CC BEC on a 2S Lipo question...

[elec-fuyu]

somebody told me this:
a CC BEC is basically a waste when you are using a 2S lipo pack.
he states that it will only lower the torque on the servo, because the BEC is eating up more voltage than when connecting directly with the battery.

which kind of make sense...
so my questions is... why not connect the RX (that will take 7.4V no problem) and Servo directly with the battery?

 

[Dr.Frank]

Hello,

some kind of "difficult" to answer. A fully charged 2s Lipo has about 8.4V and lowers down to 7.4V (and lower) during discharging. The CC BEC passes the input voltage directly to it's output, when the input voltage is equal or lower then it's adjusted output voltage. Some Hitec Servo are called 2s ready, but i know that some gone in smoke. So it's on your risk.

Greetings Frank

 

[ManxCrawler]

Plus, I wouldn't trust my expensive receiver to take 10A without something going wrong eventually, the CC BEC does the grunt, the receiver just takes the signal

 

[elec-fuyu]

the guy start stating that servos can take 8.4v no problem...
i dont kno where did he get that information, but 7.4v is already pretty hot on my Savox...
i dont kno if Hitec can take 8.4v...

btw, let's say the reciever can take power from the ESC. (i forgot about this part)

so basically... can any servos take 8.4V for a beating

 

[chevotafun]

Don't go past 7.4 look at your spec's for your servo the highest setting is 7.4 so i'm guessing thats ur answer.
I run a 7980 hitech and that monster is only 7.4

 

[elec-fuyu]

I have the Savox SB-2270SG... they run pretty hot at 7.4v...
I'll never go pass 7.4v for sure...
guess that's the answer!
thanks guys!

 

[indiana mudcat]

7.4 is nom. 2s Lipo voltage, anything rated at 7.4 is designed to be safe on 2s. Now if it'll take 2s in a crawler vs an eighth scale buggy might be a different story. I do worry about amperage through the rx so I power it off my ESC's.

My 7980 barely gets warm with the BEC set to 8.4. On my scaler I run a cheap hobbico 7.4 rated servo off 8.4 and also use the BEC to power the battery side of my winch, ESC powers rx, lights and signal side of winch.

I know a lot of 1.9 guys are running this way now and I wouldn't hesitate if I ran 2s in any of my trucks.

 

[KBrog]

I would use a BEC even on 2s. The BEC that is built in to your ESC is not rated at nearly enough AMPS to run a high torque servo. So without a BEC you still run the chance of thermal shutdown or total melt down.

 

[indiana mudcat]

I would use a BEC even on 2s. The BEC that is built in to your ESC is not rated at nearly enough AMPS to run a high torque servo. So without a BEC you still run the chance of thermal shutdown or total melt down.

You misunderstood. He wants to power the servo direct from the battery.

 

[KBrog]

You misunderstood. He wants to power the servo direct from the battery.

In that case, I would still use a BEC so it would regulate the voltage at a constant rate.

 

[elec-fuyu]

In that case, I would still use a BEC so it would regulate the voltage at a constant rate.

I emailed Hitec and Savox about this question...
on Hitec site, they stated that the servo can take on 2S battery pack directly...
I'm waiting for their reply... (hopefully there's some)

 

[ManxCrawler]

You're gonna do it anyway and it doesn't seem as though you've thought it out, YES nearly all normal/big size servos can probably take 2S as it's 8.4V, the big thing you have ignored is putting straight through your receiver, by all means go ahead and burn that out when your rig is in a bind

When people answer a post it's usually because they want to help :roll:

 

[Robbob]

A BEC can not put out more then whats put into it. I would be willing to bet your just gonna brown out your system in binds. It wont matter if you wire the servo to bec or plug the bec into the RX, your not gonna support the entire system on a 2S once you stall it out.

Good luck with running the 2S directly to the servo though ...... servo's dont have low voltage cutoffs. Id bring a bag of sand with me every time. :roll:


Servos rated for 2S were made for the racing world of single cell/1S. Those guys run mini rx packs that they charge after every run. We use them because we need the torque, not because they will handle 2S.

 

[elec-fuyu]

You're gonna do it anyway and it doesn't seem as though you've thought it out, YES nearly all normal/big size servos can probably take 2S as it's 8.4V, the big thing you have ignored is putting straight through your receiver, by all means go ahead and burn that out when your rig is in a bind

When people answer a post it's usually because they want to help :roll:

Hey man, I've done researching on this site long ago which makes me running a CC-BEC right now. And I do know everyone here is super helpful.

I'm just curious about this when that guy puts the statement out. (Well, this all happens in Taiwan, and it's all in mandarin, else i would love to just post the link to here...) I'm not putting this post up to argue with anyone, in fact, I'm the one who states that having an external BEC is better for the servo. I just like to see if there's a better prove.

And about your RX comment, i can always run the receiver thru ESC's BEC can't I?

I'm currently running CC-BEC power directly to the servo (only servo's signal cord is plugged to the RX) and no power from the CC-BEC is going into the RX. And the RX is powered by my ESC.

I know that my English is not that good, but please please don't get me wrong here...

 

[ManxCrawler]

And about your RX comment, i can always run the receiver thru ESC's BEC can't I?

I'm currently running CC-BEC power directly to the servo (only servo's signal cord is plugged to the RX) and no power from the CC-BEC is going into the RX. And the RX is powered by my ESC.

I know that my English is not that good, but please please don't get me wrong here...

1. Yes
2. Your English is brilliant!

I'm confused now because you talked about bypassing the CCBEC with a 2S straight to the servo, the CCBEC will limit amp draw to 10A so your servo won't get toasted in a bind

 

[MexicanMarauder]

Im running that set up and now I don't know if I should remove the BEC.

 

[elec-fuyu]

Im running that set up and now I don't know if I should remove the BEC.

DO NOT remove the BEC as everything is not clearified...

 

[dstrbd1]

somebody told me this:
a CC BEC is basically a waste when you are using a 2S lipo pack.
he states that it will only lower the torque on the servo, because the BEC is eating up more voltage than when connecting directly with the battery.


which kind of make sense...
so my questions is... why not connect the RX (that will take 7.4V no problem) and Servo directly with the battery?

This debate has been going on for a bit in our local club. A couple of us are running either Hitec 7955's or 7950's directly off the battery (not through the receiver) Receiver is still powered from ESC. The only thing we are noticing that the motor tends to steal most of the power from the servo during binds. In your statement about the BEC eating up voltage and lowering the servo torque you are false. Actually the BEC is able to store power in the capacitor which actually allows the servo to still have all its needed power even during binds when the motor is robbing power.

the guy start stating that servos can take 8.4v no problem...
i dont kno where did he get that information, but 7.4v is already pretty hot on my Savox...
i dont kno if Hitec can take 8.4v...

btw, let's say the reciever can take power from the ESC. (i forgot about this part)

so basically... can any servos take 8.4V for a beating

This issue was brought up a long time ago and I think Hitec's response was their hi torque servos could take 8.4v. That aside your servo will never see 8.4 volts because as soon as you draw off the battery the output drops.

 

[elec-fuyu]

This debate has been going on for a bit in our local club. A couple of us are running either Hitec 7955's or 7950's directly off the battery (not through the receiver) Receiver is still powered from ESC. The only thing we are noticing that the motor tends to steal most of the power from the servo during binds. In your statement about the BEC eating up voltage and lowering the servo torque you are false. Actually the BEC is able to store power in the capacitor which actually allows the servo to still have all its needed power even during binds when the motor is robbing power.




This issue was brought up a long time ago and I think Hitec's response was their hi torque servos could take 8.4v. That aside your servo will never see 8.4 volts because as soon as you draw off the battery the output drops.

so from your experience, you do suggest people to run off an external BEC right?

 

[dstrbd1]

The bec can't hurt. Since I run 3s on my XR I do have a bec. I am still on the fence about bec or no bec. I run without a bec on my mini with a hitec 7955 wired straight to the battery. I have not really noticed the servo power drain during binding. So for now I will continue without it just for the added weight loss.