Quote:
Originally posted by Mike_D
So batfish, i too am also thinking about lipo. I am now using 16 gp 3300's with my 7xl/9920 which is 19.2 volts, would it be ok to used two 11.1 volt lipo packs of whatever mah i choose? And what is 2s, 3s, 4s?
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First, 2s/3s/4s, the "s" means "series". This is the amount of cells the pack has that add to the total voltage. Each cell is 3.7 volts nominal, so 2s=7.4v, 3s=11.1v, 4s=14.8v, etc... Nimh packs are cells in series, so you could draw a comparison by calling a 6-cell nimh pack a 6s pack of nimh.
Next, 2s2p, the "p" means "parallel". Unlike traditional nimh packs, lipos are commonly run in parallel in addition to series. This "p" number is the amount of cells in parallel the pack has, which adds to the total capacity. Each "p" adds the capacity equal to one individual cell capacity in the pack. This concept can get a little tough to understand for the first time, so I'll try to explain more.
For example, let's take my FMA BalancePro 2s2p 7.4v 6400mah pack. The pack is made with cells that are 3.7v (same for all lipo) and 3200mah. 2s means TWO cells in SERIES, so 3.7v*2=7.4 volts. 2p means TWO MORE cells in PARALLEL with the first two, adding capacity equal to one cell's capacity in the pack, so 3200mah+3200mah=6400mah.
Therefore, 2s=7.4volts and 2p=6400mah.
Now to your first question - 16 nimh cells is roughly equivalent to 5s lipo. Of course, you could go to 6s lipo, which would add the equivalent of about 3 more nimh cells.
When you run any lipo cells in either series or parallel you must, for safety's sake, ALWAYS use the exact same cells. Do not mix capacities or even manufacturers. Although lipo cells won't really explode and destroy a major metropolitan area (like we've been led to believe) if you treat them right, you still HAVE to treat them right.
If you want to run 5s lipo, consider buying one FMA/Kokam 2s 3200mah and one FMA/Kokam 3s 3200mah and run those two packs in series. This is what Mike does on his E-Revo, so you know it works. If you want 6s, buy two 3s packs and run them in series, but make sure you're buying the same cells in both packs.
Lastly, make sure you have a controller capable of the cell count, and strongly consider a low-voltage cutoff device to save your cells. You should never discharge a lipo cell below 2.7volts, but most people (including me) stop at 3.0volts to be safe. This means 6.0volts on a 2s pack, 9.0volts on a 3s pack, etc... An over-discharged lipo pack can be damaged, preventing it from being charged again.
I hope this information helps out in your decision.