martin collins 1 Posted April 7 Share Posted April 7 I am working on a model with an NGH 38 4 stroke petrol, it will be running separate ignition and RX batteries with an optical kill switch. Not having run an electronic ignition petrol before as all my others are mag engines i would like some advice on the ignition battery, i would like to get up to 5 ten minute flights before a re charge, what capacity battery would i need and are the AA rx packs ok for this or do i need Sub C? Many thanks for any advice from those with experience in this. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7 Share Posted April 7 (edited) I've heard reports of poor performance from capacitor based electronic ignition running on AA cells as they have insufficient capability of delivering energy fast enough. Therefore, whatever the power draw while running, I wouldn't use AA - especially as high capacity versions have relatively high internal resistance which limits power delivery. If your unit is happy at slightly higher voltage, have you considered LiFe? P.S. I've found the following RCXEL instructions. Typical consumption appears to be 650mA so I'd aim at a minimum of 1200mAh so that you'll use less than half the claimed capacity. NOTE THE ADVICE TO USE A REGULATOR OR (MY PREFERENCE) SILICON DIODE TO DROP THE VOLTAGE IF YOU USE LiFe: 2.) Selecting a Power Source I.) 4.8 and 6v volt NiCd/NiMh Packs: The Rcexl Ignition ver 2.0 is rated 4.8 to 6v a max of 7 volts. A 4 cell 4.8v pack and 5 cell 6v pack with a minimum of 800 mAh is fine and creates a hot spark. The Rcexl ignition ver 2.0 runs most efficiently on 4 cell packs and 5 cell 6v pack . Do not use an old Pack!! If it’s not good enough for your receiver, it’s not good enough for your ignition.. If Use 4.8v pack the engines not highest rotational speed, Also use 6V pack II) 6.4 Volt Li-Fe(A123) Packs 2cell Li-Fe(A123) The Volts Max of 7.2 volts. Nominal 6.6 Volts, use a voltage regulator. Or connects one IN4007 diode to fall voltage the use. If engines not highest rotational speed, Also may directly use III.) 7.4+ Volt Li-Poly Packs.: We have found that 2cell Li-Poly Packs at peak charge can be as high as 8 +v. If you are going to use a 2 cell Li-Poly Packs, you must use a voltage regulator. Or Serially connects two IN4007 diode to fall voltage the use The Rcexl ignition runs more efficiently on about 4.8-6Volts and will draw more current at around 8+v, as well as operate at a higher temperature. You also have a higher chance of RFI interference. In brief in can satisfy under the engine highest rotational speed touse the quite low voltage as far as possible Once again, do not use an old pack to power your ignition! Edited April 7 by Martin Harris - Moderator Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted April 7 Share Posted April 7 Life or sub C work for me. Quote Link to comment Share on other sites More sharing options...
Eric Robson Posted April 7 Share Posted April 7 It depends on the ignition system Martin, RCEXL systems take 6v to 14v. Evolution 6v to 9v. On one of my RCEXEL units for a twin cylinder engine I have a 2c lipo 1000 which lasts for a days flying and more . On my Evolution I use a 6v 2000 rx battery which has been OK. I would not use a 3s lipo on a RCEXEL system as it can exceed 14v after charging. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7 Share Posted April 7 I think it depends on the age of the unit. Is it the earlier version that takes higher than 6V? Quote Link to comment Share on other sites More sharing options...
martin collins 1 Posted April 7 Author Share Posted April 7 The unit has on it 4.8v to 8.4v but the instructions say 4-6v, i have an Etronix ET0556 Lipo regulator here which would limit voltage to 6v, can that also be used to limit a LiFe 2s battery as well? Until the model is balanced i won`t know if the ignition pack will be readily accessible for removal to charge which may mean not using a lipo for the ignition but presumably a LiFe would be ok to charge in the model? Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted April 8 Share Posted April 8 I've used a 4 cell sub C on mine, typically do 3-4 10-12 min flights per session and the battery (3300 mah) has plenty left. BTW I fit a physical switch in series with the optical unit, to ensure complete isolation. Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted April 8 Share Posted April 8 All 4 of my petrols use a separate rx pack style battery - 5 cells in each. Two have the miniature spark plugs, two have the larger ones. All have a physical switch, as well as an opto kill unit operated by a momentary switch on my tx. They'll typically get about 30mins in the air each, with plenty of capacity left. Recently, I've started adding little voltage indicators for more peace of mind... Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 8 Share Posted April 8 Whatever solution you end up with, I would recommend flying a few sorties and then measuring the remaining capacity to give an accurate idea of your maximum safe duration. 2 Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted April 8 Share Posted April 8 My Rxcel is an early version, and the instructions contained dire warnings against using more than 4-cell NiMhs. I believe the later ones are more tolerant, but I can't speak from experience with those. AA-cells are NOT sufficient. Although the average current draw is only a few hundred mA, the PEAK draw (when charging the capacitor) is a lot higher, and AAs cannot meet that peak quickly enough. I switched to 4x sub-C cells (nominally 4.8V), which instantly solved all my power loss issues. -- Pete 1 Quote Link to comment Share on other sites More sharing options...
Manish Chandrayan Posted April 9 Share Posted April 9 Martin, If you need nose weight, use Sub C NiCd or NiMh 5 cell pack (6V) if you would rather not add much of nose weight go with a 1500/2000 mAh 2S LiFe and you will easily get the 5, 10 minutes flight . As suggested by the moderator, put in a few flights , charge back and see what was the consumption like Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted April 9 Share Posted April 9 19 hours ago, Peter Christy said: I switched to 4x sub-C cells (nominally 4.8V), which instantly solved all my power loss issues. @Peter Christyhi Pete, how did the power loss manifest? Just curious as my Stinger has started to refuse to go above 50% throttle without threatening to cut.... I've checked just about everything else..... Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted April 10 Share Posted April 10 It is in a Hirobo Bell 47 helicopter (an early Mk 1). On the AA cells it couldn't get off the ground! The engine sounded fine, no misfires or anything, just a severe lack of power. It would get light on the skids, and you might see daylight under them momentarily, but it certainly wouldn't "fly". Switching to sub-C cells restored normal power. It would lift off, hover and fly round with no problems. To be fair, it is NOT over-powered! But neither is the full-size one! It does force me to fly it in a realistic manner! 🤣 -- Pete 1 Quote Link to comment Share on other sites More sharing options...
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