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3 Cell Li-Ion pack DIY

Old 01-28-2009, 12:45 AM
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nhoj_yelbom
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Default 3 Cell Li-Ion pack DIY

i have 12 Model: Sony US18650GR G5 3.7v 2200 mah @ 47Grams per cell. i want to make 3 cell 11.1v packs for my mini lst 2, it is brushless. i wanted to know if its worth making the packs or just buying some li-poly packs. i hear that the c rating is low with cylindrical cells and i wanted to know if they will work correctly with the mamba system.

here is how im wiring them

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Old 01-28-2009, 12:57 AM
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sheograth
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Default RE: 3 Cell Li-Ion pack DIY

The discharge rate won't be great, I'd get a normal RC specific lithium polymer battery.
Old 01-28-2009, 01:02 AM
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nhoj_yelbom
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Default RE: 3 Cell Li-Ion pack DIY

thanks for the info, thats what i thought. i might make to see what happens, as they were free and brand new
Old 01-28-2009, 06:50 AM
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RC_Basher20
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Default RE: 3 Cell Li-Ion pack DIY

Could allways make a 2s pack for breaking in motors
Old 01-28-2009, 09:51 AM
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nhoj_yelbom
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Default RE: 3 Cell Li-Ion pack DIY

do you need to break in brushless? im new to brushless......
Old 01-28-2009, 11:34 AM
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Default RE: 3 Cell Li-Ion pack DIY

Many lithium-ions are not designed for high-rate discharge, keep a close eye on temperature and test it before to see how much current it can actually supply.
Old 01-28-2009, 11:39 AM
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Default RE: 3 Cell Li-Ion pack DIY

might make good packs for your receiver, last all month and then recharge


edit: I meant transmitter - doh
Old 01-28-2009, 11:46 AM
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Default RE: 3 Cell Li-Ion pack DIY

whats a good way to test output?
Old 01-28-2009, 11:54 AM
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Default RE: 3 Cell Li-Ion pack DIY

I made a pack for my dx3 remote, but the batts are too big for mounting on any of my helis or cars for reciever packs
Old 01-28-2009, 12:18 PM
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Default RE: 3 Cell Li-Ion pack DIY

I've wondered about this myself... I've used these cells for low-draw applications such as TXs, although I figured that they had a low C rating and would therefore be ill-suited\dangerous at higher draw.

How about setting these cells up in parallel? Since cells in parallel effectively doubles capacity (both mAH and C), at SOME point this should be feasible, assuming they have similar characteristics to Li-PO. Also, I wonder how 'reactive' these cells are compared to Li-PO. I haven't had a pack reach critical mass yet, and I don't intend to
Old 01-28-2009, 01:06 PM
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Default RE: 3 Cell Li-Ion pack DIY

If the cells are designed for laptop use, that is generally between 0.5C and 1.5C so you'd need to put a whole bunch in parallel, which poses problem of its own. Not all cells are equal, there is some variance, so putting 2 in parallel won't necessarily mean the current is split exactly 50/50. You have 10 in parallel and you can be almost certain it's not going to be 10% current going to each individual cell.

Also be careful with charging, Li-Ions charge to a diffferent max voltage than LiPos do. It's not 4.2V. It might be 4.1V, or it might be lower, depends on the cell chemistry.

To test the load-carrying capacity, get two 1-ohm power resistors. Measure the open-circuit voltage. Then measure the voltage with a single power resistor load. Measure it with both power resistors load (in parallel). Use the voltage-divider formula to find the 'hidden' or 'virtual' internal resistance of the battery. From this, you can calculate the theoretical voltage drop at higher C ratings. The 1-ohm resistor is approximentally a 1.5C drain for these cells, if the voltage drops even 10% (ie. 4V to 3.6V) that would make them pretty useless for a high-drain application.
Old 01-28-2009, 03:44 PM
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TheAdge
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Default RE: 3 Cell Li-Ion pack DIY

Yeah, I think 3 in parallel is the max I'd do, and even that will probably only be run in my rock crawler. I had 2C discharge in my head, although I'm not surprised it's even less. I primarily use a DTX Ice charger, which does support Li-ion. My understanding is that most li-ion cells are 3.5-3.6v nom. vs. 3.7v nom lipo. I also set my temp. cutoff only a few degrees about ambient, to help with safety. Thanks for the resistor tip - I need to try that out! I've been looking for effective ways to test these cells...

For argument's sake, what if one were to charge these cells individually, then use them together temporarily as a pack? As an example, I run NiMHs in my TX. I know they're series, but bear with me... rather than charge them as a "pack", I use a charger which charges the cells individually, 4 at a time. Might this be a viable approach to getting some additional usefulness out of li-ions?
Old 01-28-2009, 05:25 PM
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Default RE: 3 Cell Li-Ion pack DIY

ORIGINAL: d31805
For argument's sake, what if one were to charge these cells individually, then use them together temporarily as a pack? As an example, I run NiMHs in my TX. I know they're series, but bear with me... rather than charge them as a "pack", I use a charger which charges the cells individually, 4 at a time. Might this be a viable approach to getting some additional usefulness out of li-ions?
That should be fine, in fact, charging cells singulated is always preferable to charging them as a pack since you don't have to worry about balance issues.

Two things though.
First, even a crawler can use a lot of current in some cases. Be careful.
Second, Li-Ion refers not to one chemistry but to many different subsets, and some of them work at lower voltages than others. The chemistry used in those sony cells might not be designed to be charged CC-CV to 4.1V.
Old 01-28-2009, 05:29 PM
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Default RE: 3 Cell Li-Ion pack DIY

You don't have to break in brushless motors. The reason you break in brushed motors is to set the brushes. Brushless motors do not have brushes hence the name "brushless" .
Old 01-28-2009, 07:54 PM
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nhoj_yelbom
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Default RE: 3 Cell Li-Ion pack DIY

well i made the pack with 12ga deans and ultra connector, hooked it up to brushed heli and it has half power........
Old 01-29-2009, 12:23 PM
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Default RE: 3 Cell Li-Ion pack DIY

That'll be the discharge rating. If it's that gutless be real careful how you use it because Li-On will go pop.
Old 01-29-2009, 12:33 PM
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Default RE: 3 Cell Li-Ion pack DIY

Well thanks for the help, if anyone has a use for the cells let me know!

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