What is a "BEC "

[Rocker]

I was looking at an updated model I like and they have upgraded it the electric motor has been upgraded , but it has done away with the ESC and it now has BEC instead of a ESC .So what is a BEC and what is the difference between having a BEC to having a ESC ?

Edited By Rocker on 25/11/2017 13:17:30

[Rocker]

Mmm, I read it wrong .It has a built in BEC instead of a separate BEC

[Pete B]

An ESC (electronic speed controller) and a BEC (battery elimination circuit) have different functions but are often contained within the same module. All leccy models need an ESC for throttle control. The BEC, which may be part of that unit or a standalone item, supplies regulated voltage, normally at 4.8v - 6.0v to power the Rx and servos etc.

I tend to use a separate BEC (which is connected directly to the power supply in parallel with the ESC) on some models as I've found them a bit more reliable. A combined ESC/BEC is being asked to do quite a lot in terms of cooling, especially if the ESC is being used towards the top end of its power rating.

There's more on ESCs etc here....

Pete

[Rocker]

Thanks

[Geoff S]

I've now done quite a few glow to electric conversions, by which I mean I've built a model originally designed for a glow engine but chosen electric propulsion. In every case I've chosen a beefy esc and used the in-built BEC for the radio. I've never so far had any problems with that.

However, my current project is a bit bigger. It's a quarter scale Percival Mew Gull from the old Skyways plan/ pack kit. It's coming out to be reasonably light (certainly below 4kg - fingers crossed ) and will only have 4 moderately sized servos. It will be 6S and the absolute maximum current will be 60 amps (hopefully less). The esc is rated at 80 amps continuous and it has a 4 amp SBEC at 5.5v. The design called for a 60 size glow engine which isn't all that big.

I don't anticipate any problems (at least as far as radio/servo consumption is concerned) although if I have trouble getting enough weight forward of CoG to get it to balance (I find electrical installations are lighter than the glow engines they replace) I may have a separate battery for the radio and disconnect the power lead from the ESC.

I just wondered in view of Pete's comment about using separate SBECs if any had experienced problem with using inbuilt SBECs in ESCs.

Geoff

[Chris Walby]

I have not had any issues with ESC's and integral BECs on about 10 models apart from one build that was going to use digital servos and on the bench test the RX would brown out (temporary loss of power) while using a separate HK BEC.

The twist was that if you operated one servo quickly or all 3 slowly nothing happened, but stick bash once (like one of those "moments" I sometimes in get flight!) the BEC voltage would drop to a point when the RX stopped working and then would power back up (okay but it takes a couple of seconds to achieve). The solution was to buy a 4Max BEC and problem solved, but it would be worth checking the rating of your combined ESC/BEC especially is using digital servos.

The other times I have used a separate BEC is with electric twins, firstly as one set of ESC didn't have integral BEC's anyway and secondly I needed the additional weight of a separate RX battery to get CofG but not room for a larger main lipo + you can get issues with each ESC BEC fighting the other.

Why add more components than necessary, just more to go wrong (components and cable joints etc)

[Pete B]

Posted by Geoff Sleath on 25/11/2017 22:24:17:

I just wondered in view of Pete's comment about using separate SBECs if any had experienced problem with using inbuilt SBECs in ESCs.

It's just a personal preference, Geoff, probably stemming from my earlier days with smaller (up to 30A) linear BECs, which I now avoid. They tend to produce a lot more heat than SBECs so I reasoned that separating the components avoided putting too much load on heatsinks etc.

I have models with both built-in and separate BECs and it's a long time since I've had a loss of power either way. In respect of reliability, I think it's more important to consider the location and mounting of the ESC to ensure it gets plenty of cooling, particularly by not falling into the trap of using that nice flat heatsink as a convenient surface for mounting tape...

I take your point, Chris but the number of components remains the same, just separated. The supply wires are soldered together with the ESC supply at the plug and that hasn't been a problem.

Pete

[Mike T]

I never had any success with the "disconnect the red wire from one ESC" when operating twin set-ups. Invariably, the ESC with the disconnected red refused to work (who'd a thunk it?). Conversely, I never has a proble with fighting BECs either.

To be on the safe side, with twins I use 'opto' ESCs, with a separate switching BEC somewhere in the power harness. For a triple or quad, I'd use a separate rx/servos NiMH pack (or NiCad if you have 'em) with a switch, as for any i.c. set-up.