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Old 10-14-2012, 04:44 PM   #1
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Default SBEC, UBEC...what's the difference?

What's the difference between these, and what's the advantage of one over the other? Why do some use an external BEC in favor of what's built in to the ESC? Were I to use an external BEC, how would I go about disabling the internal, or would I? If the 2 ran together, would the external BEC just run the receiver, freeing the internal for motor duties? This is all a bit confusing...lot of things to consider...

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Old 10-14-2012, 05:04 PM   #2
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BEC = Battery Eliminator Circuit

The 'S' in SBEC means that the BEC uses a 'switching' type regulator to control voltage. Without getting into the technicalities switching regulators are best so they are the ones you should look for.

SBEC's can be found in both the 'built into the ESC' type, and in the 'stand alone' type (sometimes called a uBEC).

As for as the argument for 'built in' or 'stand alone', it mainly comes down to the current and voltage rating of the device. the stands alone type can be found with higher current rating than the internal ones, also many external ones (and some internal) allow the output voltage to be increased which can give more power to the servos.

The other argument for the stands alone is that if your ESC should toast itself completely the stands alone BEC will survive and with luck you will still have control.

If you find an ESC with a SBEC with a 4A or more output then that's probably fine for most small to medium models. For larger models with big servos or lots of servos a higher rated stands alone BEC is a good idea. However bear in mind that the connector into the Rx itself is only good for maybe 6-7 amps.

If you add a stand alone BEC then yes, you would normally have to disconnect the power wire from the ESC. Exceptions being if you use an 'OPTO' ESC (OPTO means no BEC is fitted), or if you insert diodes into the power wires.

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Old 10-14-2012, 05:20 PM   #3
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Heads up has a new interesting ESC available in different configs, should take care of the problem of seperate bec's for most models and it's not too pricey.

http://www.headsuprc.com/servlet/the...er--30A/Detail

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Old 10-14-2012, 05:41 PM   #4
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Originally Posted by bluzjamer View Post
Heads up has a new interesting ESC available in different configs, should take care of the problem of seperate bec's for most models and it's not too pricey.
Switchmode built in BECs are pretty common these days.
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Old 10-14-2012, 06:14 PM   #5
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So now, would this "switching" be done from the TX, or it's pre-programmed? I'm considering an external BEC for my big P47, as it has flaps, retracts, and the 4 servos for surfaces, or would the factory unit be sufficient? I honestly don't know if the electronics should ALL be swapped out for something better or just leave well-enough-alone? I've heard all kinds of conflicting things regarding that, the BEC in particular. All I'm going to be doing with the plane is non-aerobatic flying with it (well, MAYBE a roll or loop occasionally), so it wouldn't be like I'd be overworking anything. I was thinking a larger (output) battery would be really all I'd have to do, but then on the other hand, I don't want to take any chances...

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Old 10-14-2012, 06:23 PM   #6
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Originally Posted by matiac View Post
So now, would this "switching" be done from the TX, or it's pre-programmed?
The switching is something that goes on within the circuitry of the regulator, you don't really need to be concerned with it.
If you do want to know how it works: http://en.wikipedia.org/wiki/Switched-mode_power_supply
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Old 10-14-2012, 06:50 PM   #7
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Well hey, THANKS for the info, I actually am going to go pore over it. I have this rather nasty habit of wanting to know how/why something works. But fret not, for I'm pretty confident I will have more questions, unless I can find the answers already here or at RCGroups.

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Old 10-14-2012, 07:07 PM   #8
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Originally Posted by matiac View Post
So now, would this "switching" be done from the TX, or it's pre-programmed? I'm considering an external BEC for my big P47, as it has flaps, retracts, and the 4 servos for surfaces, or would the factory unit be sufficient? I honestly don't know if the electronics should ALL be swapped out for something better or just leave well-enough-alone? I've heard all kinds of conflicting things regarding that, the BEC in particular. All I'm going to be doing with the plane is non-aerobatic flying with it (well, MAYBE a roll or loop occasionally), so it wouldn't be like I'd be overworking anything. I was thinking a larger (output) battery would be really all I'd have to do, but then on the other hand, I don't want to take any chances...
If you are building a $$$$ model with a lot of time spent on it, IMHO, a dual receiver power supply is mandatory. An added benefit of a dual receiver power supply is you don't have to worry about a single point failure, like the receiver's on-off switch.

A fairly easy way to set up a dual supply is with the Castle Creations 10 Amp uBEC, and, a two cell LiFe or A123 battery with at least 2000 milliampere hour rating. Add two 10 Amp diodes from Radio Shack, a bit of wiring, and you are done. (Don't use a LiPo battery, its output voltage will be over the servos voltage rating.)

This system now has over 120 flights on it with one model, and another 30 flights on a different model. Both have been flawless.

Take a look at how I did it:
http://www.wattflyer.com/forums/showthread.php?t=63794

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Old 10-14-2012, 07:24 PM   #9
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It would be the LiFe battery, as my charger won't charge A123s. I hope you don't mind if I D.L.-ed your schematic, as I just may implement what's there in my big plane? I'll probably leave the smaller 750mm as is, it's fine. I'll let you know how it goes, still need another TX/RX rig for it, as the one it came with is now used in the 750, the stabilizer, and I can finally get going on the big one, have it ready for next season!

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Old 10-14-2012, 07:28 PM   #10
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Originally Posted by matiac View Post
It would be the LiFe battery, as my charger won't charge A123s. I hope you don't mind if I D.L.-ed your schematic, as I just may implement what's there in my big plane? I'll probably leave the smaller 750mm as is, it's fine. I'll let you know how it goes, still need another TX/RX rig for it, as the one it came with is now used in the 750, the stabilizer, and I can finally get going on the big one, have it ready for next season!
Nice thing about the LiFe and A123 batteries, they both charge to 3.6 Volts DC per cell, so if your charger can charge the LiFe's they also can charge the A123's. I'm charging my 2300 Mah A123 cells at 7.5 Amps per cell. My 12S2P A123 battery is being charged as a 6S4P pack at 30 Amps with the Cellpro Powerlab 8 charger.

(I'm from the stone age! What's D.L.? As far as using it, if it saves someones model airplane from battery issues, fine with me.)

Downloading that schematic is quite fine with me. That's why I put it into this thread. I've used this scheme several times with complete success.

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Old 10-14-2012, 07:57 PM   #11
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Oh, sorry, D.L.= Download. Also got the schematic for a parallel plug here that I otherwise never would have known about, and now use one of those to use my 500maH's together in the 750 (MAN is that thing fast!!) for more speed and flight time. But again, Thanks for that, I'm gonna get hoppin' on that!

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Old 10-14-2012, 10:08 PM   #12
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Originally Posted by JetPlaneFlyer View Post
Switchmode built in BECs are pretty common these days.
Yeah but you have to read the whole discription....these cover a lot more servos that usual. The 30 amp covers up to 6 standard size and up to 8 micro size. The 45 amp covers up to 9 standard size and up to 12 sub micro size. Thats a lot of servos covered with one unit.

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Old 10-14-2012, 11:57 PM   #13
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Originally Posted by bluzjamer View Post
Yeah but you have to read the whole discription....these cover a lot more servos that usual. The 30 amp covers up to 6 standard size and up to 8 micro size. The 45 amp covers up to 9 standard size and up to 12 sub micro size. Thats a lot of servos covered with one unit.
It's a 4 amp SBEC. That is good but not unique similar SBECs are found on a few ESCs. How many servos that will power can be debated but 4 Amps is 4 Amps.

here's one: http://www.hobbyking.com/hobbyking/s...e_Series_.html (The Mystery Blue series are great ESCs by the way, they are ZTW under a different label.)

Not sure I've seen a 4A BEC on a 30A ESC before though....
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Old 10-15-2012, 05:17 AM   #14
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Originally Posted by matiac View Post
Oh, sorry, D.L.= Download. Also got the schematic for a parallel plug here that I otherwise never would have known about, and now use one of those to use my 500maH's together in the 750 (MAN is that thing fast!!) for more speed and flight time. But again, Thanks for that, I'm gonna get hoppin' on that!
LOLOL

Thanks

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Old 10-15-2012, 05:20 AM   #15
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Originally Posted by JetPlaneFlyer View Post
It's a 4 amp SBEC. That is good but not unique similar SBECs are found on a few ESCs. How many servos that will power can be debated but 4 Amps is 4 Amps.

here's one: http://www.hobbyking.com/hobbyking/s...e_Series_.html (The Mystery Blue series are great ESCs by the way, they are ZTW under a different label.)

Not sure I've seen a 4A BEC on a 30A ESC before though....
Yeah
I've got two models with seven Hitec 645MS servos in them. By actual measurement with my $$$$ Fluke 87V meter with its peak reading function, I've measured a peak current of 14.5 Amps while just moving the two transmitter sticks round and round.

These Castle Creations 10 Amp uBEC's can handle these brief 14 Amp current pulses with no issues.

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Old 10-15-2012, 05:22 AM   #16
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Originally Posted by JetPlaneFlyer View Post
It's a 4 amp SBEC. That is good but not unique similar SBECs are found on a few ESCs. How many servos that will power can be debated but 4 Amps is 4 Amps.

here's one: http://www.hobbyking.com/hobbyking/s...e_Series_.html (The Mystery Blue series are great ESCs by the way, they are ZTW under a different label.)

Not sure I've seen a 4A BEC on a 30A ESC before though....
If you have a $$$$ model, that 4A BEC can be backed up with a Castle Creations 10 Amp uBEC with the use of a pair of Shottky diodes. Just substitute the CC 10 amp uBEC for the bottom ESC.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=67094

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Old 10-15-2012, 06:16 AM   #17
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Originally Posted by kyleservicetech View Post
.... I've measured a peak current of 14.5 Amps while just moving the two transmitter sticks round and round.
I'm assuming those currents are just transients that last milliseconds? Reason being that regardless of what you use to power the radio gear the plugs into the Rx are only 'officially' rated at about 4-5A and in my own tests anything over 7-8A risked melting the plastic plug and insulation is very short order, plus created huge volt drops. 14A would cause guaranteed meltdown of the connector unless it was extremely short duration, the wires from the BEC are unlikely to take it for long either.

Here's my test results copied from elsewhere:
I charged for 3 minutes at each rate to simulate 'constant load' condition. Temp rise was measured from room temp of 22 degC (so add 22 to get actual temp). Voltage drop measured with multimeter at each end of servo extension so includes the drop over the 200mm of wire in addition to the servo connector.

Results:
  • 3A: temp rise 6 degC, voltage drop 0.22V
  • 5A: temp rise 15 degC, voltage drop 0.3V
  • 6A: temp rise 23 degC, voltage drop 0.4V
  • 7A: temp rise 30 degC, voltage drop 0.5V
  • 8A: temp rise 48 degC, voltage drop 0.7V

The connector was held at 5A and above for a total of 12 minutes with only brief breaks while I re-set the charger. The increase from 7A to 8A signaled a much greater increase in temp rise and voltage drop compared to previous increments, this seemed to be the tipping point for the connector. At 8A the connector was at 70C and too hot to hold for long. However there was no burning smell and the insulation didn't look like melting. After the test the connector could be split and re-joined as per normal so no apparent damage.

So my conclusion is that if you can live with a 0.5V voltage drop you can put 7A through a servo/rx plug without any great issue though 5 or 6A is a more conservative limit. Peaks up to 8A don't cause any short term problems other than increasing voltage drop.
An easy fix is to split the wire from the power source into two, and use two separate Rx plugs.
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Old 10-15-2012, 06:38 AM   #18
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Originally Posted by JetPlaneFlyer View Post
I'm assuming those currents are just transients that last milliseconds? Reason being that regardless of what you use to power the radio gear the plugs into the Rx are only 'officially' rated at about 4-5A and in my own tests anything over 7-8A risked melting the plastic plug and insulation is very short order, plus created huge volt drops. 14A would cause guaranteed meltdown of the connector unless it was extremely short duration, the wires from the BEC are unlikely to take it for long either.

Here's my test results copied from elsewhere:


An easy fix is to split the wire from the power source into two, and use two separate Rx plugs.
Yup, those high current pulses drawn by the 645MG servos are very brief in duration, on the order of perhaps 20 milliseconds or so. If you load these servos down, they will pull over an ampere each, like when using large flaps on a giant model.

Another good reason on these big models to use dual DC inputs, one through the standard battery input, the second though a spare servo connector.

After using very high quality connectors at work for many years, it seems kind of strange to use these much lower quality connectors as seen on our servo connectors. Guess it's just for making all servos interchangeable. Of course, those high quality connectors we used at work were not cheap.

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Old 10-26-2012, 05:29 PM   #19
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Not all ESC's with built-in switch mode BEC's are alike, the 30 amp E-Flite BEC in my PZ Stinson Reliant is rated at 700mah (0.7 amps) max, it couldn't handle the load from five mini- servos and my Hitec Optima 6 receiver and had a brownout/reset causing a crash. During repairs I installed a Park BEC rated at 1.5 amps by Dimension Engineering. Have not had any more problems since in hundreds of flights using flaps and doing scale aerobatics. Some 2.4GHZ receivers require higher voltage and will go into reset when they "see" voltage dips due to servo amp draw problems, drag in linkage or stiff hinging.
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Old 10-26-2012, 07:37 PM   #20
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So, and I'm asking because I don't know, the S/UBEC is BETWEEN the battery and the ESC? Or between the battery and the receiver? This is what confuses me about them, still not entirely clear why a plane with flaps/retracts/4 servos that already has a BEC in the circuit needs another? Are the Chinese deliberately under-rating things like that to sell more planes?? A Communist Plot to overthrow the Hobby?

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Old 10-26-2012, 11:08 PM   #21
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Originally Posted by matiac View Post
So, and I'm asking because I don't know, the S/UBEC is BETWEEN the battery and the ESC? Or between the battery and the receiver? This is what confuses me about them, still not entirely clear why a plane with flaps/retracts/4 servos that already has a BEC in the circuit needs another? Are the Chinese deliberately under-rating things like that to sell more planes?? A Communist Plot to overthrow the Hobby?

This can be somewhat confusing.
The usual ESC's have a built in BEC that can be used to power the receiver directly through the same cable used for throttle control. Problem is, some of these LINEAR type BEC specs IMHO are not worth the paper they are written on.

The switching type BEC's sometimes called uBEC's can provide more continuous current to the receiver and its servos. The Castle Creations ICE series uses the uBECs.

A third option is to install a separate uBEC such as the Castle Creations 10 Amp uBEC to power the receiver/servos using the LiPo battery as the uBEC power, and the output of the uBEC connects directly to the receivers battery input.

If you have an $$$$ model, an option is to use both the Castle Creations ICE ESC's uBEC and the CC 10 Amp uBEC, isolating them from each other with a 9 Ampere Shottky diode. (No you can't buy them from Radio Shack)

I can provide wiring information on the ICE/uBEC wiring if desired. I've got two giant scale models using the dual battery inputs, both work very well.

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Old 11-02-2012, 09:31 PM   #22
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So now I begin to see. The BEC supplies power to RX/servos, and prevents interruption of said supply, so the ESC's sole function is to regulate current to the motor. Now I can see doing this on my big plane, should it also be done to the 750, with only 4 servos? Yes, if it's not too much trouble, I would like the schematic you describe...

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Old 11-03-2012, 12:56 AM   #23
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Originally Posted by matiac View Post
So now I begin to see. The BEC supplies power to RX/servos, and prevents interruption of said supply, so the ESC's sole function is to regulate current to the motor. Now I can see doing this on my big plane, should it also be done to the 750, with only 4 servos? Yes, if it's not too much trouble, I would like the schematic you describe...
Here you go!
Giant Scale Power System:
Battery Backup System
http://www.wattflyer.com/forums/showthread.php?t=63794 Several club members have used this setup with the LiFe cells in place of the A123's. Both work very well.

As for your 750 model, I've been using a half dozen Castle Creations 10 Amp uBEC in six of my models running at about one kilowatt as a single DC source now for four or five years without a single issue. The radio system is the Spektrum DX7 or DX8 transmitter and AR7000 receiver systems. The CC uBEC weighs in at a fraction of an ounce.

I've also got drawings for dual Castle Creations ICE series ESC's with their switching power supply BEC as receiver power for the twin electric motor setups.

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Old 11-04-2012, 10:54 AM   #24
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And just to through more stuff at you, #1 Castle states right in their paperwork, if you are planning for more then 5 amps being drawn, then you have to split the power from their BEC to multiple plugs. As said earlier, the servo plug is only good for 5 amps, otherwise they tend to melt. Ask me about that one.


And using the Castle 10 as an example, your input voltage can change the BEC's output capability. Again per Castle's site, the 10 amp BEC is only rated for 7 amps continuous if you are applying 12 volts (like a 3S lipo) to it.
Output drops to 5 amps continuous if you are running 24 volts, like a 6S pack.



Peak: 10 amps
Continuous:
<12 volts input = 7 amps*
<24 volts input = 5 amps*
*Ratings are determined with a 5mph airflow on the BEC. Servo connectors are not rated for current in excess of 5 amps. Users are encouraged to replace the connectors if more than 5 amp currents are anticipated

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 11-04-2012, 11:03 AM   #25
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And one more thing, even though we are supposed too, how many actually do?

It's called checking the output voltage of your BEC.

Come on raise your hands, how many of you actually checked before you plugged in the rest of your system? I thought so.

Yeah, I got burnt on that one. Oh those silly Chinese kids on the assembly line.
I received a BEC that was wired backwards, battery connections were soldered to the output side of the board, and visa versa. Cost me 3 receivers before I finally thought to check. Yep 16.8 volts instead of 6 sure made a mess.

Funny, after catching the boo boo, I used the BEC, in a ground vehicle, and it's been running for a couple of years now.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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