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Old Dec 10, 2008, 03:39 PM
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Mini-HowTo
Using camera batteries CR2 and CR123a for HL

There are many way to power our HL planes these days. The following is
my solution that has server well over last three years. I use high capacity lithium camera, non-rechargeable batteries, two 3V. cells in series for 6V.

These batteries are designed for fairly high pulse loads of flash and camera motor drives and they have 10+ years shelf life. They have very high capacity for their size and weight.

No regulators, no balancer, no cycling, no fire hazard, no conditioning, and best of all elimination of the greatest variable, no charging. This all adds up to greater flying safety. They are inexpensive from Amazon for about $1.55 each. And they are always ready for emergency flying trips.

They come in two sizes CR2 weighing 11g. each with a capacity of 850mA. In small 2-servo planes these last me about 22+ flying hours, or about six months.

For 4~6 servo ships the CR123a are slightly larger weighing 17g. each with capacity of 1500mA. that should go for more than 30 air hours depending on your flying.

There's quite a variation in capacity among brands, so I recommend name brands like Kodak. At Walmart they are not cheap, but here's where I get mine for very good price. Also look at the Used Prices listed on Amazon. The batteries are not used.
http://www.amazon.com/s/ref=nb_ss_p?...eries&x=0&y=0]

So why are they safe? Every battery has a fairly flat current output until the charge is used up, and you reach the "avalanche" point where the voltage drops quickly. That is the danger point with all battery types.

I face the "avalanche" with some slight risk about every 22 flying hours with 2-servo ships for example. With typical small NmHD packs you may face avalanche every 1.5~2 flying hours. That is if your charger has cut off at the right peak. Flying with the highest capacity batteries you can carry without weight penalty is safer.
John255

P.S. A step-by-step how-to on soldering CR type cells is on pg.7 post #92
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Old Dec 10, 2008, 04:12 PM
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John:
Thanks for the info.

Good stuff!

Cheers-
Dave
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Old Dec 10, 2008, 04:17 PM
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OK, so how do you hook them up?

Well if you are just getting started it may be best to start by reviewing "How to make perfect solder joints" here:
http://www.teamnovak.com/tech_info/h...der/index.html

And then take a look "How to make battery packs" here:
http://www.radicalrc.com/cellsoldering.html
As the article says too small an iron may take too long and over heat the cells.

You can use a home made cell holder from wood, or from packing foam to keep the cells from going all over the place. Wire size can be the same as what comes with servo connectors.

Next is testing. It's difficult to come up with an exact profile of our transient loads in the air. Even the thermal search has different load variations from coring a thermal where all servos are more active.

However, using D4.7 type servos most guys use fixed load substitute of 100mA for a two servo plane, and 150~200mA for 4~6 servos. This is a conservative estimate. Cable drag and flying style may cause your milage to vary.

Best method I've found is to use a digital multi-meter ($4 at Harbor Freight) with a load resistor across the leads and measure the rate of voltage decay. If decay is hundredths of a volt in 20~30 seconds you are OK. If decay is fairly rapid or approaching tenths of a volt don't fly.

Two pin male JST connector with wires are handy because they fit female servo leads that normally plug into RX. Cannot find source. They used to come on all small GWS can motors.

For anyone looking for load resistors here is one source for 5W 50 Ohm. This size make good substitute load for 2 servo planes.
http://www.radioshack.com/product/in...ductId=2062292


And for 4~6 servo planes 5W 30 ohms.
http://www.westfloridacomponents.com...+Resistor.html
John255
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Old Dec 10, 2008, 06:08 PM
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In measuring cells what we are trying to determine is where we are on the flat portion of the discharge curve where the output voltage is fairly constant. IOW, how much time do I have to safely fly.

Looking at the curve for Duracell CR2's below for 125mA continuos load you can see that the voltage stays steady until the area in the white circle (the "knee") where it bends and signals the beginning of avalanche.

If you measure the voltage with a load before every flying session you will get acquainted with the Rate of decay in 20~30 seconds being in the flat area in hundredths of a volt until you get to the knee where decay is faster.

This is not happening very fast so once you see it you will have all the training you need. Some guys just wait to hear their servos get sluggish. That's way too late for me because avalanche is unpredictable close at hand.
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Old Dec 10, 2008, 07:06 PM
Herk
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John, Just a note -- I've used these (or the equivalent) in all my HL models for 18 years and have never had a problem. With a voltage check under load (particularly right after a flying session) you can, as you've demonstrated, easily tell if they are nearing the end of their life.

Especially nice is the shelf life. (again as you've noted) You can go months without flying and the plane is immediately ready to go.
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Old Dec 10, 2008, 07:14 PM
Thermal Naked!
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And they fit nice and snug in the nose of something as small as an Apogee John!
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Old Dec 10, 2008, 07:23 PM
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The next measuring device that works great, and many folks already have is "Watts Up" power meter. When the cells are connected to the source side they will power and activate the meter, then a fixed load resistor is plugged into the "Load" side.

You would not plug the load side into the Rx because the load at that point is variable from the servos action which the meter cannot follow, and what you are looking for is the rate of decay from a fixed load of about 150mA in about a 30 seconds measurement period.
http://www3.towerhobbies.com/cgi-bin...?&P=9&I=LXLMV0

Then there are the voltage indicator LED type "on board" monitors that plug between the battery and the Rx. Problem there is they are just indicating the unloaded battery voltage which can be misleading, especially with camera batteries. The CR type cells are designed to have very rapid voltage recovery when the load is removed. This reduces flash recycle time on cameras. So when the servos stop the voltage shoots back up high.

However, if a fixed load resistor is soldered acrossthe input terminals the monitor can of some value for field testing. With the load resistor in place the monitor can no longer be used "on board" because it would run the battery down.

I guess that's about it. I probably forgot something, but I'm sure somebody will let me know. If anyone decides to use CR cells I would really like to hear about your experiences.
Regards,
John255

P.S. I only found it necessary to keep track of total flying time for my first CR pack and that was easy from the timer on the Tx. After that if you measure before you fly that's all there is to it.
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Old Dec 10, 2008, 07:25 PM
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HerkS, Hoss, and Dave,
Thanks for the support guys.
John255
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Old Dec 10, 2008, 07:37 PM
ein flugel schplinterizer
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USA, FL, Pensacola
Joined Sep 2004
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Hey John,

Just saw this thread. Thanks for sharing this stuff with everyone. I have one of these "Watts Up" but didn't realize it could be utilized this way.


BTW: For everyone else's edification: A little birdie told me Mr John225 was/is also known for building some of the sweetest home audio speaker systems in exsistence.
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Old Dec 10, 2008, 07:40 PM
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Thanks Sean, you old flying rascal.
John255
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Old Dec 10, 2008, 07:45 PM
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John255,

Thanks for pulling this info together! It's great to have here.

I'd like to get a bit more info on resistor part itself. A quick web search shows lots of varieties of resistors--ceramic, wirewound, etc--what do you recommend? Also, I can't tell from the picture how it's attached to the double banana plug...

Ken
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Old Dec 10, 2008, 07:47 PM
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More specifically, I like the Watt's Up approach. What's the easiest setup to get the correct load on the output side? Thanks
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Old Dec 10, 2008, 08:07 PM
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Ken,
The double banana plug you insert the resistor leads through the round holes and the screws shown above jam the resistor leads tight over each leg of the plug. If you had one in your hand it would be obvious. See drawing.
Here's a nice red one for $2.88.
http://www.mouser.com/Search/Product...8%252b8A%3d%3d

About the resistors: First for 4~6 servos you want about a 30~40 ohm 5 watt, any type, wire wound, ceramic, etc. will do in this application. Radio Shack may be easiest to find, otherwise Mouser.
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Old Dec 10, 2008, 08:12 PM
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Quote:
Originally Posted by kebal
More specifically, I like the Watt's Up approach. What's the easiest setup to get the correct load on the output side? Thanks
Ken,
Probably best to just solder the resistor leads directly with the black & red wires to a male Super Deans plug..

I'll look into this and get back to you.
John255
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Old Dec 10, 2008, 10:17 PM
It's a mere flesh wound!
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Woodstock,Ga.
Joined Jun 2004
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Why not just use a Tower Hobby Expanded Scale Voltmeter?
http://www3.towerhobbies.com/cgi-bin...?&I=LXNK82&P=7

It's only $6.99, it will check 4.8 or 6.0 volt batteries and has a built in load that is between 225 and 275mA and will also check your transmitter batteries with a 250mA load.

Buddy
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