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Post by Mr NCT on Jun 5, 2022 18:32:39 GMT
Saw a discussion of this on the FT forum and an article in this month's AMA magazine so thought I'd repost my test here-
This idea, length of battery wires vs length of motor wires, seemed pretty interesting to me. I saw the same conclusion in this month's AMA magazine that longer battery wires increased pulses that needed to be handled by the capacitors in the ESC and therefore would cause the caps to meet an untimely demise. The AMA article also mentioned the length of the battery wire adding extra resistance. So I thought I'd test. BTW, I'm an electrical engineer who works with electricity/electronics in the manufacturing field on a daily basis. I have a lot of real world experience with inverters which is basically what ESCs are.
This is not a comprehensive, complete test of every motor, battery, cable & ESC combination. So please don't flame me for not being exhaustive. It's only an indication of what happens on a set up that I fly regularly - my real world conditions. Your mileage may vary.
I used 16ga. battery wire, an FT C pack motor swinging a 10x4.5 prop, a 35A FT ESC and a 2200 3s battery. The battery wire on the ESC is 3" long and the battery has a 4" wire. I did my tests at the end of the ESC wire. I have a 36" battery extension that has a resistance of 0.075 ohms per wire for a total of 0.15 ohms. I didn't use a watt/amp meter, though I did use a calibrated Fluke 289 meter and a LeCroy WaveAce 102 scope to measure the two things I was interested in, the resistance of the wire and the pulse generated.
The first test I did was battery to ESC with no extension so a total wire length of 7". I cranked the motor up to full speed and saw a 0.6 volt spike that changed frequency as the motor changed speed.
For the second test I inserted the 36" extension so now a total of 43" of battery wire. This time I saw the same spike but measuring 0.8 volt.
So, in my set up there was a difference. A difference that I'm going to worry about? Probably not. Personally if I need an extension I'll still extend the battery leads. Extending the motor wires leads to a whole new set of problems like inductive resistance - there's a reason power transmission wires are so precisely spaced from each other.
Just my 2 cents.
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Post by Burkeomatic on Jun 5, 2022 18:47:57 GMT
Saw a discussion of this on the FT forum and an article in this month's AMA magazine so thought I'd repost my test here- This idea, length of battery wires vs length of motor wires, seemed pretty interesting to me. I saw the same conclusion in this month's AMA magazine that longer battery wires increased pulses that needed to be handled by the capacitors in the ESC and therefore would cause the caps to meet an untimely demise. The AMA article also mentioned the length of the battery wire adding extra resistance. So I thought I'd test. BTW, I'm an electrical engineer who works with electricity/electronics in the manufacturing field on a daily basis. I have a lot of real world experience with inverters which is basically what ESCs are. This is not a comprehensive, complete test of every motor, battery, cable & ESC combination. So please don't flame me for not being exhaustive. It's only an indication of what happens on a set up that I fly regularly - my real world conditions. Your mileage may vary. I used 16ga. battery wire, an FT C pack motor swinging a 10x4.5 prop, a 35A FT ESC and a 2200 3s battery. The battery wire on the ESC is 3" long and the battery has a 4" wire. I did my tests at the end of the ESC wire. I have a 36" battery extension that has a resistance of 0.075 ohms per wire for a total of 0.15 ohms. I didn't use a watt/amp meter, though I did use a calibrated Fluke 289 meter and a LeCroy WaveAce 102 scope to measure the two things I was interested in, the resistance of the wire and the pulse generated. The first test I did was battery to ESC with no extension so a total wire length of 7". I cranked the motor up to full speed and saw a 0.6 volt spike that changed frequency as the motor changed speed. For the second test I inserted the 36" extension so now a total of 43" of battery wire. This time I saw the same spike but measuring 0.8 volt. So, in my set up there was a difference. A difference that I'm going to worry about? Probably not. Personally if I need an extension I'll still extend the battery leads. Extending the motor wires leads to a whole new set of problems like inductive resistance - there's a reason power transmission wires are so precisely spaced from each other. Just my 2 cents. I am not an electrical engineer. I don't talk about it a whole lot, but I am about 7 classes away from my BS in ME. Why don't I talk about it alot? I couldn't finish my degree on active duty so I switched it to environmental science, and the classes were so spread out that I have forgotten about 50% of what I have learned. I have had to take some EE classes, and most of my electrical knowledge is in automotive electronics. I pretty much thought to the same conclusion. I am glad you did some testing. You can do all of the intellectual thought exercises you want, but when hard test data walks in the door, all bets are off. So according to your test, that is less than .1 volt per foot of wire. I think the longest extension I have is a 20 inch one on my F-106. That is a long jet too. Obviously there will be variances with gauge of wire, and voltage. At the end of the day, I thought that we aren't talking huge distances of wire, and we are also talking about a max $50 piece of equipment. Furthermore, failure would probably manifest gradually, and not a violent eruption of capacitors like everyone thinks. All this assuming you are running your ESC towards max capacity, which most aren't for long periods of time. I think we catastrophize about little things like this. This thought process has been around for a long time. It is odd how some parts of the RC hobby don't carry over to others. RC car dudes with their very expensive ESCs have been doing this for quite a while. I neglected to do it to my rustler. That thing has been kicking for years and I was too lazy to put caps on it after I extended the wires. Although, it is unlike me to ball out on name brand electronics, I have a full castle creations set up on it. endless-sphere.com/forums/viewtopic.php?t=35420I have other anecdotal stories like that involving cars, there are mods that you JUST HAD to do, that I never saw the sense in that I never did, and my car was just fine.
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Post by Mr NCT on Jun 5, 2022 19:04:34 GMT
It didn't smell right but I wasn't sure why so since I had the equipment I thought I'd test. Especially since my EE is from 1974 Doesn't seem to be a concern at the voltages and amp draw that I'm using.
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Post by Burkeomatic on Jun 5, 2022 19:49:05 GMT
It didn't smell right but I wasn't sure why so since I had the equipment I thought I'd test. Especially since my EE is from 1974 Doesn't seem to be a concern at the voltages and amp draw that I'm using. Yeah, some folks using big ole 6s or 12s systems, it may matter more, who knows. Not anything I am willing to get bent out of shape over. Also, think of all of the contributing factors for ESC failure. That is like saying moisture contributes, and if you fly your plane on humid days, the ESC can die faster. Or heat is the enemy, and if you fly when it is hot, the ESC will fail quicker. We want this hobby to be easy, we don't want someone younger or doesn't have experience with electronics stressed about extending their harness 2 inches to make their model work. The only time I really need to worry with it is twins and on jets or big pushers where the motor needs to be far from the battery. If I think of my nightfury, it is about a 9 inch long y connector going into one battery. If I did it right and used a power distribution board, I don't see any capacitors on those either. Makes you wonder. It looks to be an inductance issue more than anything, and me thinks if you aren't a knuckle head and use smooth throttle transitions, that would go a long way.
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Post by Mr NCT on Jun 5, 2022 22:59:52 GMT
It didn't smell right but I wasn't sure why so since I had the equipment I thought I'd test. Especially since my EE is from 1974 Doesn't seem to be a concern at the voltages and amp draw that I'm using. We want this hobby to be easy, we don't want someone younger or doesn't have experience with electronics stressed about extending their harness 2 inches to make their model work. Stressing about the length of battery wires in anything but an extreme setup is like worrying about the ripples on the FB causing turbulence and drag on the wings. Yeah, it's there but come on, get real.
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Post by Burkeomatic on Jun 6, 2022 0:10:20 GMT
We want this hobby to be easy, we don't want someone younger or doesn't have experience with electronics stressed about extending their harness 2 inches to make their model work. Stressing about the length of battery wires in anything but an extreme setup is like worrying about the ripples on the FB causing turbulence and drag on the wings. Yeah, it's there but come on, get real. At the end of the day, most people aren't needing or looking for that last 5%. The only time I was I was running a limited autocross class. By rooting through about 5 engines, you can piece one together using all stock parts that makes about 10 more hp. You can shorten wires about an inch or six here or there which ends up adding up to about 5lb. Little sneaky things, lol. Then everyone is running $2000 15 inch wheels because they are about 12 oz lighter each, and custom revalved "stock" shocks that run about $3k. All that and your "stock" class car ends up costing about $15k over what an actual off the lot car costs.
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Post by ratcheeroo on Jun 6, 2022 19:52:08 GMT
I have read and watched a couple different things on this and I agree, much ado about nothing really. I can't recall FT ever broaching that subject and they obviously aren't too worried about it considering some of the builds they have done as of late. I just put an extension of about 2 feet on the Bandit and didn't notice a difference, and the harness on my MS P-38 is huge, as well as the one on the DH-88 and my Sportwin, zero issues with any of them.
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Post by Mr NCT on Jun 6, 2022 22:28:37 GMT
Well, I got the reaction I expected over on the other forum. How dare I question popular wisdom and back it up with a test? My favorite part was " From what I understand it is not the voltage of the spike but the energy absorbed by the capacitor to contain it and the heat created that damages the capacitor over time." Not the voltage but the energy? Do volts, amps and resistance somehow decouple because it's in an airplane? Or was Ohms Law repealed while I wasn't looking? Where is Monte.C when you need him? Moooooooooooooonnnnnnnnnnnnttttttttttttttttttteeeeeeeeeeeeeeeeeeeeee!!!!!!!!!!!!
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Post by Mr NCT on Jun 6, 2022 22:31:13 GMT
Maybe I'll get banned again for trolling. After all I did post something that I knew would get a reaction.
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Post by Burkeomatic on Jun 6, 2022 23:50:14 GMT
Maybe I'll get banned again for trolling. After all I did post something that I knew would get a reaction. Oh, you got banned the first time? They have kind of turned from Flite Test to Flite buy our crap. They still do cool stuff, kind of unobtanium for most of us these days, but still cool. Anyways, is there anyway to reduce inductance rather than to use a capacitor to soak it up? Here is a very, very stupid question of me, because I can be electrodumb sometimes, if you are running an ESC say rated 2-6S, and you are at 3S, won't any voltage spikes pretty much be a non issue. You would in no way be approaching the voltage limit of the ESC, the FETs should be able to handle it. I am really, really rusty at this, but isn't the voltage change across an inductor? Like v=L(dt/di). Given a constant voltage that the system is trying to maintain (lets say 11.1v) then we can measure current difference through the inductor. Am I using the wrong formula here? If we don't know the voltage, we could get the current change, then solve for the voltage? So there are variables in it. How do you hammer the throttle? It isn't like we are jamming a switch, right? You can always add capacitors if you get worried. It probably varies drastically based on what the plane is for. Most of the planes likely to have long wires, probably won't be as susceptible to you hammering the throttle up and down, no? A pusher FPV plane will probably fly at a steady state of throttle, much as my jet or my twin engined planes will. A 3D plane will probably have the battery, ESC, and motor all jumbled up in the front will likely experience high throttle modulation. So more of a concern if you use your throttle like a light switch, or you have a EDF mounted 3 feet from the battery running 4S. Oh, what about distance between the wires? That matters too last time I checked. Are they coiled? Twisted? Difference between them? Edit: By the way, this has sent me down a rabbit hole of internet research that I semi-regret. One references a blimp with 30' wires, and then there is this. This guy seems to know his stuff, but he claims wire inductance doesn't reduce with diameter, but it kind of does, why would radius of the wire be included in the inductance formula? Also, number of strands in the wire would matter too wouldn't it? www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-workarounds
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Post by bwarz on Jun 7, 2022 0:13:38 GMT
Well, I got the reaction I expected over on the other forum. How dare I question popular wisdom and back it up with a test? My favorite part was " From what I understand it is not the voltage of the spike but the energy absorbed by the capacitor to contain it and the heat created that damages the capacitor over time." Not the voltage but the energy? Do volts, amps and resistance somehow decouple because it's in an airplane? Or was Ohms Law repealed while I wasn't looking? Where is Monte.C when you need him? Moooooooooooooonnnnnnnnnnnnttttttttttttttttttteeeeeeeeeeeeeeeeeeeeee!!!!!!!!!!!! "Ohm's Law isn't really a law - it is just a sort of guidelines..." spoken in your best Captain Barbosa voice... Lots of people just don't want to admit it when they are wrong. There's no science left - just memes!
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Post by bwarz on Jun 7, 2022 0:25:05 GMT
Maybe I'll get banned again for trolling. After all I did post something that I knew would get a reaction. Oh, you got banned the first time? They have kind of turned from Flite Test to Flite buy our crap. They still do cool stuff, kind of unobtanium for most of us these days, but still cool. Anyways, is there anyway to reduce inductance rather than to use a capacitor to soak it up? Here is a very, very stupid question of me, because I can be electrodumb sometimes, if you are running an ESC say rated 2-6S, and you are at 3S, won't any voltage spikes pretty much be a non issue. You would in no way be approaching the voltage limit of the ESC, the FETs should be able to handle it. I am really, really rusty at this, but isn't the voltage change across an inductor? Like v=L(dt/di). Given a constant voltage that the system is trying to maintain (lets say 11.1v) then we can measure current difference through the inductor. Am I using the wrong formula here? If we don't know the voltage, we could get the current change, then solve for the voltage? So there are variables in it. How do you hammer the throttle? It isn't like we are jamming a switch, right? You can always add capacitors if you get worried. It probably varies drastically based on what the plane is for. Most of the planes likely to have long wires, probably won't be as susceptible to you hammering the throttle up and down, no? A pusher FPV plane will probably fly at a steady state of throttle, much as my jet or my twin engined planes will. A 3D plane will probably have the battery, ESC, and motor all jumbled up in the front will likely experience high throttle modulation. So more of a concern if you use your throttle like a light switch, or you have a EDF mounted 3 feet from the battery running 4S. Oh, what about distance between the wires? That matters too last time I checked. Are they coiled? Twisted? Difference between them? Edit: By the way, this has sent me down a rabbit hole of internet research that I semi-regret. One references a blimp with 30' wires, and then there is this. This guy seems to know his stuff, but he claims wire inductance doesn't reduce with diameter, but it kind of does, why would radius of the wire be included in the inductance formula? Also, number of strands in the wire would matter too wouldn't it? www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-workaroundsNow you have me trying to recall stuff for long long ago! Just using my thought here and some stuff I remember (although I may be wrong, I'm just happy to be done with work for the day so I'm in a thinking without reading mood). High frequencies like to hang out on the outer surface of a wire. More strands = more 'area' when at the switching frequency? And I love the 'absorbs the energy'. The cap is trying to level the spikes. You can;t have more energy without higher voltage spikes. That little P=IV thing. Or is that just a guideline also? The higher spikes push the cap closer to its limit. If you don't exceed said rated voltage limit, you have no worries. And Burkeomatic you are for sure right - if a ESC is rated to 6S there is no way you will ever need to worry about hitting the rated voltage of the caps running 3S (well, unless you are flying control line with like 1000M of wire and the battery attached to your handle. but at that point you wouldn't have enough voltage left at the ESC to fly the plane anyways, or the wires would be so heavy it'd never even move
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Post by Mr NCT on Jun 7, 2022 0:31:50 GMT
Yeah, I got a two week time out. Don't know if it was for not jumping up and down in Matthew's defense or for quoting Robert Heinlein in one of the nonsense "Reserved" threads. I think the soaring simian just decided to make a point.
"By the way, this has sent me down a rabbit hole of internet research that I semi-regret."
It amazes me how easy that is! Maybe we should name it: EIRHS (excessive information rabbit hole syndrome). I'm going to leave my testing where it is. It convinced me that while it might be a real thing this pulse effect really is no danger to any of my set ups. My planes have way more to fear from my flying skills (or lack thereof) than any 0.2 volt increase in spike.
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Post by Burkeomatic on Jun 7, 2022 1:37:19 GMT
Well, the hottest motor any of them are ever going to run is a 3536 motor for the 'giant' scout, or the "fast" warbirds. Which is ok, but that also means this effectively doesn't matter. Do I think it matters? Sure. I do, honestly. You bet your butt I would be calculating my you know what off if I had a $500 electronic set up on the line. Buuuuuuut I don't. So I don't care. If I blow up one of my $5-20 escs, I'll just pick up another 4 pack on aliexpress and maybe extend the motor wires and not the battery wires.
I actually think @ratcheroo had asked or had a pic of something regarding his motors and I said something to the effect that "you're technically supposed to extend the motor wires, but I don't" or something stupid like that.
It looks like it is getting near time to make another account on there. Looks like I am missing out on the fun. The great thing is, no one will ever know it is me. I need to go look at this thread now, don't I.
Edit: Found it, nothing too obnoxious.
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Post by Mr NCT on Jun 7, 2022 23:06:34 GMT
Nothing over the top, just someone saying 'don't bother me with your tests and data, I'm confident with something I've read somewhere and you're going to crash if you don't believe me.'
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