Castle Creations / A123 Battery Backup system

[kyleservicetech]

Update 03-18-2012

Now, after 15 flights, the A123 backup battery was "Topped Off" with a Cellpro Powerlab 8 charger. The '8 charger shows that 215 Milliampere hours was needed to top off the battery. That includes running the receiver and servos a number of times during ground tests with the A123 battery alone. Also, my on board undervoltage alarm shows that the Castle Creations 10 Amp uBEC never dropped below 6.0 Volts DC.

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One of the issues with a giant scale model is a requirement for an absolutely reliable DC supply for the receiver and potentially many high current servos. Options are to use a 5 cell Sub "C" Nih battery, a two cell A123 2300 battery, a switching regulator type of battery backup, or a combination of several of these type DC supplies.

I've got a $1000 Goldburg Extra 330 equipped with a Hacker A60-16M motor, and 24 A123 cells configured as 12S2P. A Castle Creations 10 Amp uBEC is connected to a 6S2P tap on the 12S2P A123 power pack. Next the CC 10 Amp BEC was programmed to 6.6 volts DC, same voltage as a 5 cell Nih battery, taken right off of the Nih battery charger. This 10 amp uBEC is connected directly to the receiver's battery input. The backup A123 system is connected through two 10 Amp Silicon diodes to an unused servo connector on the receiver through a standard on-off switch harness. The backup battery is charged through its balance cables with a Cellpro Powerlab 8 charger.

(The 276-1661 is a Radio Shack part number.) I used a www.digikey.com diode # 10A01CT-ND on my Extra model. The Digikey diode is rated to carry far more than 9 amps under very short time durations. In fact, if the battery should accidentally be shorted out, the A123 battery and the two 9 Amp series diodes will simply melt its wiring before the battery or the diodes will fail. (http://search.digikey.com/scripts/Dk...-ND&x=35&y=19)

Nine or ten amp diodes are available through a number of different electronics supply houses.

These two diodes could be wired in directly to a standard heavy duty receiver on-off switch harness. Be certain to properly protect the soldering joint between the silicon diode leads and the hook up wire. These joints must be protected against vibration with several layers of tight fitting shrink tubing. For readers not familiar with diodes, note the band position on these diodes as shown on the schematic. Get one backwards, and it won't work. No damage, just won't work. As far as soldering these items, you need a good soldering iron, perhaps 40 watts or so. Those diode leads are heavy duty!

This setup has worked out very well after about 60 flights on a 3KW model. And, very few milliampere hours (perhaps 25 mah) is pulled out of the two cell A123 pack during a days flying.

(The CC BEC has an undervoltage monitor on it, and it has never dropped below 6.0 Volts DC, with a model that has seven Hitec 645MG servos on it.)

As far as the voltage limit on the typical servos, I've conducted discharge tests on a brand new 5 cell, sub "C" type 2000 Milliampere Hour Nickel Hydride receiver battery. The discharge curve on the Nih battery at 5 amps was virtually identical to the discharge curve on the two cell 2300 Mah A123 battery pack.

With this setup, the backup A123 battery only provides backup power if the Castle Creations uBEC output voltage drops to about 6.0 Volts DC. The two series silicon diodes drops the A123 battery pack to a value lower than the CC uBEC, and as a result the A123 battery does not deliver power under normal conditions.

If your radio and servos work with a 5 cell Nih pack, it will also work with the two cell A123 pack. But, some servos don't work well with the 5 cell Nih pack, so do be careful.

One good advantage to this type of system is it provides dual DC inputs to your receiver. It eliminates the "Single Point Failure" that could happen with a single receiver battery on your model. That way the model is not depending on items like a mechanical on-off receiver switch to control the model.

Take a look at the attached drawing or schematic of this setup.

(FYI, several of my club members are using this setup on their giant scale gassers with 50 cc or larger gasoline engines for power.)

[JetPlaneFlyer]

Great idea for large models.. It seems to combine the best of both worlds

[aviatortom]

Pretty cool system. I know this is an old thread, but I am considering a backup flight pack for an airplane I am building, so I am curious. Do you think your circuit would work simply as a backup to the ESC and its built in BEC? Let's suppose on a smaller model (6.25lbs AUW with a approx 890KV/900W/4S1P with a Castle IceLite 75 ESC system) you connect everything normally depending only on the lipo battery pack and the ESC/s built in BEC for power. Now, if you take your back up battery and switch/diode circuit and plug it into a spare receiver channel, will it provide flight control backup if the ESC and or main battery fail? Or will it foul up the works?

[kyleservicetech]

Originally Posted by aviatortom

Pretty cool system. I know this is an old thread, but I am considering a backup flight pack for an airplane I am building, so I am curious. Do you think your circuit would work simply as a backup to the ESC and its built in BEC? Let's suppose on a smaller model (6.25lbs AUW with a approx 890KV/900W/4S1P with a Castle IceLite 75 ESC system) you connect everything normally depending only on the lipo battery pack and the ESC/s built in BEC for power. Now, if you take your back up battery and switch/diode circuit and plug it into a spare receiver channel, will it provide flight control backup if the ESC and or main battery fail? Or will it foul up the works?

Yup it should work just fine. You need to have servos rated for 5 Nih cells. Then program the ESC uBEC to 6.5 Volts DC. For your smaller model you could use the 1100 Mah A123 cells to save weight and physical size.

If weight/size is not a problem the 2300 Mah A123 cells and their 5 ounces of weight total would do the job.

A good place with a proven track record for these A123 cells is www.voltmanbatteries.com
http://www.voltmanbatteries.com/serv...1-dsh-A/Detail

These A123 cells must be balanced, take a look at building cables for same:
http://www.wattflyer.com/forums/showthread.php?t=64209

FYI, I've been using the Castle Creations 10 Amp uBEC in four of my models for the past four flying seasons. Have had zero problems with any of them, after hundreds of flights on different models.

[ramboman]

I use nothing else than two pairs of a123 separated by schottky diodes on large planes, one pair without diode or a sBEC on small planes...
But don't forget to charge your Rx pack !
The plane I am building now has 12s2p a123, a sBEC and a pair of a123 at "float" voltage (like any alarm central)...
Look at the attached picture...
The sBEC is set to 7V...
It maintains the Rx pack at "float" level...
In case of failure, the Rx back takes over !
You are allowed to forget to charge your Rx pack.

[kyleservicetech]

Originally Posted by ramboman

I use nothing else than two pairs of a123 separated by schottky diodes on large planes, one pair without diode or a sBEC on small planes...
But don't forget to charge your Rx pack !
The plane I am building now has 12s2p a123, a sBEC and a pair of a123 at "float" voltage (like any alarm central)...
Look at the attached picture...
The sBEC is set to 7V...
It maintains the Rx pack at "float" level...
In case of failure, the Rx back takes over !
You are allowed to forget to charge your Rx pack.

Nice thing about those 2300 Mah A123 cells when used as a receiver/servo source. You will NEVER overload them and cause a voltage sag. (At least as long as they are charged)

Last year, I accidentally shorted out a two cell receiver backup battery A123 pack. That battery melted the wires right out of the receiver switch harness, and melted the switch contacts together inside the switch harness. Didn't even affect the battery pack.

After doing that, methinks that A123 pack was laughing at me.

[ramboman]

Originally Posted by kyleservicetech

Nice thing about those 2300 Mah A123 cells when used as a receiver/servo source. You will NEVER overload them and cause a voltage sag. (At least as long as they are charged)

Last year, I accidentally shorted out a two cell receiver backup battery A123pback. That battery melted the wires right out of the receiver switch harness, and melted the switch contacts together inside the switch harness. Didn't even affect the battery pack.

After doing that, methinks that A123 pack was laughing at me.

AMPS is not a problem