Michael Dearden Posted October 5, 2008 Share Posted October 5, 2008 Several comments on this forum, and in the literature supplied with my new batteries, is to make sure you don't over discharge the battery - take it below "lowest voltage".My new batteries are Tornado Professional 3300mAh 11.1v 22C batteries and the literature states a lowest voltage of 7.5 volts, motor running and 9 volts motor off. How can one tell when this point is approaching while flying? Is there some gizmo one can put in the circuit to protect the battery? They are quite expensive and I'd hate to damage them on the first flight! Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted October 5, 2008 Share Posted October 5, 2008 Most ESC's have this feature built in, but the best way is to set a timer to make sure you land before you take your battery this low. Quote Link to comment Share on other sites More sharing options...
stuey Posted October 5, 2008 Share Posted October 5, 2008 Just posted about this on the Kong thread Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 5, 2008 Share Posted October 5, 2008 Best practice is 3V per cell off load, and I guess ideally the same inder load - however in real life, discharging a LiPo cell down to 2.75V UNDER LOAD is quite usual, and I have done this with the vast majority of my 100+ packs over the last 5 yeras or so, and some of them are still going strong!As Frank states.... the correct ESC will deploy what is known as either a PCO or LVC circuit to chop power to the motor as these levels are reached....and of course in your case of 3 cells - that is 2.5V per cell under load. ( which I personally think is way too low for long cell life ).PCO = Power Cut Off LVC = Low Voltage Cutoff.Frank is also completely right in the recommendation to use a timer and land your model BEFORE this LV is reached. I normally adopt the following practice with every new setup.Maiden flight - Fully charged pack - Timer set to zero (count up mode ) Launch and fly. Keep model close to landing area during the whole flight. Fly until the motor indicates a lowering of power by change of sound /performance STOP TIMER. LAND ASAP.Check elapsed time. Deduct 30 seconds and set this in your count down timer alarm.All future flights .....land when timer tells you too... most will start sounding off 30 secs before end. Do NOT push your luck and chance "one more circuit".PS please dont cross post Michael Quote Link to comment Share on other sites More sharing options...
Bert Posted October 5, 2008 Share Posted October 5, 2008 With most fixed-wing models, if you land as soon as the power starts to 'sag' you won't have any problems. I say 'most' because with very lightweight models like my IFO it's not so readily apparent when the power drops off.It's quite noticeable with my Formosa (the original one) when the power goes and it's always above the lower voltage limit, so there's no rush to get down. The same goes for my Shocky, Bonnie, and all the other electric 'planes I have. Myself and the two blokes I fly with have been doing this for years and haven't killed any packs yet. We have worn a few out though! I bought one of those FMA cut-out things a few years'ago and I've never used it.HTH Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted October 5, 2008 Share Posted October 5, 2008 I think it depends on the plane with my E-Flite Beaver most of the flight is at half throttle or so, I only use about 3/4 for take off, so you don't see the high load on the Lipo's.What i do is measure the full throttle amps, set the timer to give about 90% of the mah out of the battery at this setting and then adjust the timer after a few flights and I've measured how many mah have gone back in to give me an idea of the actual mah used per min.I started with the timer set at 6 mins on my Beaver and its now set at 11 mins and uses about 80% of the mah available. Whereas my Fantom started at 6 mins and has stopped there Quote Link to comment Share on other sites More sharing options...
Michael Dearden Posted October 5, 2008 Author Share Posted October 5, 2008 Firstly - sorry Timbo for the cross post but I didn't get any replies so thought maybe people had finished reading that post.Many thanks gents for all the great info. I think my plan is to fully charge a lipo, install it and install my wattmeter between it and the ESC. I will then secure the plane and then run the motor and start a timer until I get to that LV number. That way I don't have to do a panic landing!Not fully familliar with all this electric stuff as you probably gathered - always flown gliders! My new build is the JP Tiger Moth 30. All balsa and wood and, having now just about built it am a bit nervous about sending it up! Only ever flown my foam Gemini in this electric game! Anybody got one of these? Do they fly nice and easy? Quote Link to comment Share on other sites More sharing options...
Michael Dearden Posted October 6, 2008 Author Share Posted October 6, 2008 Further to my last, my new batteries appear to be fully charged, each cell being around 3.7v. Do these Lipos come ready charged or should I always charge them first? Is there any harm in "topping up" an already charged battery?Just received my magnetic prop ballancer today - cleaver piece of kit! Quote Link to comment Share on other sites More sharing options...
stuey Posted October 6, 2008 Share Posted October 6, 2008 A fully charged 3s pack will be 12.6v, I believe lipo packs normally arrive about half charged which would be about 3.7-3.8v per cell. Once a pack is fully charged i dont think it needs or should be topped up. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 6, 2008 Share Posted October 6, 2008 They do have a VERY low self discharge rate and will normally be fine after several weeks or even months. However, in somne applications like power hungry EDFs I do "top em up" just prior to flight, and try to keep them warm also - the performance ( as with all batteries ) is markedly down in the cold weather.Topping up is only safe to do providing your charger is intelligent enough to handle them. LiPos are charged using CCCV methods - and this means "constant current then constant voltage" after a pre-detrermined voltage level has been reached. Some chargers just force pump a mandatory fixed charge rate into a pack for the first minute or so - to help it identify the pack configuration. If the battery concerned is only very slightly down from "full" then this could lead to overcharging which is very bad for the cells. Quote Link to comment Share on other sites More sharing options...
Michael Dearden Posted October 6, 2008 Author Share Posted October 6, 2008 OK gents. I have also just bought the Elysium LX60B Pro charger so think I'm on a winner. This has to be "intelligentt" enough to make sure it doesn't overcharge I hope but just to be safe I'll run the motor for a while on the new batteries until I get to the low voltage level and then give them a full charge.Thanks again gents.Anybody want to come and fly my Tiger for the first time???? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 6, 2008 Share Posted October 6, 2008 me pleeeease - I love maiden flights !! Quote Link to comment Share on other sites More sharing options...
Michael Dearden Posted October 6, 2008 Author Share Posted October 6, 2008 Don't know where you are Timbo but you're more than welcome! Im in Axbridge, Somerset! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 6, 2008 Share Posted October 6, 2008 Well it is easy enough to find peoples location when they have put it into their profile page.... (as I have)Too far for me Mike - sorry. Quote Link to comment Share on other sites More sharing options...
Nick Farrow Posted October 8, 2008 Share Posted October 8, 2008 One thing I have noticed is that my ripmax cheap and cheerful lipo charger (well it is red) will not charge my lipos if I fly until the esc LVC kicks in. This happens on all of my 3 packs (3S) of different ages on different planes (esc's). It seems that it needs a cell voltage of 3.05 or above before it will take the pack. Once the LVC has kicked in the cells are about 2.9v when I get home, and so I have to 'pull up' the packs with a (large) resistor and a 12v battery for 10 minutes or so. The charger does do a good job of charging and it reliable and is fine if I stop when the power sags. Is this behaviour common or just the product of spending £20 on a charger?Thanksnick Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 8, 2008 Share Posted October 8, 2008 The latter - most decent chargers will send in a "dumb" fixed figure output charge for around 30 secs or so, to "wake up "any such packs....then it can read the battery more correctly. You could also try telling it that its a 2cell pack for a minute or two, then stop and reset to 3s. Quote Link to comment Share on other sites More sharing options...
Always broke Posted October 9, 2008 Share Posted October 9, 2008 No worries about the test flight on the JP 30 Tiger Moth. It will fly a dream. Mine is on a 4s pack , needs a bit of rudder on take off and also likes the rudder in the turns. Don't have to much movement and you will be fine.It will fly lovely and slow.Keep the CG foward as well. Great model.Going to get the bigger one next. Using a timer is the best way to go with electric flight. Just keep an eye on the cell voltages as the pack gets older as it will not hold its voltage so well so you need to shorten your flight ,and adjust your timer accordingly. Quote Link to comment Share on other sites More sharing options...
MThemadhatter Posted October 12, 2008 Share Posted October 12, 2008 In answer to your question about low voltage protection another approach is to use an alarm. I use the custom idea HRPOLY-X. This has an led and more importantly a little speaker that starts beeping when you approach whatever voltage you set it to. The closer you get the faster it beeps until it sounds constantly. I set it at 9.9V on heli so I have time to land before I get anywhere near the 3.4v cut off on my esc. Having the esc pulse or cut the throttle to 50% on a heli is, er interesting. Quote Link to comment Share on other sites More sharing options...
Always broke Posted October 12, 2008 Share Posted October 12, 2008 That sounds like a good bit of kit. Have you got a link to it Quote Link to comment Share on other sites More sharing options...
MThemadhatter Posted October 12, 2008 Share Posted October 12, 2008 They can be bought here Custom Idea it is very small and neat you can see the size on the heli. Well worth the money for peice of mind. Lets you only use 80% of the battery for long life with out using the esc cut off or timer. Quote Link to comment Share on other sites More sharing options...
Michael Dearden Posted October 14, 2008 Author Share Posted October 14, 2008 Thanks Always for the reassurance on the Moths performance, also the advice on a bit of rudder to aid the turns. I'll program the Spektrum for that.That is an interesting little gizmo Hatter. Where do they plug in? One of the spare servo ports? Doesn't really matter as I've already ordered one! Quote Link to comment Share on other sites More sharing options...
MThemadhatter Posted October 14, 2008 Share Posted October 14, 2008 The go on the esc side of the battery conector, that way its measuring the voltage of battery. Two minute job to resolder the connections. Quote Link to comment Share on other sites More sharing options...
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