Polaris and capacitator

[mverhorst]

Dear All,

Can I use a capacitator together with the Polaris BEC or will it damage the BEC at startup?

Just looking for a way to secure the power for the servo and a stress relieve for the BEC. I am using one in my 450 and Gaui X5.

Regards,

Menno

[Pard]

Old thread but good question. I have heard of Capacitors hurting BECs, is that true?

[mverhorst]

Originally Posted by Pard

Old thread but good question. I have heard of Capacitors hurting BECs, is that true?

Old thread indeed... Nobody seems to knew back than.

I still don't use any caps. I did go from specky sats to JR Xbus and Futaba BLS451/251 on my X5 which made me feel I don't need the caps...

No issues to date.

[Pard]

Originally Posted by mverhorst

Old thread indeed... Nobody seems to knew back than.

I still don't use any caps. I did go from specky sats to JR Xbus and Futaba BLS451/251 on my X5 which made me feel I don't need the caps...

No issues to date.

For sure, Vbar and sats are the most common source of trouble. I think caps can damage a BEC. They seem to have done that to my Talon 35 BEC. The solution is just a better setup as you describe, not just adding caps. I think.

[mverhorst]

Originally Posted by Pard

For sure, Vbar and sats are the most common source of trouble. I think caps can damage a BEC. They seem to have done that to my Talon 35 BEC. The solution is just a better setup as you describe, not just adding caps. I think.

I think so to. Empty caps act like a short circuit for a split second as the current rushes in...

The bigger the caps, the bigger the amp spike.

[Pard]

No exactly clear, but here is what WR responded to my inquiry:

It is not recommended to place large capacitance capacitors near the BEC terminals or any other supply as it does not require it.
Having a certain type of capacitance added or remove can affect ESR, ripple current rating, rated life and current surge.


Western Robotics Information
WR_logo Western Robotics Ltd.
#215-12837 76th Avenue
Surrey, BC V3W2V3
Canada
Phone: 778-565-1332
www.western-robotics.com
info@western-robotics.com

[mverhorst]

Originally Posted by Pard

No exactly clear, but here is what WR responded to my inquiry:

It is not recommended to place large capacitance capacitors near the BEC terminals or any other supply as it does not require it.
Having a certain type of capacitance added or remove can affect ESR, ripple current rating, rated life and current surge.


Western Robotics Information
WR_logo Western Robotics Ltd.
#215-12837 76th Avenue
Surrey, BC V3W2V3
Canada
Phone: 778-565-1332
www.western-robotics.com
info@western-robotics.com

With the BEC powered off the caps will loose there charge and become empty in a split second.

The moment you plug your flight pack in the BEC will charge the empty caps (same as the cap in you ESC, some will give quite some spark when pluging in your packs).

An empty cap acts like a short circuit for the split second the cap is empty and your BEC powers on...

[Pard]

Originally Posted by mverhorst

With the BEC powered off the caps will loose there charge and become empty in a split second.

The moment you plug your flight pack in the BEC will charge the empty caps (same as the cap in you ESC, some will give quite some spark when pluging in your packs).

An empty cap acts like a short circuit for the split second the cap is empty and your BEC powers on...

Makes sense.

I wonder why caps have become so recommended in the forums if they can cause the whole BEC to fail.

Not a great solution to brownouts if it can cost you a complete power failure. Mikado even seems to recommend them, which is particularly odd.

http://www.vstabi.info/en/node/1327

My solution is to just use expensive BECs from now on.

[mverhorst]

I quess it comes down to common sense agian.

If you have trouble a cap vould help but don't go overboard and use to much to big...

Iv'e seen 2S lipo's have voltage errors on a Vbar due to servo back EMF, it could happen to any setup and is IMO more servo related then BEC...

[Pard]

Originally Posted by mverhorst

I quess it comes down to common sense agian.

If you have trouble a cap vould help but don't go overboard and use to much to big...

Iv'e seen 2S lipo's have voltage errors on a Vbar due to servo back EMF, it could happen to any setup and is IMO more servo related then BEC...

You are most likely correct, as demonstrated here:

http://www.vstabi.info/en/node/1422

That said, how do you decide if it is the servos or not without special gear? I like the high performance value servos, like KST, which may be the problem. I have to get over that habit ...

Vbar seems to be most sensitive to this effect. I never have problems with Ikon, Vortex, Skookum, just vbar.

[mverhorst]

Originally Posted by Pard

You are most likely correct, as demonstrated here:

http://www.vstabi.info/en/node/1422

That said, how do you decide if it is the servos or not without special gear? I like the high performance value servos, like KST, which may be the problem. I have to get over that habit ...

Vbar seems to be most sensitive to this effect. I never have problems with Ikon, Vortex, Skookum, just vbar.

I quess try your system, if errors occur, disconnect the servo's and try again...

Vbar indeed seems more sensitive to the these problems...

That being said, there are some servo manufacturers that are known for these problems and there are some known for there low and nice amp draw...

[Pard]

More from WR:

If you want to use the large capacitors, we recommend you to use our Battery Buffer unit, this will prevent the capacitor from feeding back any power back to the BEC.
http://www.western-robotics.com/battery_buffer_hp.html


Regards,


Western Robotics Information
WR_logo Western Robotics Ltd.
#215-12837 76th Avenue
Surrey, BC V3W2V3
Canada
Phone: 778-565-1332
www.western-robotics.com
info@western-robotics.com

[Pard]

FWIW on one of my Trex 450 standard 325 baldes, 4 TGY 306HV servos, using mini vbar.

Running the Polaris at the lowest voltage I still need a capacitor or I can brown it out on the bench. So I will keep the capacitor in line. With the capacitor, I still cannot even get 6V without brownouts.

I think the biggest factor is running the BEC off of 6s instead of 3s

[gorlandheli]

I have posted on Aerodynamics, Physics and Engineering for exactly this kind of situation:

https://www.helifreak.com/showthread.php?t=676587

Capacitors can upset a BEC and potentially destroy it. Not all BECs suffer in the same way and your system may be better or worse with the combination of RX, FBL, Servos etc. that you use.

External (to the BEC) capacitor(s) do not just cause problems at start up. They upset the fundamental arrangement inside a switching BEC regulator (sometimes even linear types too). This could make the internals unstable at a high speed (not seen by simply measuring the DC voltage). The inevitable stress and heating in this scenario causes the damage.

The purpose of the inductor in my post is to electrically separate the external capacitors from the control loop in the BEC. That way you can have your capacitors, avoid the brown outs and keep the BEC happy.

[Pard]

Originally Posted by gorlandheli

I have posted on Aerodynamics, Physics and Engineering for exactly this kind of situation:

https://www.helifreak.com/showthread.php?t=676587

Capacitors can upset a BEC and potentially destroy it. Not all BECs suffer in the same way and your system may be better or worse with the combination of RX, FBL, Servos etc. that you use.

External (to the BEC) capacitor(s) do not just cause problems at start up. They upset the fundamental arrangement inside a switching BEC regulator (sometimes even linear types too). This could make the internals unstable at a high speed (not seen by simply measuring the DC voltage). The inevitable stress and heating in this scenario causes the damage.

The purpose of the inductor in my post is to electrically separate the external capacitors from the control loop in the BEC. That way you can have your capacitors, avoid the brown outs and keep the BEC happy.

You lost me. So what is safe to use?

[mverhorst]

Originally Posted by Pard

FWIW on one of my Trex 450 standard 325 baldes, 4 TGY 306HV servos, using mini vbar.

Running the Polaris at the lowest voltage I still need a capacitor or I can brown it out on the bench. So I will keep the capacitor in line. With the capacitor, I still cannot even get 6V without brownouts.

I think the biggest factor is running the BEC off of 6s instead of 3s

I have about the same setup but 3S, works like a charm.

[gorlandheli]

Originally Posted by Pard

You lost me. So what is safe to use?

Short answer is nothing...

You can use capacitors with a risk of malfunction.

If you want capacitors without risk of malfunction you would need to add an inductor between BEC output and capacitors e.g.

RED wire from BEC -> Inductor -> Caps "+" terminal -> rest of circuitry
BLACK wire just as before but include connection to Caps "-" terminal

Adding the inductor is awkward and adds weight but can be done. Otherwise it is a case of buy an appropriately rated BEC from the outset.

[Pard]

Originally Posted by gorlandheli

Short answer is nothing...

You can use capacitors with a risk of malfunction.

If you want capacitors without risk of malfunction you would need to add an inductor between BEC output and capacitors e.g.

RED wire from BEC -> Inductor -> Caps "+" terminal -> rest of circuitry
BLACK wire just as before but include connection to Caps "-" terminal

Adding the inductor is awkward and adds weight but can be done. Otherwise it is a case of buy an appropriately rated BEC from the outset.

Thanks