thinking of building a 2S3P pack w/18650s in a bored d mag,is this safe? what do I need to do to balance the cells? I'm new at mods,but full of crazy ideas. Thanks.
2S3P lithium pack safe?
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mdocod
Flashaholic
He didn't mention how many Ds long the mag he was going to use is, so I don't see any reason it wouldn't work.
Provided it is bored to hold cells side by side, and you come up with some sort of crazy adapter to make it work, a 4D mag should have room...
The problem with this, is that there are other power solutions that would be far simpler to deal wit that would offer similar energy storage. ..you could, alternatively, just use a 6D mag instead, pack it with 6 NIMH D cells, which would have similar voltage as 2 li-ion in series, and 10AH capacity. The li-ion configuration described would have ~6.6AH capacity.
You could just use a pair of li-ion D size cells, I think kaidomain has some.
You could use 4 26700 size Emoli cells, 2s2p configuration with maybe a 4D mag with tailcap modifications and a pipe as a spacer (might need a 5D to make it fit). This would be far simpler to wire up, and be easier to charge and balance. (make 2 separate "sticks", each one with a thin insulating spacer between the cells, and the cells wired in parallel within the stick, then treat each stick as a single "cell" to be charged to 4.2V.
Provided it is bored to hold cells side by side, and you come up with some sort of crazy adapter to make it work, a 4D mag should have room...
The problem with this, is that there are other power solutions that would be far simpler to deal wit that would offer similar energy storage. ..you could, alternatively, just use a 6D mag instead, pack it with 6 NIMH D cells, which would have similar voltage as 2 li-ion in series, and 10AH capacity. The li-ion configuration described would have ~6.6AH capacity.
You could just use a pair of li-ion D size cells, I think kaidomain has some.
You could use 4 26700 size Emoli cells, 2s2p configuration with maybe a 4D mag with tailcap modifications and a pipe as a spacer (might need a 5D to make it fit). This would be far simpler to wire up, and be easier to charge and balance. (make 2 separate "sticks", each one with a thin insulating spacer between the cells, and the cells wired in parallel within the stick, then treat each stick as a single "cell" to be charged to 4.2V.
I'm loking for power density, don't want to go bigger than 3d.guess I haven't measured enough yet. From what i'm reading the d lithiums aren't yet worth the $, except for ease of use. I'm trying for something that can handle a 3amp draw with decent (relatively) runtime. suggestions?
mdocod
Flashaholic
so you need ~7.4V, as much capacity as possible, in a 3D mag...
See, 18650s are longer than D cells by 5mm each, and they can only fit side by side in a mag body that has been double or quad bored. So that configuration would require 195mm length plus whatever length is added by whatever adapter construction is required to wire up the cells like that (3D cells is 180mm long), so the total length would probably be at least an inch longer than 3D size cell, which probably isn't going to fit in a 3D, maybe with some major tail-cap modifications and a very slimly designed adapter it wold be doable.
You could comfortable fit 4 18650s in 2S2P configuration in a 3D, and the wiring would be way easier as it would not require any odd center-plates to wire it up for 7.4V.
Another option is 6 17670s, these will fit 3 abreast in a tri-bored mag as I understand it. Wire the stacks channels in series, layers in parallel for a 7.4V pack with around 4.8AH capacity.
You could run 6 NIMH cells, I believe they make NIMH cells in 17670 size that are about 3.8AH capacity. They could just be wired in series in some custom pack, and then charged as a pack with a standard NIMH/NICD pack charger, no special balancing other than an occasional trickle charge required.
idduno if that helps any. If you do decide to go with a li-ion pack of sorts, I recommend a proper balance charger, and a pack built with balance taps to each set of cells that is in parallel. Or use a single cell charger, and charge each segment of the pack individually.
See, 18650s are longer than D cells by 5mm each, and they can only fit side by side in a mag body that has been double or quad bored. So that configuration would require 195mm length plus whatever length is added by whatever adapter construction is required to wire up the cells like that (3D cells is 180mm long), so the total length would probably be at least an inch longer than 3D size cell, which probably isn't going to fit in a 3D, maybe with some major tail-cap modifications and a very slimly designed adapter it wold be doable.
You could comfortable fit 4 18650s in 2S2P configuration in a 3D, and the wiring would be way easier as it would not require any odd center-plates to wire it up for 7.4V.
Another option is 6 17670s, these will fit 3 abreast in a tri-bored mag as I understand it. Wire the stacks channels in series, layers in parallel for a 7.4V pack with around 4.8AH capacity.
You could run 6 NIMH cells, I believe they make NIMH cells in 17670 size that are about 3.8AH capacity. They could just be wired in series in some custom pack, and then charged as a pack with a standard NIMH/NICD pack charger, no special balancing other than an occasional trickle charge required.
idduno if that helps any. If you do decide to go with a li-ion pack of sorts, I recommend a proper balance charger, and a pack built with balance taps to each set of cells that is in parallel. Or use a single cell charger, and charge each segment of the pack individually.
Thank you, that's very helpful. I'm just kind of muddling through ideas in my head and costing and sourcing as i go .
mdocod, I am not about to disagree with you as you are pretty much the resident battery fitter expert around here. But are you sure you can fit 18650 side by side in a bored mag?? I was pretty sure the diameter of two 18650's wide was larger than the outside dimensions of a mag tube. Now an elephant body or something, that's a different story.
mdocod
Flashaholic
I think it leaves like 1mm of body left on either side to make em fit, might be worth a double check though before jumping on the plan. I've been wrong before.
JetskiMark
Enlightened
Definitely, I have a 2s2p Fivemega creation.
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