Steve_Wright Posted July 20, 2014 Share Posted July 20, 2014 Nearly had an issue today with my flightpack in the travelair. Its about 8 months old but not had much use, only used to setup the radio and a hours running in engines tops. Gave it a slow charge overnight & went to the field. Range checked okay, have a 3 green/amber/red LED battery check onboard and was on the highest green led. Went to start the engine & the receiver started dropping comms to the Tx, then i watched as the battery monitor counted down the lights to red in about 5 seconds then nothing. Have checked the battery & it is showing less than 1v (its a 6v aa flat pack type). Is this normal death of a NiMh battery? Or should I worry about the switch. The battery didn't overheat so doesn't seem to be a dead short anywhere. Needless to say the 3 similar packs have all gone into the recycling and new Overlander packs have been ordered. Quote Link to comment Share on other sites More sharing options...
John E ( Puffin Models ) Posted July 20, 2014 Share Posted July 20, 2014 I always replace mine as the capacity goes down - normally after a couple of years use. What I am wary of is "consumer cells" being used for receiver batteries - in fact I would NEVER use consumer cells in any model of mine, and always advise others to avoid consumer cells like the plague for receiver battery use. People seem surprised when I say that I ONLY use low resistance electric flight cells for receiver batteries, so if I am using an 650mAh receiver battery, it is capable of a 15A discharge, or even more. What does this mean in reality? It means that the battery is more than capable of carrying the heaviest of servo loads in "normal" models, I suffer absolutely minimal voltage drop, so my servos, even on 4,8V, still operate quickly, and I am unlikely to reach the the 3,2V lower limit of my receivers, even if a cell should go open circuit (normal failure for NiMh cells used at high currents), and because the cells are more than capable of handling the current that I intend to use, the cells are far less likely to fail. Of course, this is only my own opinion.... John Edited By John E ( Puffin Models ) on 20/07/2014 21:41:05 Quote Link to comment Share on other sites More sharing options...
Keith Berriman Posted July 21, 2014 Share Posted July 21, 2014 I had a similar problem recently on a new battery pack, all range checks done etc travelled out to far side of landing strip for last check and wow was I lucky the plane went full power and traversed the pitch at low level and took its undercarriage of and killed the engine. Back in the hanger various testing done and I found 1 of the 4 cells had given up. On No load all was fine when switched on the cell went down in 30 secs Quote Link to comment Share on other sites More sharing options...
Ben B Posted July 21, 2014 Share Posted July 21, 2014 A good way of assessing batteries is doing a high amp discharge cycle every now and again. If you get a reasonable capacity at 2 amps then the pack sounds okay. NiMH batteries can be charged unattended so after a days flying I just stick it on a couple of discharge-charge cycles. Tells me how much capacity I had left after flying, cycles the pack and leaves it charged. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted July 21, 2014 Share Posted July 21, 2014 Use a five cell pack - gives a degree of redundancy if a cell goes down. Nimhs are not as robust as the old Nicads, despite the claims made for them, and are easily damaged by overcharging. Personally, I only slow charge my Nimh RX packs and then only at 1/20 C, also check capacity and voltage drop when on load regularly. So far haven't had a problem, but it's a bit of a faff. Another point that is often overlooked is the voltage drop across the battery wiring and switch harness. With the flimsy wires that we all tend to use in sport models, this can be as much as 500mV when on full load with five servos all operating (I've measured it), so coupled with a failing battery (or a four cell pack) it's not good news. Edited By Cuban8 on 21/07/2014 09:50:19 Quote Link to comment Share on other sites More sharing options...
John Tee Posted July 21, 2014 Share Posted July 21, 2014 John, excuse my ignorance but I've never heard of "consumer cells". Do I assume these to be "normal" Ever Ready or Duracell types? Dry cells? John Edited By John Tee on 21/07/2014 12:13:47 Quote Link to comment Share on other sites More sharing options...
John E ( Puffin Models ) Posted July 24, 2014 Share Posted July 24, 2014 Posted by John Tee on 21/07/2014 12:12:45: John, excuse my ignorance but I've never heard of "consumer cells". Do I assume these to be "normal" Ever Ready or Duracell types? Dry cells? John Edited By John Tee on 21/07/2014 12:13:47 John, I thought "consumer cells" was a term in common use. Perhaps only in the US? Perhaps only in my head! Consumer cell: Cells or battery packs intended for use in "consumer electronics" ie at very low currents, and far less than we use with servos under load. As I said, using cells intended for high current applications, there are all the advantages I mentioned - with none of the disadvanges. Unfortunately, the thickness of plate and insulator needed for high current capability (with the resulting low resistance and reliability) means it is not possible to get a high current capability at 2300mAh into an AA case - or at least I have yet to see one, and I am happy to be proved wrong..... I do have a battery tester (that checks internal resistance and gives the results in percentage efficiency terms), and I am happy to give the results of any cell or battery pack that anyone would like me to test. Quote Link to comment Share on other sites More sharing options...
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