To BEC or not to BEC

[Garry G]

Is it safe to use a 6volt battery in conjunction with a normal Futaba 35 mhz  RX as well as connecting it to 6 volt servos ?

 

Garry G

[Peter Roberts]

Hi Timbo

Thanks for your reply. I typed "I link 3 batteries " in error but actually meant to type "two 3 series". I have two pairs of 3 series batteries 1pr x 3100 and 1pr x 3700 each pair bought together from same manufacturer. Similarly the ESC's and motors are bought from same source who have confirmed they were part of the same batch production.

 

I use the batteries in other models or would certainly take your advice to hardwire them together.

Thanks for your suggestion of BRC for harnesses. I was intending to join both flight battery outputs together and then split the joined supply so that each ESC had a matched supply.  I am planning to use a UBEC 6v 5A drawn from the combined feed wires to feed the DSM2 radio gear too.

 

I have been recommended to use 60 amp ESCs with the red middle wires disconnected from the extension cable of each - doesn't damage the original esc outputs.

 

Will this all be OK?

Thanks for your help

Peter

 

PS I'm fairly sure that the Futaba RX ceiling is 6v and you might reasonably expect that if the servos are advertised as being 4.8 or 6v capable that the RX should be also.

 

Edited By Peter Roberts on 10/01/2011 13:42:30

[gazzazh]

Great enough.. thanks .. I am new to electric flight.. the information here makes so much sense.. you hear a lot of people talking about bec or no bec but i think most don't really understand the concept.. Thanks again.. Cheers

 

[Toni Reynaud]

Connecting the UBEC to the main power lead

I use CPU fans to cool a couple of my ESCs. They have to be connected to the main power lead in the same way as a UBEC. What I do is to solder the fan (or UBEC) wires to pins with the heads cut off. These pins are then thrust through the insulation of the battery connector wires of the ESC to make the connection, and heat shrink tubing fitted over them for protection, reinforcement and insulation. Quick, easy and changeable if necessary without soldering onto the main bullet connectors. See the following on my Hurricane build thread.

http://www.modelflying.co.uk/forums/postings.asp?th=34350&p=2, post number 19/03/2010 17:56:57

[steve shaw 3]

i always use the BEC on all my speed controllers. that is what the manufactureers put it there for. I have used them right up to 6s ducted fans with 9servo's and electric retractsand have never had any issues

[robert chamberlain]

Hello, I'm converting an old sailplane to elec power for launch purposes. As I understand it so far,as the Lipo runs down the ESC shuts down the motor leaving some energy in the batt to run the receiver and servos.So far, so good. My question so far is just how much time is left to run the rec/servos? In a powered airplane one would have time to make a landing before running out of power. The sailplane, up at altitude working some great thermals,does not want to have to come down right now.Of course, there probably is very little elec demand on the batt at this point just cruising around.For this type of operation, would it not be safer to incorporate a separate batt? Even four cell AA pack would last a long time.Later,--Bob C in Kansas

[Olly P]

Bob - as you have almost said - it depends on the load!

It is not advisable to run LiPo batteries too far down anyway, and if you are on a booming thermal day, and the plane doesn't want to come down then you won't need much power to get up in the first place!

You can add a seperate battery for Rx power, and this can be either the std Rx pack or an additional LiPo with BEC type interface.

The key would be to come down as quickly as is safe and possible if you find the LVC has kicked in on the main Speed Controller, perhaps deploying flaps, spoilerons etc to speed the descent!

[Biggles' Elder Brother - Moderator]

Hi Bob,

for that I'd definitely install a separate battery. I would only trust the low voltage cut-off as an "emergency system". I don't even use it on powered planes - prefering to set my timer conservatively and land with power in hand so I have the option of a "go round" if safety (or incompetance!) requires it. This strategy also has the virtue of being kinder to the Lipo.

Having said that it is possible to set the cut off at different voltages. Setting it at a high point may mean it cuts out with considerable capacity left. But why risk it for the sake of carrying a small 4cell pack? If the Rx low voltage kicks in on you then you run the risk of lossing the model - or possibly worse.

BEB

[Chris Bott - Moderator]

To connect my BECs and UBECs into my power leads I usually shave a little of the power lead insulation off the leads, somewhere away from the ends. Then I solder one of these in and slip some heat shrink over the joints.

That means I can remove or replace the BEC, but at the same time I can't plug servo plugs into a higher voltage.

Edited By Chris Bott - Moderator on 21/02/2015 17:10:17

[Erfolg]

All my models use the LVC now.

Using a separate Nicad pack does not necessarily improve safety. One of my models ended up being scrapped as a consequence of not recognising a battery issue. The battery indicated it was charged to full capacity, it was only after a subsequent investigation, that i recognised that on load, the battery voltage suddenly fell of a cliff.

I have on the other hand flown many aircraft just using the LVC. You do not need even to time your flight, which can be an issue with a glider, you will recognise that the urge has gone, and it is time to entera landing circuit.

As Olly points out, if you hook a thermal, it is not usually when the Lipo voltage is dropping to a level that is a concern.

Another incident I have experienced occurred when a innrunner burnt out, whilst flying. I assume that the current draw was high. Which shut down the motor and the radio. The model dived, out of control from a great height. Just when I thought all was lost, the radio came back. I assume that the battery voltage recovered and the ESC/LVC started operating again. It was on landing that what had possibly happened became apparent.

I have a lot of faith in my ECS's, as I do with my radio and Lipo's. I just recognise all equipment can fail.

[Erfolg]

Chris

I do like the method you use when using a separate Nimh pack. I guess it goes into the ESC side of the Lipo plug. I also guess you use heatshrink as you see on "Y" leads.

I will remember the idea and use it my self, if I again find the need.

I have also seen an an image for a Deans type plug with separate tags for UBEC connection. I have never seen any for sale though.

[PatMc]

Bob,
I fly E-gliders a lot, I never use a seperate battery, I always use an ESC with included BEC. IMO it doesn't make sense to use a seperate battery as it's something else that can go wrong, it's a nuisance to have to remember to charge it & unlike lipo it can't be charged well in advance of use. With a BEC you know that if there's power for the motor then the Rx supply is good.
If you are worried about the capacity for extended glide times then it makes more sense to use a higher capacity lipo than a seperate Nimh, just don't run the motor until LVC & change or recharge between flights.

[PatMc]

Erfolg, I think Chris is using a seperate BEC/UBEC not a seperate Nimh.

[Erfolg]

Patmac, I am pretty sure it is an additional battery pack that Robert is considering using. I personally would be reluctant to use a separate battery pack now. I am not even sure, what advantage it could possibly have. In my case, it was ballast, that proved costly.

A different question.

I have purchased one UBEC, I have never understood how to wire it in. It looks that it takes a tapping from the Live connection, to the Rx and the Neg goes straight to the Negative connection on the Lipo.

[PatMc]

Erfolg,
As I understand your post you are refering to Chris's post with the JST plugs & sockets photo not Bob's earlier one.

The input wires of a UBEC should be connected directly to the ESC input (or via a plug/socket as Chris describes) the output direct to the Rx. If the ESC has a built in BEC the +ve wire to the Rx should be disconnected the same as if using a seperate Rx battery.

[Geoff S]

I think the use of the in-built BEC on an electric model depends to some extent on the model. I think going for the BEC built-in to the ESC is fine on smallish models like (say) a Riot or Acrowot E foamie but is certainly worth thinking about on more serious models. I even use the esc BEC on my Eezy Peezy 84" ws trainer which runs on 4S with a 60 amp esc because the demands on the flight (as opposed to the power) electrics is still quite low.

However, I would certainly go for your number 1 choice on a more serious electric model. I have aSkyshark Galaxy kit I bought on eBay some tears ago. It's a 60" wing span aerobatic low wing model with a recommended power from a 60 size glow engine. That is certainly destined for electric power (5 or 6S LiPo) and I'll definitely use a an opto esc and a UBEC driven from the main batteries (probably 2x 3S in series).

I think your range of options is spot on as regards the order of preference. It's bad enough having 3 batteries to charge on one of my models (radio/servo pack, on-board glow, retract pack) or 2 on petrol modlels (radio/servo and ignition) I'm always afraid I'll forget one.

Geoff

[Erfolg]

Although applicable to all models, I have been made aware of a model that went in, an IC model, that was using a servo to drive the UC system. In that case the servo was stalled by a jammed leg. The current drain being sufficient that the std Rx battery pack was drained and the model went in.

I am reasonable sure that all my ESC with Bec, ensure that power is preferentially available to the Rx side. Again, a stalled servo could be a problem, although Lipos have possibly greater resilience than a airborne NiMh pack, but with either type of Rx battery supply, it is just a question of how long you get.

[Tim Mackey]

Ah - as far as retracts ( or indeed aux equipment such as bomb drops lights etc ) I always use a separate supply for safety. These items are not flight critical so minimal capacity psu is used and a stalled leg or whatever could indeed spell disaster if power is drawn from the radio supply.

[robert chamberlain]

Hello all, I was "gifted" a broken sailplane into which I have installed an electric motor powered by a Lipo for the launch. Right now, the receiver is powered by the 5 volts from the ESC. So far , so good. When the Lipo finally shuts down I still have power for the Receiver but, for how long? If I am up in thermal land , I do not want to have to get down. SO,---Separate batt to run the receiver . DO I just cut the little red wire from the ESC and leave the black wire as it is. Doses the black need to stay? or do I just unplug both small wires from the ESC and plug in my separate battery source ? Very little power is required for the sailplane anyway. Any thoughts out there besides the need to have two different batt types to charge? Thanks-----Bob In Kansas USA

?

[Trevor Crook]

Bob, the way I have done this in the past is to remove the positive (red) wire from the esc connector by gently lifting the plastic retaining tab and pulling out the crimp contact. This can be left on the wire, but folded back and taped to the cable (making sure the contact is covered by the tape). This will allow you to easily return the esc to bec operation in the future if you wish.

Leave the negative and signal wires in place and plug the esc connector into the throttle channel. You can then plug your receiver supply into the battery connector on the receiver.

[Nigel R]

"I still have power for the Receiver but, for how long?"

Even a flat motor lipo will drive an RX and a couple of servos for a very long time.

If you want a separate RX battery, as Trevor says break the positive (red) wire between ESC and RX.

[andyh]

I remove the red wire from a 2" servo extension & put the extension between the ESC & the Rx. you can then re-use the ESC in the future without having to do anything to the servo plug wiring.

[robert chamberlain]

My thanks to all,--Trevor, Nigel,amdyh,Tim,Ken---------------Bob C in Kansas