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Old Jun 30, 2005, 01:14 PM
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Quote:
Originally Posted by fly_boy99
Let me refresh your memory:

Consider this. You are flying a $3000 -$5000 electric air plane or heli with a 10S4P LiPoly pack.


fb
Not with me?
I fly speed 400 size and all my packs
are from 2s to 4S, no XsXp configuration at all.
for lipos, which are prone to disaster... fire, explosion...
my best way for safety is KISS... yes keep it simple Xs only.

Have fun whatever you fly.... $30K turbine, $5000 heli or
$200 parkflyer... they all do the same thing for us... pleasure.
Oh yah the $30K turbine make you look better on the ground.
Peace
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Old Jun 30, 2005, 02:14 PM
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While the pooh-poohers nit-pick about "the masses" and big pack problems; please, the folks using simple 2 and 3-cell packs: bear in mind that the disclosures in the first two posts of this thread represent an easy, simple and cheap solution to problems which have arisen with series-charged packs.

Chinese cells, 8C 2000 mah, are now readily available @ ~ $10 per, Sermos connectors are among the least expensive, and a safe, reliable 3S 2000mah pack can now be built for less than $35.

An important advantage of parallel charging is that cells matched by medicine men are not required.

- RD
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Old Jun 30, 2005, 02:46 PM
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Quote:
Originally Posted by RD Blakeslee
BTW, I'm really not interested any more in what "The Masses" will or won't do.

These disclosures are for those who are not necessarily followers of currently fashionable practice. They will balance the pros and cons, and make their own determinations.

This system will not be offered commercially because it would undo three years of momentum in the manufacture and marketing of SMALL PACKS with their complicated, mysterious (therefore highly profitable) electronic solutions to series-charging disorders.

- RD
RD I would never reccomend that "the masses" ever tried your method of connecting cells together in series or parallel as illustrated. Far to many chances for error. We already have people that plug 2 large packs together incorrectly and that is only 4 connectors and not 6. Perhaps for the knowledgable and daring, but as a manufacturer far to much liability. Balancers are a very reliable and an inexpensive method that is very safe and nearly 100% "goof proof". And not to mention the weight and clutter os all the additional plugs. Heck the 6 seroms connectors and wire will weigh more that an OZ (35 grams) minimum. Why not just make 1 cell packs with sermos connectors??? Most small packs that are in the market place hold their balance very well, even without balancers.

Brian
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Old Jun 30, 2005, 03:12 PM
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Quote:
Originally Posted by rctoys
RD I would never reccomend that "the masses" ever tried your method of connecting cells together in series or parallel as illustrated...
I wouldn't recommend it for "the masses" either, Brian. It’s for those with the ability to build and use it.

But as you know, manufacturers COULD make a foolproof system for “the masses”:
http://www.rcgroups.com/forums/showt...ies+discharge+

- RD
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Old Jun 30, 2005, 06:46 PM
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I'd like to add another caveat against parallel charging. Not that there's anything wrong with it in theory, but in practice problems can creep in.

I modified a PC PSU to set the output to 4.2v on the 5v line, and added a variable current limit that I could adjust to suit the number of parallel charged cells. It worked fine and can deliver 45A, but I became concerned about the actual charge current each cell might receive. There's no easy way to be sure every cell is connected properly when you have say 10 cells in parallel. On 3 only cells this is naturally less of a worry. It's obvious that for each missing cell the current increases to the rest. Also depending on your charging harnesses resistance paths some cells may charge more quickly. If you terminate the charge early you may increase the likelihood of imbalance developing. If you leave everything until the charge current has tapered to a low value then I suppose that is less likely.
In contrast in a series charging system it is obvious if a connection is faulty - there's no charge current!

As you might tell from my moniker I'm a relative newcomer to electric flight and I'm still developing my own charge strategies. I've decided I'd rather build a series charger that can monitor each cell via taps and taper the charge current if any cell requires voltage clamping at 4.2v. The tapering is only to minimise clamping power dissipation during any equalisation charge. I think this is a reasonable compromise of simplicity/complexity as against building say 6 or 7 individual isolated single cell chargers in one case. It is unlikely to result in increased charging times except when equalisation is required, and then only dependent on the degree of imbalance. Regular use should mean this is minor.

It also means my series packs can be fully soldered with short, low resistance leads and the pack only needs a pair of heavy duty dis/charge leads, and a light duty ribbon for tap monitoring/equalisation. Hopefully this sort of pack construction will become more widely available in the future.

What do you think? It's for my 5s3p packs.
--
Steve
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Old Jun 30, 2005, 08:05 PM
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The perfect solution:

Use 1P packs!
I made this almost 4 years ago.
AUW: 2.2 oz.

....now all I have to do is make this work for my helis and I'm set!

All kidding asside, parrallell charging has it's place.
Many on this forum will find the info in this thread usefull. It's nice to have several technical options to choose from, each with their own unique positive/negative merrits.

Pullin'
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Old Jun 30, 2005, 09:04 PM
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And why would you since you are on the verge of selling yet another
lipo balancer on the market.....


Quote:
Originally Posted by rctoys
RD I would never reccomend that "the masses" ever tried your method of connecting cells together in series or parallel as illustrated. Far to many chances for error. We already have people that plug 2 large packs together incorrectly and that is only 4 connectors and not 6. Perhaps for the knowledgable and daring, but as a manufacturer far to much liability. Balancers are a very reliable and an inexpensive method that is very safe and nearly 100% "goof proof". And not to mention the weight and clutter os all the additional plugs. Heck the 6 seroms connectors and wire will weigh more that an OZ (35 grams) minimum. Why not just make 1 cell packs with sermos connectors??? Most small packs that are in the market place hold their balance very well, even without balancers.

Brian
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Old Jun 30, 2005, 10:36 PM
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Bravo, RD. you never cease to amaze me with your persistance (on a valuable topic too).

Rhett
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Old Jul 01, 2005, 04:45 AM
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Thanks, Rhett

"Us Folks" has gone 'round and 'round, again.

Returning to the first post: "There’s nothing new in any of this. It’s repeated here, because newbies to LiPos may not know about it and because recent discussions of LiPo charging apparatus have been dominated by means for electronic balancing during series charging, even for small, 2S and 3S packs, which comprise most of the market."

- RD
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Old Jul 01, 2005, 08:26 AM
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Quote:
Originally Posted by GlowFly
... I became concerned about the actual charge current each cell might receive. There's no easy way to be sure every cell is connected properly when you have say 10 cells in parallel...
Steve, referring to Figure 3: The charging lead to each cell is long enough to allow checking the amperage with a "clamp-on" ammeter, which I use on one lead of each cell at the start of each charge.

- RD
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Old Jul 01, 2005, 04:34 PM
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Quote:
Originally Posted by RD Blakeslee
Steve, referring to Figure 3: The charging lead to each cell is long enough to allow checking the amperage with a "clamp-on" ammeter, which I use on each lead at the start of each charge.
OK - sounds like a good move. A bit of a pain though when charging 15 cells! It's hard to shed the lazy habits garnered over many years regarding charging NiCd/NiMh. I really want a system that I can plug together with a pretty good expectation that the packs will be safely charged with no further checks. I'm more discliplined at home but at the field there's lots of distractions and I'd like a little more assurance I haven't slipped up. Safety aside, these packs are expensive!

I do find these discussion interesting though. I think I'll go ahead and build my own charger. I'll probably just finish when a commercial offering apears!
--
Steve
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Old Jul 01, 2005, 07:01 PM
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Fly boy we never had plans and never do plan to introduce a lipo balancer, if you are referring to the TANIC charger it is that ,, a charger, not a balancer, HUGE difference

Brian
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Old Jul 01, 2005, 07:18 PM
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RD, it is always good to see your posts on this alternative charging method. It is ideal for 3-cell packs which I would imagine are the most widely used. It is too bad that one of the major manufacturers have not offered a dedicated charging system like this for 3 cell packs. It really just comes down to making a good connector that would make it "idiot proof".

John
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Old Jul 01, 2005, 09:17 PM
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Brian-

Good luck to you!!!

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Old Jul 01, 2005, 09:21 PM
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Right on, John.

A prototype, using Multiplex six-pole plugs, has been built:

http://www.rcgroups.com/forums/showthread.php?t=236246

That thread is also referenced in post #6.

- RD
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