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Old Jan 13, 2007, 03:53 PM
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How to Connect an ESC & Separate BEC

I feel stupid for asking this, but........

A buddy and I are each doing an "E" conversion on a Hobby Lobby Decathlon and I have questions about the ESC and separate BEC and how they are wired.

I assumed the receiver plug of the ESC went to the BEC, and then the BEC plugs into the receiver. If this is so, then why is there a JST connector on one end of his 5 amp BEC? It didn't come with any instructions.

I have a 3 amp BEC, and I have male/female receiver plugs as I would expect.

Question #2 - Is a 3 amp BEC enough to run 4 standard Hitec servos? I cannot find any info on how much current they draw.

Thanks,

Scott DeTray

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Old Jan 13, 2007, 04:05 PM
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Forgive me if I'm misunderstanding you. The bec has to go to the battery, or else it is pulling power from the bec on the esc. In the minimum BEC configuration, it's just a power supply, so there doesn't need to be any connection to the ESC.
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Old Jan 13, 2007, 04:05 PM
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The JST is probably to connect to the flight pack, to provide the power.
The idea is to bypass the BEC in the ESC, so you need a separate connection.
Hope that helps,
Pat MacKenzie
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Old Jan 13, 2007, 04:06 PM
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The separate BEC takes power from the main battery, and plugs into any spare channel on your receiver. It drops the voltage to a regulated 5v (usually) suitable for the receiver and servos. That means you need to connect it, in parallel with your ESC, to the main battery plug.

The ESC plugs into the throttle channel on your receiver, as normal. If your ESC has an internal BEC, you normally need to disable it when you're using a separate BEC by pulling the red wire out of the plug that goes into the receiver, and taping it back on itself so that it can't touch anything.

Sorry, I can't be sure about the number of servos you can run off 3A. It partly depends on the type of flying you do. Hopefully someone else can provide that info.
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Old Jan 13, 2007, 04:09 PM
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Hi Scott,
First off, there are no stupid questions, just stupid answers
OK, now your first question, yes the BEC connects to the throttle servo port on the receiver, then the ESC servo plug connects to the BEC. The other wires, in this case with the JST connector must be connected in parallel with the battery input to the ESC, usually people solder them to the connector on the ESC, the one you plug the battery into, the BEC needs it's own connection to the battery to operate.
Question #2, Yes, in fact for 4 standard or micro servos even the 1.5A Parkbec is good for 4 servos, the reason the separate BECs can handle more servos at higher voltages is that they use a more efficient (switching) regulator that can drop greater voltage (like a 4S lipo) and not produce nearly as much heat as the linear regulators in the average ESC.
I hope my answers help
Pete
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Old Jan 14, 2007, 03:13 AM
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There's a diagram part way down this page showing how they connect http://www.koolflightsystems.com/ultimatebec.htm

Maybe things are different if it's not a UBEC, but the ones I've seen all connect up the same.
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Old Jan 14, 2007, 09:52 AM
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Abenn, a picture is worth a 1000 words! That diagram clears everything up for me!

I just discovered that the 60 amp Dualsky ESC I'm using has a 3 amp BEC built into it. Do you think we will be OK running 4 standard servos on that?

I was under the impression that the larger ESC's did not have BEC's. Guess I was wrong!

Scott

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Old Jan 14, 2007, 10:04 AM
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How many cells?
3S would be the limit for most non-switching BECs.
Pat Mackenzie
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Old Jan 14, 2007, 10:23 AM
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Quote:
Originally Posted by pmackenzie
How many cells?
3S would be the limit for most non-switching BECs.
Pat Mackenzie
I am running 4 cells and my buddy is running 5 cells on his. Sounds like he will need a separate BEC for sure. I am on the fence.

Here is some info on the ESC from the distributor:

Dualsky's NEW 60A ESC features many advanced features. We reviewed your feedback and made a better more reliable ESC! This ESC has a 5V, 3A BEC capable of controlling 4 micro servos. This ESC is perfect for 3D flying due to its precise throttle control.

This ESC is capable of up to 5 Li-Poly cells. If you plan to run 4 cells or more, we recommend using the VR-3 to power your servos, or similar voltage regulator.

Features:

Max Output 60A, 70A surges
Weight with Wires 1.48 oz (42g)
2.28x1.10x0.55in
Up to 15 NiCd, Ni-MH cells (7.2-18V) or four Li-poly cells (7.2-18.5V) with three micro servos.
Supported highest motor speed: 210000 RPM(2 poles), 70000 RPM(6 poles), 35000 RPM(12 poles)
Smooth and accurate speed control, excellent throttle linearity
Extreme low resistance, super current endurance
XMotorTM optimized timing advance.
High rate (8 KHz) switching (PWM)
Cutoff can be programmed for motor stop or reduced power
Brake/No Brake operation. Stop folding props cold or let fixed props freewheel
Full protection features: Low-voltage cutoff protection / over-heat protection / throttle signal lost protection
3 startup modes: Normal / Soft / Super-Soft startup, can be used for both fixed-wing aircraft or helicopter models
Throttle range can be configured, fully compatible with all market available transmitters
Microprocessor and BEC(Battery Elimination Circuit) use separate voltage regulator IC , with good anti-jamming capability
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Old Jan 14, 2007, 10:29 AM
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4 cells is not on the fence. You will need a seperate BEC.
Pat MacKenzie
(I do have one plane running 4S on a linear BEC, but it only has 3 older low torque servos, and the BEC is not integrated into the ESC.)
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Old Jan 14, 2007, 10:59 AM
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Quote:
Originally Posted by pmackenzie
4 cells is not on the fence. You will need a seperate BEC.
Pat MacKenzie
(I do have one plane running 4S on a linear BEC, but it only has 3 older low torque servos, and the BEC is not integrated into the ESC.)
OK.....Separate BEC it will be!
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Old Jan 14, 2007, 03:39 PM
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Quote:
Originally Posted by abenn
Maybe things are different if it's not a UBEC, but the ones I've seen all connect up the same.
Not the ones made by Dimension Engineering
http://www.dimensionengineering.com/ParkBEC.htm

The only reason for the hookup as shown in the link is for applications where 5A current is anticipated. Based on Scotts original post I suspect he has a ParkBec or one like it that is made to simply hook in line between the ESC and receiver.
Pete
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Old Jan 14, 2007, 04:42 PM
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I ended up wiring the BEC just like the diagram provided in the link on post # 6

I powered up and everything works!

If I had it to do over, I would seriously consider running a separate battery pack for the RX and servos. I am not totally comfortable with soldering tiny wires onto the deans connector, knowing if one of these come loose, it's game over! Maybe it's my soldering skills I don't trust!

Scott

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Old Jan 15, 2007, 02:42 AM
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Quote:
Originally Posted by pilotpete2
Not the ones made by Dimension Engineering
http://www.dimensionengineering.com/ParkBEC.htm

The only reason for the hookup as shown in the link is for applications where 5A current is anticipated. Based on Scotts original post I suspect he has a ParkBec or one like it that is made to simply hook in line between the ESC and receiver.
Pete
Thanks for that. I haven't experienced a ParkBEC, that's why I warned in my reply that it could be different from my experience and the UBEC

Scott, if yours is a ParkBEC, heed Pete's advice. It looks much simpler

As a matter of curiosity, presumably you could plug your ESC into your Rx separately from the ParkBEC, could you? Provided you disable the red lead?
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Old Jan 15, 2007, 08:41 AM
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I have read a few times where folks have said to pull the positive wire from the ESC when running a separate BEC or NICad pack for the receiver. What is the reason for this? Does the ESC have problems with running in parallel with the BEC?

Thanks, Terry
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