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Jan 26, 2013, 06:54 PM
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holy cow! 21 motors! How many watts each? What's this for? Very interesting. Anyway....when you say "this" do you mean "adding capacitors to the battery leads at each ESC?" If so, yes. I called Castle Creations the other day and spoke to a technical expert for nearly 1 hr, and he recommended adding ~400 uF worth of capacitors for every 4 inches of extra battery wire added. Post 1 in this document says 220 uF/4 inches, which is probably closer to a minimum. Sounds like if you add the necessary capacitors you'll be ok. You could also place all your ESC's as close to the batteries as possible and then only add 1 or 2 sets of capacitor banks to cover all of the ESC's in one location, extending the 3 motor wires from each ESC as necessary to get to the motors.
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Jan 26, 2013, 06:59 PM
Retardedly intelligent
foam and tape's Avatar
Quote:
Originally Posted by panther3001
holy cow! 21 motors! How many watts each? What's this for? Very interesting. Anyway....when you say "this" do you mean "adding capacitors to the battery leads at each ESC?" If so, yes. I called Castle Creations the other day and spoke to a technical expert for nearly 1 hr, and he recommended adding ~400 uF worth of capacitors for every 4 inches of extra battery wire added. Post 1 in this document says 220 uF/4 inches, which is probably closer to a minimum. Sounds like if you add the necessary capacitors you'll be ok. You could also place all your ESC's as close to the batteries as possible and then only add 1 or 2 sets of capacitor banks to cover all of the ESC's in one location, extending the 3 motor wires from each ESC as necessary to get to the motors.
Thats what's confusing me, since its not a whole 5ft between the last motor and the battery (the first motor starts at about 14 inches) does this affect the need for caps?
Jan 27, 2013, 01:24 AM
Registered User
Yes, this does affect the need for caps. Caps are needed for sure still, and I'm thinking about how to calculate this. I'll get back to you with my opinion when I get the chance. Will require me making a spreadsheet and doing some calcs I think.
Jan 27, 2013, 08:55 PM
Registered User
Ok done. Check out this spreadsheet I made. I assumed you were using 25A ESC's. Simply fill in all yellow cells with your real values and the equations should work out (double check them). I am not 100% sure this is correct, but I believe it is. It all makes sense to me and I've done a lot more research in this area than the average guy. I trust my calcs enough that if it were me, I'd feel comfortable building a system based on my results.
Jan 27, 2013, 08:57 PM
Registered User
Shoot, RCGroups doesn't allow Excel attachments, so I ended up having to post it elsewhere. See my blog here for the spreadsheet: http://electricrcaircraftguy.blogspot.com (click on link to "Calculations For Additional Capacitors Necessary...." on right-hand side of web page if this is no longer the most recent blog post when you arrive at the page).

Update 14 March 2013: direct link to Capacitor page is here: http://electricrcaircraftguy.blogspo...apacitors.html
Last edited by panther3001; Jul 10, 2013 at 10:48 PM.
Jan 27, 2013, 09:01 PM
Registered User
Ultimately, I divided up the wire lengths between the ESC's into "stations," then I did some calculations to estimate how many capacitors (of the same size and specs as existing ones on the ESC) you need to add to each ESC in order to make it all work. I came up with stations A through K, with each station needing between 1 and 10 additional capacitors (for my assumed 25A ESC's), and most stations only needing 1 or 2 additional capacitors.
Jan 27, 2013, 09:06 PM
Registered User
Lastly, DON'T FORGET TO TWIST YOUR BATTERY + AND - LEADS TOGETHER AS MUCH AS POSSIBLE (in order to decrease inductance-induced voltage spikes and mitigate the problem anyway)
Jan 27, 2013, 10:20 PM
Retardedly intelligent
foam and tape's Avatar
Ok, thanks very much. This will make planning it out much easier!
Jan 27, 2013, 10:25 PM
Retardedly intelligent
foam and tape's Avatar
Also, the ESC's will be 8-10A controllers.
Jan 28, 2013, 12:07 AM
Registered User
Awesome. Please keep me informed on how this goes, and after you get it all set up and get some good flight time under it let us know if it appears to be working. A flight video would be neat too. (Maybe open a new thread for it--just to show us---and put the link to it in this thread). If you ever burn up something too or have a problem, be sure to let me know, as I'm very curious how this actually turns out since I've never done anything like it. My capacitor/inductance knowledge is strictly theoretical up to this point, so you are the experimental end of this and I'd like to know if the theory (and my calculations, in this case) match up more or less to real life. Thanks!
Jan 28, 2013, 12:30 AM
Retardedly intelligent
foam and tape's Avatar
Will do, I'll start a build thread in about 2weeks. Got to finish up 3 VTOL projects up first.
Mar 13, 2013, 03:52 AM
Up-Out-&-Gone
demondriver's Avatar
Quote:
Originally Posted by foam and tape
Thats what's confusing me, since its not a whole 5ft between the last motor and the battery (the first motor starts at about 14 inches) does this affect the need for caps?
This will Be ONE-AMAZING project Peter, but you better get started if you wanna have it there For SEFF 2013.
Latest blog entry: RC 737 Max 7 Maiden flight!
Mar 14, 2013, 05:03 AM
Registered User
Quote:
Originally Posted by panther3001
Lastly, DON'T FORGET TO TWIST YOUR BATTERY + AND - LEADS TOGETHER AS MUCH AS POSSIBLE (in order to decrease inductance-induced voltage spikes and mitigate the problem anyway)

hello, very interesting excel sheet, only one thing to clear
in post #526 i got answer from Ron
about my question : Does current draw vs. battery capacity have an relationship? ...
Ron says: It's the wires the cause the inductance, not the battery (a huge capacitor)

in post #528 i ask again :
but if say current is 5AMp or current is 50AMp for a motor has the amount of current no effect? ,
(meaning you need more caps !)

i did never get an answer , on this question

and suddenly i read in your excel sheet this :
<--since Inductance is a factor of length and current, this means,
for example, that if you had a current of 50A over 4 in., you'd need an extra: (output value here) x 50A x 4in = _____uF. Ex: 3.1333 uF/(in*A) x 50A x 4 in = 627 uF

Inductance is a factor of length and current,
the higher the inductance the higher the spikes right ? the more caps you need??

in this whole thread nobody talked about that current is also important and needs more extra caps , what you tell now

i am a bit confused now , up till now i never take the amount of current into account

i only used this rule of post#1 (regardless of amount of current ):
As a rule of thumb, for every 4inch/10cm extra length/distance between battery and ESC, add an 220uF extra capacitance near the controller (electrolytic condensators, voltage the same as the capacitors already installed, low ESR type)

in your excel sheet the first motor A distance is 8 inch,
so according this rule 2 extra caps of 220uF needed
motor G distance is ( 62 inch - 6 inch for ESC of motor G =) 58 inch so 14 extra caps of 220uf needed

or am i doing the calculation wrong ??
Last edited by jaccies; Mar 14, 2013 at 05:25 AM.
Mar 14, 2013, 05:16 AM
Registered User
Inductance is not a factor of current, maybe magnetic field.
Mar 14, 2013, 03:46 PM
Registered User

inductance


http://en.wikipedia.org/wiki/Inductance

i would like to point out that inductance is part of AC theory not DC and works on current change and magnetic effects.
so your motor which is running on some type of AC supply will be prone to inductive effects the battery will have a very low rate of current change and DC will have no inductive effect acting on the wires if the ESC was designed by anybody with half a brain.

if you put a current probe from an oscilloscope on the wire you should see how smooth the current draw is.

normally in electronic design large capacitors are for smoothing. electrolytic capacitor are usually damaged by reverse polarity or to high voltage short circuit and go with a big bang.

also you must remember when a motor is turned off or changes speed there is a back EMF produced which will drive current into the circuit if the applied emf is lower than the aforementioned . this energy needs to be dissipated. this would go into the battery or capacitors.
this is actually known to destroy industrial inverters and they use may methods to get round it such as regeneration, DC breaking among other things.


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