lipos and rx battery packs.

[SONNY MONKS]

Hi,Please excuse my lack of knowledge,but when setting up an electric powered model plane,with a lipo 5s 5000mah with a total of six servos and elec retracts,do you still need to power the rx with a seperate 4.8 or 6v battery pack?

[SONNY MONKS]

I know you dont on the smaller electric planes,just checking on the big stuff!!

[Mark Howard 1]

No, large or small, the setup is the same. If the ESC has a BEC to power the electronics, the Rx is the first port of call for the power. The Rx then supplies the power to the servos etc. The positive and negative leads for all electronics are effectively linked together within the receiver.

Some people prefer to power the electronics separately via a receiver pack as a form of redundancy/backup. If you do this, remove the red wire from the ESC/BEC cable connector so that only the throttle signal and negative are connected to the ESC to avoid the Rx pack back-feeding voltage to the ESC (some ESC's won't tolerate being back-fed).

Edited By Mark Howard 1 on 29/11/2018 05:45:34

[Allan Bennett]

As Mark has said in the previous post, you don't need a separate receiver pack. But if you rely on the BEC in the ESC to power the receiver, you must be sure that it's capable of providing enough power for the number and type of servos you're using.

Even if the BEC is sufficient (for six servos it's got to be a 'switching' BEC), I personally prefer to use a separate 5v supply for the retracts in case one of them jams and compromises the supply to the receiver. I use a separate stand-alone BEC for that so that everything goes 'live' as soon as I plug in the battery, but it could be a standard Rx battery if you wish.

[cymaz]

Most of the electric pilots I know run a separate Rx battery and a motor battery.

[Toni Reynaud]

Using a 5s LiPo, the BEC bult into the ESC could get a bit warm. To check this, connect the main battery and cycle the servos for a minute or two, then check the ESC. If it's warm just driving the servos after a short time, then a separate BEC would be good.

[Adrian Smith 1]

Sonny, in relation to your query on "big stuff", my set up includes a separate RX power source. This is mainly because on say a 12S set up the ESC I use is what is called an OPTO ESC which means you have to go that route, as there is no BEC. I think this is because of the high voltages involved although I am not sure it's a simple as that. I have couple of smaller aircraft driven by 6S power packs, but the ESC has a BEC to power the electronics. All I would say is buy a good quality ESC and spend as much as you can. Better that than losing the whole plane. Hope that helps.

[Nigel R]

"with a lipo 5s 5000mah with a total of six servos and elec retracts,do you still need to power the rx with a seperate 4.8 or 6v battery pack?"

Sounds a reasonable size model.

I'd probably go for a nimh 4.8V for the RX and servos.

However, you speed controller will probably have a BEC, so, you could let the ESC power the RX and servos. But on a bigger model the weight of a battery isn't that big a deal.

You will want a completely separate nimh 4.8V for the retracts. Always a separate source for electronic (or servo driven) retracts. For safety sake. Any malfunction in the retracts, if they get bent for instance, will then not affect the flights controls.

[Former Member]

[This posting has been removed]

[Mark Howard 1]

Posted by supertigrefan on 29/11/2018 16:46:34:

Could this be utilised for the Rx and servos or retracts?

**LINK**

It only seems to output up to 2.1 A per channel so it might be a bit tight for some servos especially retracts. It might be ok for smaller models but smaller models don't really need nor have the space for it. A conventional Rx pack might be the better bet or a lipo if you're using either a regulator or high voltage servos.

[Allan Bennett]

Posted by cymaz on 29/11/2018 06:46:04:

Most of the electric pilots I know run a separate Rx battery and a motor battery.

NONE of the electric pilots I know run a separate Rx battery Most use the BEC in the ESC if it's adequately rated, or a stand-alone BEC.

Supertigrefan, that power bank, apart from perhaps being marginal for decent sized retracts, will also be heavier than a separate stand-alone BEC because of its casing and the charging/balancing circuitry it presumably has inside.

[Nigel R]

supertigrefan, I would say no, that is intended as an emergency mobile phone charger, completely unsuitable for our uses - far better value for us from 2 x 4.8V packs, or 2 x LiFe packs, they are the right tools for the job.

The retract pack can happily be a smaller capacity unit, e.g. AAA, to save weight, where the main RX pack is AA size.

[Former Member]

[This posting has been removed]

[Peter Christy]

Any model big enough to warrant a 5 or 6S lipo is big enough to carry the extra weight of a separate radio battery. The BECs on many speed controllers are marginal when driving a lot of digital servos.

Some years ago, I was at the helicopter World Champs.The then Japanese reigning world champion was just completing his hovering schedule in the fly-off rounds when his helicopter suffered a total power failure of the flight pack.

Luckily, he was powering the radio from a separate pack and was able to auto-rotate several thousand pounds worth of helicopter to safety!

A post-mortem on the flight pack revealed that one of the wires joining the cells had partially fractured, and the resulting head build up had caused the solder to melt, effectively making the pack open circuit!

If you do decide to use the built in BEC on a large model, at the very least, use on of the many back-up switches available, with a small flight back-up battery. It only needs to be big enough to carry out an emergency landing, and could save a lot of grief!

--

Pete

[Bob Cotsford]

What Peter said. 6S = separate receiver battery.

Nigel, these days I'd only use a separate retract battery with servo driven mechanical retracts as long as the receiver battery is in decent condition. The electronic units that I've used all had anti-stall cutout so they won't draw high current for more than about 10 seconds. I generally use a 2S LiFe pack for the receiver, servos and retracts. On which point I wouldn't drive retracts from an ESC BEC on any model regardless of the cell count, the startup current surge from a tricycle setup could be up to 3A on medium to large sized models. I can't recall the exact figures from when I tested some E-flite units through a wattmeter but it put me right off the idea of running without a separate battery! I generally set the retracts units up on individual channels so that I can sequence them, this way I reduce the peak current and get a nice scale-ish one leg first retraction.