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hkopium
06-13-2005, 01:39 PM
Assuming all other items are the same (i.e. Car, motor, ESC, etc)...

For the same voltage (say 7.2v), how much faster (in %) would the car be if using Lipo instead of NI-MH batt?

Any idea?

TNB
06-13-2005, 04:23 PM
It's probably more of weight issue (and size issue) if the total volts are the same. For example:
6 NiMH cells x 1.2 = 7.2v or a 2 cell lipo; and
9 NiMH cells x 1.2 = 10.8, 3-cell Lipo = 11.1v.

To get an idea of speed ratings, visit Castle Creation's website and review the different Mamba Packages since they compare the speeds of the different motors using different cells.

BLACKHAWK444
06-13-2005, 05:05 PM
Its kinda just preference. NIMH batteries are cheaper because you probably already have a charger for them. Li-Po requires a new charger and a power supply. The only difference in performance would be the weight difference. NIMH are going to go a bit slower because they are a lot bigger and heavier, but for the most part a 8 cell GP1100 pack and a 2 cell lipo pack are going to be very alike performance wise.....

akura2
06-13-2005, 05:42 PM
and you have to make sure you are using GOOD lipo batteries. Cheaper ones don't have the amp output and can burn up on you... LiPo batteries are rated slightly different than NiMh.... but either way.. you have to make sure they can put out the amps, or they will fry... and you have to set cutoffs in your ESC to make sure the batteries don't discharge too far... if they do they will be destroyed....

but you DO save in weight,which equates to speed. And two LiPo cells put out slightly more volts than 6 NiMh 7.4 vs. 7.2

TNB
06-13-2005, 07:06 PM
Based on the lipos I'm using and the lipos I've seen and read about, it doesn't appear that there would every be a perfect "voltage" match between alkaline, NiMH or LiPo batteries.

Alkaline - 1.5v each
NiMh - 1.2v each (some AAA's are rated at 1.25v)
LiPo - 3.7 each cell (2 cell = 7.4v, 3 cell = 11.1v)

And since power equals voltage multiplied by current, the lesser the voltage, the less power (assuming the current is equal). Ever wonder why automobiles moved from 6 volts to 12 volt systems and beyond? How wire size, resistence and consumption are related? Enough of that, my brain is frying. FET gone bad? ;)

mOOsE
06-13-2005, 09:27 PM
I did a lot of comparison with this question when I had my rc18t. Their was a group of 4-5 guys that all had 18t's with 6800 mamba's and 2cell lipo's. We compared the 1320 2cell, 2100 2cell, and gp1100 6 cell. One thing is for sure, the lipo's will always be lighter. But where the power issue comes in is the average discharge voltage. Sure the battery says 8,.4 or 7.2 when charged but the voltage drops under the load of the car accelerating. Lipo's have a pretty high average discharge voltage. In most of our runs, the 2cell lipo cars would win. however, the gp cells are pre-matched before they even get the gp label on them. They too have a very high discharge voltage. I built a 6cell gp1100 pack for one guy and it was very comparable to the lipo packs...even with the extra weight. So if you do go LIPO, make sure you get a higher capacity cell like 2100. I have seen people run the ThunderPower 1320 in their Half8's but they are pretty much pulling the max amps everytime they run. I would personally just go with an 8cell GP pack. They are more expensive than other cells but there is a large performance difference

TNB
06-13-2005, 10:24 PM
I would personally just go with an 8cell GP pack.
Myself, I choose Thunder Power 11.1v 3-cell 1900maH lipos originally for my Xray M18. Then I learned I could still use them in my Kyosho Mini-Inferno. Of course, it will also fit in my Losi Mini-T. Another factor in battery choice to me was "diversity."

mOOsE
06-13-2005, 10:56 PM
yeah I thought about doing two 1320 2cells wired in parallel. Still lighter than an 8cell. But kinda pricey :)

RockDragon
06-15-2005, 04:59 AM
I do not think that's a good idea to put 2 Lipo cells in parallel unless they are matched cells. If not, you are likely to put the one that gets lower power into permanent damaged as its over discharged.
When buying Lipo cell, you should pay attention on the "C" rating of the cells. The higher "C" is the higher current that the cell can deliver into the motor, therefore, High "C" and High "mA" is more torque and longer run time. Also, at least the Deans connectors to be used.
GP 1100mA NiMH has been proved and tested that can deliver 30Amp of power. It's well enough for the BL motor that needs about 25Amp continuous at top speed. But the cells will heat up so quickly and the power output will drop as the cells get too hot.
This will also happen with the LiPO cells but not as quick, therefore, you can hold up at top speed for longer time than using the NiMH cells.

Well! this's been just my opinions as I've been running my (RC18) BL system (mamba-25 ESC + Himaxx 2025-4200KV BL Motro) with 9 cell 1200mA Intellect Pack (http://i2.photobucket.com/albums/y8/RockDragon/SANY0163.jpg) and "12C" ALIGN 3cell 11.1V 1800mA LiPO pack (http://www.align.com.tw/shop/product_info.php?products_id=733).
My Half8 is on the way. I will equip it with ALIGN 35A Brushless ESC (http://www.align.com.tw/shop/product_info.php?cPath=22_73&products_id=741) + ALIGN 420LF Brushless Motor(3200KV). (http://www.align.com.tw/shop/product_info.php?cPath=22_67&products_id=853) Together with either 10-12 cell NiMH or 2 cells in serial of 7.4V 12C LiPO.
lol ... this will be fun.

TNB
06-15-2005, 05:19 AM
I do not think that's a good idea to put 2 Lipo cells in parallel unless they are matched cells.
Isn't that what a cell balancer is used for? The other comments regarding GP1100s and Deans "Ultra" plugs are on Castle's website.
http://www.thunderpower-batteries.com/html/chargers.html
http://www.castlecreations.com/

mOOsE
06-15-2005, 06:04 AM
Its perfectly fine to do it that way, Otherwise airplanes would be SOL for the high-amp brushless setups they often use. Also, there are lipo's sold this way...I had a 4 cell lipo from thunderpower that was 8.4 volts but 2x the MAH.