wayne young Posted November 22, 2013 Share Posted November 22, 2013 Hi, just brought myself the seagull yak54 and am going to put the roto 25cc into it. I want to use a li-fe battery to supply power to my futaba receiver at 6v, so My servos run at 6v .Do I need a regulator and if so want one.. And second people at my field are staring to use 2 batteries one as a back up. Now do you need to use a power box or again is there a regulator out there that excepts two li-fes. Last question people have told me that when setting up 3d planes to place the fuel tank on the c of g line is this really necessary as I am only just starting out in 3d flying. Can I just place the tank in the same place as glow.. Many thanks people for yr comments.. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22, 2013 Share Posted November 22, 2013 Simple solution to your requirements is a suitably rated diode in series with each battery. Put them in the positive leads from the switches to the receiver and charging will be unaffected. That gives you protection against a short circuited cell dropping the voltage, proper dual redundancy of the power supply and drops the battery voltage by @ 0.7 volts so you have a nominal 5.9v supply. Edited By Martin Harris on 22/11/2013 17:08:19 Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted November 22, 2013 Share Posted November 22, 2013 Start with the CoG in the correct location if you're not experienced flying 3D style. As you get confident in the airframe, then start moving the CoG back. Tank is useful in the CoG location as the CoG changes a lot less as the fuel drains. As an aircraft set up in a 3D manor will have the CoG as far back as is possible, removing fuel from the front, moving the CoG back further won't be good... For a 25CC, I personally don't think you need to bother with the extra weight of a dual battery setup. If you do, then I'd just connect them in parallel together. For Li-Fe packs, the voltage discharge curve is very flat and discharges around 6.6v, so you don't need a regulator. Also the maximum full-charged voltage of a Li-Fe pack is less than a 5Cell Ni-Mh pack too. Also 6.6V will give you faster responses than the servos being ran on 5.9V. Watch out for the flat discharge curve on Li-Fe. You can't accurately determine the remaining flying time on voltage. You need to time your flights and then recharge the pack, seeing how many mAh go back in after x minutes. Si. Quote Link to comment Share on other sites More sharing options...
wayne young Posted November 22, 2013 Author Share Posted November 22, 2013 Hi si, many thanks for that so would you recommend just using a standard Niamh battery for the receiver. I do want to run 6v though.. Have been told that futaba receivers sometimes don't like more than 6v being run through them so that's why I thought about a regulator.. May be I am thinking to much about this and should just stay as normal.. I think I will place the tank on the c of g then ,so when I do start moving the c of g back ,I won't have to many troubles from loosing weight when the tank drains.. Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 27, 2013 Share Posted November 27, 2013 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
stu knowles Posted November 27, 2013 Share Posted November 27, 2013 I've recently started using LiFe batteries and pondered a similar question. I checked the voltage of a five cell 'C' NmH and the LiFe and they were 6.7 and 6.6 volts respectively. On that basis I haven't been using a regulator. I tend to go with two RX batteries into two standard switches into the RX, one into the battery port and one into a spare servo port. No diodes, backers or any other complications. I like the added security although I take your point about there only being one battery in the TX. I know that there are different arguments about the need for diodes and backers but I prefer the simple, minimum part count approach. stu k Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 27, 2013 Share Posted November 27, 2013 I'm with you on that Stu although as fresh off charge LiFe batteries can go above 3.5V I do sometimes use diodes primarily as voltage droppers - but I'm quite happy to do without with the right servos. Percy - I think the difference is that (unless you have telemetry) only the transmitter will alert you to a failing battery - either through lack of charge or incipient failure. I have experienced the loss of a cell in flight both personally and as a witness on transmitter packs - luckily the typical failure mode of NiCd cells is to go short circuit - not sure about more modern "alternatives". I have also lost a receiver pack cell during flight (on a single pack model) but luckily my telemetry alerted me to that one. Transmitters should operate in a less hostile environment than receivers - batteries and connections not being subject to vibration, proximity to exhaust fumes and fuel, faulty servo loads etc. so lead an easier life and in extreme circumstances failure should lead to the operation of fail-safe (in almost all equipment these days) which should at least prevent a full throttle flyaway which receiver battery failure could result in - although the provision of a dual supply wouldn't be a bad idea! Edited By Martin Harris on 27/11/2013 10:04:18 Quote Link to comment Share on other sites More sharing options...
crispin church Posted November 28, 2013 Share Posted November 28, 2013 been using life / a123 for years without any regulator using in transmitter as well now as mine only take 4cell unless you are flying for the whole day 1 battery should be fine if you need to add lead then use 2 battery one on engine 1 for rx Quote Link to comment Share on other sites More sharing options...
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