Help on BEC

[kianhon]

I wanto buy the following ESC (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=5300) and BEC but I don't know is it compatible with each other. Can someone see it and let me know? I'm installing both of it on my Stock Belt-CP. I don't have a ferrite ring. I use 3S1P 11.1 2200mah 20c Lipo (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=6083), Tower Pro sg90 servo. Which BEC you recommend for the ESC?


ESC
GWS Brushless (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=6125) ESC 35A 2-4S 3A BEC, Speed Controller.
Weight: 22g
BEC: 3A


BEC1
Spec.
Output: 5v/3A or 6v/3A (Selectable via jumper)
Noise: <50mVp-p(@2A/12v)
Input: 5.5v-23v (2-5S Lipo pack, 5-15cells NiMh)
Size: 41.6x16.6x7.0mm
Weight: 7.5g

Features:
Over current and over heat protection.
Switching frequency 300khz.
Chip Efficiency is 92%. This UBEC utilises switching technology to gain a much higher efficiency than liniar BEC. Which means less heat and longer battery life.
The UBEC is equiped with a noise reduction alloy housing to reduce noise even further.
Incorrect polarity safety feature ensures the UBEC will not be destroyed should the battery be connected incorrectly.
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4319

or BEC2
Spec.
Output (Constant): 5v/5A or 6v/5A
Input: 8v-42v (3-10cell lipo) High Voltage
Size: 48x27x9mm
Weight: 37g
Quiescent current: 20mA

Features:
Type: Switching, however because of the noise reduction (thin metal case & filter) this unit gives the same noise as a Linear BEC.
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=6320

[Real_Sparky]

The first bec has the same 3A rating as the bec in the esc but the voltage can be upped to 6V. The second is a higher rated one.

My question is why do you want to go with an external bec as the one in that esc has all the power you will need for the sg90 servos.
I was running 4 sg90's off the stock belt esc with a spektrum reciever and never once did I have a problem with brown outs.
If you were to run digital servos off the stock esc that would be another thing all together.
I have watched with interest the debate on an external bec and understand the benifits of it but I have never had an issue with the stock esc pumping out enough power.

Are you into hard core 3D?
Do you running digital servos?
Have you had an issue with brownouts on a spektrum receiver?

Unless you answer yes to any of these questions I would go for the esc and just use the internal bec in that.

I run stock esc in all of my helis using the internal bec powering digital servos in the trex's and spektrum receivers and still have not had any brownouts, but I am no 3d pilot just doing sport flying at the moment.

Darin

[tom dubya]

I thought the reason for running a separate bec was if your esc failed that you would still have power running to the servos to help you do a autorotation and try to land with minimal damage.

[Real_Sparky]

If you wire it in the right way I suppose that is possible.
But all the reasons I have read so far are the reasons I mentioned in my previous post.
Dont get me wrong I see nothing wrong with a seperate BEC:thumbup:, just that I see no need for one with my style of flying.

Lets face it, if your esc stops working in a BELT CP your chances of autoing back safely are somewhere between slim and none, there is just not the weight to sustain momentum in the blades, well if you are an ACE pilot you could:).

I'm sure there are people who have benefitted from having an external BEC, maybe its me I just dont see a need.

Darin

[tom dubya]

Ya i'm so good i do auto's just for the hell of it.;)

Seriously though i see your point.

[another_finn]

Back to the original question, the ESC and BEC have nothing to do with each other - so there are no compatibility issues to worry about. Either of those BECs will get the job done. If you intend to run digital servos on cyclic at some point, I would get the 7.5A version. Otherwise the 3A will be plenty.

I know many people have run Spektrum receivers on a linear BEC without problems. I also know many people have tried it and crashed. For $7.83 and 7.5 grams, why risk it? Waiting until you do have a brown-out means you may be spending $20 on repairs to find out you needed $10 insurance. I say get the UBEC and you'll have one less thing to worry about.

It's also worth remembering that having 3A in the spec of a linear BEC does not mean you will get three amps out of it. The figure is usually given for 2S LiPos - in practice, you'll be lucky to get two amps. And if the ESC overheats due to thermal losses from the linear BEC, you're going down. Never mind the inverted auto fantasies - I just prefer to leave luck out of the equation wherever possible :D

(Edit: If the ESC was really a GWS, don't touch it. I've heard so much about them, I won't even use them on planks.)

[kianhon]

Thank for the comments, I've ordered the 35amp ESC and 3amp BEC. Getting an external BEC is just to reduce risk of crashing. My original esky esc burnt on me, my new Dynam ESC 30amp got so hot with just one Lipo and reduced my throttle speed automatically while I'm just learning to hover in midd air (stop breathing everytime he do that) and the best part was it throttle up for me too and made me crash. Thank to all the comments here, i'm going for the 35amp ESC and 3amp BEC. rather spend $40 for both of this then crashing my heli in the future because of lousy esc or heat.

[DierWolf]

Both esc and bec is rated the same, sort of a waste of time and energy hooking it up.

Reducing the risk of crashing entails getting something more than 3 amps which is pretty much the standard on all ESC's nowadays.

Number one cause of crashes is Pilot Error followed by power loss to the radio equipment, not a burned out ESC.

Suggest spend an extra 20 bucks on the 7 you already spent and get the CCBEC From Castle Creations.

If the Dynam 30A ESC (which i have one) got hot with the stock motor then there is something on your bird putting strain, suggest you check your Gear Mesh, Belt Tension and head for free movement.

[another_finn]

Both esc and bec is rated the same, sort of a waste of time and energy hooking it up.
Except that the built-in one is linear and the rating is most likely valid on 2S batteries. Don't be fooled by the numbers, find out what conditions they were arrived at.

From the Dimension Engineering website:
It is very common for speed controls to have BECs rated at 2 or 3A. However, what the manufacturers do not tell you is that this rating is only true for an input voltage of 6V. The BEC on your speed control is what engineers call a 'linear voltage regulator'. It works by burning up excess voltage and turning it into heat. The higher the input voltage, the more heat gets produced. If there is too much heat, then the BEC will either fry, or shut down! The result of this is that in real world situations, if you are running a 3S lithium battery pack, your ESC's BEC will only be able to provide about 0.5A before it overheats. At 4S, most ESC manufacturers don't recommend you use the BEC at all, or at best power two small servos.

It's all in the sticky (http://www.helifreak.com/showthread.php?t=72280) right here in the Belt CP section.