Keith Miles 2 Posted January 9, 2020 Share Posted January 9, 2020 Peter, Further to PatMc’s post.... If all the power read was heat, the motor would surely just be a heater? Correct me if I’m wrong but a motor has both a maximum current rating and a maximum power rating? If you were to clamp the prop so that it could not rotate, I bet a year’s pension that you would still get a healthy power reading on the watt meter when you connect the battery to it. But not for long! As I said to another poster, on another matter, go try it! Sorry, no, don’t try it! Or did we just misunderstand each other? 😊 Edited By Keith Miles 2 on 10/01/2020 00:06:07 Quote Link to comment Share on other sites More sharing options...
Former Member Posted January 10, 2020 Share Posted January 10, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 10, 2020 Share Posted January 10, 2020 Posted by Tom Sharp 2 on 10/01/2020 01:53:17: Can only hope Yorkman will give us a full report as to the resulting flights. I imagine that the outcome will confirm Colin Carpenter’s experience and, hopefully, end the debate! As I have said, standard practice is to begin with the load and work back from there when designing electrical systems, and not the other way around. When a power supply cannot cope with the load, either you need to reduce the load or beef up the power supply in some way in order that it can deliver the required current. A lot of the stuff on here, interesting as it may be, and educational as it may be, will not change that basic principle. That said, in this case, testing with the highest available “C” rated battery of the required voltage would be a good idea but maybe not the most economical one! It also seems, and I can fully understand why, even when you think you have the calculations right, further experimentation may be required and alterations made to achieve the most efficient set-up. Finally, let’s remember that a battery is not there to protect the motor, or anything else. Such a device might be a fuse or thermal cut-out! Keep those fire extinguishers handy! Edited By Keith Miles 2 on 10/01/2020 09:08:43 Quote Link to comment Share on other sites More sharing options...
Dickw Posted January 10, 2020 Share Posted January 10, 2020 Posted by Keith Miles 2 on 09/01/2020 23:52:39:......................... Correct me if I’m wrong but a motor has both a maximum current rating and a maximum power rating? If you were to clamp the prop so that it could not rotate, I bet a year’s pension that you would still get a healthy power reading on the watt meter when you connect the battery to it. But not for long! .................................... Edited By Keith Miles 2 on 10/01/2020 00:06:07 You are quite correct that a motor has maximum current and power ratings, but such ratings are heat related and therefore time related, so your "not for long comment" above is very relevant. It is basically why in F5B I can use a 1400watt motor at 5kW and a 135 amp ESC at up to 200 amps. A typical flight would be 12 motor runs of 2 secs on and 14 secs off - that keeps the heat build up to acceptable levels and we avoid flying again for at least 30 mins tro allow motor and ESC time to return to ambient temp. Interestingly, in the early days of brushless motor/ESCs in the 1990s, Kontronik (one of the innovators of brushless gear) stated that their 'continuous' ratings were based on the use of a 1700 mAh battery pack (a typical size for the time). I am not sure manufacturers these days bother with such nice details. Dick Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted January 10, 2020 Share Posted January 10, 2020 Keith, Maybe we might have to agree to slightly disagree on this subject, although I’m not even sure now what it is we are actually agreeing/disagreeing about any more… One point on the little anomaly about burning the motor by using a higher C rated battery, I don’t think this is ever going to be an issue. I’d have thought that at that stage the original battery/motor/prop combo performance was so abysmal that no one would want to fly it anyway. Although having said that I’ve long since not been at all surprised by just about anything that aeromodellers can do! I’ve long used my own procedures for arriving at the best size of prop to use, and it certainly doesn’t involve clamping the prop stationary and applying full power. Although this does rather make the point fairly succinctly that you can’t always get a firm handle on the speed and power of the prop by reading the battery output on the wattmeter… On reflection I’ve never seen a burnt motor and I don’t know anyone that has. I did read once about a motor that burnt a coil but that was thought to be an internal short. A few smoking and worse ESCs in the past but electric knowledge, experience and quality of the kit is increasing all the time. In the main I suspect that many electric flyers now spend many hassle free hours these days doing just that without too many problems to overcome! Good luck! PB Quote Link to comment Share on other sites More sharing options...
Nigel R Posted January 10, 2020 Share Posted January 10, 2020 Posted by PatMc on 09/01/2020 20:31:58: It's so contrived that the same case could be made for using a battery that's previously been OK during mild temperature days but on a hot day would supply slightly more current ... etc. Or if a similarly C rated battery just happens to be from a better batch & is connected... Or if ... Absolute nonsense It's just not worth considering Labelling my statement nonsense does not refute it. Quote Link to comment Share on other sites More sharing options...
Former Member Posted January 10, 2020 Share Posted January 10, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted January 10, 2020 Share Posted January 10, 2020 All you lads are vital to this site Nigel, with your flying skills and builds Steve, for keeping my head above water with the new ruling And Keith, the adept writer and deep analyst Roll On Flying Weather But for now, put all your skills in sensible format I learn from you lot everyday So do it for the Newbies Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 10, 2020 Share Posted January 10, 2020 Posted by Steve J on 10/01/2020 12:39:37: Posted by Keith Miles 2 on 09/01/2020 17:55:55: Posted by Steve J on 09/01/2020 08:51:36: Take two batteries that differ only in C rating. Connect to the same prop/motor/ESC setup. Open the throttle. More current will be pulled out of the higher C rated battery than out of the lower. Sorry, I meant to say that you are absolutely correct on that last point! Eventually the penny might drop! You seem to think that you understand this subject better than I do. You don't. Anyway, one of my New Year's resolutions was to take Mark Twain's advice regarding dealing with idiots so I am going to say goodbye and put you on my ignore list. Firstly, I think you will find a number of people on here, who do seem to know their stuff, that share my opinion, and one or two who have proved the theory, so maybe you should block them as well? Secondly, I have over 50 years experience as an industrial installation electrician so, clearly, I have never understood basic principles since day one and perhaps should have been sacked! Oh, and I’m still learning things. It is a shame when some people seem unwilling, or incapable, of even pausing to consider that they might just be wrong or may have misunderstood something. It is also not a little concerning. So, going back to the OP and aside from technical intricacies, if you are unable to accept, at the very least, that a battery is NOT there to protect a motor from overload or overspeed as your “high “C” will kill it” theory suggests, then I, for one, will waste no more time trying to change your opinion. Oh, and resorting to personal insults doesn’t help your case, either. Edited By Keith Miles 2 on 10/01/2020 17:03:42 Quote Link to comment Share on other sites More sharing options...
PatMc Posted January 10, 2020 Share Posted January 10, 2020 Posted by Keith Miles 2 on 09/01/2020 23:52:39: Peter, Further to PatMc’s post.... If all the power read was heat, the motor would surely just be a heater? Correct me if I’m wrong but a motor has both a maximum current rating and a maximum power rating? If you were to clamp the prop so that it could not rotate, I bet a year’s pension that you would still get a healthy power reading on the watt meter when you connect the battery to it. But not for long! As I said to another poster, on another matter, go try it! Sorry, no, don’t try it! Or did we just misunderstand each other? 😊 Edited By Keith Miles 2 on 10/01/2020 00:06:07 Motors have a max current rating but any max power rating is not true unless given for a specific voltage, which is covered anyway by the current rating. If I were you I wouldn't jeopardise my pension on that bet. If you clamped the prop the ESC should only energise one phase (possibly a couple as it decides which direction of rotation is correct) then give up as it's expecting to detect the rotor's new position that tells it to energise the next phase. There won't be much of a power reading recorded courtesy of Lenz's Law & the time lag of the meter in registering whatever power is achieved. However I wouldn't test this in practice as it relies on the ESC's firmware being correct. OTOH I do know from experience, gained by nosing over models a couple of times during take off (then being slow to shut the throttle), that a non event is the normal likely outcome. Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 10, 2020 Share Posted January 10, 2020 Posted by Peter Beeney on 10/01/2020 11:00:07: Keith, Maybe we might have to agree to slightly disagree on this subject, although I’m not even sure now what it is we are actually agreeing/disagreeing about any more… One point on the little anomaly about burning the motor by using a higher C rated battery, I don’t think this is ever going to be an issue. I’d have thought that at that stage the original battery/motor/prop combo performance was so abysmal that no one would want to fly it anyway. Peter, I don’t think there is a gulf of disagreement between us. Maybe it’s just a communication thing! My “clamping the prop” analogy was merely an extreme case, to help explain, and clarify, that unlike IC, the more load that you place on an electric motor as it tries to rotate in response to throttle input, the more current it will try to draw to achieve what it is being commanded to do and it will keep on doing that until something in the power train fails completely or even goes up in smoke! As you say, and as I, and others, have been trying to explain, it is only the correct combination of ALL components that will achieve the most efficient, reliable and, indeed, safe, performance. Not all flyers seem to be able to grasp either that or the fact that (to go back to the OP) the only disadvantages of fitting a high “C” battery, IF the motor/prop combo is correct, will be either excess weight, excess size or excess cost! I would further suggest that those who are running, as you say,“on the limit” and without realising it (due to the effect of volt drop at the battery) might also be amongst the group of people who report having batteries that don’t seem to last very long! ”Headroom” is often referred to when talking about ESCs but it seems to me that the same “headroom” principle could, or should in many cases, be applied to batteries as well in terms of selecting an appropriate “C” rating. And I totally agree that the only definitive way of proving a system is to test it. My advice would be to check all three parameters at full throttle i.e amps, volts and watts and in that order. I would be looking for current within the maximum motor rating (the ESC should have a higher rating, of course!) and minimal or, preferably, zero voltage drop. Neither of those should be ignored or sacrificed in attempts to achieve more power or you could be heading down a dodgy road to damage either short term or long term! So, if you see a voltage drop, the solution will probably be to either reduce the prop size or, yes, fit a battery of a higher “C” rating! Got there in the end! P.S. This stuff is possibly irrelevant, of course, if the model is flight ready when you buy it and the headaches have already been taken care of, together with a set of instructions and manufacturer’s recommendations! Quote Link to comment Share on other sites More sharing options...
Yorkman Posted January 10, 2020 Author Share Posted January 10, 2020 Posted by Keith Miles 2 on 10/01/2020 16:55:11: Posted by Steve J on 10/01/2020 12:39:37: Posted by Keith Miles 2 on 09/01/2020 17:55:55: Posted by Steve J on 09/01/2020 08:51:36: Take two batteries that differ only in C rating. Connect to the same prop/motor/ESC setup. Open the throttle. More current will be pulled out of the higher C rated battery than out of the lower. Sorry, I meant to say that you are absolutely correct on that last point! Eventually the penny might drop! You seem to think that you understand this subject better than I do. You don't. Anyway, one of my New Year's resolutions was to take Mark Twain's advice regarding dealing with idiots so I am going to say goodbye and put you on my ignore list. Firstly, I think you will find a number of people on here, who do seem to know their stuff, that share my opinion, and one or two who have proved the theory, so maybe you should block them as well? Secondly, I have over 50 years experience as an industrial installation electrician so, clearly, I have never understood basic principles since day one and perhaps should have been sacked! Oh, and I’m still learning things. It is a shame when some people seem unwilling, or incapable, of even pausing to consider that they might just be wrong or may have misunderstood something. It is also not a little concerning. So, going back to the OP and aside from technical intricacies, if you are unable to accept, at the very least, that a battery is NOT there to protect a motor from overload or overspeed as your “high “C” will kill it” theory suggests, then I, for one, will waste no more time trying to change your opinion. Oh, and resorting to personal insults doesn’t help your case, either. Edited By Keith Miles 2 on 10/01/2020 17:03:42 Have to say I'm with you on this one Keith...even if a higher 'c' rating enabled a battery to deliver more voltage that it actually contains (how?) in my experience your actual motor is pretty tolerant of voltage variations-and if the motor was actually running that close to the edge of its abilities, then,as previously mentioned, prop/motor/amps etc need revision... Quote Link to comment Share on other sites More sharing options...
Don Fry Posted January 10, 2020 Share Posted January 10, 2020 Cheers PatMc. A eureka moment. A petrol head, when I noseover a leccy creation, and it can make a lot of noise, I am continually surprised why the thing is not dead. Now I know. Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 10, 2020 Share Posted January 10, 2020 PatMc, Yes, you are correct, on the rotation thing, now I think about it. Had my “mains” head on there! Thanks for saving my pension! (Hopefully!). Always happy to be corrected or to learn something new! And yes, on the power/voltage thing, I was making that very point to someone at the field earlier today and also emphasising that maximum current is the primary consideration and that a power rating alone is useless. Edited By Keith Miles 2 on 10/01/2020 18:52:07 Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 10, 2020 Share Posted January 10, 2020 And thanks, also, to Yorkman. I’ll leave you to guess why! Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted January 11, 2020 Share Posted January 11, 2020 Keith, Thanks for your reply, but I think that there’s really very little I can add to all this now, other than that I do tend to take a bit of a different slant on the subject. Been tinkering with it for a fair time now, and it’s always worked for me, at least up till today anyhow. Like a voltage going down a wire I always take the line of least resistance; or just lazy, I guess; and I also have to be careful when overdoing the thinking bit, (also very easy for me!), like a resistor suffering from a serious overdose of amps the old brain can get a bit overheated… and well flummoxed into the bargain, too… Right, now off to brush the cobwebs out of the battery charger……. PB Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 11, 2020 Share Posted January 11, 2020 Posted by Peter Beeney on 11/01/2020 13:51:13: Keith, Thanks for your reply, but I think that there’s really very little I can add to all this now, other than that I do tend to take a bit of a different slant on the subject. Been tinkering with it for a fair time now, and it’s always worked for me, at least up till today anyhow. Like a voltage going down a wire I always take the line of least resistance; or just lazy, I guess; and I also have to be careful when overdoing the thinking bit, (also very easy for me!), like a resistor suffering from a serious overdose of amps the old brain can get a bit overheated… and well flummoxed into the bargain, too… Right, now off to brush the cobwebs out of the battery charger……. PB No problem, Peter, but, at the risk of being pedantic, if not actually so, there is no “different slant” in terms of what a “C” rating is and it is absolutely not, in itself, a “motor killer” because any battery or power supply will only supply the current that the load is demanding/pulling and as current demand reaches the limits of a “C” rated battery, the voltage will drop thereby limiting the maximum motor/prop speed. A high “C” battery is, therefore more capable of supplying higher current and allowing higher motor/prop speed without the corresponding voltage drop of a low “C” battery. As you like tinkering, you could easily prove this yourself by careful experimentation with a given load. Try connecting a low “C” rated battery to a load and driving it until the voltage drops to a stable level, then measure the current at that voltage. Do the same with a high “C” battery, BUT first measuring the current at the previous obtained value, THEN check the voltage. Ideally, I would use batteries of the same make with the widest difference between “C” ratings and of the same capacity in order to get the clearest and most accurate result. Usual safety procedures apply, of course, like opening the throttle progressively and choosing the right components for the job! Happy experimenting! And don’t kill any spiders! Edited By Keith Miles 2 on 11/01/2020 15:11:00 Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted January 11, 2020 Share Posted January 11, 2020 Keith, Again I shall have to gently agree to disagree with you, for a start I’m not sure that I ever mentioned the C rating as being a motor killer anyway. Maybe rather the opposite, perhaps. I was simply considering choosing the right motor/battery/prop aspect of the discussion. In my view the battery C rating is only a peripheral of this, just needs to be pondered over somewhat whenever a constant high current supply becomes an issue. As it so happens, sixty plus years ago I was starting to get involved with amongst many other things battery installations such that the C ratings had to be big enough to maintain the voltage between some quite narrow limits under heavy current supply conditions. Usually this lump was an original spec. and well up to the job of course, but occasionally there was an emergency breakdown to fix. In those days you were basically on your own so then you had to do a quick calculation; this simply consisted of wanging in a backup that was definitely big enough for all eventualities and then some to spare, too. However, along the way I did at least begin to get a little bit of the hang of battery speak……. Very unlikely to be doing any experimenting, either; did all that a while back. Feet up and just read the newspaper nowadays. The spiders have all died already….. of old age! PB Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 11, 2020 Share Posted January 11, 2020 Posted by Peter Beeney on 11/01/2020 18:46:43: Keith, Again I shall have to gently agree to disagree with you, for a start I’m not sure that I ever mentioned the C rating as being a motor killer anyway. Maybe rather the opposite, perhaps. I was simply considering choosing the right motor/battery/prop aspect of the discussion. In my view the battery C rating is only a peripheral of this, just needs to be pondered over somewhat whenever a constant high current supply becomes an issue. As it so happens, sixty plus years ago I was starting to get involved with amongst many other things battery installations such that the C ratings had to be big enough to maintain the voltage between some quite narrow limits under heavy current supply conditions. Usually this lump was an original spec. and well up to the job of course, but occasionally there was an emergency breakdown to fix. In those days you were basically on your own so then you had to do a quick calculation; this simply consisted of wanging in a backup that was definitely big enough for all eventualities and then some to spare, too. However, along the way I did at least begin to get a little bit of the hang of battery speak……. Very unlikely to be doing any experimenting, either; did all that a while back. Feet up and just read the newspaper nowadays. The spiders have all died already….. of old age! PB For the record, I was not suggesting that you used the phrase you mention but someone else did. You and I, I think, are “cool” as they say. No pun intended. Quote Link to comment Share on other sites More sharing options...
PatMc Posted January 11, 2020 Share Posted January 11, 2020 Posted by Keith Miles 2 on 11/01/2020 15:03:02: ... as current demand reaches the limits of a “C” rated battery, the voltage will drop thereby limiting the maximum motor/prop speed. Keith, not sure if that's literally what you mean, but being pedantic, no matter what the C rating is, the internal resistance of the battery will cause a voltage drop as soon as the motor is connected. The voltage will continue to drop throughout the motor run. Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 11, 2020 Share Posted January 11, 2020 Posted by PatMc on 11/01/2020 21:41:38: Posted by Keith Miles 2 on 11/01/2020 15:03:02: ... as current demand reaches the limits of a “C” rated battery, the voltage will drop thereby limiting the maximum motor/prop speed. Keith, not sure if that's literally what you mean, but being pedantic, no matter what the C rating is, the internal resistance of the battery will cause a voltage drop as soon as the motor is connected. The voltage will continue to drop throughout the motor run. Pedantic, yes, but that’s fine by me! Yes, I would agree that your comment is a more accurate statement. And, yes, internal resistance is lower, the higher the “C” rating, and therefore the lower the volt drop for a given current. And, throwing something else into the mix, as I understand it, for certain non “C” rated cells, the higher the capacity, for a given physical sized battery, the higher the internal resistance and the higher the voltage drop for a given current! I believe this is, or was, the case with NiCd and NiMh AA and AAA, for example? Happy to be corrected! Quote Link to comment Share on other sites More sharing options...
Pete B Posted January 12, 2020 Share Posted January 12, 2020 I'm a little late to the party but can I remind those concerned that on this forum we conduct ourselves with courtesy and civility towards other members. You can disagree with someone without resorting to insults. If that's not possible, then either scroll past the post or use the PM system to argue. Thanks for your cooperation - I'll put this down to being weather-related..... Pete Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted January 12, 2020 Share Posted January 12, 2020 Seems to be a lot of ‘weather’ about atm. Need to have more fun ( or Sun) Tim 🌞 Quote Link to comment Share on other sites More sharing options...
Former Member Posted January 13, 2020 Share Posted January 13, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Keith Miles 2 Posted January 13, 2020 Share Posted January 13, 2020 Posted by Tom Sharp 2 on 13/01/2020 01:22:52: As an old workmate of mine was always saying, "It all brings night". And early morning! Quote Link to comment Share on other sites More sharing options...
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