cad Posted February 6, 2014 Share Posted February 6, 2014 Having only returned to modelling in the last few years I was advised to build in an easily accessible switch to immobilise the motor, ie, not have to fiddle with removing hatches etc to break the battery contact. The method suggested was to extend the negative wire from the esc to the battery via a loop that came external to the fuselage. At this point to introduce a simple ( banana I think it is called) connector, as these can be easily pulled apart. Alternative connectors like Deans or bullet type are a much firmer fit and not always easy to separate. It would appear much easier to have a simple on/off switch fixed externally. More experienced fliers observations would be appreciated. Currently finishing off a Popsie and would like to resolve this issues. Thanks CAD Quote Link to comment Share on other sites More sharing options...
Masher Posted February 6, 2014 Share Posted February 6, 2014 Hi cad This question crops up regularly and is a good one. The simple answer is that a suitable switch would be large, heavy and expensive because its current rating has to exceed, with some margin, the maximum motor current. We are talking automotive type switches here. There are electronic solutions, using power FET's etc, but these are expensive and reduce reliability. The only real option until manufacturers come up with something better, is to use the method you have been advised of Edited By Masher on 06/02/2014 12:41:03 Quote Link to comment Share on other sites More sharing options...
cad Posted February 6, 2014 Author Share Posted February 6, 2014 Thanks for your quick response Masher, Will continue as planned then. Regards CAD Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 6, 2014 Share Posted February 6, 2014 Plenty in this thread, Cad. Only thing I would say is that it is the positive lead which should have the break for the arming plug, not the negative. Pete Quote Link to comment Share on other sites More sharing options...
Dave Miller Posted February 6, 2014 Share Posted February 6, 2014 Posted by Pete B - Moderator on 06/02/2014 12:48:51: Plenty in this thread, Cad. Only thing I would say is that it is the positive lead which should have the break for the arming plug, not the negative. Pete That's interesting, why do you think that it will make any difference? Quote Link to comment Share on other sites More sharing options...
cad Posted February 6, 2014 Author Share Posted February 6, 2014 Appreciate the redirection Pete B quite a bit there to chew on. CAD Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 6, 2014 Share Posted February 6, 2014 Posted by Dave Miller on 06/02/2014 12:59:26: Posted by Pete B - Moderator on 06/02/2014 12:48:51: Plenty in this thread, Cad. Only thing I would say is that it is the positive lead which should have the break for the arming plug, not the negative. Pete That's interesting, why do you think that it will make any difference? Got me scratching my head too! Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 6, 2014 Share Posted February 6, 2014 Posted by Dave Miller on 06/02/2014 12:59:26: Posted by Pete B - Moderator on 06/02/2014 12:48:51: Plenty in this thread, Cad. Only thing I would say is that it is the positive lead which should have the break for the arming plug, not the negative. Pete That's interesting, why do you think that it will make any difference? Good question, Dave. I don't know, TBH, but it seems more logical and is the accepted practice from what I see. Something to do with potential difference, perhaps? My knowledge of elecrtrical theory is way below that of many other forumites, so I'd welcome an explanation - in words of one syllable, preferably! Pete Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted February 6, 2014 Share Posted February 6, 2014 It shouldn't make any difference which lead you put the connector in - the important thing is to break the circuit - I can't see that matters where you break it. BEB Quote Link to comment Share on other sites More sharing options...
Malcolm Blake 1 Posted February 6, 2014 Share Posted February 6, 2014 On most electrical appliances the switch should always be in the positive (live) lead. If you break in the negative lead then the motoe still has a live feed into it and if there is an accidental touch with another negative surface you will have a complete circuit and the motor would run. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted February 6, 2014 Share Posted February 6, 2014 But the same would be true if you break the positive lead - an accidental touch with a positive surface and it might complete the circuit. I think your analysis is sound in the case of say a car - where often the whole chassis and body are connected to the negative. Then if you break the negative as a switching operation - any conductor touching the body could restore the circuit. But that's not the case in a model - there is a total separate negative 'wire based' circuit. The body is not being used as zero potential. BEB Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted February 6, 2014 Share Posted February 6, 2014 possibly some confusion with mains where you do have a live and return wire even though it's ac electricity which doesn't care for polarities, and as BEB points out, for vehicles where the chassis is the return path. Quote Link to comment Share on other sites More sharing options...
Toni Reynaud Posted February 6, 2014 Share Posted February 6, 2014 The simple answer is that a suitable switch would be large, heavy and expensive because its current rating has to exceed, with some margin, the maximum motor current. This has always interested me. Are switches rated for current carrying capacity, or for safe current breaking ability? DOes anyone know? Quote Link to comment Share on other sites More sharing options...
PatMc Posted February 6, 2014 Share Posted February 6, 2014 Single pole switching on the positive lead is the safe convention where the negative is at earth potential. E.g a mains connected PC will have it's case connected to the earth wire of the plug. In the case of a model there's no earth so it doesn't matter which wire is broken. Quote Link to comment Share on other sites More sharing options...
jolliffee Posted February 6, 2014 Share Posted February 6, 2014 I have two ESC's that have a separate disabling switch built in, there make it very easy to use but I still don't trust them totally and keep well away from the propeller. I wonder why there aren't more ESC's with this feature? Quote Link to comment Share on other sites More sharing options...
Dave Miller Posted February 6, 2014 Share Posted February 6, 2014 Posted by jolliffee on 06/02/2014 16:12:16: I have two ESC's that have a separate disabling switch built in, there make it very easy to use but I still don't trust them totally and keep well away from the propeller. I wonder why there aren't more ESC's with this feature? Possibly because it's not considered to be a fail-safe system. Quote Link to comment Share on other sites More sharing options...
PatMc Posted February 6, 2014 Share Posted February 6, 2014 Posted by jolliffee on 06/02/2014 16:12:16: I have two ESC's that have a separate disabling switch built in, there make it very easy to use but I still don't trust them totally and keep well away from the propeller. I wonder why there aren't more ESC's with this feature? The switch won't actually disconnect the power into the ESC, just the negative (& if double a pole switch possibly signal) wire to the Rx. Trouble is that the ESC still draws some current & if left plugged into the battery, even switched off, will flatten the battery - irreversibly in the case of a lipo. I also have a few ESCs with switches that date back to pre-lipo & nickel/lipo days before this was recognised as a problem. Edited By PatMc on 06/02/2014 16:43:33 Quote Link to comment Share on other sites More sharing options...
Martin Whybrow Posted February 6, 2014 Share Posted February 6, 2014 Posted by Toni Reynaud on 06/02/2014 15:02:06: The simple answer is that a suitable switch would be large, heavy and expensive because its current rating has to exceed, with some margin, the maximum motor current. This has always interested me. Are switches rated for current carrying capacity, or for safe current breaking ability? DOes anyone know? Switches are usually rated for carrying capacity; breaking capacity depends on a great many parameters, including supply voltage, load inducatnce and load capacitance. Switch and relay manufacturers ofter publish de-rating graphs or charts for breaking capacity. Quote Link to comment Share on other sites More sharing options...
Shaunie Posted February 6, 2014 Share Posted February 6, 2014 As far as ESCs are concerned it matters not if the positive or negative Lipo wire is disconnected, it is after all a circuit and a break anywhere will disable the motor. To disable the Rx the break in the servo wire should be in the positive not the negative unless you want some nasty circulating currents going through the throttle signal line to the ESC (which could damage the Rx or ESC) although as mentioned this does not prevent the ESC running the Lipo down. As far as cars are concerned you should never work on the positive terminal while the battery negative one is connected. The logic is simple, when disconnecting the negative terminal the only way to cause a short with your spanner is to bridge it to the positive one. Working on the positive on the other hand the way to cause a short is to bridge it to anything, battery tray, negative terminal, suspension turret, that little sticky-out-bracket-thing- you-don't know-what-it-does, basically anything at negative potential. The only safe way is to disconnect negative first, reconnect it last. Shaunie. Quote Link to comment Share on other sites More sharing options...
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