Lipo and Nimh Cell Count Comparisons
09-23-2004, 11:13 PM
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Lipo and Nimh Cell Count Comparisons
I have a AXI 4120/14 and Jeti 70 to power a Seagulls PC9 that I want to do sport flying/beginner aerobatics and I am trying to figure out what battery pack to use.
Right now the plane weights around 3.00 lbs with out Motor/mount and Battery pack, Hitec 6 channel receiver and speed controller, so the end weight minus a battery pack is probably going to be around 4.25 lbs. I am thinking I will need somewhere around 500-600 watts of power.
Looking at the website http://www.modelmotors.cz depending on various props looks like I will need a 14 -16 cell pack
How do Nimh cell counts map over to cell counts and pack configurations in lipos, example a 16RC X 1700.
Any help would be greatly appreciated.
Right now the plane weights around 3.00 lbs with out Motor/mount and Battery pack, Hitec 6 channel receiver and speed controller, so the end weight minus a battery pack is probably going to be around 4.25 lbs. I am thinking I will need somewhere around 500-600 watts of power.
Looking at the website http://www.modelmotors.cz depending on various props looks like I will need a 14 -16 cell pack
How do Nimh cell counts map over to cell counts and pack configurations in lipos, example a 16RC X 1700.
Any help would be greatly appreciated.
09-24-2004, 09:25 AM
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RE: Lipo and Nimh Cell Count Comparisons
7-8c= 2S
10c = 3S
14c = 4S
16c = 5S
18c = 6S
There is some overlapping there (ie- 10-12= 3S.....12-14= 4S etc.), but that is generally a Cell to Cell comparison.
-Mike
10c = 3S
14c = 4S
16c = 5S
18c = 6S
There is some overlapping there (ie- 10-12= 3S.....12-14= 4S etc.), but that is generally a Cell to Cell comparison.
-Mike
09-24-2004, 11:57 AM
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RE: Lipo and Nimh Cell Count Comparisons
Aha, the perfect opportunity to debut my simple NiCd-to-LiPoly formula!
Two LiPoly cells in series (2S) is about the same as a 7-cell NiCd
Three LiPoly cells in series (3S) is about the same as a 10-cell NiCd.
Every LiPoly pack can be split down into base 2S, and 3S units. For example, a 5S LiPoly is a 3S and a 2S. A 4S LiPoly would be 2S and 2S.
To go from NiCd to LiPoly, you would find the closest combination of 7-cell and 10-cell NiCd packs, and make the simple conversion.
Let's say you have a plane that calls for 16 cells. You can get close with one 10-cell and one 7-cell (17 cells) or two 7-cell (14 cells). So, the equivalent LiPolys to those two choices are either 5S (3S+2S) or 4S (2S+2S).
On a 16-cell plane, you will be MORE than happy with a 4S LiPoly, BTW, if you're coming from a 16-cell NiCd.
Two LiPoly cells in series (2S) is about the same as a 7-cell NiCd
Three LiPoly cells in series (3S) is about the same as a 10-cell NiCd.
Every LiPoly pack can be split down into base 2S, and 3S units. For example, a 5S LiPoly is a 3S and a 2S. A 4S LiPoly would be 2S and 2S.
To go from NiCd to LiPoly, you would find the closest combination of 7-cell and 10-cell NiCd packs, and make the simple conversion.
Let's say you have a plane that calls for 16 cells. You can get close with one 10-cell and one 7-cell (17 cells) or two 7-cell (14 cells). So, the equivalent LiPolys to those two choices are either 5S (3S+2S) or 4S (2S+2S).
On a 16-cell plane, you will be MORE than happy with a 4S LiPoly, BTW, if you're coming from a 16-cell NiCd.
09-24-2004, 04:47 PM
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RE: Lipo and Nimh Cell Count Comparisons
In short, each cell in series (S) in a NiMH or NiCD pack is worth 1.2 volts.
Each cell series (S) in a Lipoly pack 3.7 volts (nominal)
Multiply these number by the number of individual cells in the pack for a total series pack voltage.
So, an 8 cell (S) NiMH pack = 9.6 V
A 3 cell (S) Lipoly pack = 11.1 V
When joining 2 of more packs together, (In Parallel, or "P") it's time to note the Ma/H rating of each pack. Make sure they are the same.
2 x 1100 Ma/H packs in Parallel = 2200 Ma/H. This means more duration (flying time) than a single 1100Ma/H pack, for the same voltage.
Doesn't matter if they're NiMH, NiCD Li-ON or Lipoly packs. The same rules apply.
Pack weights of battery packs do differ, depending upon the Ma/H rating of the pack.
A 4.8 volt 1700 Ma/H NiMH pack will be heavier than a 4.8V 700Ma/H pack, for example.
Likewise a 2 cell(S)2200Ma/H Lipoly pack when compared to a 2 cell (S) 700 Ma/H Lipoly pack, so don't forget to factor the all up pack weight in when doing your calculations.
The much lighter pack weight of say a 3S 1500 Ma/H Lipoly pack (11.1 Volt) will more than compensate for the slight voltage disadvantage it suffers, when compared to a 10 cell 1500Ma/H NiMH pack (12 Volt.) The Lipoly pack would probably weigh in under 1/2 the weight of the NiMH pack. Far less "ballast" for the model to lug around the sky.
The upshot is that you could then look at fitting another identical Lipoly pack in, connected in Parallel, to give the same voltage but double the flight time and STILL be lighter than with the NiMH pack.
This is the beauty of Lipoly packs in electric flight. I have been able to quadruple the non stop flight times of my electric models by switching them over from NiMH packs, as well as improving performance, without adding any extra weight. Try doing that with a glow engine!!!
Each cell series (S) in a Lipoly pack 3.7 volts (nominal)
Multiply these number by the number of individual cells in the pack for a total series pack voltage.
So, an 8 cell (S) NiMH pack = 9.6 V
A 3 cell (S) Lipoly pack = 11.1 V
When joining 2 of more packs together, (In Parallel, or "P") it's time to note the Ma/H rating of each pack. Make sure they are the same.
2 x 1100 Ma/H packs in Parallel = 2200 Ma/H. This means more duration (flying time) than a single 1100Ma/H pack, for the same voltage.
Doesn't matter if they're NiMH, NiCD Li-ON or Lipoly packs. The same rules apply.
Pack weights of battery packs do differ, depending upon the Ma/H rating of the pack.
A 4.8 volt 1700 Ma/H NiMH pack will be heavier than a 4.8V 700Ma/H pack, for example.
Likewise a 2 cell(S)2200Ma/H Lipoly pack when compared to a 2 cell (S) 700 Ma/H Lipoly pack, so don't forget to factor the all up pack weight in when doing your calculations.
The much lighter pack weight of say a 3S 1500 Ma/H Lipoly pack (11.1 Volt) will more than compensate for the slight voltage disadvantage it suffers, when compared to a 10 cell 1500Ma/H NiMH pack (12 Volt.) The Lipoly pack would probably weigh in under 1/2 the weight of the NiMH pack. Far less "ballast" for the model to lug around the sky.
The upshot is that you could then look at fitting another identical Lipoly pack in, connected in Parallel, to give the same voltage but double the flight time and STILL be lighter than with the NiMH pack.
This is the beauty of Lipoly packs in electric flight. I have been able to quadruple the non stop flight times of my electric models by switching them over from NiMH packs, as well as improving performance, without adding any extra weight. Try doing that with a glow engine!!!
10-04-2004, 04:37 AM
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RE: Lipo and Nimh Cell Count Comparisons
Woody 51 said, "When joining 2 of more packs together, (In Parallel, or "P" it's time to note the Ma/H rating of each pack. Make sure they are the same.
You don't have to have the same capacity when paralleling packs, just the same number of cells of the same electro chemistry. The packs will discharge in proportion to their capacity. Connected in series the MUST be of the same capacity however. 2s2p 1500 mA Packs connected in parallel will give a slightly better voltage level than only one 2S 1500 mAh pack as the combined internal resistance is only 1/2 of the single pack.
The devil is in the details
You don't have to have the same capacity when paralleling packs, just the same number of cells of the same electro chemistry. The packs will discharge in proportion to their capacity. Connected in series the MUST be of the same capacity however. 2s2p 1500 mA Packs connected in parallel will give a slightly better voltage level than only one 2S 1500 mAh pack as the combined internal resistance is only 1/2 of the single pack.
The devil is in the details
