Caution advisory! induction voltage cause by servos.

[Freeskiken]

Quote:

https://www.facebook.com/georges.vangansen?fref=nf

Caution advisory!
induction voltage cause by servos.
We have seen some report of our 6S120A SBEC shutting down the BEC when you are moving the swash servo very quickly, causing the flight system to reboot, this generally can be tested before flight, just move all 3 servo with your radio at the same time and move it fast, do some fast full up and down movements and see will your flight system reboots due to BEC protection been activated.
Some servo will feed back induction voltage caused by servos motors to the flight system and ESC, Our BEC
has a over voltage protection, if the inline voltage goes over 9.2V, the BEC will shutdown to protect the flight electronics
( servo, Jyro, receives etc…) so when the servo induction voltage is over 9.2V, this will trigger the protection to kick in,
we have recently tested some servos and have witness induction voltage cause by servos up to 14 volts, obviously due to induction, so how to avoid this, first we recommend to use maximum 7.2V and not higher BEC voltage so you have more head room, second is to install capacitors on your receiver so it can act as a buffer, you can find this readily available in many hobby shop,
To recap, do this test before flight for a new installations, if you see this happening, do the above mentions step to eliminate the voltage surge caused by induction !
When using HV servo, set your BEC voltage at only 7.2 volts is the best and we recommend you to do so, And always use a backup power source such as Scorpion Backup Guard.

[ragge1]

what size capacitor is recomended

[Freeskiken]

I just read this and need to test my setups. It is just a warning to test your setup.

I used to run the Futaba FUTL6500 RX Capacitor it is 1800 uf. It is meant for this type of application. I may add them to my setups.

Two of my Helis that have 120-06 ESCs are at 6.1 V and one at 8.2 volts. I will have to change it to 7.2 V.

I bench tested my Diabolo 550 with MKS HV9767 cyclic servos and MKS HV9780 tail servo. I do not have a backup power system on this Heli. I tried moving the sticks up and down fast and it did not restart. I will reset the BEC and add a capacitor just for safety.

[Freeskiken]

This is what I use.

http://www.futabarc.com/accessories/futl6500.html

[acidla]

Originally Posted by ragge1

what size capacitor is recomended

10v 4700μF

[ragge1]

thank guys

[Freeskiken]

Originally Posted by acidla

10v 4700μF

Where did you see this recommendation? Why 10 volt ? Where can you buy them from ?

The Futaba one is 16 v 1800 uf.

[Number]

Any voltage above servo voltage would be fine. 10V is pretty much as low as you can easily find that will work with 8.4V BEC output. Voltage is not so important... it's the capacity that matters. Higher is better. Lower voltage just means that the size will be smaller than a higher voltage one of the same capacity.

These are the ones I've bought in the past. I actually put 3 of them in parallel for a total of 10V at 14,100uF. That's probably not necessary to put more than one but I did it anyway.

http://www.ebay.com/itm/4700uF-10V-R...CY7kzM8BXEFAWw

[Freeskiken]

Jeti sell these:

https://shop.jetiusa.com/Jeti-Receiv...ti-ac-10as.htm

They are 10mf.

[Number]

Quite expensive

Anyway, 10mF is 10,000uF.

[Freeskiken]

So I guess you could just take one of the 10V at 14,100uF capacitors. Solder a servo plug on it. Negative on one pin and possitive on the other pin and some shrink and you are done.

[Number]

It's not one 10V 14100. It's three 4700 in parallel. The Jeti one is two 5000uf in parallel.

[acidla]

Originally Posted by Freeskiken

Where did you see this recommendation? Why 10 volt ? Where can you buy them from ?

The Futaba one is 16 v 1800 uf.

When i was searching for capacitors in a system i found out that many are using the 10volt which is all you need. This cap is small in size and has low weight.

Hobbywing now includes them together with their esc's.

[Freeskiken]

Originally Posted by Number

It's not one 10V 14100. It's three 4700 in parallel. The Jeti one is two 5000uf in parallel.

The Jeti one says it incorporates logic for managing the initial, gradual charging of the system capacitors.

Would it be large enough?


Quote: The AddCAP 10AS incorporates logic for managing the initial, gradual charging of the system capacitors. The AddCAP design makes it suitable for use in configurations where the receiver is powered by a switching regulator. Output power is transferred to your receiver through double 0.5mm2 (20AWG) cables with a JR servo type connector. Simply plug the JR type connector to any open receiver channel.

[Number]

That just means that it has circuitry that prevents huge current spikes when you first apply power. Capacitors have a very low series resistance which means that, until they're charged to their input voltage, a very large current flows to charge them up. It's not ideal. Though on this small scale I don't think it is really necessary. If it was a big deal, so many people wouldn't be using regular old caps, like I do.

It would only be useful for things that use a BEC (which is a switching regulator).

[Freeskiken]

I am using a BEC. I guess the Futaba one I have are too small. Funny they would sell them for this application.

[mverhorst]

Originally Posted by Freeskiken

I am using a BEC. I guess the Futaba one I have are too small. Funny they would sell them for this application.

It would only be to small if you have issues...

My advice is not to overthink this. Not all servo's induce back EMF and if you have servo's that do and your cap is preventing the system to shut down it's fine...

And the bigger the Cap the higher the peak current on startup...

I've seen caps shutdown a BEC on startup do to the in rush current of big caps...

[Freeskiken]

Thank you. I guess you are right if I am not having a back emf issue on the bench where it shuts down the BEC then I guess there is no issue. The Futaba capacitor would just smooth out the peaks.

Quote: Ditch the glitch with this great accessory!
Stores power from the BEC and acts like a filter to eliminate noise and static that can cause glitching between the transmitter and receiver
Also has the benefit of reducing the load on the ESC's BEC
Features high capacity and low resistance, and comes pre-wired and ready to plug into any open channel
Compatible with 2.4GHz systems

I was reading the info sheet that comes with the Futaba RX Capacitor and it says "supports 4.8 and 6 volt power supply and voltage receivers." Yet the capacitor itself says 16v 1800uf. So it should most likely be OK at 7.2 volts ? I guess I will try it out.

[flint723]

IMO a capacitor is always a good idea, a while back a bought a bunch of 10v 4700uf capacitors that I've been using on every heli.

[Number]

Originally Posted by Freeskiken

Thank you. I guess you are right if I am not having a back emf issue on the bench where it shuts down the BEC then I guess there is no issue. The Futaba capacitor would just smooth out the peaks.

Quote: Ditch the glitch with this great accessory!
Stores power from the BEC and acts like a filter to eliminate noise and static that can cause glitching between the transmitter and receiver
Also has the benefit of reducing the load on the ESC's BEC
Features high capacity and low resistance, and comes pre-wired and ready to plug into any open channel
Compatible with 2.4GHz systems

I was reading the info sheet that comes with the Futaba RX Capacitor and it says "supports 4.8 and 6 volt power supply and voltage receivers." Yet the capacitor itself says 16v 1800uf. So it should most likely be OK at 7.2 volts ? I guess I will try it out.

Yes it will work. The voltage on the cap is its absolute maximum, but it works with lower voltages. It's best to get as low voltage as you can though purely because it will be physically smaller. That's why 10V is probably the best.

It likely says 6v and 4.8v systems because it's very old, and 7.4/8.4v systems didn't exist back when it was originally put out, so they had no reason to say it would work with higher voltages.