Espritmodel.com Telemetry Radio
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Old May 26, 2012, 07:34 AM
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earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
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They do look quite attractive. I would simply run them through a smart battery charger once and cycle them to see what the approximate capacity is. Is they pass the cycle test Ok, then you are in business and got a great deal. The Ebay business is in the USA located in Fremont California according to their online store. So you aren't dealing with someone from Asia then.
So warranty support ought to be much better.
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Old May 28, 2012, 08:46 AM
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USA, MA, Weymouth
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That "internal resistance" figure for ANY cell IS an important parameter...

Dear Fellow RC-Groupers:

The PIPE Here again - just a quick one to start for Wacky1, since I AM an NHL fan I'd be much more likely to say "Go BLACKHAWKS" if I was from the Windy City, which I'm not...they DID win the "big silver mug" two years ago after a half-century "Cup drought", and MY favorite team of all, DID win it last year...I simply do NOT want to see New Yuck's "Rags" win it all (usual Beantown vs. Big Apple sports rivalry sort of thing), so for this playoff run, I was QUITE glad to find that the New Jersey Devils team brought down "King Henrik", who gives my B's ALL SORTS of trouble when he's in net......and that's even with one Braden Holtby of the D.C. Caps sending my Bruins out of the playoffs and on an early summer vacation this time around!

Now, back to that "internal resistance" sort of thing for airborne battery packs for our model aircraft!

The usual choice for a nickel-chemistry (NiCad OR NiMH) AA-sized rechargeable pencell CAN keep things nicely compact inside the model when the radio's airborne components get installed, but the usual internal resistance for those cells...in a PER-CELL situation...is some 25-30 milliohms apiece !!!

For an RC transmitter's lower, 250-to-300 mA relatively constant current drain for a VHF-band Tx (that's one on 50 or 72 MHz), or an apparently under-200 mA figure for a typical SpredSpec-band Tx on 2.4 GHz, the rechargeable cells' internal resistance isn't such a big thing. But when one gets into AIIRBORNE packs, especially with the newer, higher drain DIGITAL servos, now one IS talking much higher current demands, which can be seriously TROUBLESOME for high internal resistance celled airborne battery packs.

The "80%-length sub-C" Sanyo NiMH cell I specified in an earlier response in this thread HAS a lower 7 milliohm internal resistance per cell. For a "regular" four cell NiMH pack, since resistance adds up in series, that's about a 30 milliohm total resistance for the entire pack. But, if one's using the AA-sized NiMH cells, now we're talking...with the minimum of 25 milliohms per cell...a much higher 100 milliohms as a "lowest figure" for a four-cell NiMH pack, and the higher current drain that multiple digital servos CAN place on the airborne pack starts to get QUITE serious, which is where one WOULD want a cell that's got the lower internal resistance, to be able to deliver the higher current that multiple digital servos would require.

GeetarJoe's idea to go with the A123 cells for a lithium-iron-phosphate airborne pack, instead of a nickel-chemistry celled one, IS a great idea I'm seriously considering for my own needs. Dave Thacker's RadicalRC page for these IS where I'd be getting mine from, and with A123 Systems even having a relatively new "whopper" 4.5 amp-hour LiFePO4 cell out there (that one's not YET available through RadicalRC) the picture for lithium-iron celled airborne packs just seems to be getting brighter and brighter as time goes on.

For my own needs, as I NEED to stick to what I've got before I can afford to get back to RC flying again (remember, that little matter of yours truly GETTING BACK TO WORK again???) I'd be going for the 7-milliohm NiMHs, in four-cell airborne packs, to use with my existing FMA SuperNova pair of non-lithium-capable smart chargers. When I'm back at work and CAN afford a multi-chemistry charger, like Hitec's X4 quad-output unit, I'd be giving LiFePO4 cells a FULL suite of tasks in helping me power my return to the RC hobby after I'm back at work once more...even for my Sullivan electric starter for my four-stroker mills !!

Just doing some AutoCAD 2009 LT practice with my home PC today, as I'm waiting to hear on at least one opportunity using AutoCAD for full-time work...tomorrow night it's rehearsal time for my graduation this coming Friday, and then I'll have THREE areas of work I can possibly get a job in (electronic manufacturing, CAD/drafting OR business office work)...and get back to RC flying some time down the road.

Yours Sincerely,

The PIPE....!!
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