PatMc Posted July 30, 2016 Share Posted July 30, 2016 Shaunie, I too have a long time electronics background. I'm well aware of the shortcomings of parallel batteries in some applications. IMO in this particular application diodes would add little if any value & introduce a potential source of failure that outweighs any practical benefit. Quote Link to comment Share on other sites More sharing options...
cymaz Posted July 31, 2016 Share Posted July 31, 2016 You could have something like THIS. Automatic redundancy. Quote Link to comment Share on other sites More sharing options...
.. Posted July 31, 2016 Share Posted July 31, 2016 Posted by trebor on 30/07/2016 22:44:50: Now what do I do ? Leave it as it is or change it Personally Bob I would strip it out & revert back to one Batt and switch, Simplicity is your friend in my experience and it will save on weight too. What Seagull edge is it ? Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted July 31, 2016 Share Posted July 31, 2016 Having lost one model when one cell in a pack failed and another when a switch failed I would say that in any model capable of carrying two batteries, that is the way to go. Definitely two switches are better than one whether using one or two batteries, and in my opinion diodes are optional. Power supplies are one area where an excess simplicity can be your enemy, sorry Justin. edit following Bob's next post - for a model of that size I most certainly would want more than one battery and one switch! Edited By Bob Cotsford on 31/07/2016 10:12:29 Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 It was a bargain, I could not resist it for £110 with a 150 Laser **LINK**. Mind you I ended up stripping it down due to things I didn't like the look of. Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 31, 2016 Share Posted July 31, 2016 I am with Justin on this one. Keep things as simple as you can and go for it Given that the model is 2nd hand I would always treat its power system with suspicion. You do not know the age of the batteries, how long they sat in a drawer before they were used and if they have been left to go stone dead flat a few times then recharged at 2amps until the cells began to sizzle. At the very least those packs should be cycled, left a few weeks, and then cycled again to get a feel for how well they hang on to their claimed capacity, but if it were me I would buy a new switch (futaba, jr etc not a cheap one) and a new good quality 6v battery. If you are using a lot of digital servos in that Edge then I would use a 3000mah 6v sub C cell battery pack through a futaba heavy duty rx switch. This is the setup I use on all of my 80'' warbirds and it will be more than enough for the edge. I use the sub c packs as their voltage is more constant when under load from the servos as the cells can deliver more current than AA cells. Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 All the servos are Futaba s3001 so nothing special. Although I shouldn't need anything special as I won't be 3D flying . Some of the wiring has been joined together in a lot of places which is the reason I've pulled it out. Quote Link to comment Share on other sites More sharing options...
cymaz Posted July 31, 2016 Share Posted July 31, 2016 Posted by trebor on 31/07/2016 10:38:03: Some of the wiring has been joined together in a lot of places which is the reason I've pulled it out. Resist the temptation of keeping it for spares.....throw now Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 I can say I'm tempted, but my spares box is full of junk already Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted July 31, 2016 Share Posted July 31, 2016 Personally, I'm a great believer in simplicity when it comes to battery packs. Nearly ever case of strange radio behaviour that I've come across has gone away as soon as battery backers / voltage regulators / multiple packs were replaced by a good single pack of adequate capacity and a good quality switch harness. Keep it simple, use good quality components, and reliability will follow! -- Pete Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 31, 2016 Share Posted July 31, 2016 Futaba 3001's are not that powerful and to my mind are marginal for an aerobatic model of that size. I have flown 70 inch warbirds on them but the control loads are so much lower as the surfaces and deflections are much smaller. If you don't change them then a 6v 2000mah pack will be fine, and as cymaz right says, bin anything you aren't sure of or, in the case of a servo, put a knot in the lead so you know its suspect. I keep my suspect servos as I can steal gears and other parts from them to make a good servo somewhere down the line. I also fit them in my 1/8 scale nitro car as the vibration kills servos pretty quickly anyway and the worst that can happen is it will drive into a wall Quote Link to comment Share on other sites More sharing options...
.. Posted July 31, 2016 Share Posted July 31, 2016 Posted by trebor on 31/07/2016 10:10:42: It was a bargain, I could not resist it for £110 with a 150 Laser **LINK**. Mind you I ended up stripping it down due to things I didn't like the look of. I saw that one , where are you hiding them all mate ? Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 Spare bedroom, it's a good job the kids have flown the nest Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 Some good news the aileron servos are Futaba s3010 which are rated more than s3001 so I might spend more money on the elevator and rudder servos while I'm at it. Do you think a full set of s3010,s would be better ? Elevator has 2 servos and rudder is on a push pull wire with 1 servo. Quote Link to comment Share on other sites More sharing options...
iqon Posted July 31, 2016 Share Posted July 31, 2016 Please note that if you remove the battery it will / may alter the cg. I have the edge with a church roof up front ( and only the 1 battery for RX ) Quote Link to comment Share on other sites More sharing options...
trebor Posted July 31, 2016 Author Share Posted July 31, 2016 I think your correct, the engine mount on mine is made of pure steel. Solid angle and square bar which I've mounted on new hard rubber joints. It should save on lead. Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 31, 2016 Share Posted July 31, 2016 Be careful with metal mounts trebor, especially rubber damped ones. We don't recommend them because they do a decent job of protecting the airframe, but it can often cause the engine to vibrate massively which will damage it. As for servos, 3010's would be great and more than sufficient. if you use them all round I would suggest you go for the sub c 6v pack Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 31, 2016 Share Posted July 31, 2016 Posted by Peter Christy on 31/07/2016 10:56:12: Personally, I'm a great believer in simplicity when it comes to battery packs. Nearly ever case of strange radio behaviour that I've come across has gone away as soon as battery backers / voltage regulators / multiple packs were replaced by a good single pack of adequate capacity and a good quality switch harness. Keep it simple, use good quality components, and reliability will follow! -- Pete I'm with you on the backers and regulators but I can see little reason why a redundant battery pack/switch won't increase reliability by a massive factor over any possible negative factor. I'm not sure, but don't the LMA (i.e. the CAA designated authority) insist on power redundancy for large models? Quote Link to comment Share on other sites More sharing options...
cymaz Posted July 31, 2016 Share Posted July 31, 2016 I have a plane weighing in at 18.5 kg. As an LMA member I ask a couple of inspectors for some advice, even though it's under the 20kg limit. They advised twin battery for the Rx. Twin ailerons and a few other things. I invested in PowerBox Professional. Edited By cymaz on 31/07/2016 20:27:20 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted August 1, 2016 Share Posted August 1, 2016 I'm a bit late to this, but, on the dual nicd/nimh pack thing: "Their low internal resistance and negative voltage characteristic at full charge can cause thermal runaway situations." I'm with shaunie - parallel nicd/nimh cells or packs are a complete no for this reason. A fully charged nimh pack in 100% working order, hot off the charger, would be at great risk of starting to be charged further by a second pack connected in parallel. Nothing has to fail to get into this situation. A switch by itself isn't enough resistance to prevent this. The addition of a diode fixes this problem and prevents any cross (dis)charging. The chances of the diode failing are miniscule. Lipos are a different kettle of fish of course, parallel them up no problem. Edited By SuperNash on 01/08/2016 11:54:37 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted August 1, 2016 Share Posted August 1, 2016 Forgive me if I'm wrong here, but don't LiPos have a much smaller internal resistance than nickel cells at all states of charge/temperature? This seems to totally negate your argument! Perhaps there's something I've missed regarding "negative voltage characteristic" - if so, please explain how this affects the situation. Cross charging is a minor consideration - even connecting a fully charged pack of nickel cells to a discharged one will only result in minor energy transfer in the order of a few mA. I really can't see why a freshly charged pack would receive charge from an existing pack paralleled to it - I would have thought that if anything it wold be the other way round...and of a negligible magnitude anyway. By all means, add a diode if you feel the need but to my mind, it adds two joints and a (admittedly very reliable, if specified correctly) component to the possible chain of failure. Edited By Martin Harris on 01/08/2016 12:06:14 Quote Link to comment Share on other sites More sharing options...
Shaunie Posted August 1, 2016 Share Posted August 1, 2016 You just need to think about the charging methods used for different battery chemistries. Lead acids. Float charge to a finite voltage. Current tapers towards zero, charging can be continued indefinitely with no detrimental effects as long as the float charge voltage is not exceeded. Suitable for parallel operation. Lithium Polymer. Float charge to a finite voltage. Current tapers towards zero, Charging can be continued indefinitely with no detrimental effects as long as the float charge voltage is not exceeded. Suitable for parallel operation. Nickel Cadmium/ Nickel Metal hydride. Constant current charge at either 1/10C max for 16Hrs or fast charge until temperature rise or negative Delta V signifies charge must be terminated. If charging is not terminated promptly then cell destruction is most likely to occur. As the cell reaches full charge the terminal voltage actually dips slightly. Float charging cannot be used as the cell will continue to draw current until destruction. Not suitable for parallel operation. As Supernash says "A fully charged nimh pack in 100% working order, hot off the charger, would be at great risk of starting to be charged further by a second pack connected in parallel. Nothing has to fail to get into this situation." The warm fully charged pack will have a lower terminal voltage than a the not so freshly charged one and a circulating current will occur. Likewise with two cells permanently in parallel one may peak before the other, it's voltage will dip and a strong circulating current will pass between the cells, with one getting hotter and hotter until it self destructs. In short it's not the internal resistance that is the problem it is the voltage characteristic. On balance I would prefer to see diodes, when we look at the complexity of modern radio installations are two diodes and four joints really that much of a problem? I think however, that normal length switch harnesses using a switch for each pack would probably be Ok. as the circuit resistance between the packs would be sufficient to limit any circulating currents. Shaunie. Edited By Shaunie on 01/08/2016 12:57:30 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted August 1, 2016 Share Posted August 1, 2016 That's a better explanation that I would have given Shaunie! "Perhaps there's something I've missed regarding "negative voltage characteristic" - if so, please explain how this affects the situation." The only thing I'd add is that the negative voltage characteristic means, if you continue to charge a fully charged nicad/nimh, the voltage continues to drop; that means that if pack A starts feeding into pack B, the situation becomes worse, pack B just keeps dropping voltage which makes pack A feed more and more into pack B. So pack B becomes more charged, and its voltage drops, pack A feeds even more current to pack B, and so on an so on until pack B goes pop. Edited By SuperNash on 01/08/2016 13:27:17 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted August 1, 2016 Share Posted August 1, 2016 Posted by Shaunie on 01/08/2016 12:56:02: Nickel Cadmium/ Nickel Metal hydride. Constant current charge at either 1/10C max for 16Hrs or fast charge until temperature rise or negative Delta V signifies charge must be terminated. If charging is not terminated promptly then cell destruction is most likely to occur. As the cell reaches full charge the terminal voltage actually dips slightly. Float charging cannot be used as the cell will continue to draw current until destruction. Not suitable for parallel operation. As Supernash says "A fully charged nimh pack in 100% working order, hot off the charger, would be at great risk of starting to be charged further by a second pack connected in parallel. Nothing has to fail to get into this situation." The warm fully charged pack will have a lower terminal voltage than a the not so freshly charged one and a circulating current will occur. Likewise with two cells permanently in parallel one may peak before the other, it's voltage will dip and a strong circulating current will pass between the cells, with one getting hotter and hotter until it self destructs. While there is a small dip (@5mV?) on charge termination I doubt that a freshly charged pack will be at a significantly lower voltage than one previously charged but whatever, the current will be very low. Continuing to charge a NiMH pack at low current is not best practice but will not lead to thermal runaway as far as I've always been lead to believe. I am certainly NOT advocating parallel charging which is unacceptable. Quote Link to comment Share on other sites More sharing options...
Shaunie Posted August 1, 2016 Share Posted August 1, 2016 Martin, Agreed the dip is very low. But what happens in continuous high current overcharging? I haven't seen Manufacturers graphs for that. I am not saying a problem will occur only that it may occur. My statement about terminating promptly was only applicable to fast charging and not trickle charging, in this case it only shortens their life, thermal runaway will not occur. Perhaps I should have put it in two separate sentences, sorry, clumsy grammar/poor punctuation. Nevertheless it was something the manufacturers put in their data sheets and so is worth knowing. Shaunie. Quote Link to comment Share on other sites More sharing options...
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