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Benefits of a Cap(icitor)

Old 12-17-2007, 05:59 PM
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Jake Ruddy
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Default Benefits of a Cap(icitor)

Hey guys,

While looking at the Buy and Sell section I found this http://www.rcuniverse.com/market/item.cfm?itemId=340475

This is a cap installed parallel to your battery system which is suppose to help with 2.4 reboots. While I understand in theroy why this could help.. I am torn about whether or not it's actually going to be effective.

I don't have an electronics background... so excuse my crude explianation of how a cap works.. but we used to use much larger ones in High end Car Audio. The reason for this is because a Cap can charge and release energy extremely fast. In car audio when you have a high end system with some large subwoofers your bass can get sloppy and loose some of it's punch. While not really worried about in everyday applications.. but I used to compete and what's not commonly known is that there is a lot more to it than having a loud car stereo

Needless to say, this was a good way to keep your amps powered well under heavy loads. But percussion is not constant so the cap has time to recharge.

I am trying to decide whether this would actually be beneficial in this application and why.


Explain it to me like I'm a 5yr old
Old 12-17-2007, 07:07 PM
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Richard D Bahmann aka/Wrongway
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Default RE: Benefits of a Cap(icitor)

""Explain it to me like I'm a 5yr old """

Buy A123 batteries...Power with a super switch or other high capacity fail safe type, or two high quality switches running on dual leads to your A123. Should easily be good up to 35% (I have one two cell on my 35% on PCM)

End of story!!

Ask RCU name "Absolute Yak" who on his second try with the spectrum went to A123 and is not looking back. 60 amps continous 120 amps surge, just get the power reliably to the receiver.
Old 12-17-2007, 07:59 PM
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Default RE: Benefits of a Cap(icitor)

what rdb127 said

Also, you need to learn what your normal useage is per flight so you have an idea of how many flights with some safety factor built in. I saw where you are going to Spektrum and it's important to not let the receiver see 3.5 volts or less as that is where it will reboot so I think I'll be charging at 3.7 volts per cell when I convert all my stuff to A123. Vinny has been doing loads of research on this. Give him a call, he can certainly help you out as he is planning to use the AR9000 receiver he has and I'm planning on the AR9100 for the 2 40% planes and the AR9000 for everything else (since "everything else" already has them installed)
Old 12-17-2007, 08:06 PM
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Absolut Yak
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Default RE: Benefits of a Cap(icitor)

What Richard said!

My Spektrun AR7100 receiver rebooted on me for an unknown reason. I am highly suspicious of a regulator that could not handle the through-put while under momentary high amp loads. I slapped my Yak in flat, but tore up the motor box and gear box, but good. I rebuilt and flew the plane on my Futaba system with the exact same setup, but I also knew that setup had flown 200 times before in my prior Yak (R.I.P. wing failure in flight.) I refused to go back to the Spektrum until I found a complete setup I was happy with. Thanks to Dick Hanson, Josey Wales, rdb127, and others, I decided to take a leap forward in technology and simplicity.

So, one A123 2300mah 2-cell on the receiver with Deans plug to Smartfly failsafe switch with Dean's plug in and double universal leads out to the receiver. I run 5955's on all the flight surfaces and fly aggressive 3D. 40+ flights since and I don't worry anymore. Spread Spektrum technology mated with a sound power supply makes me a happy guy. Hey, I rhymed!

Doug
Old 12-17-2007, 08:11 PM
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Richard D Bahmann aka/Wrongway
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Default RE: Benefits of a Cap(icitor)

""Spektrum technology mated with a sound power supply makes me a happy guy. Hey, I rhymed! "

How Doin Doug? Coming down to FX3D in Jax, FL Feb 29- Mar.2? Hope to see ya there.

Richard
Old 12-17-2007, 08:22 PM
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Default RE: Benefits of a Cap(icitor)

A capacitor might help maintain the receiver voltage during a short period when a high servo load dragged down the battery voltage, however it would require a diode in the circuit to stop the capacitor charge leaking back to the servos.

Bringing the diode into the circuit would also have the effect of reducing the receiver voltage by the forward voltage drop across the diode.

The way it would work is that normally the receiver would run off the battery, and the capacitor would charge to the supply voltage minus the drop across the diode.

If the supply dropped enough the diode would switch off, and the Rx would get power from the capacitor. However, as the charge drains out of the capacitor the voltage across it would fall, and would continue to do so until the supply voltage came back up again (or until it ran out of charge).

The key issue here is the size of the capacitor, and this in turn would be dictated by how long the supply voltage is likely to be below that required by the receiver. Haven't got around to doing the calculations, but I suspect that a rather large capacitor would be required to give any meaningful protection.

Terry
Old 12-17-2007, 08:38 PM
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Default RE: Benefits of a Cap(icitor)

We use super caps where i work that are much larger 50-800Farad's.
The ones we use are good for a working voltage of 2-3volts each.
The one shown must be of much smaller capacity for it to work on 6-7volts with out seeing the part number,(correct me if wrong).
They use a special charge circuit for proper operation.
In our use they work for a few hundred milliseconds with hundreds of farads, how much dip-time do you expect?
The caps blow out - leak out of the top (not the lead end) when they give it up usually, they have a Y cross stamped in for the goo release on the brands we use.


The best practice here is provide adequate power, not rely on a bandade fix. Spend your money on a good power-battery system.
Major profit on the item being sold.
I could have done the same thing on a few setups I have, but it is best to fix the problem not the end effect.
I would have also used a simple proper charge circuit for them.

Just my 2 cents,
Tony
Old 12-17-2007, 09:18 PM
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Jake Ruddy
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Default RE: Benefits of a Cap(icitor)

Thanks for the input... I def. don't view this as a solution.. I was more intrigued by the concept and wheather or not it was sound.. in my mind it would help briefly but not for an extended high amp manuever?
Old 12-17-2007, 10:28 PM
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Default RE: Benefits of a Cap(icitor)

Richard, I have requested time off to attend the FX3D event. Had too much fun in Atlanta with you guys to miss this one. I'll catch you on the proper thread, though.

Doug
Old 12-18-2007, 12:37 AM
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Jake Ruddy
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Default RE: Benefits of a Cap(icitor)

Actually I just re-read all that and Terry and Tony made sense... thanks for all the input.


Thanks!

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