emoli battery
The cells used to make these can only be procured by deconstructing Milwaukee Power Tools V28 battery packs. Although each cell weighs more than a comparable capacity Lipo cell, they cost about one third the price of lipos. Balancing taps can be purchased and added to whatever configuration is desired and work identically to lipo packs. The above pictured pack is a 4S1P 3000 mAh for use in the Hirobo Lepton.
In flight data logging on the Lepton, and on rfaster's Ion-X (using 10s2p configuration) has concluded that emolis start to lose voltage sharply at 80% of their capacity. Note that the mAh used is most accurately determined by inflight logging. When using the mAh charged back as read from a lipo charger, understand that a portion of the reported capacity isn't actually stored in the battery. It's a by-product of the charger peaking the pack's voltage. In the absence of in flight data, a charger's mAh report will be more conservative. It's recommended to determine the safe flight time to reach the 80% point based on your flying style, then subtract a minute and use that time in your transmitter's countdown function.
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Update: After flying the Hughes 500 (12+ lb aircraft) with two of my 4S packs in series ( in an attempt to lighten the Hughes), I've concluded that a more realistic discharge rating for these cells is 10C continuous, 15C surge (rather than 15C continuous). I flew the Hughes for 5 minutes and the batteries got to 160+F on contact. The shrink wrap started splitting. After cooling them off, I checked imbalance and only saw 0.010v, which had been typical of less stressed flights. The packs took back a full charge and balanced perfectly . They have subsequently been flown twice each in the Lepton and are behaving noramlly. So bad news...only 10C capability, good new..takes a beating and keeps going!!!
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emoli build guide by Lenny970
| I've been asked by a few folks to elaborate on how to go from naked emoli cells to the 4S stick pack shown above. This pictorial guide supplements Lenny's great guide, linked above. |
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I use a dremel to grind off welding residue and to roughen up the surface to accept solder. |
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Do both ends. The negative side is trickier to solder to since the heat is wicked away so fast. |
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I make my own battery bars by snipping them out of copper sheeting I found lying around the construction site. |
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Tin the bars, both sides, front and back. |
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Tin the cells |
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After soldering on the bar, I carefully fold it over to make an inline pair. I'm not very good at soldering cells directly to each other! |
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Take two pairs, and solder them together with a third battery bar. |
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Add power leads. |
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Look at how you're going to arrange balancing leads. |
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Cut balancing leads to length so that no wires need to be folded back. Note that I keep the red wire, for future potential use. It's not required for this pack. Be sure to tin the ends. |
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I shave off a little of the paper insulator for the inter-cell balancing leads. |
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Solder them on |
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I like to balance and charge the pack while it's still naked in case I need to fix something. |
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When you're sure the pack is good, goop it together where the in-line pairs sit next to each other, then shrink wrap. |
Power Systems
I use the KC spreadsheet to evaluate electric power systems for our helicopters. I've added parameters for emoli cells, as well as the larger ESC's and motors we use.
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