First of apologies to Bob Hunt for hijacking his thread on his wonderful new twin project with a prolonged discussion on retracts.  I am very interested in this subject because of a future project. 

As it stands right now I have to make a decision on which of two FM-9 retract timers I need to purchase.  One uses the BEC of the ESC to power the retract units or retract servo if an air retract system is used.  The other requires an external BEC if the ESC does not have a BEC or the BEC does not supply enough current to power the electric retracts.  My preference would be not to use and external BEC just for weight reasons.  After seeing Will's block diagrams it became clear what was available, now I need to understand what is required.

1.  Do the retracts Bob is using in his new plane require more current than the popular ESCs available with a built in BEC?
2.  Is it a better approach to use an ESC without a BEC and go with the external BEC, if so could you experts make some recommendations?

Finally thanks Will for the block diagrams, except as was pointed out already, the second diagram is off by a pin on the wiring.  I feel like I am playing catch  up with the rest of you, I do have a strong backround in electronics and that should help.   
Andy Borgogna

Hi Igor,

Below are two Castle Creations stand alone BECs from the Horizon web site. Does one of these meet the needs for our CL retracts?

The 1st one is 28 grams, but it has a large heat sink and the 2nd one is smaller at 14 grams, without a heat sink.

If the smaller one works, it is only 1/2 oz. I would think that even a weight conscious guy like BH could live with this? ;-)

Thank you in advance for your help. 

Castle BEC PRO V2 by Castle Creations
 
$38.21
List: $44.95

Usually ships in 2-3 Business Days
CSECCBECPRO by Castle Creations

A high-output switching BEC

Castle BEC PRO V2
Key Features
Rated for up to 12S input (50.4 volts)
Peak Output of up to 20 amps
Fully adjustable using the Castle Link USB Adapter and a Windows PC
Length: 1.69 in (43mm)
Width: 1.3 in (33mm)
Height: .94 in (24mm)
Weight: 1 oz (29 grams) without wires
Overview
The Castle PRO BEC is intended for use in larger RC cars, electric aircraft, and helis that have high power demands for their radio/servo systems.  It is ideal for most electric helis 500-size and larger.  It will also work well in larger electric powered RC aircraft and RC crawlers and Monster Trucks that have high-powered servos.

Or a smaller one:


Castle BEC by Castle Creations

$21.21
List: $24.95

CSECCBEC by Castle Creations

Castle BEC
Key Features
Elemenates the need for a sperate battery for the reciever and servos
Overview
Our Battery Eliminator Circuit is a little device that eliminates the need for a receiver and servo battery pack. It draws higher voltage from the motor batteries and drops it to a voltage level that is suitable for your receiver and servos. This is required in applications which draw high power for multiple servos or use more than 3S motor packs, as most ESCs with linear BECs are not designed for these applications.

Specifications:

Current Output: 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.

Output Voltage: Output 5.1 volts out of the package, user may set output voltage from 4.8 to 9 using the Castle Link (sold separately).

Input Voltage: 5v to 25.2v (2S to 6S LiPo)
Length: 1.2” (30mm)
Width: 0.6” (15mm)
Height: 0.4” (10mm)
Weight: 0.4 oz (11 grams)

I'll repeat the block diagram for retracts for an ESC that provides an adequate BEC (battery eliminator circuit) for the retracts. Although the FM-9retract is illustrated, the same connections are required for any timer: it must put out a pulsed signal to 5 volts that is maintained for 1 to 2 milliseconds (off to full throttle) at a frequency of about 50Hz, to both the ESC and the retract servo. (The throttle channel initially just drove a servo that moved the throttle valve in a glow engine, so that is why it needs a standard throttle signal.)

The two well-known ESCs that should work well are the CC ICE and the JetiSpin, because both have switching power supplies for the BEC. Both appear to promise up to 5A, which should be quite adequate. The JetiSpin is relatively expensive, especially because it requires the external programmer, but it is a very good match with Plettenberg and Axi motors -- just ask Igor!

Retract servos in general differ from regulator servos in that they respond only to throttle signals up to about 50% throttle with fully counterclockwise position and to greater throttle settings with a smooth but relatively rapid move to the clockwise-most position. One has to use a regular servo in order to control the rate at which retraction and extension takes place, and then it can be smoothly done over, for example, four seconds. My retract programs default to fully counterclockwise for gear extended and fully clockwise for gear retracted.

The $10 one from the Hobby Lobby site you kindly referenced should do the trick, although it's still overkill at 3A continuous. 

Thanks for the verification Howard. I was hoping this would work. At 3 amps it should even handle a sticky gear door, or even some draggy grass caught on the wheel.

FROM HOBBY LOBBY WEB SITE:  http://www.hobby-lobby.com/3_amp_switch_mode_bec_1034267_prd1.htm?pSearchQueryId=1042774

People interested in using a standalone BEC may want to go to the link above. HL has an excellent full color block diagram showing how the entire system is setup. This, along with Will's clear block diagram, makes it easy to see how all this works together. Below is some info on this BEC. 

3 Amp Switch Mode BEC

WEIGHT:  15 grams (1/2 oz) including wires

Status: In StockProduct#: SRCBEC3Price:$9.99Qty

Switching BEC with selectable 5 or 6 volt output

This highly efficient (>90%) switch mode BEC can provide a constant 5 or 6V (selectable by you) to your receiver with flight batteries of up to 6 cells (26V). If you are using this with an ESC with BEC function you will need to disable the ESC's BEC by disconnecting the red wire from the ESC. The switch mode BEC is enclosed within a metal shield to reduce possible electromagnetic interference. Compact in size and easy to install this unit provides a lot of peace of mind by reliably providing power to you radio receiver and servos. The input wires on the BEC will have to be soldered to the input wires from your ESC to receive the power from your flight batteries.

Click for Sky RC 3 Amp Switch Mode BEC Instructions

COMPANY INFORMATION
Phone:
  (866) 512-1444
Phone Hours:
  9AM-6PM M-F CST
  10AM-5PM Sat
Address:
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  Brentwood TN 37027 USA
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Rudy,

Disregard my suggestion.  I didn't notice that the 3 amp Sky RC battery eliminator circuit weighs four grams more than the 10 amp Castle.  Might as well go for the Castle, despite its not being edible (see the FAQs on Castle's Web site).

I think Andy is on the right track by eliminating weight and connectors.