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 ESC's and BEC's,

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Nuttcaze
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PostSubject: ESC's and BEC's,   Tue Sep 22, 2009 12:08 am

Here is an article about why using a Serparate BEC is a good thing (especially for BIG helis), this is directly from HeliDirect

http://www.helidirect.com/Manual/bec.pdf

Quote :
ESC’s and BEC’s

Why the battery eliminator circuit in your electronic speed control
may not be up to the task.
Many electronic speed controllers (ESC’s) have built in battery eliminator circuits (BEC’s).
The manufacturers provide this as a convenience to end users and in certain applications they do work well.

However, many BEC’s are under rated (output current wise) for the tasks we are asking.

So be careful if you are thinking of using the BEC build into your ESC. Carefully check its maximum continuous and peak current ratings, and compare this to what you expect your servos and receiver actually will draw in flight. Typically a BEC built into an ESC may only be capable of delivering 3‐4 amps. Even if it is a 120 amp ESC – which you are going to use on a 600 size electric helicopter – you may expect the BEC output will be okay, but often it wont be – this class of model with high end servos may draw 6‐8 amps or more! Of course, this same ESC used in an aircraft with ‘sport’ servos may work just fine with the low current built in BEC.

So the Solution:
In most medium or larger models the ESC’s BEC current rating is likely to be inadequate. Furthermore, for the sake of reliability, a separate BEC / regulator should normally be used in medium size or bigger models – perhaps even using its own dedicated battery.

Picking a Separate BEC
There are many options for separate BEC’s / regulators. They have different output voltages, different basic design (switch mode or linear) and different current ratings. We suggest you pay careful consideration to picking one you are sure will work with your equipment.

Some Background:
All radio control models have (by definition) a receiver, which typically requires a ‘4.8 volt nominal’ power supply (I say 4.8 volt to refer to the traditional 4 cell nicad pack – in fact most receivers are happy with a 5‐6 volt input, and some even higher – for example the Spektrum 2.4g receivers). This same supply driving the receiver (again, there are exceptions) drives the servos. Most servos are rated for ‘4.8 volts nominal’, some are compatible with 6 volts, and some even 2S lithium (7.4V nominal).

Again, without introducing undue complication, most current helicopter tail rotor (TR) servos are only rated to 4.8 volts nominal, so some sort of additional voltage reduction is needed for the TR servo if the receiver supply is greater than this (perhaps by way of diodes if the receiver is getting a regulated supply, or by a small voltage regulator if the receiver is running on an unregulated higher voltage).

On a glow (nitro) model, one would have a battery pack specifically designated to drive the receiver and servos. There are many possibilities – 4 or 5 cell nicad/NiMH, 2 cell lithium, etc with or without voltage regulation to the receiver and all servos, or just some servos (eg TR).

On an electric model, we have the option of powering the receiver and servos in the same manner as described above for a nitro model, or using the (typically larger) electric motor battery to power everything. The voltage can be regulated to the required (lower) voltage using either the BEC built into many ESC’s, or a separate regulator/BEC still using the main motor battery.
Advantages of a totally independant receiver/servo power supply in an electric model:
The receiver power supply is totally independent of that for the electric motor.
The motor battery / ESC BEC has a certain failure rate (in part due to high voltages and currents involved). If the battery / ESC BEC fails, the model typically crashes.
Disadvantages a separate receiver/servo power supply include:
Added weight
Added space usage with more components to mount.

So Typically:
With smaller models (where weight and space are at a premium), the receiver/servos would be normally be run using the main motor battery and using the BEC built into the motor ESC.

With medium sized models often you may use the main motor battery, but use a separate regulator/BEC rather than the one built into the ESC.

With larger models, most would recommend a separate battery (and separate regulator /BEC if required).

The definition of model size is rather arbitrary. But as a guide a small model may typically be a 250‐450 size helicopter. A medium model a 500 size helicopter, and a large model a 600 size helicopter or bigger.

So at Last, We Arrive at the Question:
Why the battery eliminator circuit in your electronic speed control
may not be up to the task?

Carefully check the specifications of your BEC (whether it is built into the ESC or not)

You of course need to know the expected current draw of receiver, all the servos, gyro, governor, etc in your model. Calculating this figure is difficult, and deciding on a conservative (or otherwise) total current draw to plan your installation is not simple. You need a device to measure current draw, and look at dynamic and stalled current draw of all your servos, etc.

To give you some idea, the stalled current of a Futaba 9256 TR servo is in the order of 1.5 amps. The stalled current draw of a JR 8717 is in the order of 3 amps or so. Of course, we should not stall our servos should we?

Just the on bench ‘wiggling of sticks’ moving 3 x 8717’s (unloaded – ie no flight loads) can cause current draws of 4‐6amps continuous.

So you can quickly see if you are running modern high speed high torque servos in a ‘600’ size or larger model, you need a very robust receiver / servo power supply!

And I Will Repeat Myself………

Be careful if you are thinking of using the BEC build into your ESC. Carefully check its maximum continuous and peak current ratings, and compare this to what you expect your servos and receiver actually will draw in flight. Typically a BEC built into an ESC may only be capable of delivering 3‐4 amps. So even if it is a 120 amp ESC – which you are going to use on a 600 size electric – you may think the BEC output will be okay, but as you can see it wont be! Of course, this same ESC used in an aircraft with ‘sport’ servos may work just fine with this low current built in BEC.

So the Solution:
In most medium or larger models the ESC’s BEC current rating is likely to be inadequate. Furthermore, for the sake of reliability, a separate BEC / regulator should normally be used in medium size or bigger models – perhaps even using its own dedicated battery.

Picking a Separate BEC
There are many options for separate BEC’s / regulators. They have different output voltages, different basic design (switch mode or linear) and different current ratings. We suggest you pay careful consideration to picking one you are sure will work with your equipment.

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Donnie D

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PostSubject: Re: ESC's and BEC's,   Tue Sep 22, 2009 7:17 am

Better safe than sorry I guess, and for usually less than 20 more bucks, why not.

Donnie D smiley-happy088
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P3tras

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PostSubject: Re: ESC's and BEC's,   Tue Sep 22, 2009 10:16 am

Now I think, will 5A BEC would be enough for e-smart? orange78
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Mozzy

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PostSubject: Re: ESC's and BEC's,   Tue Sep 22, 2009 3:35 pm

I think I will use an BEC with at least 8A for my HKH-500. In that way is has enough juice to power some LED-lights. Days are already getting shorter, and in winter time after work it will be dark. You need to be prepared.
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Donnie D

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PostSubject: Re: ESC's and BEC's,   Tue Sep 22, 2009 9:30 pm

This is the BEC I use on my E-Smart. Do I need to change it?

http://www.helidirect.com/hobbywing-switchable-ubec-56v-p-4405.hdx

I have about 80 flights on it and so far no problems. Of course I have my E set on slug.

Donnie D smiley-happy088
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Crash & Burn

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PostSubject: ESC Belt CP V2   Sun Oct 04, 2009 8:08 am

Yes Nuttcaze was right ,The ESC 25A on the V2 went up in smoke second time out.
Then I put on a 30A volcano the same thing happed, now I have a 40A volcano on
the V2.
The HBK3 has the factory ESC still working after 12 times out. making smileys




whatt
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Nuttcaze
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PostSubject: Re: ESC's and BEC's,   Sun Oct 04, 2009 12:02 pm

P3tras wrote:
Now I think, will 5A BEC would be enough for e-smart? orange78

I'm pretty sure it will be fine

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Nuttcaze
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PostSubject: Re: ESC's and BEC's,   Sun Oct 04, 2009 12:05 pm

Donnie D wrote:
This is the BEC I use on my E-Smart. Do I need to change it?

http://www.helidirect.com/hobbywing-switchable-ubec-56v-p-4405.hdx

I have about 80 flights on it and so far no problems. Of course I have my E set on slug.

Donnie D smiley-happy088

if it works then don't fix it BUT beware that your BEC is not meant for 6S batteries. I recently forgot that and fried my old BEC, but kinda glad I did cause I upgraded to these and haven't had any probs yet, I use them on both of my ES600's, my ES500, and Blazemobs HDX 500. His ES600 will also be getting one too, the price is right for me at $18

http://www.helidirect.com/maxpro-high-voltage-210s-lipo-switchable-bec-p-8149.hdx

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Donnie D

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PostSubject: Re: ESC's and BEC's,   Sun Oct 04, 2009 4:41 pm

Boy, I'm glad you pointed that out to me. I didn't even notice. Good thing I've been using 5s batts. I was planning on getting a 6s to try out. I'm gonna take it off and order a new BEC for it next week.

Would it be a good idea to install the one I take off (the small on you said was not for 6s batts) onto my stock 25A ESC that is on my Belt CP V1?

Donnie D smiley-happy088
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Mozzy

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PostSubject: Re: ESC's and BEC's,   Sun Oct 04, 2009 4:50 pm

@ Donnie D

Or you could power the BEC you are using at the moment with a separate 2S or 3S battery. This setup prevented Akent from crashing his E-Smart.
And it might be a cheaper solution as well.
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P3tras

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PostSubject: Re: ESC's and BEC's,   Sun Oct 04, 2009 5:38 pm

Donnie D wrote:
Would it be a good idea to install the one I take off (the small on you said was not for 6s batts) onto my stock 25A ESC that is on my Belt CP V1?

I think it is good idea! Belt cp ESC will work cooler :bigthumb: Just cut red wire that goes from ESC to receiver. I think 3A is under power for E-smart. You really don't want that servos stop working at mid flight headbeat
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