Castle BEC minimum voltage drop?

[Jim85IROC]

I'm looking at a Castle BEC for my bomber. I would like to set it at 8.4v for when I run on 3s. If I run 2S, what can the BEC put out? For simplicity I want to solder the BEC power to the esc battery feed, but if my voltage on 2s is going to be much below 7.4v, I'll build a harness that can pull servo power from the 2s balance plug instead.

[mikemcE]

It cannot increase voltage, it regulates it


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[84yoda]

Doesn't matter if you hook it up to esc plug or balance plug, if your running 2s its going to put out whatever the battery voltage is since you'll have it set to 8.4v. Its easier to hook it up to esc plug so you can run 2s or 3s without having to have 2 different harness for 2s or 3s off the balance port.

[Jim85IROC]

Originally Posted by mikemcE

It cannot increase voltage, it regulates it


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I know that. That's not what I'm asking. Most voltage regulators can only output about 1v less than their input voltage, but I'm not familiar with switching regulators like the Castle.

[Jim85IROC]

Originally Posted by 84yoda

Doesn't matter if you hook it up to esc plug or balance plug, if your running 2s its going to put out whatever the battery voltage is since you'll have it set to 8.4v. Its easier to hook it up to esc plug so you can run 2s or 3s without having to have 2 different harness for 2s or 3s off the balance port.

I guess I wasn't clear. If I'm going to experience too much voltage drop on 2S, I'll bypass the BEC by parallelling 2s and 3s balance plugs, with the 3s plug powering the BEC, and the 2s plug feeding the servo directly.

Castle's literature says that it can pass battery voltage with almost no drop, but I'm skeptical because most regulators max out at 1-1.5v below battery voltage.

[mikemcE]

You need to ask Thomas from Castle, not us users.


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[84yoda]

You might have 0.1v drop. If you dont believe castle who made it, you can test this yourself if you have a multimeter. Why would they make a bec that would drop that much, lol.

[Ninomaniac]

Because sometimes technology dictates that much drop... not saying that's the case here.

Can't someone just measure this? Sometimes I'm stumped by how generally low-tech folks in the hobby can be.

[84yoda]

I just tested this for you, 3s battery with bec hooked up to balance port, bec is set to 7.4v. Output was 7.39v.

[Jim85IROC]

Originally Posted by 84yoda

I just tested this for you, 3s battery with bec hooked up to balance port, bec is set to 7.4v. Output was 7.39v.

I appreciate the help, but that's not what I'm asking. I'm trying to see how close to 8.4v it gets when powered by 2s. I'm confident that it will properly regulate when I run 3s, it's how well it can pass thru 8.4 on 2s that I'm trying to learn.

Just to provide a better explanation, normal voltage regulators that bleed off excess voltage can only output a maximum voltage ov about 1v to 1.5v below the input voltage. In other words, if you have a BEC set for 8.4v, in 3S it will output 8.4v, but that same BEC might only output 6.9v when powered by 2s. Because I don't have any experience with switching-style regulators like the Castle BEC, I'm asking the question before I piss away $20 for a BEC and another $20 for the Castle Link, only to find out it won't do what I want.

[nedmo]

A BEC doesn't 'create' voltage. To get 8.4v from a 2s you would need a step up converter.

[Jim85IROC]

Originally Posted by nedmo

A BEC doesn't 'create' voltage. To get 8.4v from a 2s you would need a step up converter.

I know a BEC can't step up the voltage. That's not what I'm asking. A fully charged 2s puts out 8.4. Im just trying to find out how much drop I'll get through the BEC!

[nedmo]

Originally Posted by Jim85IROC

A fully charged 2s puts out 8.4. Im just trying to find out how much drop I'll get through the BEC!

I will test tonight for you. I have the BEC 2.0 WP and will set it to 8.4v and plug a fresh 2s in and read the voltage.

[84yoda]

Why don't you understand that its going to put out whatever the battery voltage is. I just did another test for you, using a 2s battery. Same bec set to 7.4v, my 2s battery is at 7.34v and bec output was 7.34v. So like castle and I said, no voltage drop or if anything 0.01v drop.

[Jim85IROC]

Originally Posted by 84yoda

Why don't you understand that its going to put out whatever the battery voltage is. I just did another test for you, using a 2s battery. Same bec set to 7.4v, my 2s battery is at 7.34v and bec output was 7.34v. So like castle and I said, no voltage drop or if anything 0.01v drop.

because that's NOT what happens with linear regulators. Linear regulators are lossy and cause a voltage drop, as I explained above. Castle BECs use a different topology called a switching topology that I'm not as familiar with, so I asked in the hopes that just maybe somebody here would have enough experience with them to know the answer.

Thanks for comparing the 2s output voltage to the input. That's what I needed.

[Jim85IROC]

Originally Posted by nedmo

I will test tonight for you. I have the BEC 2.0 WP and will set it to 8.4v and plug a fresh 2s in and read the voltage.

thanks, I appreciate it!

[nedmo]

Originally Posted by Jim85IROC

thanks, I appreciate it!

Testing done.

One charged battery testing at 8.3v and one semi flat testing at 7.5v.

Bec set at 8.4v

So the BEC will pass through what ever voltage the battery can give up to the voltage limit you set on the BEC.
So yeah a 2s will start out at 8.xx but as you run it down you will finish your run only giving servo 7.4v

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[nedmo]

Also, I think the large voltage drops are because:

1. The 2.0 Bec has two outputs which you encouraged to run in tandem to your receiver.
2. I was trying to test across the exposed parts of the pins on the plug whilst trying to take a photo = not great connection.
3. Voltmeter is pretty shitty. Good one was flat.

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[Jim85IROC]

Thanks! It's impressive that the switching regulator can pass the input oower through so efficiently. Thanks for the confirmation!

[maslin]

Rob did say the MambaX internal bec will drop a half volt. I only run 3s on my Bomber, never payed much attention to it.

Originally Posted by robert@castle

The internal BEC will try to regulate the voltage to be as close as it can to the desired voltage. If the set point is too high, the BEC will keep the voltage half a volt under the input voltage.