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78Triumph

School me on BEC's .

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I've never used a BEC on any of my cars or trucks.  Should I be?  Is it all dependent on servo current draw?  Should you use them in any certain situations and not others?  I suppose a google search could answer my questions, but I'd like to hear first hand accounts if you have any.  Cheers!

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Here’s how it was explained to me when I bought a used servo/BEC/ESC package

“It just regulates voltage, most electrics in RCs suffer from what's called brown out, it's basically when theservo is pulling power and the ESC can’t properly operate.”

and the blurb from the Castle BEC on the Modelsport site...

Our Battery Eliminator Circuit is a little device that eliminates the need for a receiver and servo battery pack. It draws higher voltage from the motor batteries and drops it to a voltage level that is suitable for your receiver and servos. This is required in applications which draw high power for multiple servos or use more than 3S motor packs, as most ESCs with linear BECs are not designed for these applications.

 

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34 minutes ago, 78Triumph said:

I've never used a BEC on any of my cars or trucks.  Should I be?  Is it all dependent on servo current draw?  Should you use them in any certain situations and not others?  I suppose a google search could answer my questions, but I'd like to hear first hand accounts if you have any.  Cheers!

So do you always use a separate battery to power the receiver? Dont most modern ESC have BEC built in?

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14 minutes ago, Busdriver said:

So do you always use a separate battery to power the receiver? Dont most modern ESC have BEC built in?

That exact question came to my mind also.  

 

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You should check the voltage output of the ESC's built in BEC. Some of them will allow more voltage out then what your receiver can handle.

 

The ESC that came with my re-release Avante had this issue, I had to add a resistor to prevent the BEC's voltage from damaging the receiver.

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1 hour ago, spankrjs said:

You should check the voltage output of the ESC's built in BEC. Some of them will allow more voltage out then what your receiver can handle.

 

The ESC that came with my re-release Avante had this issue, I had to add a resistor to prevent the BEC's voltage from damaging the receiver.

Correct. 7.2 and up battery voltage can fry your receiver, which is meant to operate at a lower voltage (once handled by those 4 extra AA batteries we used in the olden days). The receiver or ESC may have the BEC incorporated into them. The receivers generally call this out on the case. If neither has the BEC, you run the risk of receiver failure. This is important as many of the older 101 and 104 Tamiya ESCs do NOT have BEC. Like  @spankrjs mentioned, I've added resistors to the older Tamiya ESCs to use them safely with non-BEC quipped receivers. Some receiver manufactures dropped BEC as most ESCs began coming standard with BECs, but every once in awhile you get a curve ball like the older Tamiya ESCs that don't have it and you're  left vulnerable. 

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Thanks for the responses.  I know BECs are pretty cheap, i think I'll start adding them to my cars just to keep my bases covered.

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Once you swap from MSC's to ESC's the BEC is taken care of.

Bitd, I used to solder a diode to the power feed terminal on the MSC, and pull the 6v from there, (which I think is what the Ultima came with on its msc?) but then I went to esc's in the late 80's, and used esc's since.

The diode, did have the downside of the servos stopping working whilst the motor still had power, but it would only crawling, so just a quick jog to catch it.😂

 

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3 hours ago, Saito2 said:

This is important as many of the older 101 and 104 Tamiya ESCs do NOT have BEC

Some models still come with these in. Probably old stock but if you use them without reciver battery or separate BEC they may well fry the receiver. Somthing in the back of my mind is telling me that it is also necessay to disconnect one of the wires from the ESC to the receiver if you are using a separate battery, Not sure which of the three wires but google it. Otherwise you have two power supplies going to the receiver. I remember this from using multiple ESC in boats. Maybe just a dream!

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Most receivers can handle the voltage (check the specs to confirm though), the biggest concern is going to be the steering servo though, unless its HV rated, its quite likely to fail with the extra voltage coming from the battery.

In Nitro 1/8, almost all receiver packs (2 servos are used in these) are lipo these days (7.4v) and any modern radio equip can handle this voltage through the receiver, but unless HV servos are used, they will fail eventually.

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1 hour ago, mtbkym01 said:

Most receivers can handle the voltage (check the specs to confirm though), the biggest concern is going to be the steering servo though, unless its HV rated, its quite likely to fail with the extra voltage coming from the battery.

In Nitro 1/8, almost all receiver packs (2 servos are used in these) are lipo these days (7.4v) and any modern radio equip can handle this voltage through the receiver, but unless HV servos are used, they will fail eventually.

I can confirm that 100%.
The supply voltage is not really a problem for a modern receiver.
You should be more careful when choosing the servos. Especially when powerful servos are used, I would take a close look at the performance of the BEC's, because most standard ESC only provide up to about 2A BEC current. A powerful servo quickly gets into this range during operation.
 

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I only ever experience BEC's with manual speed controllers.
Plus and minus leads came off the msc and plugged into your receiver. The receivers I had back then would lock the steering in one direction, hard right I think, once the voltage dropped to a certain level. I was very happy back then not having to by four AA batteries to go into the car and the stuffing about that entailed.....not to mention shedding weight.
As far as I know this is all taken care of internally with modern receivers and Electronic Speed Controllers.
I think I have one or two out of many ESC's that need an external power supply to operate. The vast majority draw voltage from simply plugging the ESC into the Receiver.

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I use a stand-alone BEC if:

The BEC in the ESC can't be adjusted to a full 6.0 or 7.4v, depending upon which servo(s) I want to use.

I'm using multiple high-power servos.

I'm using a monster power servo that's working hard.

I'm using a lot of lights.

Basically, the ESC's BEC is sufficient for race cars, runners, vintage, etc., while a auxiliary BEC is for crawlers, giant scale, and scale builds. Good higher-end ESCs have higher amp adjustable switching BECs, while more basic ESCs have lower amp linear BECs that are adequate for more modest servos.

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+1 on high torque servos 

Although the issue only raises its head when you put them in places outside their normal ESC / battery combo 

Crawlers etc therefore should be fine

Hopped up racers with overweight on the front wheels for grip on the other hand ...

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As already mentioned, it really depends on your amp draw.  Savox servos are known in some scenarios to draw almost 5 amps.  Amain Hobbies actually now puts warning on the Savox servos:

https://www.amainhobbies.com/savox-sc1258tg-black-edition-standard-digital-high-speed-titanium-gear-servo-sav-sc-1258tg-be/p465806

Most ESC's that have internal BEC's are typically rated around 3 amps.  The higher priced ones will have larger internal BEC's.  That doesn't have much impact on the ESC itself, but it will the receiver which will also take power from the ESC.  This is where people see brown-outs with their gear.

 

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12 hours ago, Mahjik said:

Savox servos are known in some scenarios to draw almost 5 amps.  Amain Hobbies actually now puts warning on the Savox servos:

I run Savox servos, and with a Cap in the reciever, they seem to run without issues. (Capacitor cost pennies off eBay, and relieved an old reciever battery pack of its lead) 

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