Selecting a Ubec

[Erfolg]

I am converting a old IC model to electric. It will be using one old servos and 2 +9g type servos. I an fearful that the power demands could be to much on occasion for the BEC on my speed controller.

To ensure this does not happen I am thinking that a UBEC will avoid this issue. Looking at the HK site, there appears to be so many.

So what I want to do is get a handle on what I need to consider. They all seem to give at least 5v or 6. So what else is important?

What is a SBEC?

Edited By Erfolg on 21/11/2012 21:21:50

[CrosstownTee]

What I've learned about them so far:

1. Make sure the uBEC can handle the power your servo's will draw at peak moments. How to measure this? Well, a setup could be made, with a tool to measure the current, while you stress all servo's a simultaneously as possible...

2. Cheap plane: don't bother with expensive uBEC's...

3. Precious plane: pay as much as you can. I've heard Caste Creations are virtually market leaders in innovation and quality in these kind of products: **LINK**

4. Most ESC onboard BEC's now are 3Amps. You'll need to look for a uBEC that's bigger I presume. How much Amps? Back to 1....

From RCGroups.com:
UBEC (Ultimate BEC) is/was the trade name of one of the first add on bec's that allowed you to use more servos at higher pack voltages and produced by Kool Flight (Jeff Myers, SEFF organizer) It now has seemed to morph into "Universal" bec because a bunch of the Chinese stand alone bec's are referred to as UBECs.

SBEC stand for Switching BEC vs the built in linear bec which was limited to 3 or 4 servos and 3 or 4 lipo cells. The new lines of Switching BEC speed controls basically incorporate a "UBEC" into the esc itself instead of having to use a stand alone system.

 

Just fyi; I have no hands on experience at all with uBECs; I have looked this information up because I once had 2 servo's (futaba s3107) that browned out my receiver because they drew too much power, and cut out the ESC... They were probably faulty, but one part of the solution would have been to put those servo's on a sepearte uBEC, to see if my brown-out problem still occured.
I eventually ended up replacing them with cheap £2 micro servo's .

Edited By CrosstownTee on 21/11/2012 21:33:50

[WolstonFlyer]

I already use one of these from HK in a "Park Jet" plane with 6 digital servos and have ordered another to put in my Tucano build. It seems to do the job nicely and you can select 5v or 6v with the little jumper pins.

The "S" in SBEC means "Switching" as far as I know meaning it is a switched regulator rather than a linear regulator, and doing a bit of Google magic...

UBEC is/was a brand name, "Ultimate BEC" developed by Jeff Meyers' Kool Flight Systems in 2002

[Edit].. and I should have read the post above first because it has the same info about the name UBEC from RCGroups..

Edited By WolstonFlyer on 21/11/2012 21:43:17

[cagey]

One way to eliminate all that hastle is to use a separate flight pack plugged into the batt socket on the r/x.The ESC centre lead is removed which makes it a UBEC set up.. For example a 2100 mah LiFe 2s will power my FMS Mustang 1400mm with 7 servos electronic retracts for over an hour before it needs recharging. The main power Lipo is then left for driving the whirly bit at the front and consequently allows for a longer flight times.

One extra bonus on this system is that when powered you can do all your servo, gyro retracts etc setting up without the motor being live, very advantageous on a heli for certain, I got a hole in the ceiling to prove that LOL

[Pete B]

SBEC = Standalone BEC, same as a UBEC. Check the input voltage limit - some are for 2-3S, others 2-7S for example, so make sure your pack isn't too big for the BEC.

I'm using this one and it's been fine; this too on my larger models and this type has been trouble-free. Plenty of others there, too.

The only time I've killed one is by wiring an ESC plug incorrectly and fried both the ESC and UBEC. You only do it once!

As a belt-and-braces thing, I use them on any model with more than 4 servos and on models with 4S packs upwards, regardless of the number of servos. Whilst most ESC's of 40A upwards with switching BECS should cope with 3-4 servos, the small price of a separate BEC, and the much greater reliability I have enjoyed, makes it a must for me.

Pete

[Tim Hooper]

I'm using Turnigy UBECs in several multi-servo models, and never had an issue.

As an experiment, I'm also flying a 4 servo model on a 5S pack, using nowt but the Turnigy Plush 80 ESC as a power source. Rock solid so far.....

tim

[Chris Bott - Moderator]

Erfolg I would have thought that one old servo and two 9g servos would be fine on the BEC in the ESC.

[Erfolg]

Chris

I am a little concerned that my old servo on the ailerons via torque rods, will draw more current than my current practise of using 2 * 9g servos, with short pushrods. I have also noticed that the hinge pins are pretty chunky things. The whole assembly seems that bit tighter than my current arrangements.

The rudder and elevator use bowden cable, rather than Sullivan golden rods, Again these seem fractionally tighter than my current arrangements.

Given that the model is almost 30 years old, it is perhaps not surprising that things are not as loose/free as I would like. They have not seized, just, well, not loose, I you can get the gist.

To get the model to fly, I am also a little concerned that it will draw a lot of current. I had considered a separate pack to the Rx,. I am not that keen, as I have found that is not without its own issues either.

[Peter Beeney]

Erfolg, - May I ask, please, what particular issues do you have with using a receiver battery?

PB

[Allan Bennett]

Even if the BEC built into the ESC is adequate for the number of servos and battery voltage you're using, using a separate BEC gives you one benefit apart from extra amps capability -- if your ESC burns out because of some motor-related problem, the stand-alone BEC (or indeed a separate receiver battery) will continue to power your receiver so you can land dead-stick.

I haven't used HK BECs. I started out with a couple of genuine UBECs from Kool Flight in the USA, but more recently I've been using UK-sourced Hyperion and Castle units. Horizon Hobby are now the UK dealer for Castle, so your local model shop should be able to get them for you if you're not a fan of mail-order.

If you're using any kind of stand-alone power supply for your receiver, don't forget to disable the ESC's built-in BEC (if it has one) by pulling its red wire from the plug that goes to the receiver.

[Erfolg]

Peter

I had a sports model where it was convenient to carry a separate Nicad pack to power the Rx, rather than just use lead.

I had a problem with the model, which I put down to me tip stalling the model.

After a repair, I recharged the Lipo and nicad, all seemed well with both batteries after charging. I launched the model, it cleared the edge bounding the field, i turned to fly a circuit and the model went in.

Recovering the model to the field, a cell tester showed that the Nicad was essentially empty, I cannot remember the figures.

At home I did a recharge and it took a charge. The multimeter showed full charge. The Nicad was then put under load and the volts immediately could be seen to be collapsing.

To date I have not had a Lipo to fail in the same way. I guess there was no real diversity, just two systems which could go wrong.

[John Cole]

If you are converting an old IC model then it seems likely you'll need a powerful ESC. Powerful ESCs often have switched-mode high-capacity BECs that will easily power your Rx and servos. What ESC are you using? Do you have a meter to test current draw from the BEC?

[Erfolg]

John

To date I have retrieved the model from storage, cleaned it, as it was very dirty.

I have weighed the body and wings, without gear, having removed the fuel tank. So pretty much a bare airframe. The body is about 750g (complete with wheels etc) and the wings are approx. 400g = 1.150kg.

I flew an identical version (the same design) with a 0.20 Enya engine. The model was very marginal on take off. Requiring very short grass. Once airborne the model flew well, although only moderately aerobatic, simple loops etc.

From this i am at present thinking about 200-250w. On that basis the ESC could be as low as 30 amp, although I will probably go for 40 amp.

At this stage my thinking and decisions are subject to change.

My biggest internal debate is one I am struggling with, is the Lipo. Normally I use 3s, yet I can see advantages with 4s, in this application. Given that the model is only being re-commissioned to suit an end, I am reluctant to buy a 4s or 2*2s batteries. Combining my existing batteries to make a 6s, seems a little excessive, taking me voltages I would prefer to avoid.

[John Cole]

HobbyWIng FunFly (was Pentium) 40A ESC has a switched-mode 5V 3A BEC which I think will drive your servos very easily.

Bare airframe 1.15 kg. Plus LiPo, servos, ESC, Rx, motor, prop, mount....... At 250W I it will look pretty sitting on the runway with the prop whizzing round. But will it take off? Maybe think about a heftier set-up.

Also, if it's a straight conversion of the powerplant then you MAY be limited to IC-sized props. Maybe better with a bigger prop and longer U/C.

[Erfolg]

You are correct with respect to the prop John. I have not checked as yet, although I would expect I will have had a 9" prop as the minimum, possibly as much as 12" (with minimum clearance).

Although retired, I seem to have less time than I anticipated. At present it is working on the bathroom. Which allows a few minutes here and there. My wife has plans for me doing 2 days a week, grandchildren minding.

As I also do the cooking, my dedicated time on models is spasmodic. Although Internet time is easier to fit in.

[Peter Beeney]

Erfolg,

Thanks for your answer. Certainly your experience of nicads matches that of a great many others over the years, which is why I’ve always advocated checking the capacity on a regular basis; and in more recent times, considering that an on-board voltage monitor is a good idea. Nickel batteries have always been a tiny bit of a headache, charging etc., and again, as I’ve said many times, the quality can be suspect, right from new. But they can also give good service, too, I’ve always rolled my own, and they’ve invariably lasted a long time, a number of years, in fact.

It’s also a very valid point that most folks would not be aware that the cells can gradually deteriorate over time, in general I’ve seen little or no instructions with replacement packs, and probably very few people check the capacity on a regular basis.

But now there are LiFe PO4 cells, made into receiver packs as well. Ideal voltage, two in series are around 6.6 volts. Very low impedance, this means they can deliver current at a high rate, and also be fast charged if necessary; the soft package types are quite a low weight, a 850mAh version weighs 50g. There was a query recently relating to the fact that a pack had some spare heavy duty leads attached, this is for a fast charge connection; and as yet, 'cos it remains to be be seen, but it’s claimed that the longevity is also quite remarkable, too. To complete the package, the self-discharge rate is so slow that’s there's not enough time left to measure it! Well, maybe that’s stretching things a tad, but it’s a fair interval, anyway. I’d personally think that one of these, plus an added safety measure here, is never going to be of any concern.

If I were toying with this model I’d personally consider that a 3A BEC would be perfectly adequate. Up to 3S anyway, but even that can depend, some ESC’s specifically say suitable for 4S. But if I were concerned about this, I’d just chuck in a 5A UBEC instead, that would drive anything, I’m sure; and again, it’s a personal thing, but I’d not worry about disconnecting any wires, because I’ve never been convinced it makes any difference.

I’m not into electric at all, but I think if I were doing a conversion like this I think I’d be looking a fairly lively motor with a bit of get up and go. Wind up the watts! I just don’t go much on underpowered model planes. I watched a large trainer type recently, the large prop was turning at about a fast tickover, and it lumbered around the circuit for about 3 minutes, and then the battery was flat. The pilot thought it was magnificent. At the end of the day, it’s just an individual person’s choice.

The Hextronik Display costs less than £1:50, is very accurate, and you can’t miss the bottom ultra bright red led. LiFe’s drop off their initial voltage quite quickly, so it soon goes to the second green, but then stays there for a very long time. They have a nice flat discharge curve.

Good Luck.

PB

[John Cole]

Your bare airframe + u/c weighs 1150g. I have just weighed a 30-equiv motor, prop, ESC, plugs, Rx and they come to about 270 g. Add a 2200 3S LiPo at 200g and some servos (maybe 80 g if you have 2 * 9g and an old heavy one. No rudder?) My add-ons come to 550g. So your t/o weight is going to be about 1700g (3.75 lbs). Allowing 220 w/kg or 100 w/lb indicates you should have about 375 watts, or draw about 34 amps from a 3S. This would give you about 8 minutes flight on 50% power.

Edited By John Cole on 23/11/2012 12:26:46