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Old Nov 17, 2015, 11:45 PM
G.F. Beurling is offline
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Do I have this right about connecting 3s 3000mah lipo batteries in series?

If I buy two batteries that are 3s 3000MAH 30C and wire them together in series, then I will essentially have a 6s 6000MAH battery. Is that correct? If so, then what I don't understand is why one 6S 5000 mah battery not only always costs more (about $60) then the two 3s 3000mah batteries (about $25 each), but why the 5000mah battery is also a fair bit heavier too! (??)

Am I wrong to conclude that I'd be better keeping two, three, or four 3s 3000mah batteries on hand for when I need them, and grab two and just jump wire them together inside the plane whenever I need a 6s 22v battery to go flying? My thinking is that I'll have more mah capacity (6000mah vs 5000mah) and I also eliminate the risk that if just one of those cells in an expensive 6s battery goes bad, then the whole $60 battery is no good. Am I misunderstanding how this works?
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Old Nov 18, 2015, 03:14 AM
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Your first premise is wrong, that's why the rest doesn't make sense.

2 x 3S 3000mAh batteries in series makes one 6S 3000mAh.

Series doubles voltage. Only.
Parallel doubles capacity. Only.

6S 6000mAh has four times as much energy as 3S 3000mAh. That's why you can't make it out of only two of the smaller packs .

Steve
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Old Nov 18, 2015, 10:00 AM
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Quote:
Originally Posted by slipstick View Post
Your first premise is wrong, that's why the rest doesn't make sense.

2 x 3S 3000mAh batteries in series makes one 6S 3000mAh.

Series doubles voltage. Only.
Parallel doubles capacity. Only.

6S 6000mAh has four times as much energy as 3S 3000mAh. That's why you can't make it out of only two of the smaller packs .

Steve

Huh.....? Pardon, and have patience with me....... but just using bare logic I have trouble wrapping my head around what you're saying. Putting two batteries together in either form (parellel or series) will not double the mah capacity? I would think that when adding a 1lb battery to another 1lb battery, the 2lbs of battery should show up as increased mah capacity......double presumably. Isn't this why a flashlight lasts longer with 2 standard large "D" batteries compared to a penlight flashlight with 2 "AA" sized batteries, though both are the same 3 volts in series? As for parrellel batteries; I had always understood that the quantity of mah is doubled while the voltage stays the same.
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Old Nov 18, 2015, 10:16 AM
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Originally Posted by Randall Miller View Post
Huh.....? Pardon, and have patience with me....... but just using bare logic I have trouble wrapping my head around what you're saying. Putting two batteries together in either form (parellel or series) will not double the mah capacity? I would think that when adding a 1lb battery to another 1lb battery, the 2lbs of battery should show up as increased mah capacity......double presumably. Isn't this why a flashlight lasts longer with 2 standard large "D" batteries compared to a penlight flashlight with 2 "AA" sized batteries, though both are the same 3 volts in series? As for parrellel batteries; I had always understood that the quantity of mah is doubled while the voltage stays the same.
As Sliptick mentioned, two 3S 3000 batteries connected in series will be the same as a 6s 3000 battery, having only doubled in voltage, with capacity unchanged.

Two 3S 3000 batteries connected in parallel will be the same as one 3S 6000 battery.

Four 3S 3000 batteries, connected 2S2P (2 series, 2 parallel) will yield one 6S 6000, effectively doubling the voltage and doubling the capacity, which gives 4 times the total power as a single 3S 3000 battery.

Hopefully this clarifies the issue.
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Old Nov 18, 2015, 10:42 AM
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And just to use a little conservation of energy, if you could put two batteries together in some way that both doubled the voltage and doubled the amp hours giving four times the energy of one battery, you would solve the words energy needs and you could make a lot of money selling this amazingly light and cheap battery. And there would be no reason to start with a 3S 3000mah as the building block, if you could build it with 3 * 1S 1000mah which should weigh and cost less.

The capacities you are talking about are only capacities of current. If you think in terms of energy capacity - watt hours instead of amp hours - it may be easier to understand.
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Old Nov 18, 2015, 11:09 AM
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Watch this video. It may help you understand the series vs parallel setups.
Connecting batteries in series or parallel (LIPO) (5 min 28 sec)
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Old Nov 18, 2015, 11:36 AM
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Quote:
Originally Posted by Randall Miller View Post
Huh.....? Pardon, and have patience with me....... but just using bare logic I have trouble wrapping my head around what you're saying. Putting two batteries together in either form (parellel or series) will not double the mah capacity?
I'm not too sure how you can misunderstand
"Parallel doubles the capacity. Only" but I'll expand a bit-

Series only the voltage is doubled, capacity isn't (i.e. 2 x 3S (11.1V) 3000mAh in series = 6S (22.2V) 3000mAh)

Parallel only the capacity is doubled, voltage isn't (capacity is measured in mAh so 2 x 3S (11.1V) 3000mAh in parallel = 3S (11.1V) 6000mAh).

O.K. now ?

Steve
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Old Nov 18, 2015, 12:05 PM
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A lot of people don't seem to grasp the idea of series vs parallel connections. The video is pretty good but doesn't mention that the "C" rating of the two batteries in a parallel circuit doubles in that you can, in theory, pull double the current.

It is good to know that the top of the "T" in a Deans Ultra connector is normally the where the positive or red wire goes and the vertical part of the T is where the negative or black wire goes. Some Deans type connectors have tiny "plus" and "minus " symbols to show where the red and black wires are to be connected. The male Deans Ultra is normally soldered to the speed control and the female connector to the battery . When soldering a Deans Ultra connector to a new battery pack or speed control , do one wire at a time, don't forget to install heat shrink tubing onto wire away from soldering heat, and finally sliding heat shrink tubing over soldered connection when cooled and shrink it with heat gun to prevent possible shorting when soldering on the other wire. Never try to cut through both red and black battery wires at the same time or you may short the battery and cause a fire with injury. Use 60/40 or 63/37 tin/lead alloy solder with rosin core intended for electrical/electronic soldering. Do not attempt to use "lead free" solder, it requires more heat and expert technique for soldering with an iron, read the fine print. Proper tinning of wires and connector tabs and use of rosin paste flux helps make soldering easy. There are some pretty good You Tube videos on soldering of Deans and bullet connectors.
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Last edited by E-Challenged; Nov 18, 2015 at 12:14 PM.
Old Nov 18, 2015, 12:32 PM
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Quote:
Originally Posted by slipstick View Post
I'm not too sure how you can misunderstand
"Parallel doubles the capacity. Only" but I'll expand a bit-

Series only the voltage is doubled, capacity isn't (i.e. 2 x 3S (11.1V) 3000mAh in series = 6S (22.2V) 3000mAh)

Parallel only the capacity is doubled, voltage isn't (capacity is measured in mAh so 2 x 3S (11.1V) 3000mAh in parallel = 3S (11.1V) 6000mAh).

O.K. now ?

Steve
I understood you clearly the first time, but wanted to hear this from others as well. It's only because you are knowlegable about this stuff and know how it works, that you seem to scoff at my logic. That newbie "logic" was that if one is to double the mass and volume of something, then one can likely expect double the capacity too. In the law of physics, this reality holds true with many things, but evidently not with batteries.

You were the first to reply on this thread. Because I had trouble processing in my mind how doubling mass and volume does NOT change mah capacity, I simply wanted to hear some verification from others. I now understand this, accept this, and don't dispute it.

THANKS TO ALL FOR THE INPUT. Knowing how this works I now have a better understanding of motor and battery options for my project,
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