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Helicopter
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Other › My T-Rex can fly 40 minute
04-02-2005 04:51 PM  13 years agoPost 21
bevoduz

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Normal, IL

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Could you imagine what Tesla could do with a heli in this era!

Bevoduz

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04-02-2005 06:56 PM  13 years agoPost 22
dkshema

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Cedar Rapids, IA

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I am always amused by the water analogy used for voltage and current. Makes gross explanations easy for the average guy who knows little about electricity, but beyond that, it is usually worthless.

I've done a bit of Web surfing following my post with regard to parallel connections of batteries. In several hours of searching, I have not found ANY reference that recommends placing batteries of different mah ratings for use in the same application. I have found numerous and unrelated admonitions AGAINST parallelling different capacity batteries.

From the Lithium Polymer application guide posted on the FMA Direct website (you know, the Kokam LiPo guys) is the following:
k. When using Li Poly packs in parallel, all cells in a pack must be the same capacity.
There are periods where the higher capacity pack charges the lower capacity pack. In those instances extremely high currents exist in the loop between the two cells. The current is limited by the parallel combination of the pack's internal resistance which is VERY low, causing very HIGH currents. Parallel connection of different rated batteries will result in SHORTER run times.

Parallel connection of battery packs of different mah ratings is a bad practice, not recommended by battery manufacturers, in spite of the buckets of water analogy.

Dave

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04-02-2005 08:14 PM  13 years agoPost 23
patti

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about my idea is not joke (I test it 5 flight and no problem). I want to explane why I do this, because I get those two Pi-Poly for free then I just got this idea and I ask some of genius guy in thailand (he very genius because he can built brushless ESC and Li-Poly charger by him self) to proof my idea and he told me "it OK to parallel it because it reduce discharge current for each pack and the larger capacity pack can't charge the smaller pack by them self because if you want to charge Li-poly you must have a litle over voltage at 1C charge current (in my case two pack have same voltage). but if you want to do this you must not charge them at same time if you do that you will blow the smaller pack"

so.
Quote
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k. When using Li Poly packs in parallel, all cells in a pack must be the same capacity.
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is ture if you want to charge them at same time but in my case I charge it seperate and difference of mah of two pack only 300 mah then it no problem about cut off voltage. (smaller pack reach cut off voltage first)

but the perfect way to parallel Pi-Poly is use same capacity. In my case I know it not perfect.

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04-09-2005 09:25 AM  13 years agoPost 24
DisGuy2K

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Melbourne, Australia

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If you use the same brand/capacity (ie 12C) of LiPo you are basically just adding cells to the pack to make a larger pack. As for the flight time, we can achieve an easy 30 mins on an Etec 2400 8C (170g) pack using the newish Align 400LF 2800 kV. With an ambient temp of 20°C the motor was just under 50°C the ESC was about the same, and the battery was about 55°C. This was driving the chopper conservatively. Basically just FFF and other simple non-3D stuff.

As a side-note. Beginers like me should all sling their batteries in between the landing skids, fixed with some velcro tape, and a velcro strap. It makes landing (at funny angles) so much easier. Many a time I've landed on 1 skid with the spinning rotor blades literally holding the chopper up.

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Helicopter
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