Lipo questions

[Jbreddawg]

Ok, so I'm building my e-revo and have zero experiance with lipo's . I am "probably" going to go with 2 batts instead of one but have a few questions first. I was going to go with a 4s 5000 mah batt , can I use 2 2s with less mah for less weight ? Like 2 2s 2000 mah ? I know I wont get 35 min run times but will I still get the power output from them ? I dont mind 8-10 minute run times as thats about what I'm used to and will have 2 or 3 sets of batts . Am I on the right track ? Or way off ? I will be using a 9xl and an mm with a target speed of about 40 mph. Not sure on gearing yet but am using a monster rc motor mount with the revo tranny. any advice it appreiated !! Thanks, Jerry

[Hickoryhead]

your on the right track. You understand the concept. I personaly don't give up MAH for 20 to 80 grams of weight but thats me. I run 2 2s2p 6000 mah Lipos in series. The difference in weight between both batteries together compared to a 4s2p 6000 mah battery was close by like 60 grams.(I think) I would go with a little bigger batteries. I get about 35 minutes to an hour run time each time I charge them up. I run 2 batteries because I distribute the weight on my G2R chassis. 1 battery is better if your running the Revo chassis. Do you plan on sticking with the MM or upgrading to the MMM when it finaly comes out? Also if you buy 2 batteries remember they need to be matched. By this I mean you need to keep them charged the same amount of times. They need to be balanced the same amount of times. Everything needs to be done the same for each.

[Jbreddawg]

Thanks for the great info ! I also have a G2R chassis and would like to run dual batts. I'am also in the process of building my own chassis that I would like to run dual batts on too. There is also a pricepoint considering. i figure I could get two sets of 2s 2000-3000 for the cost of one set of 6000's ? I already have an ICE LIPO charger so I can keep them matched pretty well. I'm just wondering if smaller mah batts will still have the same punch as bigger mah batts will ? Will I just lose runtime ? Or performance too ? Thanks, Jerry

[Jbreddawg]

Something like these . Maybe not this paticular brand but this size x 2 would give me 6400 mah and 14.8 volts . they say there 20c also. So in reality two of these would be better then one 4s 5000 mah ? Thanks for the help, just trying to understand lipo's a bit better. Jerry

[Sammus]

Notice that a lipo's discharge rating is often given as a "C" value. That means it can discharge at that many times its capacity. So say you have a 6000mah = 6ah battery with a 25C rating, it can deliver 25*6 = 150A. If you have a 3000mah battery rated to 30C, it can deliver 30*3 = 90A. So basically the higher capcity batteries tend to have slightly lower C ratings, but because theyre much larger they deliver more current.

Secondly, didn't quite gather if you got this, so I'll tell you anyway :) one 4s 6000mah is not the same as two 2s 3000mah. The latter will either give you a 2s 6000mah (parallel) or a 4s 3000mah (series).

[Jbreddawg]

My understanding "way back from high school though lol " Is that when you run them in series you add the two so two 2s 3000's would equal one 4s 6000 ? And run in parrallel you would get 7.4 volts but 6000 mah ? is my memory not serving me correct ? It has been more then 20 years since school !!!

[Jbreddawg]

I forgot to put the link in my earlier post !!

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=016

[Hickoryhead]

Originally Posted by Jbreddawg

My understanding "way back from high school though lol " Is that when you run them in series you add the two so two 2s 3000's would equal one 4s 6000 ? And run in parrallel you would get 7.4 volts but 6000 mah ? is my memory not serving me correct ? It has been more then 20 years since school !!!

Your close. To run in series you add the cells together but not the mah's. To run in parallel you add the mah not the cells. Like Sammus stated:

two 2s2p 3000 mah packs---

2s2p 6000mah (parallel)
4s2p 3000mah (series)

And of course paraelle gives you double the run time and series gives you double the power output.

Be careful about the Lipo's you buy. They are very sensitive creatures. You get what you pay for. Just because the numbers on the packs look good does not mean they will perform good. I would not suggest to anyone about getting those batteries. There are to many factors when it comes to Lipo's. You don't need to buy the very best lipo but don't buy the cheapest you can find. Like I said you get what you pay for with Lipo's. That battery might be fine on a Helo but in a truck that is bashing and crashing they may not stand up to a beating or the cells might not put out the amps your looking for. Just my 2 cents though.

[Sammus]

Originally Posted by Hickoryhead

And of course paraelle gives you double the run time and series gives you double the power output.

Close, theoretically series gives you double voltage with the same potential current draw, parallel gives you the same voltage with twice the potential current draw - so the power is really the same, just in different forms :)

But for what it's worth, higher voltage is generally more efficient than high current, so it is better :P just being my pedantic self...

[Jbreddawg]

I really appreiate the great advice ! I was just using those as an example, i have enough money invested why cheap out now !! i do plan on getting good batts, i used to race along time ago and the quality batts made hugh differences !! I was just wondering if I could go with less mah but as i see now that will also hurt the output capability . thanks again for the teachings !! Jerry
p.s. my gorillamax G2R chassis and rc-monster motor mount showed up today !! And I purchased "dont tell the girlfriend" another roller to continue on with my own custom chassis build !!