How to install a UBEC

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28 Feb 2018 19:18 #1 by Eric
How to install a UBEC was created by Eric
Following on from a remark in the last BMFA rag, I was asked by my local club to put together an explanation of how to put a UBEC into an electric model.
A UBEC is also applicable to some i/c models, where the owner wants to use a 2 cell lipo to power the radio, rather than the usual nimh packs.



Different ways to power the receiver in your Electric model.

The obvious one is with a separate 'flight-pack' battery, as you would with an I/c model, a four or five cell nimh, via a switch – to the receiver 'batt' socket.
This is fine if you have the space and carrying capacity for the extra bulk and weight - until you forget to switch it off after a flight, or charge the battery before the next session!

But what do you do when your model is full of lipo flight pack, and there is no room for more batteries?
The majority of 'plug and play' type models on the market have a Battery Eliminating Circuit (BEC) built into the speed controller, and this plugs into the 'throt' socket on the receiver, powering the receiver and servos, and at the same time carrying the command data signals to the speed controller.
This works just fine for most of the time – but – and it is a big BUT – should there be a mishap, and the speed controller fails in flight, it will also 'take out' the BEC, resulting in a total loss of control over the model, and usually the total loss of the model! (and we all know that the manufacturers are very mean with their sizing, so the 'speedo' is only just powerful enough for the motor/prop/battery combination).
This is where the UBEC (Universal BEC) comes into play. It is a small add-on electronic gadget that can by-pass or replace the BEC in the speedo, and if connected up correctly, can still provide power to the receiver if the main speed controller fails. This failure will of course convert your highly aerobatic over-powered missile into a glider, but that's only a minor difficulty – you still have control!

The UBEC is a small device, weighing a few grammes, and is around 5cm long and 1 cm wide – costing a couple of ££ on the popular websites. It has two wires at one end, usually bare-ended, and the universal three and a plug at the other.
What do we do with it?
My preferred method is to solder the two bare-ended wires to the same plug as the power connector for the speed controller, making sure the polarity is the same – red to red, black to black. This way, when you plug in the battery to the model, the UBEC and speed controller are both powered up together.
Simple, so far?
The tricky bit comes next. The UBEC plug goes to the receiver 'batt' socket, and the speed controller plug goes to the 'throt' as before.
BUT
If the speedo has a built-in BEC you need to disconnect the RED (+) wire from the speedo plug, or the two power feeds will 'fight' each other. On some plugs, you can ease the pin out, fold the wire back, and put a wrap of insulating tape on it, to prevent accidents. On others, you will need to cut and tape both ends of the wire.
Leave the black (-) wire (ground/negative) and the (usually white) signal wire intact.
Some user-fitted speedo's do NOT have a BEC, the notes in the packet will tell you this. You cannot tell by looking at the device, unless you can read Chinese micro-print, as it still has the three wire plug for the receiver, or it would not get any throttle position data!

Now – with larger models, big motors, big props, and big batteries, I like to add a fail-safe cut-out between the battery and speed controller, so the motor is still 'safe' when the radio is awake. This I do by putting a bullet connector pair in the red wire. When this is unplugged, the speedo – and therefore the motor - is not powered, and the model is safe, as it cannot bite!
DO NOT use a switch here! If you think about it, that circuit breaker can be passing 100 plus amps and a lot of volts, depending on the lipo cell-count, and a 'normal' miniature switch will melt or burn in seconds!

if you are calm and collected when all about you are going berserk - you've missed something important!
Thanks: THE BLACKBIRD, boz, Squirrelnet

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28 Feb 2018 19:22 #2 by Eric
Replied by Eric on topic How to install a UBEC
The drawing didn't attach!



if you are calm and collected when all about you are going berserk - you've missed something important!
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Thanks: THE BLACKBIRD, boz, Squirrelnet

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28 Feb 2018 19:49 #3 by Quorneng
Replied by Quorneng on topic How to install a UBEC
Very nice and clear.

In my experience with smaller ESCs (30A or less) a failure of the 'power' side does not necessarily take out the BEC but I would expect a 100A might completely destroy itself.
I have several ESCs that failed in service but I now use for testing servos. They are duly marked up "BEC only". :P
Thanks: Eric

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01 Mar 2018 06:48 #4 by Ex-Member
Replied by Ex-Member on topic How to install a UBEC
Thanks Eric, that's very useful for me too as I'm currently looking at a Radio DT system and on-board Gyro Stabilisation for FF models; both are powered by LiPo and will require a BEC/UBEC.

I do enjoy your occasional electric missives, please keep 'em coming! ;) ;)

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01 Mar 2018 09:38 #5 by Eric
Replied by Eric on topic How to install a UBEC
Re-drawn without the line error!



if you are calm and collected when all about you are going berserk - you've missed something important!
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Thanks: Klipkopwildlife, Ex-Member

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01 Mar 2018 11:26 #6 by Klipkopwildlife
Replied by Klipkopwildlife on topic How to install a UBEC
I see you don't show a negative wire to the receiver battery connection, to be honest I would not remove it from the Ubec 5volt out.

Do it now, you may never get another chance

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01 Mar 2018 12:25 #7 by Eric
Replied by Eric on topic How to install a UBEC
I drew it as a single wire, Klippy, to keep the thing simple!
I assumed that everyone else would assume that the cable to the rx was the three-core!
-
Anyway - my order finally turned up, so I've put one together, patch-lead style. I've deliberately not shrunk the neg insulator - or covered the bullet plug and socket - for the club meet.



if you are calm and collected when all about you are going berserk - you've missed something important!
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Thanks: Klipkopwildlife, Quorneng, Ex-Member, boz

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