10 lover/clive Posted January 13, 2011 Share Posted January 13, 2011 what is the current capacity of silicon cable nobody tells you Quote Link to comment Share on other sites More sharing options...
Hamish Posted January 13, 2011 Share Posted January 13, 2011 A bit more detail required. Quote Link to comment Share on other sites More sharing options...
10 lover/clive Posted January 13, 2011 Author Share Posted January 13, 2011 ok hamish the big fish and the others sell silicon cable in american wire gauge but nobody says what the amperage its rated at Quote Link to comment Share on other sites More sharing options...
10 lover/clive Posted January 13, 2011 Author Share Posted January 13, 2011 i'm running 40 amps over a metre long cable what should i use Quote Link to comment Share on other sites More sharing options...
Keiran Arnold Posted January 13, 2011 Share Posted January 13, 2011 not sure but I think 14AWG is about right Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted January 14, 2011 Share Posted January 14, 2011 With 2,5mm2 (which is more or less the same as 14AWG) you get a conductor temperature of 80deg C at 40 Ampere - this is not a problem for Silicone compounds as they are fine up to 180deg C. But you may burn your fingers if you touch the wire at this temperature. The loss per cable per meter would be around 11Watt/meter and the voltage drop is 0,2Volts per meter So if the cable is on the DC side (2 cables) 22 Watt are gone just for heating the cable ... Suggestion: shorter cable? Cheers VA Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 14, 2011 Share Posted January 14, 2011 This is a very difficult area for several reasons.... 1) Not all cable is equal...higher quality cable (ie better copper) will create less heat for a given current. 2) The insulation material matters (silicone will handle more heat than PVC as Vecchio notes) 3) The length of cable has an bearing also how it is run....a single cable in free air will be able to carry more heat than one in the middle of a bunch of cables 4) Most cable tables will give a continuous maximum current so if a table says a 14AWG cable will take a max of 50A then it will carry 50 amps from now until the end of time (or until I learn how to do a rolling circle....which ever is the longest...) But we don't run current through our wires continuously & rarely at the maximum current....the 50amps we might see on our wattmeter at full throttle is probably closer to 30A for much of the flight & for how long? 8 minutes? 10 perhaps? Then we land & let the wire cool down which we charge or swap batteries. So where does this leave us in practice....my personal rule of thumb is to use the same gauge wire as the battery (it is usually printed on the insulation) & to try & keep the wires as short as possible. As Vecchio points out, losses in the cable can be significant when they get longer hence it would be good practice to go up a size for longer runs.....larger cables have less resistance for a given length. Lots of conversion/current tables on t'internet if you need 'em!! I'm intriuged however.....why do you need such long wires? Another point that might be worth noting is that it is considered best practice to keep the battery/ESC wires as short as possible & lengthen the ESC/Motor wires if you need to....the rapid switching from the ESC is believed to cause large inductance spikes which can harm the ESC if the wires are too long. Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted January 14, 2011 Share Posted January 14, 2011 Just another comment - especially for those running 35 or 40 or 72MHz - the long cable also serves as an antenna which sends out a frequency which may disturbe the radio The disturbance is comming from the ESC - and the frequency can be quite high - not only because the electric field has to change with a few KHz if your brushless motor is running fast but also as such curcuits create harmonics which are much higher than the actual frequency of the ESC. If you run a brushed engine - the problem is similar and you have also the disturbance coming from the brushes itself. So: keep the cables short. Cheers VA Quote Link to comment Share on other sites More sharing options...
B. Bradley Posted January 27, 2011 Share Posted January 27, 2011 I scratch built a 72" JU-52, and the advise I was given was to keep the motor to ESC wire short and ESC to battery what ever length needed. I had some very long heavy silicone wires from the wing motors to the fuselage. I did not have heating problems, just flying problems. Quote Link to comment Share on other sites More sharing options...
Michael Leach Posted March 15, 2011 Share Posted March 15, 2011 Posted by B. Bradley on 27/01/2011 23:52:43: the advise I was given was to keep the motor to ESC wire short and ESC to battery what ever length needed. I agree - the important wires to keep short are the connection between the motor and its ESC.It is also desirable to keep the battery connections short too but not as important. The connections to the motor contain fast rising currents that produce radio frequency harmonics which not only radiate from the longer wires but the inductance of the longer cable causes resonances which can more than double the voltages seen by the switching devices in the ESC. The battery leads only see a fraction of these sharp edges and are also reduced by the high ripple current capacitors that you see on the end of your ESC. As a professional designer in exactly this area, but at higher power, I speak with experience of learning this the hard way!Mike. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 15, 2011 Share Posted March 15, 2011 Then you guys are pretty much alone in that thinking. Its always been preached that cables to the battery from the esc should be kept short, as the battery helps to damp out the back emf and high voltage spikes experienced by the ESC. Lengthening these cables reduces considerably this dampening effect and can cause damage to the input capacitors of the ESC. Quote Link to comment Share on other sites More sharing options...
Andy Green Posted March 15, 2011 Share Posted March 15, 2011 Timbo is right, this info is in a thread somewhere here. I had the same issue on my pterdactyl. You have to keep the batts to esc short or add more capacitance to the input of the speed controller. A Quote Link to comment Share on other sites More sharing options...
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