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I must say up front that I am quite a fan of A123 LiFePO4 cells and I use them almost exclusively in my RC-hobby for many years.

Many people are fed up with 8 cell NiCd and NiMH packs in their RC transmitters and have started to use 3S LiPO packs instead. With LiPOs it is wise to drop the 3S pack voltage with resistors as fully charged 3S LiPO is close to 12.6V and also TX built-in low-voltage alarm would otherwise kick in at ~2.8V per cell, which is too low for LiPO health.

I noticed that with some modification 1100mAh A123 cells would fit in my Futaba FF7/T7C transmitter and voltage range also fits just perfect (10.6V max, 9.9V nominal and 8.5V TX built-in low-voltage alarm is fine for A123 cells at 2.8V per cell).
[attachment=126]

It is a tight fit and some cutting of the TX tray is necessary (I have glued some plastic in the opening above and have yet to clue a cover to the bottom. There is enough room and the A123 pack is not touching the electronic components on the board below the battery tray):
[attachment=127]

I use Deans Ultra connectors as standard as the pack may come handy for other purposes too:
[attachment=128]

And here is the pack in the TX tray and the lid is no struggle to close:
[attachment=129]

I tested that the TX low-voltage alarm kicks in about 5 hours and 15-20 minutes at 8.5V and since there is no self-discharge with LiIO and LiPO cells, you are guaranteed to get over 5 hours operation every time, even if you have not flown in weeks or months in between! And with less than 15 minute charge time my A123 TX pack is convenient to top off at any time.

Needless to say, my 2600mAh NiMH TX pack pales in comparison is never used in my TX again.

Enjoy,
HaKK

Hakk!

Thank you very much for posting this for the forum (And me)

I think the whole idea is a great one and that you can get 5 hours runtime as the lipos dont discharge is great!!!

i am really going to look into this more!

(06-28-2009 11:47 AM)Cosha Wrote: [ -> ]Hakk!

Thank you very much for posting this for the forum (And me)

I think the whole idea is a great one and that you can get 5 hours runtime as the lipos dont discharge is great!!!

i am really going to look into this more!

Hi Cosha,

I am glad you found it useful. If you do not have a A123/LiIon capable charger (I use Hyperion EOS0610i NET), then LiPO might be an easier route for you. Also, with LiPOs a larger capacity than the 1100mAh A123 pack will likely fit in the TX tray without cutting.
At least with A123 packs I never have to worry about my TX bursing in flames if I happen to forget to turn it off

If you do go LiPO route, then I highly recommned droping the volts with resistors. You gonna have to search the net for tips for that.

If you want to play with A123 cells then a good source for the smaller 1100mAh A123 cells are the Black&Decker VPX battery packs (2 cells are inside). I have bought them from US and do not know if they are available elsewhere. In Europe guys at http://www.first-products.de will make you any size A123 at a decent price. I have ordered from them and can highly recommend them.
For the bigger 2300mAh A123 cells the best source is the 36V DeWalt battery pack with 10 cells inside and best sourced from US via e-Bay.

HaKK

(06-28-2009 09:45 PM)HaKK Wrote: [ -> ]

(06-28-2009 11:47 AM)Cosha Wrote: [ -> ]Hakk!

Thank you very much for posting this for the forum (And me)

I think the whole idea is a great one and that you can get 5 hours runtime as the lipos dont discharge is great!!!

i am really going to look into this more!

Hi Cosha,

I am glad you found it useful. If you do not have a A123/LiIon capable charger (I use Hyperion EOS0610i NET), then LiPO might be an easier route for you. Also, with LiPOs a larger capacity than the 1100mAh A123 pack will likely fit in the TX tray without cutting.
At least with A123 packs I never have to worry about my TX bursing in flames if I happen to forget to turn it off

If you do go LiPO route, then I highly recommned droping the volts with resistors. You gonna have to search the net for tips for that.

If you want to play with A123 cells then a good source for the smaller 1100mAh A123 cells are the Black&Decker VPX battery packs (2 cells are inside). I have bought them from US and do not know if they are available elsewhere. In Europe guys at http://www.first-products.de will make you any size A123 at a decent price. I have ordered from them and can highly recommend them.
For the bigger 2300mAh A123 cells the best source is the 36V DeWalt battery pack with 10 cells inside and best sourced from US via e-Bay.

HaKK

Here is a thread for the Lipo voltage drop using diodes (1N402) instead of resistors (also stops anybody from using the wrong charger on the lipo through the transmitter charge port.