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Author Topic: To BEC...or not to BEC?  (Read 3561 times)

Patrick Henry

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To BEC...or not to BEC?
« on: November 17, 2011, 08:04:02 PM »

What do you guys think of using a BEC on your radio installations?

I've used them before on surface boats and had the main battery drop down enough to cut the power to the radio...result, a stranded boat. In a sub that could mean a sub down on the bottom with not enough power to get up again, I guess.

My new submersible will be a dynamic dive boat to start with, so the problem isn't quite that bad, but I do plan to fit a pump and bag later, that's when the problems could arise.

So, what do you think...fit an extra battery pack for the rx? Or go with the BEC?
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john s 2

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Re: To BEC...or not to BEC?
« Reply #1 on: November 17, 2011, 08:13:30 PM »

Id say no problem using a bec especially if its more convenient.The fitting of a low voltage cut off of the type that will reduce power but enable sub to still sail at a reduced speed could be your answer.John.
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Subculture

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Re: To BEC...or not to BEC?
« Reply #2 on: November 17, 2011, 08:26:30 PM »

Depends on the voltage you're running at, type of BEC and what you have hooked up to it.

If you're running between 6-12 volts, with no more than three servos that aren't heavily loaded, then the BEC's built into most ESC's work very well.

If you have more servos than that, or use a voltage outside the 6-12 volt range, then a separate heavier duty BEC based on switchmode technology or a separate battery pack is probably the best solution.

Patrick Henry

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Re: To BEC...or not to BEC?
« Reply #3 on: November 17, 2011, 08:55:06 PM »

So far I've got two mini servos(one for the steerable nozzle and one for the rear planes)and an electronic switcher for the lights(2 x 12volt HiIntensity LEDS's). Battery packs are 2 x 7.2volt 1600a/h nimh packs hooked up to give me 7.2volts at 3200a/h.

The motor is  Swiss made ESCAP(380 size).



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Re: To BEC...or not to BEC?
« Reply #4 on: November 17, 2011, 09:10:05 PM »

The BEC in the ESC will be fine with that combo. Not sure how LED's rigged for 12 volts will fare with 7.2 volts though.

Patrick Henry

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Re: To BEC...or not to BEC?
« Reply #5 on: November 17, 2011, 09:19:52 PM »

They last longer!

I've had three of them running for over five hours in the Neptune with no problems, and they seem plenty bright enough, even around three feet down in semi murky water you can see them quite nicely.
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Re: To BEC...or not to BEC?
« Reply #6 on: November 18, 2011, 10:44:52 AM »

Sounds like they're current limited via resistors.

Martin [Admin]

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Re: To BEC...or not to BEC?
« Reply #7 on: November 18, 2011, 11:48:51 AM »


Many moons ago when I was building my Darnell British U type sub, I found a circuit that would flash a LED depending on battery voltage.
At full charge it would stay on but as the voltage dropped, it would start to flash and the lower the voltage dropped, the faster it would flash!

... I wish I could find that damn circuit again, it would be very useful.
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Patrick Henry

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Re: To BEC...or not to BEC?
« Reply #8 on: November 18, 2011, 12:21:18 PM »

Martin, if you ask John Robinson (sub john on here) he'll knock you up the thing you need, he made me one exactly the same only for a lipo pack....he's the main man.



Rich
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Martin [Admin]

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Re: To BEC...or not to BEC?
« Reply #9 on: November 19, 2011, 01:02:35 AM »


         "Hello John!"  :-)
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sub john

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Re: To BEC...or not to BEC?
« Reply #10 on: November 19, 2011, 05:38:21 PM »

HI Martin

  Circuit that you are talking about shouldn't be a problem to make but at the moment i am up to my neck in it doing some other electronics for myself if you leave it a few days i will send you a PM and sort it out from there. Hope this will help
                All the best John


One of the other things i would like to say is using BEC regulator circuits is if you use one of the 7805 reg series which is linear this reg will only give 1 AMP but if you wrap a transistor around it it can quite easy deliver 15AMPS but main problem with this reg is if you wonted 5VOLTS out of it you would have to have 7.5VOLTS going in other wise reg will shut down. Other problem is because it is linear it will run hot but one of the main things with linear regulators is that you will not get radio interference. Some of the new linear regulators will deliver 5AMPS i can not see this being a problem in a submarine as it is in water and water is the ideal cooler for reg to be in


But some of the new linear regulators are low voltage drop out types more often than not they are 3.3VOLTS but these can be modded to give 5 or 6VOLTS

Some BEC circuits weather it be switch mode of chopper circuit the run at about 300KHZ main problem with this is if you use them on 27 35 or 40MHZ because of the way they work as you load them on the output they will produce interference up and down the band you are using i have seen some of these circuits knock off a quarter of your range as most man made interference stops at around 400MHZ you will find most of these will work fine on 2.4 GHZ using one of these on a lower band is like using a radio jammer good thing about them is they run cool and are officiant and are small  i myself hate them. And are  a cheep solution to use them
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Patrick Henry

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Re: To BEC...or not to BEC?
« Reply #11 on: November 19, 2011, 08:10:43 PM »

erm..yes. I think...JR, I wish you'd talk English!


I've solved the problem by fitting an Mtroniks Viper esc with built in BEC, saved me an awful lot of room in the radio box.
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Shipmate60

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Re: To BEC...or not to BEC?
« Reply #12 on: November 19, 2011, 08:46:44 PM »

Rich,
If you need more power from the BEC (but mini servos wont) subtronics do an Mtronics ESC with upgraded BEC up to 2.5 amps i believe.

Bob
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Davy1

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Re: To BEC...or not to BEC?
« Reply #13 on: November 20, 2011, 08:55:23 AM »

John's comments are very interesting.

I've used the switch mode power supplies quite a bit (they are efficient and they prevent overheating BEC problems when running on higher voltages (12V)) but I have suffered interference problems and I wonder if this was the cause?

I've now moved onto using dual conversion receivers and this seems to help matters. 

David
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malcolmfrary

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Re: To BEC...or not to BEC?
« Reply #14 on: November 20, 2011, 11:24:27 AM »

The typical 7805 regulator does a good job of providing 5 volts, but does need a bit of spare voltage to play with.  If the supply drops below this critical level, the regulator changes mode, and starts just dropping this headroom voltage.  Most radios will just carry on working with what is left, more or less.  The now imperfectly stable voltage might cause the timing circuits in both the radio and things plugged into it to not be as accurate as they were.  If the voltage drops to the point where the radio no longer works, or more likely the servos, it doesn't really matter whether the radio is BEC powered or a separate battery, it will have nothing to give instructions to.  I have had times when the servo was just capable of creeping about to signals due to an over extended sail, so although the battery was obviously low, the radio was still functioning.
Interesting about the switched mode thingys.  Can the output and input lines not be fitted with decoupling components?  The usual values of suppression capacitors spring to mind.
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sub john

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Re: To BEC...or not to BEC?
« Reply #15 on: November 20, 2011, 05:10:09 PM »

Reply#13
HI Davy1 I am not supprised that you had radio interference you did the right thing going duel conversion receiver this will help quite a lot i was using a switch mode power supply in one of my planes i had to take the unit into work and tested it on a lot of test equipment and even as i had put this inside a tin screen around it and had put feed through caps in and out on all wires the interference was still coming out of this unit. All i can say i can not believe how bad the interference was still coming out of it i would not use one myself. All the ones i use in my planes or subs are linear regs the one in my big plane will deliver 15 AMPS at 5VOLTS, i would not even use switch mode BEC even on 2.4GHZ
  All the best John
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malcolmfrary

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Re: To BEC...or not to BEC?
« Reply #16 on: November 21, 2011, 11:41:42 AM »

Oddly, looking at the graphs on http://www.murata.com/products/emc/knowhow/pdf/20to22.pdf  feedthrough types show no improvement below 50MHz for a two lead capacitor, or 100MHz for a three legged one on the graph showing a 1000Pf device.  It would probably need a couple of turns on a ferrite ring or bead as well.  Next trick would be to run the power in and out through coax.  Seeing that ours work on 27 and 40 MHz (or 35 for the flyboys) using a feedthrough type would offer no benefit over a conventional RF rated capacitor.
In the data sheets for linear types, there is usually advice to fit capacitors to discourage the active elements from self oscillating at high RF.
If I needed more power than the BEC in the ESC could comfortably supply, I would definitely go for a separate battery, even if it does involve the hassle of remembering to charge more of them up.
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Davy1

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Re: To BEC...or not to BEC?
« Reply #17 on: November 21, 2011, 12:54:55 PM »

The last 2 posts are most interesting and I think I can now see where some of my problems have been coming from.

I have found the switch mode supplies good and I think I will hang on to them now, particulary now that I am using dual conversion.

Interference is always a bit of a "black art" especially in submarines where everything is so packed in. Events where there are lots of transmitters seem to make things even worse.

I have (I think!) found ferrite rings useful and I scatter them liberally througout my wiring. it would be nice to be a bit more scientific though!
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ACTion

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Re: To BEC...or not to BEC?
« Reply #18 on: November 21, 2011, 01:00:56 PM »

I wouldn't personally take the risk of putting into a submarine any device which is known to dissipate heat as part of its normal function, let alone one which has a reputation for bursting into flames for no apparent reason  8) OK - so motors get warm but they shouldn't get hot and certainly shouldn't be a fire risk.
I would suggest replacing one of those big 6-cell packs with a 4-cell one for the Rx power. The 385 motor takes very little current anyway, but as/when the main motor pack does run down just fetch the sub up and put a freshly-charged pack in.
Incidentally our Battery Eliminator uses a low drop-out LM2940 1A linear regulator, so the power supply can drop to 5.5v and the regulator still works OK.
Suit yourself, Mr Uggett - you usually do  ;)
DM
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sub john

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Re: To BEC...or not to BEC?
« Reply #19 on: November 21, 2011, 05:52:16 PM »

Reply#16
Feed through caps where just a means to a end to get power cables in and out of screen box PCB inside of tin box had quite a bit of other circuits for filtering, for power in and out has unit had to knock out 15 AMPS you would of had to use some very thick coax to stand the currant and as this was going in a plane cannot afford the weight as plane can fly competition even a few grams matter
            John
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