lipo questions....????
 

I have been into rc on and off for over 20 years now. Needless to say the advances in brushless motors and lipos is awsome to me. Anyway here is my issue. I have a rc18t that has a mamba in it. I got a 3s lipo and it is unreal.
I have a xl5 stampede for my wife and I know the 11 volt lipo is too much for her. I want to know what kind of difference a 7.4 volt lipo will be. I am really just looking for more runtime. I have seen a lot of 5000mah 7.4v lipos will they give me a ton more runtime or just a little more? Or would I be better off to just buy some 4600mah 7.2v nimh packs? We are not looking to race jsut bash around in the yard. Thanks in advance Rob

I bought a 2s 4000Mah protek pack($59.99) from amain about a week or 2 ago as a intro into the whole lipo scene, and that thing is unbelievable I put it in my brushless stampede and it'll wheelie on demand and as far as run time i'm bored of running the car up and down the street before the pack runs outta juice. it's wicked awesome, i'm almost afraid to see what a 3S pack would do to my poor little stampede.

the 3s i got for my rc18 is a 1400mah and I get over 30 min of run time out of it I love it. But i just didnt know how well the bigger and heavier brushed 10th stuff I have will do on a 5000mah 7.4v

OK first of all you need to keep in mind that it is the voltage of the battery that gives you the power and the capacity (run time) is the current (mah). The good thing about LiPo is that the discharge curve is nearly flat or in other words, it puts out about the same voltage at the end of the run as it did at the begining. Whereas NiMH has very good initial punch but tapers off as the run progresses.

To answer your question regarding the Stampede, it will run about the same perhaps a tiny little bit faster but not by a lot with a 2cell LiPo over a 6 cell NiMH (7.4volts vs. 7.2volts nominally). What you need to look at is the continuous discharge rating that is more important than just voltage or capacity. A discharge of 25C is very good and suitable for stock motor racing. A 20C, 15C or 10C means that it discharges softer and lacks the punch of a 25C or higher. So this is the real measurement to look for if you're after performance. A 3200mah 25C pack will outperform a 5000mah 15C but will run a shorter amount of time under the same load.

I guess I should have said I was looking at a 20c pack. So to make this short and easy. will a 7.4v 5000mah 20c lipo run a stampede or a xxxt a lot longer that a 6 cell 3800mah??

Yes, a lipo of even the same mah rating will run longer than a nimh. Reason is the lipo converts very little energy into heat, unlike the nimh. The difference depends on how hard you are discharging and thus heating the nimh, but 20 to 30% improvement is not uncommon.

Also the lipo handled correctly will be more stable over time. Both in runtime and performance (actual voltage under load, not the common 7.2/7.4 nominal voltage rating). Depends some on the nimh, they vary from brand/cell type to another. I suppose the same is true of lipo, but since they are much more stable to begin with the differences from lipo to lipo seem to be smaller.

Combine a good lipo like you mention with a say 17.5 or 13.5 brushless motor and you will probably get 30 to 40 minutes of run time. As a fellow old timer this stuff is sweet indeed. :nod::nod:

Thank you that is the answer I was looking for. And yes I love the technology. I still remember the time before the esc. Wow what a change.LOL