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Old 04-29-2011, 10:14 AM   #1
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Default Explanation of BEC and capacitor please :)

Hello all,

I have a few question on a BEC and a capacitor out of pure curiosity.

First of all, is a BEC equivalent to a capacitor ? Is it just a capacitor with a litle receiver plug to allow easier connection to the receiver ? So does that mean that it can be connected to the ESC as well as the receiver simply by removing the plug ?

Second, why is a BEC good to have in onroad electric racing ?
I read loads on internet and stuff explaining the use of a BEC, but I dont understand why BEC in onroad electric xD ...

These days alot of the ESC's require a capacitor soldered at the + and - plug on the ESC, can this capacitor on the ESC be replace by the use of the BEC pluged in the receiver ?

Thank you to anyone who clarifies this
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Old 04-29-2011, 10:36 AM   #2
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BEC and a power capacitor are definietly not the same thing.

BEC (Battery Eliminator Circuit) supplies a constant voltage from the ESC to power the receiver (it eliminates the seperate battery pack that electric cars would need to run the receiver 30-odd years ago).

The power capacitor is to smooth the power supply to the ESC itself, which makes it operate more efficiently.
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Old 04-29-2011, 10:42 AM   #3
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Two completely different animals.

BEC = Battery Elimination Circuit. This is built into every Electronic Speed Control (with very few exceptions) made. It eliminates the need for an external receiver pack and steps down the voltage from the main power pack to about 5V for the receiver and steering servo. External BECs are commonly used with 3 cell and higher lipo packs to provide a steady current to the Receiver and servo bypassing the internal BEC of the ESC.

Capcitors are temporary electric storage devices sort of like a mini battery. ESCs use them to stabilize the power coming from the main battery pack. It helps the ESC run cooler but does not modify the voltage coming from the battery. You can use capacitors plugged into the receiver to smooth out any brown-outs caused by a power hungry servo. i.e., stutter-stopper, glitch buster among other names.
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Old 04-29-2011, 10:43 AM   #4
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Quote:
Originally Posted by digitrc View Post
BEC and a power capacitor are definietly not the same thing.

BEC (Battery Eliminator Circuit) supplies a constant voltage from the ESC to power the receiver (it eliminates the seperate battery pack that electric cars would need to run the receiver 30-odd years ago).

The power capacitor is to smooth the power supply to the ESC itself, which makes it operate more efficiently.
You're kinda right...

The bec's job is a voltage regulator basically, not many receivers can take much over 6 volts, as back in the day receivers/servos were powered via 4cell 6 volt receiver packs...

the bec basically just takes whatever the input voltage is, and lowers it down to usually around 4.8 to 6 volts to make it receiver safe..another BEC number to look out for is the amperage...alot of newer servos suck alot of amps!



the power capacitors are used to store energy for those quick burst's of throttle/braking/reversing, it helps lessen the load, and amp draw, as it takes the stored energy in the caps, and uses it when needed..think of them exactly like a powercap for a high power stereo that stops your lights from dimming, its the same concept.
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Old 04-29-2011, 11:31 AM   #5
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If you are running a sensored motor with a 13mm sintered rotor with 3 cell LiPo use two of Novak's power trans cap modules

#5685

I use Novak's BALLISTIC 3.5T/10500KV for drag racing

Solder them in the power supply wires going into the ESC

2cell LiPo can get away with one of the #5685


I do not like smoked ESCs
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Old 04-29-2011, 11:38 AM   #6
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does this means we can simply change to a higher capacity capacitor in hope for more power storage capacity?
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Old 04-29-2011, 01:43 PM   #7
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Ok, things are clearing up :P
And regarding K_Takuya's post, does it mean we can use higher rated capacitor to get more power ?

So a BEC might look like a capacitor but it's a total different thing, right ?
So how come there the exact same writings on a BEC and a capactior ( mentioning the uf and voltage ) ?

So the first conclusion is that a BEC cannot be soldered to a ESC to act like a capacitor ? Right ?

Thank you for the help and sorry for the hassle :/
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Old 04-29-2011, 02:19 PM   #8
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You are no doubt confused because you can plug both into the receiver.

BECs generally do not look at all like capacitors but some capacitors may look like a BEC (Speed Passion's for one, four cans on one board).

Let me simplify this; if there are more than one set of wires (two bare with no connector, one red and one black, and another three with a connector) coming out it is a BEC, if only one set of wires (usually a pair) it is a capacitor.

Capacitor: http://www3.towerhobbies.com/cgi-bin...&I=LXNRE0&P=ML or http://www3.towerhobbies.com/cgi-bin...&I=LXZKU6&P=ML

BEC: http://www3.towerhobbies.com/cgi-bin...&I=LXSWL3&P=ML or http://www3.towerhobbies.com/cgi-bin...?&I=LXJJF6&P=7
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Old 04-29-2011, 02:28 PM   #9
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Ok, Im looking at mine which I think is a capacitor xD , It has a big single can with written " 2700uf " and " 16v", then it has 2 wires, one black and red (as you said) and at the other end ther is a connector that is the same as the one on a servo but the 3rd hole is empty because there is only 2 wires.
I guess its a capacitor right ?
Can I solder it to my esc ?
Or can I directly plug it to the receiver?
Thanks alot
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Old 04-29-2011, 02:56 PM   #10
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Quote:
Originally Posted by cyclone speed View Post
Ok, Im looking at mine which I think is a capacitor xD , It has a big single can with written " 2700uf " and " 16v", then it has 2 wires, one black and red (as you said) and at the other end ther is a connector that is the same as the one on a servo but the 3rd hole is empty because there is only 2 wires.
I guess its a capacitor right ?
Can I solder it to my esc ?
Or can I directly plug it to the receiver?
Thanks alot
What you have there is something else again. It's a receiver capacitor, again designed to smooth the power supply to stop radio problems.
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Old 04-29-2011, 04:33 PM   #11
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Quote:
Originally Posted by K_Takuya View Post
does this means we can simply change to a higher capacity capacitor in hope for more power storage capacity?
not exactly. there are 2 different types of capacitors commonly used.

there is the fast switching type that the ESC mfg will supply. these act like a filter, smoothing out the spikes in the ESC power draw. this is happening at the drive frequency of the ESC. (fast like 10,000Hz or at least 1,000's) these are installed across the + and - ESC battery terminals.

the other cap is a slow discharge type that works like a storage device, these are used to avoid 'brown outs' in the BEC that can cause the spektrum receivers to reboot. the reboots of the latest spektrum recievers are so quick they seem like glitching. the original spektrums rebooted so slow they seemed to die and then come alive. these 'antiglitch' etc caps are usually equipped with a receiver plug, and the plug directly into the receiver.
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Old 04-29-2011, 06:21 PM   #12
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Ah finally the old cap myth debunked.

I never could see how a power cap could store any worthwhile energy in a RC circuit. The math doesnt really add up.
Its just in parallel with the batt, both will drop voltage equally, at the same time.
In fact if the batt has lower internal resistance( I assume it has), the power cap wont do anything (except filter spikes, noise etc)
Cap can be usefull power stores in AC power supplies, not DC.

Just From my experience...with spektrum receivers
The receiver cap has nothing to do with voltage drops, it smooths out spikes & noise - as seen when I scoped it up.
My esc has a 3A BEC, yet rx was still glitching/resetting/restarting with some nasty standard servos.No way the servo draw 3A.
Was just all the noise the servo was putting into the RX causing the issues, nothing to do with voltage drops. Spektrum RX will work below 4v.
Some receiver works perfectly with power cap if using a Ko Pro or Fubaba servo
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Old 04-30-2011, 02:26 AM   #13
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Ok, so now I understand
So there are BEC's ( used to replace a receiver pack ), ESC capacitors ( red goes to the red wire and black to black wire to store energy) and there are Receiver capacitors which is the one i described right ?
But can I remove the receiver plug on my receiver capacitor so that I can solder the wires of my capacitor to the ESC ?
Thanks
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Old 04-30-2011, 02:39 AM   #14
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Quote:
Originally Posted by cyclone speed View Post
Ok, so now I understand
So there are BEC's ( used to replace a receiver pack ), ESC capacitors ( red goes to the red wire and black to black wire to store energy) and there are Receiver capacitors which is the one i described right ?
But can I remove the receiver plug on my receiver capacitor so that I can solder the wires of my capacitor to the ESC ?
Thanks
Why would you want to do that?

The receiver capacitor is made to do a certain job. So use it for that job.

If you need a power capacitor for the ESC, use the capacitor the manufacturer recommends.
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Old 04-30-2011, 02:55 AM   #15
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Quote:
Originally Posted by digitrc View Post
Why would you want to do that?

The receiver capacitor is made to do a certain job. So use it for that job.

If you need a power capacitor for the ESC, use the capacitor the manufacturer recommends.
I'm not planning on doing it, but yes, what im asking might be weird but its just out of plain curiosity, I already have a ESC capacitor on my ESC, but I just wanted to know if there was a difference in using a Receiver capacitor on a ESC etc ...
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