You have made a nice pack in pics but basics are pt any number of cells in parallel and you get the same voltage but current adds up
you put cell in series the voltage adds up current remains the same
more current rating= longer flight time
so put cells in series x4
make 2 such sets
you can put both of them in parallel/ keep one on standby

try not to paste them but use a plastic mounts( you will easily get in radio shops) this will help you charge batteries on a simple charger and isolate batteries that have gone bad a single pack will not tell you health of an individual cell (if you dont have a balance charger) and above all idea is to get the plane home in one piece
There is a strange but actual condition where one of the cell due to aging discharges early and other cells drive it to reverse potential this phenomenon is typical to NiMH batteries in this case you will have almost immediate battery pack failure thats why i suggested you to use a plastic mount for your bank and charge cells individually you can secure the batteries in flight using thick rubber bands cut out from a used cycle tube
well hope this helps
Anup
If you donr want to keep changing batteries then put

Quote from: KALYANPRODHAN on March 20, 2011, 01:54:15 PM
Anwar, 5 NiMH = 5 x 1.2 = 6V, He told for 5 Cell in series.
But Max voltage of 5 Cell = 5 x 1.35 = 6.75 Volt.

You have to add 1 1N4007 in series to drop out the voltage about 6 volt.
And 4 cell also should work that give 4.8 volt.

Futaba is selling 5cell (6volt) Rx pack and they never mentioned about using VR, because Futaba Rx work on 4.8 and 6volt. Futaba also know about this nominal/peak voltage and their Rx made such way to works on 4cells and 5 cells Rx pack. I'm using A123 2S (6.6Volt) pack directly and many other people are using it too.

Adding IN4007 could be dangerous because this diode can handle maximum 1.0amp current which mean by adding this diode you're limiting maximum current flow up to 1.0 Amp, but four or five standard servos draw more than 1.0amp while they work together this much I know. I am not electronics engineer so I am not very sure about this,, I just have doubt about using IN4007 but Mr. Kalyan you can tell me if I'm wrong with your logic.

Datasheet of IN4007: http://pdf1.alldatasheet.com/datasheet-pdf/view/329387/CHENG-YI/IN4007.html

Quote from: lynxheli on March 21, 2011, 04:57:06 PM
try not to paste them but use a plastic mounts( you will easily get in radio shops) this will help you charge batteries on a simple charger and isolate batteries that have gone bad a single pack will not tell you health of an individual cell (if you dont have a balance charger) and above all idea is to get the plane home in one piece

Plastic battery holders are an absolute no-no, in my opinion. The contacts are prone to oxidation and will not be reliable.

Charging cells on an individual  basis is again a bit dicey as most "simple" chargers will not necessarily provide the same charging current for all cells. Most charge 2 cells in series, so 4 cells will charge via two separate circuits.

The balance port is not applicable to NiMh or NiCd batteries. If your pack is made up from cells of similar age and use, they will seldom discharge unevenly. And if any cell is bad, it would be safer to discard the others also.

If "above all idea is to get the plane home in one piece" then, most of the suggestions, however well meant, are ill advised.

Rajib

i am in total agreement. Use of a series 1N 4007 diode is both unnecessary and not recommended.

Even i was a bit worried regarding reverse flow due to aging of a few cells in series, but here the batteries are all brand new. And i have seen all battery packs(Nimh) are made in similar way, and they do last long.So, what the problem with these?.
I have used a nimh pack for more than three years in chordless phone(3 years back).

Regarding reverse flow to drive other faulty cells in series, i dont think the diode will have any action to prevent reverse flow.
If it helps, ill go for it. But im still doubtful.

As far as plastic holders are considered, i totally rely on soldering. A little accumulation of salts or faulty terminals may lead to disasters..

better go for NiCds.. in tx, problem reduced.

Quote from: sushil_anand on March 21, 2011, 06:07:45 PM
If "above all idea is to get the plane home in one piece" then, most of the suggestions, however well meant, are ill advised.

well oxidation one can easily see when charging batteries and replace the mount
as far as balance charger is concerned there are available for NiMh/Nicd also
and about reverse polarity well buddy it happens in the same set of cells only there is nothing identical in nature these cells are manufactured and frankly if something has to go wrong it will so its matter of choices and preferences
I am not trying to start a debate here but thought i'll clear my point

Cheap battery packs detoriates their performance for charge balance as balance chargers are not used. If you are making your own pack, Make terminals out for manually balancing with multimeter and charger.

As the prop is not driven by Battery, therefore, the maximum current consumption
(Rx+Servo) must not exceed 3A Max. Therefore, 600-800mAh Li cells (5+ C) can be safely used ( 600mAh, 5C = 3A, costs 30x2 = 60Rs. ) and much less in weight. But 2S will make 8.2 - 7.4 voltage and a small regulator is required. If you use the PCB of each cell, even balance charger is not required as it safeguards the cell from overcharge.

The advantage is less weight. And balance charging is possible which enhances the cell pack life.
Disadvantage is BEC required.
For simpler DIY BEC, you may search google with "Black Regulator".

Thanks

Why are we talking about "balance chargers" for NiMH  

If the cells are of the SAME type (same chemistry/manufacturer and same capacity), just string them up in series and charge them together, right ?

Quote from: lynxheli on March 22, 2011, 06:40:26 AM
1well oxidation one can easily see when charging batteries and replace the mount
2as far as balance charger is concerned there are available for NiMh/Nicd also
3and about reverse polarity well buddy it happens in the same set of cells only there is nothing identical in nature these cells are manufactured 4and frankly if something has to go wrong it will so its matter of choices and preferences
I am not trying to start a debate here but thought i'll clear my point

1. Even slight oxidation - that is NOT VISIBLE - can cause problems.
2. Not common, neither are packs with access to individual cells.
3. That  is in  theory but, in more than 25 years of RC flying, I have not yet come across this. May happen with really old cells. Have you actually experienced this? And I was referring  to "similar" - not identical - cells.  

And my point is that of being practical. A battery holder is MUCH MORE likely to cause problems than an "unbalanced" pack.

Cheap battery holders are very dangerous because they are made of very poor quality materials; they break easily and tend to oxidation easily. In fact they are not made for r/c application, Futaba has made battery holder for r/c application and it is not cheap at all because it is made of very good quality materials. I just know those companies though made these all r/c stuffs they have experts and while they have made such battery case for r/c application then it is okay to use, at least I am using it and I have never faced any problem yet. Not only me, even my ex NCC unit also prefer to use such battery case but only good one, not those cheap Rs.15/- battery holder available at local electronic store. So I think if we use right product for right application then it is much safer.

URL: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCUG8&P=7

Absolutely right, Rajib.

Though I would, personally, still opt for a "hard wired" pack for peace of mind.

sushil_anand, i agree with you on this, these chinese cells are highly unreliable.

I'll get some new NiMh cells and string them up in a 4s2p configuration.

Soldering them seems to be a 'safe' option to me, however charging these cells individually would be easier if i use cell holders instead.

Does anyone have a way to charge this pack without taking the cells out??
I still have the charger of the chinese 8.4V pack, can that be converted to charge the new 4.8V pack??

U can make your own tickle charger using a transformer and diodes. Like i have made one.
But make sure, after adding all the resistance(including the Internal resistance of the cells and transformer), the overall supply to cells should not exceed 1/10 C.

I took help from kalyan sir when i got confused, and i have successfully made charger for my Tx as well as Rx battery. however i keep a multimeter with me every-time to check faults if persists.

Again kalyan sir:  

Regards,
Abhay

Quote from: lynxheli on March 22, 2011, 06:40:26 AM
and about reverse polarity well buddy it happens in the same set of cells only there is nothing identical in nature these cells are manufactured and frankly if something has to go wrong it will so its matter of choices and preferences

http://cgi.ebay.in/Envie-1-2-Hr-LCD-Battery-Charger-AA-AAA-Ni-MH-Ni-Cd-/270724164920?pt=LH_DefaultDomain_203&hash=item3f086aed38#ht_7450wt_1022
this link says it all plz do research and rebuke

Quote from: abhay1290 on March 23, 2011, 12:38:52 AM
I took help from kalyan sir when i got confused, and i have successfully made charger for my Tx as well as Rx battery. however i keep a multimeter with me every-time to check faults if persists.

can you please mail me the details how you did it i will like to make my own charger
elaborate 1/10C plz
my mail ID is

Quote from: sushil_anand on March 22, 2011, 12:25:40 PM
3. That  is in  theory but, in more than 25 years of RC flying, I have not yet come across this. May happen with really old cells. Have you actually experienced this? And I was referring  to "similar" - not identical - cells. 

i agree but reverse polarity happens in higher voltage batteries No never happened to me but you are always worried about theory like oxidation etc when it comes to a flying object

Quote from: lynxheli on March 23, 2011, 01:06:31 AM
http://cgi.ebay.in/Envie-1-2-Hr-LCD-Battery-Charger-AA-AAA-Ni-MH-Ni-Cd-/270724164920?pt=LH_DefaultDomain_203&hash=item3f086aed38#ht_7450wt_1022
this link says it all plz do research and rebuke

What exactly does this prove or disprove

Quote from: lynxheli on March 23, 2011, 01:09:16 AM
elaborate 1/10C plz

"1"C charging means charging a (say) 2000mAH (which is 2AH) battery with a current of 2 amps. So "1/10"C charging means charging such a 2000mAH battery at 200milli-amps.

Similarly, "1/10"C charging of a 850mAH battery would mean charging it using a current of 85milliamps... and so on.

Charging at "1/10"C is the recommended charging rate for NiCH and NiMH cells, as this rate is very "comfortable" for these cell chemistries, and there is no risk of overheating or damaging these batteries, thereby prolonging their life.

Quote from: abhay1290 on March 23, 2011, 12:38:52 AM
U can make your own tickle charger using a transformer and diodes. Like i have made one.
But make sure, after adding all the resistance(including the Internal resistance of the cells and transformer), the overall supply to cells should not exceed 1/10 C.

Abhay please post a circuit diagram of your charger mentioning all the specs of the components you have used.

A little bit theory. The Li-ion cells have much less self discharge than a normal NiMH cell (Ecept Low discharge cells). Now, the cells though made of same batch, the active chemical (Liquide/Gel) concentration an the gland seal is not so proper. Moreover, during charching/discharging, the breathing of the cell is better to the cell near the periphery (As nearest to open air) and the insider cells are not so good and tthat creates the imbalance. But multiple charge/Discharge will increase the charge storage difference in the cell pack.

This makes the inter-cell terminal connection and/or terminals weak and creates overcharge/undercharge the strongest/weakest cell overcharge/deepdischarge (and further detoriates it's performance.

The same thing happens to Li cells also but not so much. But still for it's safety, balance chager/overcharge protection circuits are used for it's chance to explode.
Moreover, generally Li cells are not used to made cylindrical (Except a few Handycam cell of 2S pack) so that it can take care against gassing a/attention. Li cell voltage is 3+ times higher and need less ckt for balance charger.

This all sums up for balance charger for Li, and Ni based cells in series operation. But still, balance chargers can improve the performance or even manually balancing can prolong the life of batterypack.

Quote from: lynxheli on March 23, 2011, 01:17:55 AM
i agree but reverse polarity happens in higher voltage batteries No never happened to me but you are always worried about theory like oxidation etc when it comes to a flying object

Not quite sure of what you mean. Is the "you" referring to me? And, as for myself, I have seen problems due to oxidation/poor contact. That puts it beyond theory, at least for me.

Hello buddies, here is a free hand circuit dia for the tickle charger i use for my rx battery pack(4.8v 650mah)..

I connected a multimeter in series at the terminals of switch.when 3ohm resistor was not added.
current read near to 185mah.

After adding 3ohm resistor(1+2 ohm in series)
i got it near to 60mah.. which is nearly 0.95C.
I charge my battery for 8-10 hrs.

i used of 2 watts resistor for low heat emission.
1/2watts will do nice.


I need a feedback from kalyan sir, how can i get to know when the battery is fully charged? Or please suggest me to implement an indicator when battery is fully charged.
Im trying to add a LED for that but till now unsuccessful.

A 100 mAh transformer was sufficient, but i selected this transformer keeping in mind to charge upto 1800 mah NimH/Nicd in future.

The voltage stablization could be done through a zener diode as well, for further refining of circuit.

The cost of whole charging assembly including transformer was   43.

thanks alot Abhay...