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RE: Real world data on power requirements - 1/29/2008 4:55:17 AM   
krayzc-RCU



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RE: Real world data on power requirements - 1/29/2008 11:28:56 AM   
rctom



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quote:

ORIGINAL: Scoubidou

Hello Tom
I understand A123 batteries can deliver 30C but many pilots use two batteries for redundancy in their Giant planes whatever if it's Nicad/Nimh/Li-ion/lipo but you recommend only one A123. Could you explain the idea using only one pack?

Is it for weight saving?
Do A123 chemistry safer than the other and they will never fail? What happen when one cell goes bad?

Daniel


Since I have been using the A123 packs I have come to understand their operation and maintenance. They are very ruggedly constructed with a laser welded aluminum case. They seem to be extremely reliable.

I started out using 2 packs, then I went to a single pack to allow me to use a data collector module. Using 2 packls I would have needed 2 modules and then would have to manually calculate the total used, so it was a lot easier to just use one pack.

Never fail? Sooner or later everything fails, I just hope it won't be in my plane. I advocate a single pack only to save money and weight, there is absolutely no other reason not to use 2 packs. I will probably put a second pacl back in my main plane now that I am done testing.

Also, I had the opportunity to test a plane using one pack for both receiver and ignition. I am using Spektrum radio with an AR7000 receiver. It worked fine, no problems at all. I think that in the future what I will be doing is using 2x 2300mah packs, one for receiver exclusively and one shared between receiver and ignition. This will give me redundancy, reduce cost and reduce weight.

TF

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RE: Real world data on power requirements - 1/29/2008 1:44:10 PM   
krayzc-RCU



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Status: offline 		tom does these 123 batteries use a special charge ?

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RE: Real world data on power requirements - 1/29/2008 2:35:03 PM   
Scoubidou



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From: Boisbriand, QC, CANADA
Status: offline 		Hello Krazy,
I think you need to do some readings Here is the A123 summary from another site:
So you are interested in A123's but don't know a lot about them. I have complied a list of information that may help you make your decision to switch to A123's.

A123's have a 30C nominal discharge and 60C burst. What does that mean? That means that a 2300 Mah pack can deliver a constant 69Amps or 138Amps burst! These are not mis-types, these are actual facts.
A123's (2300 Mah packs) can be charged at up to 10Amps safely, with no negative effects on the battery. What does that mean to you and I? It means that charging at 4Amps, like with the FMA CellPro 4S, your battery will be charged in just ovr 30 minutes. At 8Amps, it will be charged in about 15 minutes. These numbers are from completely dead to fully charged!
They offer a 10 year shelf life and 1000+ cycles, compared to ~200 cycles with Lipo's.
They have a flat discharge curve, and have a nominal voltage of 3.3 volts per cell. What does that mean to you and I? A 2 cell pack will have a nominal voltage of 6.6 volts, and the voltage will pretty much stay at 6.6 volts until the energy in the pack is extinguished. Lipos go from 8.4v at their peak, all the way down to 6.5v (or whatever your personal cut-off is). Whereas a Lipo can have about a 2 volt swing, an A123 battery has about a .5 volt swing. The 6.6 nominal voltage allows users to run the batteries without regulators, if they so choose. The voltage of an A123 pack is about the same as a freshly charged 5 cell Nimh pack.
Balance or don't balance, the choice is yours. While Lipo's almost demand to be balanced, A123's do a good job of staying in balance by themselves. While you may get a slight voltage variation from cell to cell, it is not as critical on an A123.
NO EXPLOSIONS! A123 is an inherently safer chemistry and does not explode if droped, or even a nail driven through it. While no battery should be intentionally mis-handled, tests by A123 Systems show that an A123 cell will not spontaniously ignite from over-charging or dropping (or driving a nail through the case). I personally would not recomend trying any of these yourself.
They hold a charge for a very long time. No more having to "top" the batteries off right before flying. The batteries will maintain ~95% of their charge over a 1 month period of time.
Lighter than comparitively sized Nicads or Nimh. They are slightly heavier than their Lipo comparison. A 2 cell pack with 14ga. wire leads weighs in at about 5.8oz.
How do you charge them? The chemistry is still relatively new, so charger manufacturers are fighting to get A123 capable chargers to market. Right now, the two most popular solutions are the FMA CellPro 4S, for balance charging, and the "Dapter" which converts any Nicad capable charger into an A123 capable charger. There are other chargers that are A123 capable, like the ThunderPower and Orbit Pocketloader, but I do not have much experience with either. Both of them require a software update to be A123 capable.
The battery's only downside is that you can not tell how much energy is left in the pack by reading the voltage. Because the discharge curve of the pack is so flat, the voltage will be almost the same throught its cycle, and then "cliff dive" at the end of its cycle. Because of this, it is important to become familiar with how much energy your vehicle uses during each use. For planes, I advise people to fully charge their batteries and then fly 2-3 flights. Then, fully charge the packs again and see how much energy (Mah) you put back in to the packs. Then simply divide the amount of energy by the number of flights and come up with your average Mah per flight. This will allow you to set your safe cut-off. It is advisable to only use 1800-2000 of the pack's 2300 Mah's.



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RE: Real world data on power requirements - 1/29/2008 3:21:08 PM   
rctom



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quote:

ORIGINAL: krayzc-RCU

tom does these 123 batteries use a special charge ?


They charge the same as a Lipo except that they mustcut off at 7.2 volts insted of 8.4m Some Lipo chargers already support A123, I use the Cellpro 4s available for $75 at fmadirect.com

TF

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RE: Real world data on power requirements - 1/29/2008 3:43:12 PM   
3D_Junkie


 

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Status: offline 		Tom,
Do you happen to have a block diagram of your test setup? It would be nice for the engineers amongst us to correlate the data you generated to a setup.

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RE: Real world data on power requirements - 1/29/2008 4:23:33 PM   
rctom



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From: Flower Mound (near Dallas), TX, USA
Status: offline 		Here is how this test was set up.

TF

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< Message edited by rctom -- 1/29/2008 4:35:34 PM >

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RE: Real world data on power requirements - 5/16/2008 5:13:58 AM   
dredknot


 

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From: valley, ANGUILLA
Status: offline 		Hello Tom



Somewhere i saw that you were using 1, A123 battery to power both the receiver and ignition.

This is something i would like to try with my wild hare yak.

The big question is would you advise it when i i'm still using 72MHz,should i worry about interference form the ignition.

Also at what would voltage should you stop flying with A123 battery.

Verne Carty


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RE: Real world data on power requirements - 5/16/2008 5:40:30 AM   
aaxiss



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From: Orange, CA, USA
Status: online 		A123 cells won't explode like lipos because of the chemistry and also because they have a built in vent for anyone who has seen a single cell or built their own packs like I did the batteries are reversed from your typical nicad or Nimh in that the button end of the cell is actually the negative side, and the button is where the venting action happens. this is not a passive thing though... This is a safety feature in the event that something bad happens like the battery becomes shorted out or something along those lines, but with the discharge rates of these packs I would rather have a couple of cells pop than burn down the house or the car. I personally know of 2 people local that lost cars charging lipo's on the way to the field in the car and both of these instances were due to wanting to top off the packs back when the best thing going for lipo's was an astro 109 and a blinky hehe


As for the single A123 on FM or even pcm I would say no, the main reason for 2 separate batteries in the past was to help keep Ignition noise on a separate circuit away from the radio circuit. 2.4 ghz is way more forgiving. Tom may have a different opinion or be able to add other reasons for not doing it also. Just my .02



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If there is a 40% plane out there drawing 42 amps it's because it has an on-board welder.

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RE: Real world data on power requirements - 5/16/2008 2:20:41 PM   
rctom



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From: Flower Mound (near Dallas), TX, USA
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quote:

ORIGINAL: dredknot

Hello Tom



Somewhere i saw that you were using 1, A123 battery to power both the receiver and ignition.

This is something i would like to try with my wild hare yak.

The big question is would you advise it when i i'm still using 72MHz,should i worry about interference form the ignition.

Also at what would voltage should you stop flying with A123 battery.

Verne Carty




I advise you to test it very carefully and possibly try it in another plane of lower value before committing it to a big scale airplane. That's what I did with my Spektrum stuff, until I had built up enough confidence in the setup.

It's always been a taboo, but people told me I shouldn't do it with the 2.4 stuff either. I'm always the guy who doesn't believe the stories and tests it for myself. Sometimes I get burned, other times I am rewarded.

Once the A123 gets below 6.6v static it's very hard to tell their state by measuring voltage. What most of us do is to measure carefully what is taken out and what is put back in.

Discharge/cycle your batteries a couple times until the voltage seems to start to fall off. You'll need a load tester, make one from a couple 1157 automotive light bulbs. When the light starts to dim a little then recharge and note how much the charger puts in. After you do this a couple times you'll have some confidence in how long the battery pack will last.

Then when you fly recharge after 2 or 3 flights and see how much it takes. This will give you an idea of how much power your plane consumes. Then you do that math, leave a 25% margin for safety.

For example a pack will typically supply 2000mah before the voltage begins to drop off. 25% margin would be 1500mah. If your plane uses 250mah per flight, you can safely get 6 flights with a safety margin.

TF

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RE: Real world data on power requirements - 5/16/2008 10:17:55 PM   
dredknot


 

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Status: offline 		Great,Thank you tom and aaxiss

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