Dumb Castle BEC question

[steve050773]

Okay, I know this is remedial but I want to confirm before sending the wrong voltage to the BEC...

To install a castle BEC with a mamba max in a standard emaxx style vehicle with 2 2s packs wired in series, how do you wire the BEC's battery leads?

I have the battery leads on the mamba max setup in a typical y series configuration, where one positive lead is connected to a deans and one negative lead is connected to a separate deans plug each and then the two plugs are bridged in series.

This page looks like it is telling me that I wire both BEC leads to the plug that sends the negative lead to the battery (the free lead).

http://www.castlecreations.com/products/cc_bec.html#

But I think I've also seen people with the BEC wired with the black lead on the negative free lead, and the positive on the positive free lead (on the second deans plug).

Here's an example if you scroll down a little and check out Stum's pic -

http://monster.traxxas.com/showthread.php?t=402433

That looks like the "don't do this" picture #2 on the above link... but I know these people are actually running their trucks...

Thanks,

Steve

notice the message below the "never do this" picture 2.

"Never connect the CCBEC to a combination of packs in series that results in more than 25v to the CC BEC".


this means the wiring in the picture you linked to is fine for up to 6s LiPo. Using 2 2s packs, I just connect my BEC to the ultra plug where the Y plugs into the ESC. You can put it on the ESC side, or the Y connector side, whichever is more convenient to your installation.

[BrianG]

OK, here's where it gets a little tricky if you have a hard time understanding what's going on. It IS ok to hook the UBEC across both battery packs (as a whole) IF the whole battery voltage of both packs combined is less/equal to the UBEC max input of 25v.

I'll explain the reasoning of the "Don't do this" sections:

• The Castle UBEC is only rated up to 25v, so 6s is the max battery you can use. Castle's picture shows dual 6s packs, for a 12s total pack, which would be far higher than the UBEC can take. That's why they say to hook the UBEC positive lead to the "bridge" wire of the pack Y adaptor (the UBEC will see only the voltage from a single 6s pack).
  
  
• Just about all UBECs (Castle included) do NOT isolate the ground wire from the battery pack ground. So, if you hook the UBEC negative lead to the pack "bridge" wire, you are making the UBEC ground "float" at half the pack voltage. So, if the main battery ground is tied to the UBEC output ground ANYWHERE else in your setup, you WILL fry a wire, the UBEC, receiver, servos or any combination of these. Even if you ensure this is not the case, it is always best practice not to do this.

I hope that made sense...

Dang, 83gt beat me to it. I type too slow and talk too much.

[steve050773]

Thats what I was missing - the 12s part of the diagram.

I will set it up like Stum's picture so the BEC see's the voltage from both 2s packs.

[MTBikerTim]

Originally Posted by BrianG

OK, here's where it gets a little tricky if you have a hard time understanding what's going on. It IS ok to hook the UBEC across both battery packs (as a whole) IF the whole battery voltage of both packs combined is less/equal to the UBEC max input of 25v.

I'll explain the reasoning of the "Don't do this" sections:

• The Castle UBEC is only rated up to 25v, so 6s is the max battery you can use. Castle's picture shows dual 6s packs, for a 12s total pack, which would be far higher than the UBEC can take. That's why they say to hook the UBEC positive lead to the "bridge" wire of the pack Y adaptor (the UBEC will see only the voltage from a single 6s pack).
  
  
• Just about all UBECs (Castle included) do NOT isolate the ground wire from the battery pack ground. So, if you hook the UBEC negative lead to the pack "bridge" wire, you are making the UBEC ground "float" at half the pack voltage. So, if the main battery ground is tied to the UBEC output ground ANYWHERE else in your setup, you WILL fry a wire, the UBEC, receiver, servos or any combination of these. Even if you ensure this is not the case, it is always best practice not to do this.

I hope that made sense...

Dang, 83gt beat me to it. I type too slow and talk too much.

Your info was still quite informative brian. I couldn't work out why the second setup wouldn't work but of course what you said makes perfect sense. Personally for a 12s setuo I wouldn't be using a bec that couldn't take the full voltage. That could lead to a over worked pack fairly easily couldn't it.

[BrianG]

Thanks! I just gotta learn to be less "wordy" to get my answer on the page before a dozen other answers show up.

TBH: I wouldn't want to hook any UBEC to only one pack because then that pack will drain slightly faster and the dual packs will take longer to balance out when charging. If HV is what you want, then a HV UBEC or a receiver pack would be the best option IMO.

[MTBikerTim]

Originally Posted by BrianG

Thanks! I just gotta learn to be less "wordy" to get my answer on the page before a dozen other answers show up.

TBH: I wouldn't want to hook any UBEC to only one pack because then that pack will drain slightly faster and the dual packs will take longer to balance out when charging. If HV is what you want, then a HV UBEC or a receiver pack would be the best option IMO.

I was thinking about it a bit more and thought a 12s configuration would typically be used in a large heli or plane. Both of these have lots of servos and especially in the heli get worked really hard. So you would be sucking a lot extra out of that one pack. Then I realised you wouldn't be using the CC Bec in a large heli as it would explode. It's only rated to 10A and one big digital servo can suck more then half of that at full load.

[BrianG]

Technically, you CAN parallel some types of multiple UBECs. The output of both together won't quite be 6v, but close. See this. Since most regulators are built around the same basic circuit design, this probably applies to others as well, but I haven't found anything to confirm this.

[MTBikerTim]

Originally Posted by BrianG

Technically, you CAN parallel some types of multiple UBECs. The output of both together won't quite be 6v, but close. See this. Since most regulators are built around the same basic circuit design, this probably applies to others as well, but I haven't found anything to confirm this.

The guys at dimension engineering make some sweet stuff. Shame they don't make escs. I was wondering about paralleling the becs. I wouldn't want to run too much current through my receiver though.

[BP-Revo]

Well, to cure "too much current through receiver" issue all you would need to do is simply wire up the positives and negatives of the servo's to the UBEC outside the receiver (basically, bypass it). This way, the current just goes straight through the wires.

However, you would obviously still need to power the Receiver, and the signal wires would need to reach the receiver as well...