Dylan Reynolds LaserCraft Services Posted February 22, 2013 Share Posted February 22, 2013 I am just sorting out my new Sebart Sebach 342, its has a thumper C3548 motor 1100kv, 750 watt, a 60 Amp ESC, both of which state 3-6 S lipos, when i put a 3s in all is fine, but when i put a 5s in the ESC gets hot instantly, can anyone shed any light please Quote Link to comment Share on other sites More sharing options...
PMIKEY Posted February 22, 2013 Share Posted February 22, 2013 Are you using the same prop as you did when running 3s?? as the amp draw will go off the chart if you are. Pop out and get a watt meter it will be the best investment you make this year!! Quote Link to comment Share on other sites More sharing options...
John Privett Posted February 22, 2013 Share Posted February 22, 2013 If you're swapping a 3S battery for a 5S battery then unless you change to a much smaller prop you're going to fry just about everything! Quote Link to comment Share on other sites More sharing options...
Dylan Reynolds LaserCraft Services Posted February 22, 2013 Author Share Posted February 22, 2013 this is without a prop, just sorting the setup, but its doing it without running it up at all, all i did was connect the battery Quote Link to comment Share on other sites More sharing options...
John Privett Posted February 22, 2013 Share Posted February 22, 2013 Ummm... OK... That shouldn't happen! Are you sure you've got the polarity correct? Quote Link to comment Share on other sites More sharing options...
PMIKEY Posted February 22, 2013 Share Posted February 22, 2013 Is the ESC bleeping to indicate 5s when you connect??? Quote Link to comment Share on other sites More sharing options...
PMIKEY Posted February 22, 2013 Share Posted February 22, 2013 Also are you using the built in Bec circuit?? if you are disconnect the bec and hook up a seperate power supply to the receiver and try again, you can dissconnect the bec by pulling out the red lead from the plug that runs from your esc to the receiver. Sorry if it sounds like im teaching you to suck eggs!!! just not sure of your experiance. Edited By PMIKEY on 22/02/2013 21:39:22 Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted February 22, 2013 Share Posted February 22, 2013 Not going to answer the ESC getting hot, but a 1100 kv motor on a 5s battery seems a bit much, it will try and turn at around 15,000 rpm unless the plane is a pylon racer. Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted February 22, 2013 Share Posted February 22, 2013 A 5S battery using an standard internal BEC is a bit much too! Unless the internal BEC is a switching BEC then at most you can use a 4S pack (but only with 2-3 servos). The alternative is an external switching BEC or (depending the size of the aircraft) a seperate Rx Pack. Especially as Sebart are expensive airframes, you want to make sure that your Rx power supply is beefy and not going to fail... Si. Quote Link to comment Share on other sites More sharing options...
Dylan Reynolds LaserCraft Services Posted February 22, 2013 Author Share Posted February 22, 2013 yes the esc beeps 5 times cheers PM i'll try that the 1100kv recomends a battery range of 3 to 6s which i'm using a 5s 20c 5000mAh I bought all the gear and frame 2nd hand from my LMS, and the owner knows the guy whos model it was and he says it ran sweet as a nut with a 5s when he had it, nothing has been changed other than i am using my batteries, which the polarities are the correct way round. I did have it flying a few weeks ago with a 3s, it was fine, just lacked a bit of oomph Edited By Dylan Reynolds on 22/02/2013 23:33:50 Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted February 23, 2013 Share Posted February 23, 2013 You'll need to run it through a watt meter. I run a wot 4 on a 900kv motor, 12x8 prop, 4s pack and its drawing 90A. 1100kv on 5s will be considerably more! What ESC are you using? Si. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted February 23, 2013 Share Posted February 23, 2013 A wattmeter is key here....it will tell you how much current you are drawing.....as Frank points out the motor will be spinning in excess of 15000 rpm.....it will need a very small prop to achieve that. What size prop have you fitted? Quote Link to comment Share on other sites More sharing options...
John Privett Posted February 23, 2013 Share Posted February 23, 2013 Agreed, Steve, but not in this case (yet!) As Dylan said earlier, "this is without a prop, just sorting the setup, but its doing it without running it up at all, all i did was connect the battery" So as he's not even running the motor the prop size doesn't yet affect anything. Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted February 23, 2013 Share Posted February 23, 2013 It seems to me, after reading Dylan’s narrative, that his ESC starts to get hot as soon as he connects the battery and before anything is actually operated. This would definitely seem to indicate that an overly amount of current is flowing somewhere where it shouldn't. I’d personally consider it unlikely to be the BEC, unless there is short circuit somewhere. Even if it’s the linear flavour, I’m not entirely sure it’s going to get that hot. Although the radio is powered up, there are no servos working, so I think we can assume the idle current will be around the 100 milliamp mark, and, indeed, probably a lot less. If we call the 5 cell pack voltage 20 volts, and the BEC 5 volts, there is a voltage difference of 15 volts across the regulator. 15V by 100 milliamps, or 0.1amp, equals 1.5 watts, hardly likely to be setting the woods on fire, I’d have thought anyway. I’m inclined to think that overheating problems tend to occur when everything is working hard, at say about three quarters throttle perhaps. I’m only guessing here, I still have to yet have a go at those power/heating tests that I intend to do on an ESC, but in Dylan’s case the ESC is cold; so in that respect it’s acting like a heat sink for the BEC anyway. And the higher cell count/smaller prop syndrome is really only yet another case of Ohm’s law, too. PB Quote Link to comment Share on other sites More sharing options...
PatMc Posted February 23, 2013 Share Posted February 23, 2013 It sounds like the ESC is wrongly rated at 6s should probably only be 4s. I doubt that it's the BEC but this can easily be eliminated by dissing the red wire & using seperate Rx 4.8 nimh. Quote Link to comment Share on other sites More sharing options...
Dylan Reynolds LaserCraft Services Posted February 23, 2013 Author Share Posted February 23, 2013 OK, thanks for all thr replies guys, the problem has been eliminated, a new 60A esc is now installed, with a 12x6 eprop fitted on same motor, with a 3s battery I am getting 54.92A max draw and 9310 rpm. I presume the problem lies within the esc itself as I have replaced it with exactly the same. Although both esc and motor rated for upto 6s, the draw was just too much for the motor. Test flight number 2 coming up tomorrow, will let you all know how it goes But like I said, thanks again. Quote Link to comment Share on other sites More sharing options...
Dylan Reynolds LaserCraft Services Posted February 24, 2013 Author Share Posted February 24, 2013 Not a very happy chappie today, set her up at the strip, connected my watt meter, gradually started winding her up and all of a sudden, bang! bits and pieces everywhere, prop goes flying off in one direction, narrowly missing me, motor appears outside the cowl! needless to say a new cowl is required. the reading at full chat prior to this was 44A so I know the setup is now correct, trouble is I dont think a rebuild is going to be viable, I do it myself its going to be too heavy, I buy the parts its going to be too expensive. Looking at it closely, it looks like there may have been a fracture in the ply on the mounting box, its the only clean break visible, Absolutely gutted, my most expensive airframe and this is the plane I have been working so hard for to get in the air. Quote Link to comment Share on other sites More sharing options...
PMIKEY Posted February 24, 2013 Share Posted February 24, 2013 Sorry to hear that Dylan, i would not give up though, have a chat with inwood models or steve webb models, spares are available they just take a little time to get ordered. I know that sebart even do a replacement motor mount / box. The great thing about these airframes is that it is actually very easy to repair them to a good standard. Best of luck. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted February 25, 2013 Share Posted February 25, 2013 Ooo poor you Dylan....not good at all. Still it sounds like you managed to avoid any injuries so lets be thankful for that. I'm sure it could be rebuilt.....can you find all the bits from the firewall? If you can piece them together & then fix them with cyano you can use this as a template to cut a new one......use good quality birch ply to prevent a re-occurance..... As for it being too heavy I wouldn't worry too much about that.....these airframes are built very light & can certainly carry a few extra ounces.....Seems a shame to just bin the whole airframe after all.... Good luck..... Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 25, 2013 Share Posted February 25, 2013 That really bad luck, Dylan, commiserations...... It' always worth reinforcing the ply motor box with some triangular strip to beef it up - does make a difference If you can bear to post a pic, perhaps the guys here can offer some help with the rebuild? Pete Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.