Horror Story

Depends on the time frame. If it happens between flights, most do not look at the ends of the cells.

There is nothing different, Red is convinced that the diodes are unnecessary. In a practical sense, they may not be for our normal short duration flights. I tend not to get in arguments based on anecdotal evidence. My personal packs are diode isolated. I would suspect that it all has to do with the modality of a failure.

the Lithiums are

( > weeks, plane

Only if it happened to be fully charged. In the real world the short occurs when the cell is discharged and shunts any attempt to charge the cell. You may have what is termed a "soft short" develop which is the presence of some conductive material in the separator or protruding through the separator that has deteriorated. This will cause an abnormal high self discharge to the point where a hard short develops. Shorts caused by physical abuse to the cell while fully charged is about the only scenario where you would see a cell "spill its guts" so to speak. This can be brought about quite dramatically by overcharging a cell at high rate until the separator melts from the heat allowing the charged plates to touch. The heat then generated by trying to dump all the energy in the cell causes the electrolyte to turn to steam, which can force molten separator into the vent mechanism and make it inoperable and eventually the cell rapidly disassembles.

-- Red S. Red's R/C Battery Clinic

Oh, I see what you all are poking fun at now. That went right over my head. What I should have said was "a resistor to give a 350 ma load on a

If you read my other response, you would see that I had a unit that I could dial up anything from 0 ma, to 1.5 amps, on any reasonably sized pack.

-- Jim in NC

Since no one else has mentioned this possibility, I'll throw out the one that has happened to me on more than one occasion. Simply the switch from the battery pack to the receiver went open, and on one of mine it opened and closed intermittently. On one of these events, I was lucky enough to get the thing safely landed while it happened to be closed. On at least two others I was not so lucky. My take on this subject - after using the switch supplied with the radio package for some months TRASH IT and buy a decently made switch! Or preferably start out with a decently made one.

Olin McDaniel, W4PFZ, AMA 30932

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----------------------------------------------------- "Ignorance is treatable, Stupidity is incurable. Sometimes the difference is hardly distinguishable, however."

One of the first things they thought of was the switch. I was told that it didn't appear to be the problem. The only actual component failure found was a battery pack that had one dead cell.

At one time I was skeptical of simply wiring two packs in parallel with no isolation. So, being the skeptic, I took two 4 cell packs and ran discharge test. To simulate a pack with a shorted cell I used three cells in parallel with a 4 cell pack. I placed an ampmeter between the packs and saw an 80 ma charge rate to the 3 cell pack. Also the voltage was decreased to about 4.6 volts. After much pondering about the effect on a plane it suddenly dawned on me that typical flights only last around 15 minutes. Even with a shorted cell, you would not notice any effect. The shorted cell pack would be found before the next flight by using a voltmeter check. I always turn on one pack and wiggle the servos. Then turn on the second switch and the first one off and wiggle the servos. Then I turn the first switch back on. On subsequent flights I alternate the first on switch. You would even find a 3 cells pack this way as the servos would be very slow if they worked at all.

I concluded that Red was very correct and the diodes are not needed and only insert at least 6 more failure points.

If you are skeptical, run your own test.

Dan (WB4GUK) Dan Thompson (AMA 32873, EAA 60974, WB4GUK, GROL) remove POST in address for email

I think thi sis true and valid. However the diodes may protect agianst one sort of fialure - and one that has haoppend to me - and that is shorted pack wires. On a fullpcak these normally result in a lot of heat but on a semi-discharged pack, they don't,

The issue is whether he faulty pack will drag the voltage on teh decenbt pack down or not. Most modes of failure won't - as Red points out. Some may.

Whether these, or a diode failure, are more likely, is where the points get moot.

If I were doing a BIG expensive scale project, I think I would run a completely separate battery, receiver, and servo for every surface. i,e. one for each aileron, flap and elevator half, and split the rudder linkage and throttle linkages mechanically somehow.

Experience suggests that a switch is, probably more so than a pack, the most likely thing to go.

Visiting ny grey haired very old mum trofday, and one light she rarely uses wouldn't work - tried three bulbs. Eventually flicking the 50 year old switch up and down a few times caused illumination.

She thinks I have magic electrical fingers :-)