View Full Version : very very VERY tempting.. Need advice.
henrik04
04-05-2008, 06:43 PM
Looking at a concept. Don't know if it has been covered or not.. (Sorry if it has).
Looking at 10S batteries for my E-620. As the custom made CF frame is pretty large, I thought it would be nice to use individual cells instead of already made packs.
Why? one would ask.. Well I look at it this way:
- Each cell can be easily monitored for physical expansion.
- As I intend to place them separated by 4 or 5 millimeters apart, they would be very well ventilated unlike when they are enclosed within a pack.
- If a cell starts to be 'tired' or don't hold charge as the neighbors then replacement of this 'bad' cell is more economical than replacing 10 of them.
That my current thoughts.. Please let me know what you think.
http://www.maxamps.com/Lipo-10000-Cell.htm\
or
http://www.maxamps.com/Lipo-4000-Cell.htm
Happy flying
I think it's a poorish idea.
If you are going to use connectors x10 then you will end up adding a fair amount of weight to the pack, and a lot of potential for poor connections/overheating. For example, if you get a connector dirty, it may overheat and melt.
If you're going to solder... You might as well get a regular pack, and if one cell goes bad insert a new cell of higher or equal capacity/C-rating.
In theory, you may get away replacing a cell with one of higher or equal capacity, but if all of your cells are not well matched this might cause some of them to fail prematurely.
Personally I'd be quite wary of soldering up a LiPo pack, even though I do a lot of soldering and am generally confident at it. The risks of misplacing a blob of solder and causing a short seem too great.
K
henrik04
04-07-2008, 12:29 PM
Thank you for your comments.
Indeed my intention is to solder them.
Not really sure I understood your comment.
Are you are saying that if there is a mismatch in the internal resistance in the pack that would lead to failure of other cells?
Happy flying.
Are you are saying that if there is a mismatch in the internal resistance in the pack that would lead to failure of other cells?
If the cells are not well matched this may lead some of them to die earlier than others, because they'll be more highly stressed under the same conditions, and the ones with a lower capacity will be discharged to a greater extent than the others. I don't know how realistic a concern this is - some of my A123 packs seem to charge to 2250mAh and others only to 2150 - all well balanced. Some of the expensive brands advertise that they test all their cells and try to match them, even from the same batch. Some other brands don't, as they expect you to run in your own cells before using them in earnest and I think - though I'm not certain - that this means they can't have tested their capacities.
Are you going to buy a PCB ready made to solder them to, or design one yourself? Or hand-wire them?
In the light of day, perhaps it isn't such a bad idea and now I read back over my first post, I'm sorry I was so negative. I do like the idea about leaving more space between the cells. On the other hand, if you buy ready-made packs, they're only about $2 a cell more for the same brand with the same capacity and all the ticklish work's been done already. Why not buy ready made packs, and a spare cell or two in case one goes bad?
I solder A123 cells, which leave a lot more space for maneuver than LiPos, where the tabs of adjacent cells will be nearly next to one another. I also solder surface-mount stuff, so it's not that I'm generally clumsy. But out of 10 A123 packs I've built (9s2px3, 3s1px5, 2s1px1) I think I've shorted a cell or two perhaps 3 times that I can recall. With LiPo, if you got a solder-bridge on the PCB and the current didn't blast it away immediately, I can imagine ending up with a very expensive flameball on the desk. That's the real reason I'd be so wary of doing this myself.
K
ginnz
04-07-2008, 07:04 PM
I think it's a poorish idea.
If you are going to use connectors x10 then you will end up adding a fair amount of weight to the pack, and a lot of potential for poor connections/overheating. For example, if you get a connector dirty, it may overheat and melt.
If you're going to solder... You might as well get a regular pack, and if one cell goes bad insert a new cell of higher or equal capacity/C-rating.
In theory, you may get away replacing a cell with one of higher or equal capacity, but if all of your cells are not well matched this might cause some of them to fail prematurely.
Personally I'd be quite wary of soldering up a LiPo pack, even though I do a lot of soldering and am generally confident at it. The risks of misplacing a blob of solder and causing a short seem too great.
K
hmmm.... ive soldered many things, from miniscule electronics, to the big stuff..... (bga packages/water pipe)!
anyways, as long as you have the right iron/solder for the job, you're golden.
ive soldered many lipo packs. its just all about having the right amount of heat, and good flux-less solder......
i'd like to find a source for individual cells, and make my own packs. maybe i could make 4s packs for 15.00 this way?
henrik04
04-08-2008, 12:43 PM
I didn't think of the $ side.
When I looked at http://www.maxamps.com/Lipo-10000-Cell.htm the idea slowly made it's way..
And 10S @ 10A for this price is a bonus in my books. Won't win over the A123 price but it's not too bad.
I agree with the comment saying that soldering will add weight, but I don't think my E-620 will mind too much.
I have an idea for the connectivity in between the cells but I'm first going to try and measure.
PCB is an easy and economical way but looking a the peak current the beasts can deliver I'm not confident to use this solution.
My thoughts were more towards 6x4x millimeters short pieces of copper wire embedded in the holding frame. Battery tabs soldered to these.
As I said I'll try, measure and post results..
Happy flying.
The price differential is certainly very different for those cells - much cheaper bought alone.
Let us know how they work, and post some pictures of your solution. I'm impressed by the prices - really not a lot less than A123 at their current prices.
Regards,
K
DKNguyen
04-30-2008, 01:08 PM
Have you considered these?
http://www.modelelectronicscorp.com/
They don't have soldering so you can be lazy and also remove individual cells at will. Compared to buying a premade A123 or Lipo pack here and somewhere else, it seems to be a lot cheaper because there is no soldering labour involved, even at the cost of $15 per cell.