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Old Jan 19, 2010, 10:58 PM
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Orange County, CA
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Hyperion LiFePO4 packs

OK, I bought a few of these to try out. I have not gotten a chance to fly them yet, but I have run them in my Futaba 4PK FASST radio I use for boats. The radio comes stock with a 1,700 mAh 5-cell NiMH. Attached is a graph showing the discharge curves of both the stock NiMH and the Hyperion pack. This is a 2S pack just like I plan to use in the planes. Both packs had an initial voltage of 7.2 volts.

Hyperion says to never discharge below 2.5 volts per cell, and that is exactly where my TX went to and shut off. I just finished recharging and my Hyperion DUO says I put back 2,074 mAh into the 2,080 mAh pack!

The end of pack drop is as dramatic and fast as I have ever witnessed. I will use 6.5 volts as my stop flying voltage. That still gives me an hour or more of reserve, but why push it. Futaba says this TX has a max current draw of 250 mA. Based on this test it looks about right with a calculated draw of 208 mA. I've calculated average loads of 300 to 400 mA for my 6-servo TD ships so this should be a decent reflection of how they will perform in the plane. Once I get the Xplorer airborne I will do a timed use/discharge test to see how it does in the plane.

I like how flat the discharge curve is and how well it maintains voltage. At least 0.3 volts higher than the NiMH under the same load.

I forgot to add that the RX packs need any A123 capable charger and can be charged at up to 4C using one of those. The packs made for a TX like the one I show here actually has a board in it that allows the use of a normal NiMH wall-wart charger. Which I tested and works fine. You CANNOT fast charge with a non-A123 charger and you can only use a non-A123 charger on the packs marked as such and intended for use in the TX.
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Old Jan 20, 2010, 03:01 AM
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Jyvaskyla, Finland
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Interesting, I propably test 123 cells in future. Just little worried about the dramatic voltage at the end of the curve - I would not call it a safety feature...
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Old Jan 20, 2010, 09:11 AM
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Orange County, CA
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Quote:
Originally Posted by Tuomo View Post
Interesting, I propably test 123 cells in future. Just little worried about the dramatic voltage at the end of the curve - I would not call it a safety feature...
If you fly your packs that close to the edge then perhaps it is a concern. I am estimating based on the data I collected that my 2,100 mAh pack will give me 3 hours of flight time with a healthy safety margin (+/- 1 hour). And, since these cells are tolerant of high charge rates I can recharge a totally dead pack in the field in about 15 minutes.

Over the years I have gotten away from using voltage as any kind of indicator of the packs status. I have long used the method of figuring the average usage of the plane and then tracking flight time. Never failed me yet. I test the voltage between flights just to make sure nothing unusual is going on. (dropped cells, broken wires, etc.)
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Old Jan 20, 2010, 10:21 AM
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Quote:
Originally Posted by Tuomo View Post
Interesting, I propably test 123 cells in future. Just little worried about the dramatic voltage at the end of the curve - I would not call it a safety feature...
Quote:
Originally Posted by Silent-AV8R View Post
If you fly your packs that close to the edge then perhaps it is a concern. I am estimating based on the data I collected that my 2,100 mAh pack will give me 3 hours of flight time with a healthy safety margin (+/- 1 hour). And, since these cells are tolerant of high charge rates I can recharge a totally dead pack in the field in about 15 minutes.
I was just listing pros and cons of coventional rx packs vs 123.

Quote:
Originally Posted by Silent-AV8R View Post
Over the years I have gotten away from using voltage as any kind of indicator of the packs status. I have long used the method of figuring the average usage of the plane and then tracking flight time. Never failed me yet. I test the voltage between flights just to make sure nothing unusual is going on. (dropped cells, broken wires, etc.)
Neither do I use voltage indicators. However, I have just moved to the very nice Jeti Duplex 2.4Ghz with full telemetry. The simplest use of this is warning beeps when rx voltage drops under certain (preset) level. No extra sensors etc. needed for this feature.
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Old Jan 20, 2010, 08:47 PM
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This link takes you to a post about the LiFePO4 packs by Hyperion versus a Sanyo Eneloop pack.

http://www.rcgroups.com/forums/showp...&postcount=177
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Old Jan 21, 2010, 01:39 AM
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Sydney Australia
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Quote:
Originally Posted by Tuomo View Post
I was just listing pros and cons of coventional rx packs vs 123.



Neither do I use voltage indicators. However, I have just moved to the very nice Jeti Duplex 2.4Ghz with full telemetry. The simplest use of this is warning beeps when rx voltage drops under certain (preset) level. No extra sensors etc. needed for this feature.
Not neccesarily legal though for F3J competition. Not that I care. Just mentioning and issue that has come up in F5B.
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Old Jan 21, 2010, 03:59 AM
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David, I am aware thet using telemetry is not allowed in FAI-competitions. But maybe we should make a difference between performance and safety related telemetry. As an example, Jeti 2.4GHz monitors rx reception all the time - tx sarts to beep when rc link gets weaker or there are data lost due to interference. This safety feature cannot be switched off.

And it is the same with rx pack voltage. Tx monitores it all the time. User can set the alarm level, and to use (or not to use) Jeti Box for numerical info, but this does not change the basics of telemetry.

Futaba fasst is different, no telemtry at all. But I guess these types of safety features are integrated into every new generation 2.4GHz system?

Sorry offtopic
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Old Jan 21, 2010, 05:45 PM
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One more test. a 1,450 mAh LiFePO4 versus an Elite 5-cell 2/3A 1,500 mAh NiMH

http://www.rcgroups.com/forums/showp...&postcount=180
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Old Jan 23, 2010, 06:07 AM
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Launceston Tasmania
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Good info, thanks for sharing av8r.

Chris.
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