A123 as receiver pack - no fly voltage?  
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A123 as receiver pack - no fly voltage? - 2/15/2007 10:54:07 PM   
ncrego



Posts: 469
Joined: 8/28/2002
From: Ankeny, IA, USA
Status: offline 		Hello, I'm thinking about replacing some Li-ions and regulators in one of my giant scale gas planes with a pair of the A123 2s packs. What I'm wondering is, what is the safe no fly voltage with these packs? Looking at the discharge graphs, they give little to no warning before they dump, and stay pretty constant through the entire discharge. With regular Li-Ions, my no fly is 7.1v under a 1a load, what would I use for the A123 cells?
       Post #: 1

RE: A123 as receiver pack - no fly voltage? - 2/15/2007 11:58:11 PM   
BocaBen


 

Posts: 157
Joined: 4/12/2002
From: Boca Raton, FL, USA
Status: offline 		I have the same question, but I'm not sure there's an answer yet.
This is in my view the key drawback to those packs when used for Rx.
I think that you have to monitor the number of mA that went in during the charge, and then cross your fingers that at least the same amount will be able to get out.

(in reply to ncrego)
       Post #: 2

RE: A123 as receiver pack - no fly voltage? - 2/16/2007 2:30:52 AM   
everydayflyer



Posts: 856
Joined: 8/21/2005
From: Buchanan, GA, USA
Status: offline 		Graph here clearly shows that @1A load and 3V per cell the end is near.

http://www.a123systems.com/html/a123racing/rcdevkitspecs.pdf

It also shows that there is little voltage difference for the complete discharge at this rate.

I would think anyone using these cells in such an aircraft would have a good idea of how long they can fly before using 2000 mAh capacity.
They can be charged / toped off quickly so my advise would be to time usage and top off when approbate.

Charles

(in reply to BocaBen)
       Post #: 3

RE: A123 as receiver pack - no fly voltage? - 2/20/2007 4:04:28 PM   
A123 Racing


 

Posts: 101
Joined: 8/25/2006
From: Hopkinton, MA, USA
Status: offline 		Hello NCR and Ben,

Charles is definitely pointing you in the right direction. The problem is that with such a light load the voltage difference during discharge is very very small. You can try 3.0V, even 3.1V or 3.2V could be helpful.

However my primary advice would be to utilize the fast charge capabilities and simply top it off before you take it out. If you only used 80% the last time you took it out it should only take 2-3 minutes to charge (at 10 amp charge).

Good Luck,

Brian


(in reply to everydayflyer)
       Post #: 4

RE: A123 as receiver pack - no fly voltage? - 2/22/2007 12:45:13 AM   
dick Hanson



Posts: 9741
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		My CellPro 123 recharges extremely quickly - I wired my packs using a 3 wire JR HD male end so I treat the pack exactly as I would any other pack such as a NIMH.
My external JR switch is used as a charge port - I mated a JR HD Female lead to the Cellpro pigtail
Now - I just carry a small 12v battery and the charger in a small plasic tool box -- then plug in charger to batt then charger to model -- in a few minutes -- beep beep beep . full of fuel ready to go
I don't know yet the full charge life for the model but inasmuch as recharge is sooooo simple n quick - it can happen while I refuel the gas tank.
Why pack around 4 hours of battery?
If your battery leads are capable of supplying current needed for YOUR setup - just go with one pack
two sets of leads can be soldered to the pack - then go thru two switches to allow greater amperage transfer.
I think-- one pack is plenty for up to a 40% model but definately two sets of leads and two switches. to keep up the flow .

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       Post #: 5

RE: A123 as receiver pack - no fly voltage? - 3/2/2007 7:13:06 PM   
ferincr


 

Posts: 25
Joined: 11/7/2004
From: san jose, COSTA RICA
Status: offline 		Hi everybody, I'm too thinking in adopting these cells as Rx pack.
In this case is a 90 size nitro heli.
My questions are (since I'm not 100% sure about my graphics understanding capabilities)...
If I'm not wrong the above graphic shows that at 1A discharge these cells keep a voltage above 2.5V toi the very end, am I correct there???
Does that mean that they would be safe to use them for the lenght of let's say 75% of the charge without triggering the F/S on the Rx?
I never used 6V pack before (only 4.8V 4300Mah NiMh) what would happen if your 6V pack goes down to 4.9V would the system keep working as it is a 4.8V pack???
I guess that with these cell it would be impossible to get them that far (according to the discharge curve) it seems like they go from being "alive to death" pretty fast.
The other question is do you need any type of reglator to plug this pack to the receiver or would it be ok to plug it straigh in to a PCM futaba Rx?
All my servos are rated for 6V (ecxept the rudder one for which I'll need a step down to 5.3V)
I'll appreciate any help you can give me to understand all this new technology since I'm really reluctanct to experiment with my model.
Thanks again,
Fernando

(in reply to ncrego)
       Post #: 6

RE: A123 as receiver pack - no fly voltage? - 3/3/2007 12:35:37 AM   
everydayflyer



Posts: 856
Joined: 8/21/2005
From: Buchanan, GA, USA
Status: offline 		Hi Fernando


Even at a 10A load the voltage stays at or above 3 volts per cell until after 2000 mAhs are consumed. A 5 cell Ni Cd / NiMH would have similiar voltage so there should be no need of a regulator.
Since the A123 do dump all at once I would try not to use more that 1600 or 1800 mAh between charges.

Charles

(in reply to ferincr)
       Post #: 7

RE: A123 as receiver pack - no fly voltage? - 3/5/2007 3:38:17 PM   
ferincr


 

Posts: 25
Joined: 11/7/2004
From: san jose, COSTA RICA
Status: offline 		Charles,
Thank you for your reply, that is good news I think it's time to dump the NiMh and move on with technology.
I wouldn't like to abuse of your kindness with somehow silly questions but do you have any estimates (timewise) of for how long can a 2300Mah be used with 5 digital servos, plus a governor (roughly)? I'm not sure if you are familiar with RC helis or just planes.
I understand that I need to think the current draw could be around 3Amps. that would make around 40min. (rough calc.) per pack, would that be the correct way to do this? Or should I estimate more load? I know in an heli the servos are a lot more active than in a plane, but I'm not sure how to calculate the top A draw. Is the specs on the servos info the max draw? Therefore should I add everyone up?
Since you are familiar with electric flight for sure you know better than me.
I'll apreciate any thoughts about this,
Fernando

(in reply to everydayflyer)
       Post #: 8

RE: A123 as receiver pack - no fly voltage? - 3/13/2007 2:32:27 PM   
dick Hanson



Posts: 9741
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		don't try to calculate this !
not enough info to get there
Instead - -get a Cellpro or a very accurate meter and read installed "fresh voltage " aprox 7.2 v
now fly the chopper on the ground for a minute . stop and read again -
likely the 2 cell pack will now read 6.6+volts -that is typically what I see on my packs loaded with rx/servos ON .
I am reading ,using a Whattmeter in series from pack to on/off rx switch
so---get some power on voltage numbers and some "power off" numbers before 1st -second -third flights and write down the exact voltage example: 6.45 - watch this drop each flight - the Cellpro will display 80% --70%-- 60% --etc., as well as voltage per pack and per cell so is very handy method as you can read /charge / test as you go and it is inexpensive .
At about 80% used up -I think mine read 3.2 per cell- (6.4)- so an accurate check is needed !
It isn't risky as it sounds - especially if you wire up for the Cellpro 123 - -I just read after each flight n charge if needed
charge is at 3 amps and full charge occurs when charge rate drops down to about .15 amp -so it is simply a larnin curve.




< Message edited by dick Hanson -- 3/13/2007 2:36:41 PM >

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       Post #: 9

RE: A123 as receiver pack - no fly voltage? - 3/18/2007 3:22:37 PM   
everydayflyer



Posts: 856
Joined: 8/21/2005
From: Buchanan, GA, USA
Status: offline 		If you know the average amp. load then you can calculate the available safe flying time.

It is safe to use 2000 mAh capacity from the 2300 mAh A123 battery so.

2000 mAh (2Ah) available . Now if th load is 3A average then 2/3=.66 of one hour or 39 min.
Years ago I flew a .50 size Heli with a 1000 mAh 4 cell Sub C Ni Cell battery and only recharged at the field if I flew for more than 40 minutes but I was not a 3D flyer..



Charles

(in reply to dick Hanson)
       Post #: 10

RE: A123 as receiver pack - no fly voltage? - 3/24/2007 12:16:50 AM   
Delta Mike


 

Posts: 123
Joined: 7/17/2002
From: Tulsa, OK, USA
Status: offline 		Dick, would these be safe to run using 2 of the 2300's seperate switches into the batt port and a aux channel,,Like I have always done with me Nicads?

Dennis

(in reply to dick Hanson)
       Post #: 11

RE: A123 as receiver pack - no fly voltage? - 4/1/2007 4:41:53 PM   
dick Hanson



Posts: 9741
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		Safe?
If all is in correct working order - It should be just fine -for even a 40% model

My 33% EDGE model with 8611A servos and a really strong engine can really suck th juice if I flog it
Up to 25 % of full charge on the single 2300 ma pack- so I just top it off when refueling and go fly.
One thing I found -- the "top off" is not always the same the max voltage may be off a little between cells I guess it varies as internal heat varies -I don't fret about it . same thing on Li Po's.
My42% model will get two packs on two switches just as it did on the previous 2700ma POS Expert cells -which had horrible impedance character and voltage went to hell as you cranked hard on all surfaces .
afte doing comparative checks on servos loaded /unloaded on 3 differet size gassers -- the 123 cells show higher voltage holding -under load- than ANY other cells I use . The 4300 Ma low impedance 5 cell packs were closest.
Now, I think I have a feel for how hard I can drive a single or dual pack -as a receiver pack.
Frankly I am now far more comfortable with these- than any of the other setups for RX. especially LiIons and regulators - those have always and remain at the bottom of my list .

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(in reply to Delta Mike)
       Post #: 12

RE: A123 as receiver pack - no fly voltage? - 5/20/2007 3:36:07 PM   
sergeflavigne


 

Posts: 70
Joined: 2/18/2003
From: Acworth, GA, USA
Status: offline 		Hello Dick,

I put A123 cells in all my planes, and I'm using the Cellpro charger. My question to you is: If I fly say my Bling with 7 HS 5645's for 15 Min. using two, 2 cell A123 packs with only using 7% of the charge in each packs, do you think I can safely fly with using one 2 cell pack and topping off after every flight?

(in reply to dick Hanson)
       Post #: 13

RE: A123 as receiver pack - no fly voltage? - 5/22/2007 9:34:17 PM   
sergeflavigne


 

Posts: 70
Joined: 2/18/2003
From: Acworth, GA, USA
Status: offline 		Dennis, Are you using regulators, or streight into the receiver?

Serge

(in reply to Delta Mike)
       Post #: 14

RE: A123 as receiver pack - no fly voltage? - 5/26/2007 1:38:51 PM   
dick Hanson



Posts: 9741
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		yes - be sure you understand what the CellPro is sayng - -you don't have to balance each time really but I would watch and find a number of flights which pull voltage down to say 3-1 - the recharge from lower voltage , appears -not positive yet but appears to exercize and allow cells to balance.
again -fer Chrissake forget "calculations" -
it is good to know the usable power output but the variety of servos and the loads from various setups can can change the calculated load by huge factors .
measure the loads and then record typical use . with this profile , you will have the best chance of not over running the batteries.

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I am watching you ----
Libby

(in reply to sergeflavigne)