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Old 09-21-2008, 07:34 PM   #16
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I appreciate all of the info...and for those thinking I "can't afford it"...that's just untrue. I'm just not spending the money on something I know nothing about...that's why I started this thread. I'm planning on upgrading to some much better brushed motors like the Trinity Wilds that are a direct fit to the eRevo and should give it much more punch for not much cost. I also intend on getting some lipos strictly for the longer run times. I don't have a charger that will charge them yet...but that is soon to come.

I'll post my findings once I get those motors and batts. If you have ideas on better motors, please feel free to post the info. I can get two Wild's for under $80, so that's pretty reasonable for a boost in performance. Plus, I can sell the originals on eBay to re-gain some of the cost (not that they are worth much LOL).

I just found someone that has this for sale...would this work for my eRevo if I bought another to pair with it? It's brand new...just didn't fit his application.

RC Lipo Battery 7.4 V 4000 mahr
*7.4 volt Lipo Battery 4 Amp Hour
*5 1/2" X 1 7/8" X 1/2"

Thanks again!
http://www.hobbycity.com/hobbycity/s...idProduct=7028
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Old 09-21-2008, 07:53 PM   #17
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RB, is that charger CC/CV? nice price and features if it is.
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Old 09-21-2008, 07:58 PM   #18
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Can someone spell it out for me? What is the diff between 2s, 3s, etc...all the different specs of lipos. I know what mah are, just the rest of the specs.

Thanks!
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Old 09-21-2008, 08:15 PM   #19
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2s means two in series.

Lipo cell nominal voltage is 3.7v, NiMH/NiCd nominal voltage is 1.2v. So the 6-cell NiMh packs are made of six 1.2v cells wired in series (their voltage is added, mAh stays the same), and have 7.2v in total. 2s Lipos have two Lipo cells in series and are thus 3.7v*2 = 7.4v nominal. 3s is 11.1v, etc.

Lipos also have a continuous discharge rating. It is usually 20C for normal Lipos, and 25 or 30C for high quality exepensive and usually heavier ones. 1C corresponds to a current that would take 1 hour to charge the battery.

So if a battery is 5000 mAh, it would take 5000mA (5Amps) to charge it for 1 hour, and that's 1C for that battery. 20C is therefore 5A * 20 = 100Amps. That says the battery can be continuously discharged at 100 Amps or less and not overheat, and still put out close to 5000 mAh. Basically, 100 amps continuous is its spec. They can always give more current, but only for short bursts.

Another example, a 3000 mAh 30C battery (i.e. 1C for it is 3 Amps) can be discharged at up to 90 amps (30C * 3 Amps = 90 Amp).

Lipos also generally retain their high voltage even as they're discharged and under high load (high current) compared to NiMH/NiCd. The latter is usually very powerful right after you've peak charged it, but get much weaker as they're discharged. Depending on their quality, they can also drop much of their voltage under high load (current) and thus you get less power. Lipos are more consistent.
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Old 09-21-2008, 08:19 PM   #20
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So for standard, stock motors or brushed motors, 2s is the top lipo you can get due to the voltage, right? 3s and above is for BL?

Thanks for that descriptive run down...very informative.
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Old 09-21-2008, 09:54 PM   #21
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if your want kick ass budget lipos check out trueRC.com or get some zippy packs from hobbycity.com from everything ive read maxamps are constantly referred to as Crapamps as they are overpriced and over rated spec wise that is

zippy or truerc all the way

i have the zippy and it kicks ass in my revo conversion
good luck
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Old 09-21-2008, 11:26 PM   #22
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No, if both built using same batts, no diff in performance. The big diff is side-by-side construction lets you use a discharge tray to bring down each cell to teh same voltage before recharging. This gains you a more even charge and a little better batt performance and maybe a little more life too. You can replace a bad cell easier in a s-b-s pack than in a shotgun stype pack.

Stick pac is a little smaller than same cell count s-b-s so there are some application considerations. I've converted most of mine from stick to s-b-s so I can better maintain them.
Very informative. Thanks!
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Old 09-22-2008, 05:28 AM   #23
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Originally Posted by rccrazy_racer View Post
So for standard, stock motors or brushed motors, 2s is the top lipo you can get due to the voltage, right? 3s and above is for BL?

Thanks for that descriptive run down...very informative.
Yes, running a pr of those you'll have 14.8v since the stock esc puts them in series. Lipo has both a nominal voltage 3.7v/cell and a max voltage when fully charged of 4.2v/cell. So a pr of freshly charged 2S lipos would give you 16.8v.

You'll need a separate low voltage cutoff since stock esc does not have one. This prevents you from running lipo below its min voltage of 3v/cell. If you run them below min voltage, can damage them, causing a cell to swell or puff. Once thats happened, its generally considered unsafe to use anymore. You can run without lvc, but you're taking a risk.
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