Ian Newton Posted July 22, 2008 Share Posted July 22, 2008 I have just suffered an esc failure while setting it up with an unloaded motor attached (no prop). The esc I had was more than adequate (supposedly) current wise and should have been suitable voltage wise although at its maximum (6s LiPo). I had a wattmeter attached at the time and there was negligible current draw (mA) so can only assume it was the voltage that did the damage. I have seen a recommendation to ensure that the esc has a current rating 50% greater than the expected maximum load to minimise the risk of it burning out which seems sensible since the current generates the heat. howeer, can anyone advise whether the same applies to the voltage rating? I wish to use a 6s LiPo pack to power an AXI 4130/16 with a 15*10 prop (expected to draw 40A). This would suggest a 60A esc to give a good safety margin (The failed unit was 100A and I thought to do the same again to give maximum versatility if I use the esc in another set up requiring greater current loading) but can I safely use an esc rated at 22V or should I go for an HV model which can handle 8+ cells. Any suggestions on a suitable esc? Additionally, I intend using a 6V flight pack. Does this cause any problems in general to the esc (OPTO) or are they all compatible with a 6V supply? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 22, 2008 Share Posted July 22, 2008 I have used a 6 x lipo cell ESC on an 8 cell MI pack . The max voltage rating was therefore 6 x 4.2 = 25.2...so lets call it 26V. The 8s LiFe pack equates to 28.8V. The result was erratic - sometimes it worked and others it didnt - it did not however let out the magic smoke! It was a cheap Turnigy unit ( 60A and opto ) under 20 squid.I now use an 8s Lipo capable 70A unit in this particular model...as again they are cheap these days. It is this one here - simple...but cost effective at under 16 squid -and performs well so far.As for the 6v supply...no problem - the opto ESC is completely isolated from this supply - thats the point ! Quote Link to comment Share on other sites More sharing options...
Ian Newton Posted July 22, 2008 Author Share Posted July 22, 2008 Thanks Timbo. I'm learning all of the time! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 22, 2008 Share Posted July 22, 2008 We all are Ian...and just like house maintenance .....it never stops Quote Link to comment Share on other sites More sharing options...
birdy Posted July 23, 2008 Share Posted July 23, 2008 Were you at a low throttle setting - apparently the FETs (what ever they are) are doing more switching, and producing more heat? Quote Link to comment Share on other sites More sharing options...
Ian Newton Posted July 23, 2008 Author Share Posted July 23, 2008 Yes, it would have been at 'zero' throtle setting at the time. I would have expected the FETs (Field effect transistors - I know the name but without getting the books out don't remember much more myself) to be off (non-conducting) although I suppose it may not have been absolutely zero. The current draw was definately a matter of mA at this stick position however. Quote Link to comment Share on other sites More sharing options...
Lee Burke Posted July 23, 2008 Share Posted July 23, 2008 GiantCod in its (his?) guarantee information warns: Never run your setup with no load - this is an instant guarantee disqualification. Quite why this is, I myself don't know, but Giantcod must believe it has a very negative effect. Quote Link to comment Share on other sites More sharing options...
birdy Posted July 23, 2008 Share Posted July 23, 2008 Quite how this happened I am really begining to puzzle over... Quote Link to comment Share on other sites More sharing options...
Ian Newton Posted July 23, 2008 Author Share Posted July 23, 2008 Just one additional point. I was still setting the esc up at the time and the motor was not being 'run'. It was obviously connected but I was working through the various setup options. I have checked the motor out with another esc, albeit only with a 3s LiPo as this was all that that particular esc was rated for. It worked perfectly ( and ran the motor up to full throttle with no prop connected - but I not your warning Lee). I had not seen a warning re running the motor on no load anywhere before but then I am very new to the electric side of fliying, having been solely IC until very recently.Thanks all anyway. I have a new esc on order from Giant Cod so hope for better luck this time and will take all of the advice on board. Quote Link to comment Share on other sites More sharing options...
Lee Burke Posted July 23, 2008 Share Posted July 23, 2008 Better luck with the new one, Ian I understand that even if the motor is not being run the ESC is still taking current from the battery and would even eventually drain it, even if the ESC switch is set to Off. So that is a point to watch. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 28, 2008 Share Posted July 28, 2008 I wonder why GiantCod say not to run with no load??? Personally I always try to set up my leccy models with no prop, hence no load. If you've ever had a prop inadvertantly start up I can tell you it isn't half scary...luckily this was only a small foamy...I hate to think of the damage a monster motor on 6s would cause. Remember...zero revs equals max torque......thats gonna hurt!!!! Also remember that unlike ic, when the obstruction (bench, hand, leg, genitals....whatever...!!) is removed the prop is gonna start turning again!!!!!!I wonder if by no load he means the ESC must have a motor connected before powering up? As we all know our ESCs like to play merry tunes when first connected & these come from pulses in the motor windings.....maybe if these have nowhere to go they will pop the FETs....... Quote Link to comment Share on other sites More sharing options...
winchweight Posted July 28, 2008 Share Posted July 28, 2008 Is that true? Lower throttle settings generate more heat in the esc? Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 28, 2008 Share Posted July 28, 2008 Yes absolutely.......the ESC generates whats known as a quasi sine wave to replicate the 3 phase AC input to the motor...this is done by switching the DC supply from the battery on & off very rapidly.....effectively the longer the FETs stay "on" the greater the "voltage" the motor sees. Hence it follws that the longer the FETs stay "off" the lower the voltage & the lower the motor speed. The FETs are basically just a switch that turns on & off several thousand times a second.....by varying the rate (or speed) of switching, the voltage the motor sees varies. To provide a low voltage & hence low speed the FETs must switch more frequently. Nothing is 100% efficient so it follows that every switch will generate some heat.....more switches to provide low speed equals more heat in the ESC !!Luckily the manufacturers know this too, so they design products that can stand this extra heat....although there are some honourable exceptions to this rule!!!!!Obviously if we draw more current than the FETs can handle they will completely melt & release the magic smoke!!!You really wouldn't believe just what that little heatshrinked package with the all the wires hanging out of it actually does, nor the speed with which it does it!!!! If you did you wouldn't moan when the price exceeds twenty quid!!!!!! Quote Link to comment Share on other sites More sharing options...
winchweight Posted July 28, 2008 Share Posted July 28, 2008 So, as part of my diagnosis into what went wrong with my Sea Fury, I should conduct the test at half power perhaps, as this is approx the power level set when the esc / UBEC went into failsafe mode. I bench ran at full power yesterday and nothing really heated up except the motor. But perhaps I should repeat it at a lower setting then? Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 28, 2008 Share Posted July 28, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 28, 2008 Share Posted July 28, 2008 Yeah......might be an idea....lets face it, can't do any harm!!! I say again though ESCs are rated to allow for this extra heat generation so it might not prove anything.Gutted for you on the Seafury by the way...I read the thread. I'm certainly no expert on 2.4 not by any standards. I do have a bit of common sense though & even though everyone says it's immune to interference I really don't buy that. I accept that it's technologically improved but ANY radio link can fail...its a noisy world out there & we only use very small power outputs......it might be just be "one of those things"....but I know how you feel....plays on yer mind doesn't it Quote Link to comment Share on other sites More sharing options...
Lee Burke Posted July 28, 2008 Share Posted July 28, 2008 Shaun, you have to try to do it just as it was in field, preferably in that field as well. You want to try to find a foam box that has about the same size as your cockpit and put the electronics in there as they were in the Fury. Then you need to sit it on the wings and the tailplane and connect everything up again. Its the only way to repeat the event. Maybe you could jam toothpicks into whats left of the fuselage and stick it back together like that just for the test. In that way you are getting as close as you can. Run the motor at the same speed as you did before the crash. The thing has to fail again. It just has to. Hopefully. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 28, 2008 Share Posted July 28, 2008 Guys...we're hijacking the thread here (he sez in a Timbo-esque way!!!!) Maybe we should continue in Shauns posting........ Quote Link to comment Share on other sites More sharing options...
Lee Burke Posted July 28, 2008 Share Posted July 28, 2008 Timbo-ESC way, more like Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 28, 2008 Share Posted July 28, 2008 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 28, 2008 Share Posted July 28, 2008 That sounds more feasible. However some motor manufacturers also do not recommend running them flat out with no load - again, not really sure why this should be problem, other than the potential for very high revs - but again theoretically speaking this should not exceed the rated Kv anyway. Quote Link to comment Share on other sites More sharing options...
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