounds good. I think the "gotcha" is going to be the current draw. I can't find a maximum rating online but these batteries are probably designed for the much smaller current draw of a cell phone, and might not be able to handle the 15-20A or whatever that the heli can suck down.

But if you don't have a better use for the batteries, grab a fire extinguisher, head outside someplace safe and give it a shot

picassolsus

gnd2,

Yeah, you have a point. I was wondering what "rating" is used to measure things like the situation where you're hovering and decide to go full throttle to climb-- I'm sure that move puts a strain on the battery and demands a high current draw. So, what I expect will happen- my hypothesis I suppose- is that it will work but for only about a minute. That's going to be my scientific wild @$$ guess is one minute (with absolutely nothing to back that up, heh). Soon will see!

Coyote64

My thoughts are mass ball of firey plastic heading to terra ferma at an astounding rate lol

picassolsus

Well, lord knows wind is enough of a problem for this little guy, and as I witnessed this weekend water faired well enough, so let's see how fire stands up .

Coyote64

Go for it anyway and take a digicam with you......... i feel a youtube moment coming weather bad result or good lol

gnd2

Shall we start a pool? I'm gonna take 2 min 30 sec.

bonsaidude

I think the relevant rating is the "C" rating of the battery, how well it performs related to the current draw.

From http://www.helitown.com/LipoBattery.html:

"Discharge Rate (C): C-rate - Capacity Rate - of a Lithium polymer (Li Po) battery. This is a critical information of a Li Po battery pack each RC pilot should know. The C- rate is used to determine how many amps a battery can deliver the power. For example, my APEX 2200 mah pack rated 12C can deliver 2.2 * 12 or 26.4 amps of power."

Replacement packs for the CX2 seem to be 10 to 15C. I doubt that a cell phone would need to draw at that rate, but on the other hand, I doubt our packs are specially built for our uses, the prices are just to close to the packs for things like cell phones and laptops, that have 100s of times the volumes.

picassolsus

Ok guys the jury's in....


I won't even bother with attaching any pics of videos. Wired everything up, double checked polarities, checked the new pack with the multimeter and got right around 8.0v. Turned the transmitter on, connected the Frakenbattery- the 4in1 armed! So far so good. Slowly started to throttle up, so far everything nominal, then right as I hit what would normally have been the "lift off" threshold on my stick, the unit just powered down. No smoke or flash or anything exciting, the 4in1 just powered off.

Hmmm.....I removed the Frakenbattery, and checked voltage again- still 8.0v. Plugged my regular E-Flite battery in and the heli worked perfectly so no 4in1 or otherwise damage. I disassembled the batteries and put one back in a motorola cell phone which indicated a full charge.

So, it must be the current draw as some predicted that is the "show stopper". Opinions or speculations as to what you anyone else think may have happened?

Oh well =). It was something to do.

Derek

bonsaidude

Probably the voltage dropped as the current draw increased. If you could wire up a voltmeter up and bench test it, you would probably see the unit shut down as the voltage feel below some threshold.

nitrohog

Thats cool that you actually tried it, as I was reading I expected some sort of fire explosion of flaming lithium. Too bad it didn't work, but I give you props for at least trying.

gnd2

Oh ya, I can't find it now but I think I read somewhere that Li Ion batteries used in things like cell phones have a current limiting circuit in them to protect them from catching fire. Either that or the internal resistance just caused the voltage to drop so much that the 3-in-1 just shut off.

Coyote64

As i said before i thought voltage drop would be too great.......

But hats off to ya.......... you did it !

No fire ball of melting plastic but hey you cant have everything

xyster101

It is the "C" rating. The cell batteries can not deliver enough amps to run that.
I have a 11.1V lipo off a crashed Hydro plane/boat thing that i use in my #4 tx since that runs off 12 volts. Works great!

You can use your cell batteries on your tx. If you have a CX2 then use one battery and if you have a CX then use 3 cellphone batteries. with the CX you should be able to fly for a month on one charge.