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Old Aug 26, 2008, 02:20 PM
Southern Pride
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Haralson County GA. USA
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Idea
Receiver packs . Why not LiFePO?

Approx. 1 1/2 years ago I started advocating using A123 (LiFePO4) cells in place of Ni cad and NiMH ones for receiver / servo packs.

During this time many who fly 30-40% gassers have indeed switched and all that I know and many post I have read post from are extremely well pleased. Yes I have heard of a few who do not feel like a 2S 2300 mAh A123 will maintain en ought volts under load driving 10 or 12 high torque digital servos. Could be so but then I do not fly such aircraft and then again many say they have had no such problems.

Those who feel more comfortable with a LiPoly and a voltage regulator / BEC / UBEC ,etc. should continue to do as they see fit. I have used 4 cell Sanyo Ni cad packs for receivers for many years and have never had one fail me. During the past few years I have found the IB 2/3A 1400 NiMH cells to be great cells. I use them in my Traxxas Revo and have used them in my Sig Fazer and my son uses one of my packs in his Fat Free Taco.

Sanyo 4 cell AA 700 mAh Nicad and Traxxas 5 cell 2/3A of unknown brand 1100 NiMh were cycled prior to testing and discharged fresh off of charge of 1C by means of Thunder Power 1010c Ver. 2.3A. K2 2S 1250 was charged on Cell Pro 10 at 3A or 2.4C.

Will a 2 cell LiFePo work in place of a 4 or 5 cell Nicad /NiMh battery? Will it work in place of a 5 or 6 volt bec? Which is better and most reliable?





Charles
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Old Aug 26, 2008, 05:41 PM
Southern Pride
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Haralson County GA. USA
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All of the above could have done better with heavier leads and better connectors but they are all wired like standard receiver batteries are wired.

The Two cell K2 has one cell that is on the weak side and in fact is the worse of the 8 cells that were used in the 4S2P pack flown in my Extra 300.

Back in my glow days I found it very normal to get well over an hours flying time on a .40 - .60 size aircraft using 4 standard size analog servos nad a 4S 600 mAh battery. When I first converted my Sig fazer to electric I used a 4cell 1400 NiMh in it for several months and approx. 40 flights. I only charged it a couple of times and on average it used 20 mAh per 6 min. flight.


Charles
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Old Aug 26, 2008, 11:10 PM
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Thanks for the graphs

Thanks for the graphs! I had thought 2 LiFEPO cells would have been a little on the high side (voltage-wise) than a 5 cell NIMH. Your graphs show there is not but a very slight difference. (didn't want to add the complexity of a regulator). Ordered a few 750MAH LiFePo CR123 style batteries from all-battery.com to try since I need a little different shape than the 18650 style Li-ion. Thought you might be interested, there is another container and MAH choice in A123 chemistry.
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Last edited by Rudy F; Aug 26, 2008 at 11:22 PM. Reason: Thought K2 batteries were Li-ion, but are LIFEPO
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Old Aug 27, 2008, 01:23 AM
Electric Hippy
Brisbane
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I use 2 packs of 2S 2300 on my 35% and use 2 packs of 2S 1100s on my 30%. The 35% has ten servos and the 30% has 6. The little extra volts is still less than a fully charged 5S NiMH or NiCd. SOme servos have ext. of 4ft so a little extra voltage is good.

IMO there is no better packs for large scale.
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Old Aug 27, 2008, 07:54 AM
Southern Pride
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Haralson County GA. USA
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Quote:
Originally Posted by Rudy F
Thanks for the graphs! I had thought 2 LiFEPO cells would have been a little on the high side (voltage-wise) than a 5 cell NIMH. Your graphs show there is not but a very slight difference. (didn't want to add the complexity of a regulator). Ordered a few 750MAH LiFePo CR123 style batteries from all-battery.com to try since I need a little different shape than the 18650 style Li-ion. Thought you might be interested, there is another container and MAH choice in A123 chemistry.

Just a heads up. Be careful using other cells. Many other cell with 123 in their name are in fact nonimal voltage of 3.6 / 3.7 and charge to 4.1 / 4.2volts per cell. Many of these also have some type of protection / battery management module built into the cells and are limited to the max. amps. they can supply under load.

One 800 mAh example from that site
Quote:
Product Specifications

Capacity: Nominal 800 mAh

Dimensions:
Diameter 14
Height 49

Weight (Typical) Approx. 21 g

Nominal Working Voltage: Average 3.6V

Peak Voltage: 4.2V

Discharge Cut-off Voltage: 2.75V

Internal Resistance: <80 mOhm

Cycle Performance: 85% of initial capacity at 300 cycles

Cycle life: > 300 cycles

Max. Charging current: 1C ma

Max. Discharging current 2.5C ma (for continuous discharge)
So resistence is approx. 4 times greater than K2 1250s or A123 1100s, charge rates are lower, expected cycle life is less and nonimal voltage is to high to be used without a regulator.

Charles
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Last edited by everydayflyer; Aug 27, 2008 at 08:06 AM.
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Old Aug 27, 2008, 10:02 AM
Southern Pride
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K2 1250 cells as receiver battery.

How much difference does the size,quality of the power leads and connector make?

These two cells with 16ga. leads from same 4S2P pack as ones tested yesterday. Included one discharge ofTraxxas battry and other K2 pack with normal receiver leads for comparison.

Note ,for these three discharge test A,5A,10A battery was charged on TP1010C @ 3A ,no balancing and charges took 21-23 minutes.


Charles
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Old Aug 27, 2008, 11:10 AM
wolf49
washington
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The real question is why not lipo? They are lighter and last longer
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Old Aug 27, 2008, 11:25 AM
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http://www.ritehobby.com/Li-Ion-Batteries

used on TOC 40% planes and also for powering ECU on gas turbine JETs
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Old Aug 27, 2008, 11:28 AM
Southern Pride
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Quote:
Originally Posted by wolf@ma
The real question is why not lipo? They are lighter and last longer
Simple . Two LiPoly cells have a nonimal charged voltagae of 8.3-8.4 volts nd without a regulator / diaodes etc. would fry many receivers and most servos.

I could provide links to post where very expensive aircraft have been lost due to LiPoly / BEC/ubec / smart redundent backup power systems failures.

That is exactly why I posted

Quote:
Those who feel more comfortable with a LiPoly and a voltage regulator / BEC / UBEC ,etc. should continue to do as they see fit.
Lighter? A 3 oz. receiver pack is not an issue in most .40 size and above aircraft, I guess you missed the fact that a 2S LiFe weifghs less than a 4S NiCD 700.
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Old Aug 27, 2008, 01:14 PM
CNC Cutter
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United States, IN, Indianapolis
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seems like this was Run Up the Ole Flag pole a while back

http://www.rcgroups.com/forums/showthread.php?t=321239

I'm revisiting my 3 paks of US18650S STG too see how they perform now.

My Duratrax ICE, set to Lion, doesnt want to re charge them to what they were.
i.e.
I got 800ma out of the 1st attempt at 700ma discharge rate over 4200 seconds.
They had been just on the shelf for a coupla years. not too bad.
But then it would not charge up more than 130ma before stopping the charge ???!!!

A second pak at 1A discharge yeilded 782ma.
I'm attempting ot charge it just now - we'll see

Looks like I may have to give up on these and bust up my 4S1p of
B&D VPX A123 1200's .
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Last edited by birdofplay; Aug 27, 2008 at 01:39 PM.
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Old Aug 27, 2008, 01:38 PM
Southern Pride
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Quote:
seems like this was Run Up the Ole Flag pole a while back
Where is there a reference in that thread using them for receiver packs?
Once again those cells have a higher voltage that LiFePO / A123 / K2 Energy Solution cells.

Charles
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Old Aug 27, 2008, 01:49 PM
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My post was not intended as an attack.
Just a lead in to how I am dealing with your proposal, given my stocks and resources.

As you can see in my edited post I'm agreeing and heading in the same direction.
Editing that was occurring before I read your post.

I guess I'll have tochoose my words more much carefully if I ever participate again.
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Old Aug 27, 2008, 02:00 PM
Southern Pride
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Haralson County GA. USA
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Not perceved as an attach just OT as this Thread clearly states using as receiver packs and your reference thread seems to be motor flight power useage.

IMO to many get to easily confused when Li cells of different voltages are intermixed in a Thread.

Charles
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Old Aug 27, 2008, 02:09 PM
Southern Pride
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Haralson County GA. USA
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Quote:
Originally Posted by hall woo
http://www.ritehobby.com/Li-Ion-Batteries

used on TOC 40% planes and also for powering ECU on gas turbine JETs
hall those are 3S LiIon packs which require a regulator. A123 2S packs do not require a regulator and IMO which is shared by many others is a much better ,simplier, more trouble free solution.

Charles
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Old Aug 27, 2008, 03:39 PM
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K2 has a 1400mah 18650 cell that might work better for this.

http://store.peakbattery.com/lithium...lfp18650e.html
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