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voltage/brown out capacitors

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rcaddict16/11/2019 20:57:58
519 forum posts
2 photos

are thay worth installing - do they work

link

Geoff Sleath16/11/2019 21:22:56
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3493 forum posts
319 photos

Probably not.

That looks like an aluminium electrolytic capacitor. They are typical quite inductive because of the rolled construction of the etched alumimium plates (the etching increases the surface area and hence the capacitance). That means they have low resonanmt frequency even without adding a separate coil (the inductor) and so will change voltage quite slowly and not respond to sharp, high frequency glitches very well. They may help and probably won't do any harm.

The best way to avoid brown outs is to fit a battery capable of sourcing easily the peak currents of your system. Personally I'm dubious of very high capacity (2AH) AA sized batteries because they have a high internal resistance and are more likely to result in low voltage troughs when you overload them temporarily.

If you must fit an electrolytic capacitor then use a solid tantalum type. They typically have the same inductance as a lump of metal the same size (ie very low). I haven''t neded to buy any since I retired (over 20 years ago) but they were expensive then and probably are now. Better to use a decent battery in the first place.

Geoff

Chris Walby16/11/2019 21:46:59
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1026 forum posts
238 photos

IMO, of no benefit and possibly making your set up less reliable by increasing the number of components that could develop a fault.

On the subject of RX supplies I took some advice from a UK manufacturer of batteries, ESC's UBEC's and motors and used 3S2200 lipo and 20A UBEC on the basis of keeping it simple (using lipos I already had) and it was suggested that if a servo developed a fault/stalled then the UBEC would provide sufficient current to "burn it out" without dropping the voltage to the RX.

I have a couple dual battery switches, but of course the switch is a common point of failure + both batteries' discharge at the same rate. Only advantage is if one battery cell goes open circuit, then the RX will be supported by the other battery.

From experience cheap switches have caused the biggest issue and not ventilating ESC's sufficiently, oh and UBEC's that don't supply their rated current without "browning out" the RX

Cuban816/11/2019 23:50:01
2809 forum posts
1 photos

Don't waste your time with capacitors. Get a properly specified battery or Ubec for your installation. No one size of battery will fit all and will depend on servo type. Please seek advice if you're not clear on how to check on your models servo power requirements. Not a straightforward exercise.

Stephen Smith 1417/11/2019 14:30:19
154 forum posts
Posted by Chris Walby on 16/11/2019 21:46:59:

On the subject of RX supplies I took some advice from a UK manufacturer of batteries, ESC's UBEC's and motors

Really? Who's that, or are they a UK labellers?

gangster17/11/2019 14:58:12
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969 forum posts
17 photos

Nooo it’s papering over the cracks. Brownout is a technical word that some modellers have latched onto. I believe the technical definition really means poor installation or maintenance in terms of model flying. Get a decent switch harness and be prepared to change it frequently Also heed the words about batteries given above . For a normal sport model go with makers recommendation or if it’s big and fancy consider a back up system

Martin Harris17/11/2019 18:42:24
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8955 forum posts
221 photos

There are/were receivers which took a couple of seconds or more to re-establish a connection after a voltage dip on 4 cell packs or high IR NiMH packs which were subjected to high loads and I suspect that this popularised the brownout as a reason for having to break out the bin bags.

I've certainly seen instances where models being flown on one popular system have suffered from this but fortunately my own radio still works on voltages where the servos have long since given up working when tested.

Steve J17/11/2019 18:52:48
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1631 forum posts
49 photos

The only case where I would see some merit in fitting such a capacitor is when you are using the BEC on a cheap ESC to power the receiver and servos. Such BECs tend to be very basic and putting some more capacitance on the output may be beneficial.

If you are using a battery or UBEC, I wouldn't bother.

PS Having said that, here is a photo of a receiver -

3916530-0.jpg

Edited By Steve J on 17/11/2019 19:06:31

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