Weyfly Posted December 14, 2012 Share Posted December 14, 2012 With the 8 cell Nimh 2100 mah (4years old) battery showing signs of failing, I now have a Lipo 3S 2650mah, I fitted two diodes (in line) in the power supply (battery lead side) and stepped the voltage down from 11.5v (part charged) to 10.5v, when attached to the TX (9X2) and switched on the voltage shows up as 10.0v on screen, the battery is showing 11.4v via its balancing lead after 1.5 hr. After 1.5 hours we now have 9.9V showing on the screen, I'll leave it switched on and see how long it will last. It is a dedicated 'TX' Lipo battery. The diodes are slightly warm, no heat elsewhere. The battery also supplies the FR Sky telementry screen. Sound OK? Quote Link to comment Share on other sites More sharing options...
IanN Posted December 14, 2012 Share Posted December 14, 2012 There's a piece in the latest BMFA news re use of "alternative" TX batteries that you might find useful Quote Link to comment Share on other sites More sharing options...
Brian Hammond Posted December 14, 2012 Share Posted December 14, 2012 I wonder what the insurance cover would be as you have modified the equipment? Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted December 14, 2012 Share Posted December 14, 2012 Posted by Brian Hammond on 14/12/2012 15:22:50: I wonder what the insurance cover would be as you have modified the equipment? i would say - if the claim was for a fair old amount of dosh....'you wouldn't be covered'.. ken anderson ne..1 ...legal dept/north east Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 14, 2012 Share Posted December 14, 2012 See how long it continues to transmit a strong signal after the low-battery alarm sounds. Quote Link to comment Share on other sites More sharing options...
Weyfly Posted December 14, 2012 Author Share Posted December 14, 2012 After 4 hours the on-screen rate is 9.6v and from the balance plug is 11.1v. As for 'modifying equipment', that may well refer to every part of a model and we as builders of these aircraft are not renowed for leaving everything as standard are we? Even a different battery size or a different plug could be 'modifying', a different servo, where does it end? Should a modeller be certfied to a standard for building aircraft and all the parts built to a standard? or would common sense prevail? Quote Link to comment Share on other sites More sharing options...
Weyfly Posted December 14, 2012 Author Share Posted December 14, 2012 Yes, I did read the BMFA news about power supplies after I'd ordered the battery. John-Its been on for 10 hours now and we're down to 9.1v on screen and via the balance lead its 10.7v, the low battery warning has come on twice now with about 15 minutes in between and still transmitting without any problems. The alarm has just gone off for a 3rd time, still at 9.1v on screen, time to switch off. Quote Link to comment Share on other sites More sharing options...
Weyfly Posted December 15, 2012 Author Share Posted December 15, 2012 Update-the TX has been on for about 12 hours, the on screen figure is 8.8v, the 'low batt' warning has been on for over an hour and its still transmitting. I have had a Nimh battery failure before with a Spektrum DX6 that was was very sudden, from power to low battery warning to shut off in a few seconds, no time to do anything but stare as the screen figures dissapeared and my glider went down. Is this test with the Lipo a reasonable one? At a guesstimate this battery will give me, on a full charge, many hours (15+?) with a very gradual fall off and hours to land. Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 15, 2012 Share Posted December 15, 2012 Pretty much the same as I get with an Instant low-self-discharge NiMH pack from VAPEXTECH (the green ones, not the red). £12.50 delivered, with a Futaba plug on, and no worries about how to charge: in the Tx using the Futaba wall charger. Why make it complicated? Edited By John Cole on 15/12/2012 11:25:48 Quote Link to comment Share on other sites More sharing options...
Daithi O Buitigh Posted December 15, 2012 Share Posted December 15, 2012 As almost every transmitter actualy operates on 5 volts, fitting a 3S Lipo is simply going to produce heat as the regulator struggles with the higher supply. Far better to use a LiFe pack instead of Lipo (the self-discharge rate is far lower and it doesn't have the 'over-srain' problems of Lipos) Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted December 15, 2012 Share Posted December 15, 2012 Posted by John Cole on 15/12/2012 11:23:41: Pretty much the same as I get with an Instant low-self-discharge NiMH pack from VAPEXTECH (the green ones, not the red.............................. Why make it complicated? Edited By John Cole on 15/12/2012 11:25:48 What's complicated? You buy a Tx LiPo, charge it, put it in your transmitter and go fly. Most modern NiMh packs. low discharge or not, need something more than a wallwart charger to get up into the right charge current range. My experiences are that Lixx technology has far lower self discharge than LSD Nixx. If I were buying a new battery now I'd follow DOB's advice and go LiFe. I don't know what regulator chips are used in transmitters, if they are switched mode the input voltage is irrelavent within reason, if linear there will be a small increase in heat dissipation using Lipo compared to LiFe or Nixx but my Futaba FF9 has been coping with it ok. Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 15, 2012 Share Posted December 15, 2012 I was referring to what WeyFly had done as complicated. WeyFly: buy a LiPo pack and fit a charging plug. In parallel fit an output lead including 2 in-line sillicon diodes. Terminate with a Tx plug. Test to establish in-use voltages and correct operation (and no overheating or blowing of the output stage), test the reliability of the Tx low-voltage alarm and the remaining useful safe period of use after this sounds. Remove LiPo from Tx every time for charging and re-fit (or risk the Tx if the LiPo catches fiire if overcharged - no overcharge-prevention circuitry fitted as you would find in e.g. a laptop battery/power pack). Me: buy NiMH pack pre-fitted with Tx plug and put in Tx. Charge after use with normal Futaba wall charger, and only recharge before use after a long gap between sessions (sevral weeks). Can't charge a low-self-discharge pack with a wall charger? Rubbish. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted December 15, 2012 Share Posted December 15, 2012 The wall chargers I've seen have been around 70mA, at that rate it would take an awful long time to charge a 2000mAHr pack. Not impossible but why() when you can charge in an hour or so with a delta peak unit? I see your other point and I agree Weyfly has gone a little beyond what most of us would consider reasonable when replacing a battery but a) it's an interesting academic excercise that raises a question or two about the BMFA advice (how unusual) b) now he has done the tests others don't have to c) it's a hobby, a pastime. Some like to fly, some to build, some to experiment. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted December 15, 2012 Share Posted December 15, 2012 Dare I suggest using a 3S LiFE pack in the Transmitter......? Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 15, 2012 Share Posted December 15, 2012 When you charge a battery after use, all you do is replace what you take out, plus a factor for the charge/discharge inefficiency. The capacity is totally irrelevant. My Futaba Tx draws 250 mA and my charger supplies 70 mA constant current. I nowadays fly only electric so flying time = Tx-on time. For a typical example: 3 flights of 15-20 minutes = 1 hour Tx on-time. So it recharges in 4 hours to 11.3 V on the Tx display ( 4 * 70 = 280, which allows for the inefficiency). Or, as it's a low-constant-current charger I can safely leave it on all night. What could be simpler, cheaper or safer? Quote Link to comment Share on other sites More sharing options...
Weyfly Posted December 15, 2012 Author Share Posted December 15, 2012 John, I have done as you said, I'm only copying someone else. I think this was successful and I have now ordered a second battery (Life 3S 1800mah) and a charger for car use but since the main battery only goes between 12.2v and 10.5v it doesn't take long to charge, its a 1C battery. Fast charging the low self discharge batteries, even occasionally, doesn't do much for them, mine was a Model Power one, I see the problem as mine rather than makers/distributors and it was over four years old so lots of use. Quote Link to comment Share on other sites More sharing options...
Tony Smith 7 Posted December 17, 2012 Share Posted December 17, 2012 Posted by Weyfly on 15/12/2012 11:16:03: Update-the TX has been on for about 12 hours, the on screen figure is 8.8v, the 'low batt' warning has been on for over an hour and its still transmitting. Nice testing. I don't see the need for 3S, but I guess that depends on the transmitter. I should do similar testing with my set which uses 2 18650 Li?? cells. What transmitter is yours? Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted December 17, 2012 Share Posted December 17, 2012 Posted by Weyfly on 14/12/2012 14:48:45: With the 8 cell Nimh 2100 mah (4years old) battery showing signs of failing, I now have a Lipo 3S 2650mah, I fitted two diodes (in line) in the power supply (battery lead side) and stepped the voltage down from 11.5v (part charged) to 10.5v, when attached to the TX (9X2) and switched on the voltage shows up as 10.0v on screen, the battery is showing 11.4v via its balancing lead after 1.5 hr. After 1.5 hours we now have 9.9V showing on the screen, I'll leave it switched on and see how long it will last. It is a dedicated 'TX' Lipo battery. The diodes are slightly warm, no heat elsewhere. The battery also supplies the FR Sky telementry screen. Sound OK? Sounds ok to me. Surprised that the diodes are warm, as the current draw is low. What current rating are they for? Or even the part number, if you have it? Be aware that the voltage drop can change with temperature (infact often diodes are used as simple thermometers), but that should be small enough not cause a significant problem. Along as you know roughly the voltage on the transmitter LCD to know when they need charging you'll be alright. This mod has been done plenty of times around the world. In regards to the insurance being invalid, I don't want to go round this argument again and again (as always seems to be the case with insurance), but it's a load of cobblers. Firstly, putting a non-OEM battery in would be a modification - so those putting in low self discharge batterys are modifying their transmitter. Especially as LSD discharge curves are different to ordinary NiMh batteries, so the low battery warning voltages will be different. Secondly, insurance protects against accidents that you as a person cause - I don't remember seeing any exclusions in the insurance documents to say that modifications would render the insurance invalid... Of course if you made a modification that was negligent (i.e. if you knew a repair/modification had an intermittent fault but you flew anyway), then you could find it invalid. In fact I think the insurance does state it doesn't cover negligence and intentional damage. In a small claim, I can't imagine an insurance company would investigate too much. A big claim, then it'd probably be for some expensive lawyers to debate and the courts to decide anyway... There is no way I can see, that putting two diodes to drop the voltage of a LiPo for a transmitter could be seen as negligent behaviour. The only contributing way to an accident would be if a diode failed (unlikely - the transmitter itself is more likely to fail as a whole), a solder joint failed (depends on the quality of the solder joint + the person soldering it) or the user not aware that the battery is flat (i.e. lack of alarm, etc). Si. Quote Link to comment Share on other sites More sharing options...
Greybeard Posted December 17, 2012 Share Posted December 17, 2012 What level of voltage readings should one expect from a Ni-MH tx battery with a nominal 9.6 volt rating. Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 17, 2012 Share Posted December 17, 2012 Fully charged, I see 11.3 or 11.4 volts on my Futaba - on load. Quote Link to comment Share on other sites More sharing options...
Greybeard Posted December 17, 2012 Share Posted December 17, 2012 Posted by John Cole on 17/12/2012 16:13:29: Fully charged, I see 11.3 or 11.4 volts on my Futaba - on load. and how long is that maintained for and what would you consider to be the safe minimum battery voltage? Quote Link to comment Share on other sites More sharing options...
John Cole Posted December 17, 2012 Share Posted December 17, 2012 I charge AFTER flying and ony bother to check the night before I go if it's more than a couple of weeks since I last flew (I use LSD cells, see above). I only then bother to re-charge if it's significantly below 11.0 volts. Minimum safe? Totally academic as far as I'm concerned. But this is what it says in the Futaba manual. The Low Voltage Alarm sounds at 8.5 volts. SUGGESTED GUIDELINES 9.4 Volts – No more flying until recharge. 8.9 Volts – Land as soon as safely possible. 8.5 Volts – Emergency – Land immediately! Quote Link to comment Share on other sites More sharing options...
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