On Mon, Nov 08, 2004 at 11:56:14AM -0600, Brian Smith wrote: | For the convenience of it I had assembled a couple airborne packs from | Wal-mart 2200 Nimh batteries..
You can do much cheaper than that -- about half the price. The local Frys sells similar sells for about 1/2 the price of what you can find at Wal-Mart. | All was well till I crashed my Wonderful Ava-Gea...Two of the cells | failed at the same time..They had been charged for a couple months | on a Sirius Smart charger..So I blame the cells and not the | charger... It's a good plan to cycle packs (to measure the capacity) that you make a few times before you fly, to see what the capacity looks like. If the capacity is lower than the rated capacity for new cells, you may not want to risk using it. If you solder too long, you can damage a cell or two and you want to catch that before you fly. (Actually, cycling even factory made packs at least once to measure the capacity, and periodically afterwards, is a good plan. Most battery failures happen gradually ... | My friend Jon Stone suggested he does/ I should use nothing but | sanyo batteries in my airborne packs..A couple months later, so far | so good...My 2 cents about off brand batteries.."You pays your | money/You takes your chances" I've not found any particular differences between brand name packs and non brand name packs. I have found that a few of the packs I've made had diminished capacity after soldering them -- presumably I kept the battery hot too long during soldering -- but that hasn't happened in a while after I got the hang of it. Like it or not, batteries fail. Sometimes suddenly. You can catch most of the failures on the ground with occasional cycling (and measuring the capacity, and tossing packs that get less than 80-90% of the rated capacity), but not all. One thing I've done lately is for a plane that I'd normally use 4 AA cells, I use *two* seperate AAA packs. (With two switches and two seperate charging harnesses, with both switches plugged into the receiver on different servo plugs (or using a Y harness if needed.)) Unless a cell is physically damaged, they rarely short circuit themselves -- instead, they usually either fail open, or the internal resistance rises to a large value (rising to an infinite value = failing open.) With two redundant packs, even if one pack fails, you've still got power. I'm also fond of the Hobbico Air Alerts, so if the voltage drops (usually indicating a battery that's about out of juice), I know about it unless it's either a noisy plane or way up there where I can't hear it. (If you do do two packs, be sure to charge each pack seperately. Putting the packs in parallel for charging is a recipe for not charging both fully.) That said, I've never had a plane crash due to failed batteries. I'm lucky, I know, but I'm also careful. And I have at least once found that the low battery alarm was going off on a battery that I thought was fully charged -- turns out the battery was just about to fail. That $15 spent paid for itself several times over right there :) And if your plane needs some ballast to get the CoG right, might as well just throw in another pack or a bigger pack rather than some lead, right? Might as well make that weight do you some good! -- Doug McLaren, [EMAIL PROTECTED] `absorbent and yellow and porous is he!' RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
