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Mar 16, 2013, 06:33 AM
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Quote:
Originally Posted by jaccies
... A clubmember with a Hercules plane( wingspan 540cm ( 216 inch) with 4 motors , each has his own battery ,the outer motors battery cable length is 180cm (72 inch) and inner 2 motors battery length is 120cm (48 inch) , after a couple of flights the outer ESC 's from JETI went into smoke due to long battery cable length.

The capacitors on the ESC were exploded , totally gone !!, due to the high voltage spikes the caps got overheated and exploded ...
Thanks for that real-life example I suppose with 180cm leads it was to be expected.

Personally, I use capacitors since reading this thread a long time ago, but my comment in post #568 was aimed at people who add, say, 10cm to their leads to get a better layout. I should have made that clear.
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Mar 21, 2013, 12:14 AM
Registered User
Quote:
Originally Posted by jaccies
but thats not what you were saying ,
you saying the amount of caps is also depended of the current , the more current the more caps. ( see result of first cap high value on Motor A ESC)

i think you will also have an excel sheet for 1 battery to 1 ESC which takes the current also into account , right ??

my post 528 nobody answered, where i ask:
but if say current is 5Amp or current is 50Amp for a motor
has the amount of current no effect ?, with result using more caps when current is higher ?

your post tells now : amount of current has to take into account
That's all correct. I still say current has to be taken into account. However, for the 1 battery to 1 ESC case, if you use the 220uF/4 inches rule I think you'll be fine, as it seems to me, based on my spreadsheet estimator for "foam and tape's" strange motor setup, that the 220uF/4 inches rule is basically taking current into account by assuming the current passing by the ESC is equal to the ESC's max rating. For "foam and tape's" setup, though, this is not the case. Check out the new updated/corrected spreadsheet by downloading it using the link here: http://electricrcaircraftguy.blogspo...apacitors.html.

Carefully look it over, and read my notes, and you'll see that my rule of thumb, roughly taking current into account, is to use 2.35 uF/(in*A), which for the example in the spreadsheet, comes out to 235 uF/in, IF YOU HAVE ONLY ONE ESC AND ONE BATTERY. However, in the case of "foam and tape's" strange consecutive motor setup, again, the 220 uF/4 inches rule is completely inadequate, as it doesn't account for the fact that the voltage spike will be much stronger at the first ESC since there will be up to 175A running up to the wires (but in parallel with) the first 25A ESC. In other words, the first ESC sees a voltage spike of a strength corresponding to a magnetic field collapsing from a 175A current, but the last ESC sees a voltage spike of a strength corresponding to a magnetic field collapsing from a 25A current. (this is using my assumptions in the spreadsheet....that each ESC is 25A, though this is not the real case for him; he'd have to change some numbers in the spreadsheet). Anyway, the first ESC will see a much stronger voltage spike since the current (and hence magnetic field) is so much larger, and is repeatedly pulsing on and off according to the FETs rapidly opening and closign the current channels in the ESC to control throttle. So...the first ESC needs more capacitors than what the 220uF/4 in. rule would suggest. I believe my spreadsheet is at least a good ballpark estimate of what needs to be done for such a setup.
Last edited by panther3001; Jul 10, 2013 at 10:48 PM.
Mar 21, 2013, 12:30 AM
Registered User
Quote:
Originally Posted by keithtsr
I am confused....really nothing new for me but Jeti recommends not to extend the motor wires.
I run mostly Castle esc's will it hurt to extend the motor wires with this controller?
I would extend the motor wires, absolutely, regardless of which ESC I'm using. From my experience with Castle on the phone, and taking everything into account that I know, it seems to me that the reason ESC manufacturers recommend not extending motor wires is *completely* different from their reason for not extending battery wires. Extending battery wires can create large voltage spikes and blow capacitors. However, extending the 3 motor wires does not damage anything. Rather, it simply has the potential to create timing issues with your motor running smoothly, so the ESC manufacturers recommend not doing it, so that they can guarantee their equipment will work well. The reason it can create motor timing issues is that the brushless motors we use in RC are sensorless, and hence the ESCs manage timing using back EMF (Electromotive Force) pulses (rather than sensors in the motor), returning from the motor. However, changing the motor wire length affects when the pulses arrive, and can cause the motor to run weird. Basically, what I'd do is lengthen the motor wires, then experiment. If your motor runs weird, shorten *or* lengthen them a little more, and/or play with your timing settings in the ESC. It might sound counter-intuitive, but if I understand correctly, lengthening the motor wires even more, if it runs funny after lengthening them some, can help because it may change the timing such that the back EMF pulses arrive back at the ESC at an interval equal to a multiple of what the ESC was expecting, which might also be ok.

So, lengthen the 3 motor wires, play with settings, etc. I'd also try twisting the 3 motor wires together after lengthening them, as Post #1 in this thread tells us to do. Tell us how it goes if anything interesting happens, or even if it works just fine. I'm curious.
Mar 21, 2013, 07:21 AM
Registered User
PS. 2 more things really quickly:

1) If I am wrong about my calcs, Foam and Tape's setup should quickly let us know. If I am wrong, the caps in his ESC's at the very end of the line should fail rather quickly. If that happens, I hope he lets us know.

2) Be sure to use large gauge wire, as necessary, to take the appropriate amount of current, especially since the wire stations nearest the battery, in his setup, will see a very high current. Use this calculator here: http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
Mar 21, 2013, 08:36 AM
Keith Thomas
keithtsr's Avatar
Panther, Thank you. I have run it up and it seems to run smooth and no heating issues. I have the timing set to low. I am running 8 awg wire and twisted them together.

I have not run it up in the aircraft to see what changes. I will keep you posted. Would you add additional caps to the esc side anyway?

I can't thank you enough for helping!

KT
Mar 22, 2013, 05:16 AM
Registered User
You say:
That's all correct. I still say current has to be taken into account. However, for the 1 battery to 1 ESC case, if you use the 220uF/4 inches rule I think you'll be fine.

still bit confusing, you saying : current has to be taken into account
example 1 :
-1 battery to 1 ESC (100Amp) , battery leads are 40 inch
current = max 80Amp
How much extra caps do I need?
example 2:
-1 battery to 1 ESC (100Amp) , battery leads are 40 inch
current = max 30Amp
How much extra caps do I need?
Mar 22, 2013, 07:23 AM
Registered User
Quote:
Originally Posted by keithtsr
Panther, Thank you. I have run it up and it seems to run smooth and no heating issues. I have the timing set to low. I am running 8 awg wire and twisted them together.

I have not run it up in the aircraft to see what changes. I will keep you posted. Would you add additional caps to the esc side anyway?

I can't thank you enough for helping!

KT
No, since you lengthened only the 3 motor wires, as long as your battery leads are not extended you don't need any caps on the ESC side. Any inductance-induced voltage spikes due to increased motor wires are going into the motor not the ESC, and since the motor is already one huge coil of wires, you've only marginally increased its inductance, so I believe you are fine as-is.
Mar 22, 2013, 07:26 AM
Registered User
Quote:
Originally Posted by jaccies
You say:
That's all correct. I still say current has to be taken into account. However, for the 1 battery to 1 ESC case, if you use the 220uF/4 inches rule I think you'll be fine.

still bit confusing, you saying : current has to be taken into account
example 1 :
-1 battery to 1 ESC (100Amp) , battery leads are 40 inch
current = max 80Amp
How much extra caps do I need?
example 2:
-1 battery to 1 ESC (100Amp) , battery leads are 40 inch
current = max 30Amp
How much extra caps do I need?
How many Caps are in your 100A ESCs for each example? And what size are these caps? You will likely need to cut open the wrap to know. Also, what was the length of the battery wire leads on the ESC-side only (ie: how long were the 2 battery wires that came attached to each 100A ESC?).
Mar 23, 2013, 03:49 AM
Registered User
Quote:
Originally Posted by panther3001
How many Caps are in your 100A ESCs for each example? And what size are these caps? You will likely need to cut open the wrap to know. Also, what was the length of the battery wire leads on the ESC-side only (ie: how long were the 2 battery wires that came attached to each 100A ESC?).
there are 2 caps of 470uF 50V , and ESC cable length is 5 inch

i will wait for your results, may be an excel sheet would be nice thanks
i can fill in myself next time
Mar 26, 2013, 07:48 AM
Registered User
Quote:
Originally Posted by jaccies
there are 2 caps of 470uF 50V , and ESC cable length is 5 inch

i will wait for your results, may be an excel sheet would be nice thanks
i can fill in myself next time
I modified my other spreadsheet. Download it at the bottom of the post here:
http://electricrcaircraftguy.blogspo...apacitors.html

Again, this is only a simple estimate, assuming that the ESC designer knew what he was doing and designed to a certain set of specifications, and then I am just estimating how many more capacitors we need to keep to the same specifications. It is by no means exact, but for me I think it's good enough until I can get an exact result by someone who knows way more than me.

You'll see in the spreadsheet:
-for your ESC, I estimated you need an additional 0.94 uF/(in*A) (using 50V capacitors), since this (0.94 uF/(in*A) is what your ESC already has, of capacitors of this voltage.

Example 1 (100A ESC, 40" battery leads, 80A max current draw): add 5 capacitors (for this case, I estimated you need an additional 300.8uF/4in [0.94*80*4])

Example 2 (100A ESC, 40" battery leads, 30A max current draw): add 1 capacitor (I estimated you need an additional 112.8uF/4in [0.94*30*4])

And another example I added (100A ESC, 40" battery leads, 100A max current draw): add an additional 6 capacitors (I estimated you need an additional 376uF/4in [0.94*100*4])
Last edited by panther3001; Jul 10, 2013 at 10:47 PM.
Mar 28, 2013, 04:33 AM
Registered User
Quote:
Originally Posted by panther3001
I modified my other spreadsheet. Download it at the bottom of the post here:
http://electricrcaircraftguru.blogsp...apacitors.html

Again, this is only a simple estimate, assuming that the ESC designer knew what he was doing and designed to a certain set of specifications, and then I am just estimating how many more capacitors we need to keep to the same specifications. It is by no means exact, but for me I think it's good enough until I can get an exact result by someone who knows way more than me.

You'll see in the spreadsheet:
-for your ESC, I estimated you need an additional 0.94 uF/(in*A) (using 50V capacitors), since this (0.94 uF/(in*A) is what your ESC already has, of capacitors of this voltage.

Example 1 (100A ESC, 40" battery leads, 80A max current draw): add 5 capacitors (for this case, I estimated you need an additional 300.8uF/4in [0.94*80*4])

Example 2 (100A ESC, 40" battery leads, 30A max current draw): add 1 capacitor (I estimated you need an additional 112.8uF/4in [0.94*30*4])

And another example I added (100A ESC, 40" battery leads, 100A max current draw): add an additional 6 capacitors (I estimated you need an additional 376uF/4in [0.94*100*4])
Thanks Gabe for explaining , up till now nobody took into account the current, and as you can see in the examples there is a great difference in extra cap's use due to amount of current.

1 cap=470uF
- According the rule of thumb : 220uF/4inch
40" battery leads extra length = 2220 uF required is approx: 5 extra cap's

- your calculations:
ESC 100A , 40inch extra wire , Current 30Amp , extra caps 1
ESC 100A , 40inch extra wire , Current 80Amp , extra caps 5

My conclusion is: :
-For the 1 battery to 1 ESC case :
Use the rule of thumb 220uF/4inch and you are doing it very safe, independent of the current value.

-For the 1 battery to 2 or more ESC's case :
use spreadsheet of Gabe (panther3001)
Last edited by jaccies; Mar 28, 2013 at 04:52 AM.
Apr 14, 2013, 07:44 AM
Registered User
~>Miha<~'s Avatar
Folks, any idea what is wrong with this ESC?

ESC start-up problem (0 min 45 sec)


The short 45s video shows the start-up sequence (turn on speakers). After 3s lipo gets connected, it makes the typical 3-beeps welcome, then 3-beeps for 3s lipo detected, but then instead of 3-beep all-is-okay it beeps endlessly. Well, almost, after appr. 30s the nearly-endless beeping stops and the 3-beep all-is-okay comes and motor can be used.

Capacitor?

I've removed the shrink wrap to check soldering and all seems okay (was my first thought).
Apr 15, 2013, 03:18 AM
Registered User
Quote:
Originally Posted by ~>Miha<~
Folks, any idea what is wrong with this ESC?

http://www.youtube.com/watch?v=9_ewadpJebs

The short 45s video shows the start-up sequence (turn on speakers). After 3s lipo gets connected, it makes the typical 3-beeps welcome, then 3-beeps for 3s lipo detected, but then instead of 3-beep all-is-okay it beeps endlessly. Well, almost, after appr. 30s the nearly-endless beeping stops and the 3-beep all-is-okay comes and motor can be used.

Capacitor?

I've removed the shrink wrap to check soldering and all seems okay (was my first thought).
capacitor cant be the problem.
this beeping is normally an indication throttle level not low enough, or no signal provided , or signal level to low

try to set throttle low level lower ( trim should be down ), may be it is just on the edge of beeping no beeping
Apr 15, 2013, 06:01 PM
Registered User
I agree with Jaccies. Sounds like the low throttle isn't being properly detected. On a computer radio, you can either move trim down to fix the problem, subtrim down to fix the problem, or expand your low-end throttle endpoint adjustment to fix the problem (best solution). Ex: I would set your throttle trim to center, your subtrim to 0 (neutral), and I would increase the %value of the low-throttle endpoint until the ESC initializes as normal. Perhaps this will occur at a low endpoint of -110%, -120%, or -130%, etc. Once you find the exact value that works, go a couple %s beyond that value to make sure you're never right on the edge.
Apr 24, 2013, 10:25 PM
Keith Thomas
keithtsr's Avatar
I have an off the subject question that I feel good about asking here. I hope you don't mind.

Last weekend we were flying a T-45 on 8s 4400 40c packs. My clamp meter is not working so I figured I would have about 3 minutes of flying......wrong at 2:15 the packs were dead. I needed about 50' to make the runway, now I have a rebuild project.

To the question, is there a way to figure amps given the mah and run time? I'm guessing the amps must have been pretty high. I was using a Hobby Wing 120hv that still works.

Thanks


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