# LiPo?



## ChrisHarris (Feb 26, 2002)

OK, the forum says LiPo but nobody has anything to say? 

I haven't heard a ton about these other than the dire warnings about charging correctly. 

I did see in the Horizon catalog that the ones designed for planes clearly don't seem to have the current capacity that we drivers need. One listed an average current of 11A. And peak current should be in less than 10 second pulses. sounds fine for planes perhaps but are they usable for cars/trucks?

Thoughts?


----------



## hankster (Jan 1, 1998)

There are currently LiPo packs on the market that allow constant 40 to 50 amp draws. Most of the packs you have looked at are for small "park flyers". High powered/performance planes draw more higher constant amps then a car... I've seen pics of NiMh packs melted from the heat generated by the amp draw of a plane.

Some info in this thread http://www.hobbytalk.com/bbs1/showthread.php?t=94750

BTW, charge a NiMh cell wrong and it can explode too!


----------



## ChrisHarris (Feb 26, 2002)

hankster said:


> BTW, charge a NiMh cell wrong and it can explode too!


 Cool! No, probably not...


----------



## Fred B (Sep 26, 2001)

LiPo cells actually catch fire when they're overheated (shorted or overcharged). It's quite an impressive fireball. NiMh cells will also explode (and more violently) but without the fireball.

I use LiPo cells in my Mini-T and they work great. I'm just careful not to short them out or get them hot.

There are newer consumer LiPo cells that have a built in thermal shutdown and that will make them much safer to use.


----------



## kcobra (Dec 3, 2002)

How many amps will a typical stock motor draw under load in a 1/10th scale pan car? I was thinking about testing out a 3000mah or so lipo pack in my RC10L3.


----------



## hankster (Jan 1, 1998)

A stock motor will average about 27 amps during a 5 minute run.


----------



## ChrisHarris (Feb 26, 2002)

hankster said:


> A stock motor will average about 27 amps during a 5 minute run.


 (not meaning to hijack the thread) Doing the math, 27 amps for an _hour_ would be 2700 milliamp hours. (doh) How close to reality is that? Does that mean one doesn't need to worry about dumping a properly charged 3000 or 3300 pack over a 5 minute run. Ever?


----------



## hankster (Jan 1, 1998)

You math is a little wrong. 27 amp hours is 27000 miliamp hours. Move the dec. point *3* places to change from amps to milliamps. But I will agree that a stock motor in a pan car may draw a little more then that on average... maybe 30/32 amps.


----------



## kcobra (Dec 3, 2002)

So what I need to find is a couple loose 3000mah li-po cells that can handle a 10C discharge rate. I could wire them up like a saddle pack. Anyone got a link on relatively cheap loose li-po cells?


----------



## ChrisHarris (Feb 26, 2002)

I actually had the math right, I just didn't finish my sentence! I was thinking of six minutes, not an hour so I went to 60 and failed to divide by 10... My bad. Thanks for the clarification. So, bottom line is that people still have to conserve even with a 3300 I guess.


----------



## hankster (Jan 1, 1998)

27 Ah does not equal 2700 mAh! There are 1000 milli(anything) in a whole so you multiply the whole by 1000 to get milli. You are right, the rest of your math was incorrect too.

A motor drawing 30 amps for 5 minutes will use 2500 mAh. A typical NiMh pack discharged at 30 amps will have about 400 seconds of run time. 400 seconds = 6.6 minutes.

Most oval races are 4 minutes long so a 3300 pack should easily last a full 4 minute race.


----------



## ChrisHarris (Feb 26, 2002)

thanx


----------



## FASTALJR (Sep 27, 2001)

I have a vid of a lipo catching fire, its not pretty, a 30 second blowtorch is the only way I can describe it. The technology is still pretty young, as it gets better the cells will be able to handle more, and they will be safer. I believe there are already lithum batteries in solid cases like a AA.


----------



## darkultra (Dec 30, 2004)

_ It also has a built in circuit that automatically shuts off the battery unit when the voltage gets below a certain point. Several people has been using this battery without any problems in a brushless system._

http://www.thunderpower-batteries.com/html/batteries.html

some one said it on the traxxas forum
http://monster.traxxas.com/showthread.php?s=&threadid=264877

I think id rather have the lipo batteries in packs because that is lighter then metal cases. With a 4S 4400mah 14.8v pack, a BEC and Revo plastic drive shafts the monster truck will be both light and agile and fast, lighter then a Nitro!


----------



## DynoMoHum (Sep 25, 2001)

A 30 second blow torch... now that would probably really look cool in a plane. I can imagine this plane looking like it just got shot by some enemy fighter, erupting in a ball of flame and then spining out of control back down to it's demise when it hits the earth...

My wife's uncle in Taiwan who sells RC stuff for a living (Mostly plane stuff) was telling me that the lipo batteries loose proformance over time, simmilar to what you would see with NiCd or NiMh cells... That is they proform at there best when new and then deteriorate over time. Just like in car RC racing, the top level cometition plane guys will buy new packs quite offten to maintain their competive level of power... 

When I glance at the price of those lipo packs and think about buying new ones every so often to maintain high proformance... I get thinking about how much my wallet would hurt... I think I'm going to stick with NiMH for a while longer....


----------



## kyoshojoe (Oct 14, 2004)

*Soldering Li-poly cells in parallel?*

How safe is it to solder together these types of batteries in order to get extra run time? (i.e. two 7.4v 2000mah packs in parallel to get one 7.4v 4000mah pack). Has anyone done it yet, and what were the results?

Also, what kind of cell discharge rate am I needing to get in order to run the SS5800 brushless system or low turn modified brushed motors for good performance? I've been seeing the Li-poly floating around with a 10C to 12C discharge rate...


----------



## purehobby (Feb 4, 2005)

I would not recommend soldering your own packs together however it is done but can be dangerous with lithium Polymer. You may look at buying two packs and paralleling the two. Or even look at my PQ2S-4400N packs no need to use two packs if it fits for you. check it out www.purehobby.com 
Let me know if you have any questions
Robert


----------

