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RE: Are 2 Batteries worth it? - 9/7/2012 3:47 AM   
acdii


 

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quote:

ORIGINAL: JohnBuckner


quote:

ORIGINAL: acdii
I replaced a 5 cell Nimh that would discharge rather quickly, especially if it sat in the back of the truck on a hot day fully charged the night before, and find it doesn't have enough for one flight.



Hi acdii if thats the case then that Nimh's capacity as well as that packs physical cell size was woefully undersized for the loads you were putting on it or it was in fact defective.

John


Im leaning towards defective. I will know on Tuesday when I check the pack, If it shows up as low, then I will know for sure.  A 2000mah pack should last a lot longer than this one did.



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RE: Are 2 Batteries worth it? - 9/7/2012 4:22 AM   
jester_s1


 

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Status: online 		FWIW Gray Beard, the cheap little 2-3 cell LiFe only chargers that Hobbico sells are a viable way to start using them without upgrading your primary charger. The old Triton can even do a discharge test on the LiFe batteries if you set the voltage limit right.

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RE: Are 2 Batteries worth it? - 9/7/2012 5:40 AM   
JohnBuckner



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quote:

ORIGINAL: acdii

Im leaning towards defective. I will know on Tuesday when I check the pack, If it shows up as low, then I will know for sure.  A 2000mah pack should last a lot longer than this one did.




May well be just a defective battery but another possibility yet that sometimes seems to happen to most of us and this is the battery did not receive a full charge for whatever reason. Lets suppose you have a 2000 and elected to keep using the average 50 to 70ma wall worts.

Yes they can be charged this way and many say just charge them longer. Well sure but how much longer and what if you fly frequently and it becomes very easy to reach the point that there are not enough hours in the day to fully charge before the next flight. Its very easy to buy a high capacity battery and never acheve anywhere near the rated capacity simply because of poor charging habits and methods.

Another senario is a momentary power outage at home in the middle of the night and if you are using a smart charger it does not come back on in charge mode. Its easy to miss something like this also and go to the field with only a partially charged battery.

John

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RE: Are 2 Batteries worth it? - 9/7/2012 1:08 PM   
aspeed


 

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Status: offline 		I find the NiMh are not as reliable as NiCd.  They self discharge over a short period of time when they get a bit older.  I would rather go to a 4 or 5 cell sub C pack or LiFe for a higher draw application.  For my smaller stuff (.45 and less) I just make up a bunch of dollar store battery packs and keep a few around if I fly more than 3 times.  Maybe that is just me though.  Some of the RC car guys charge the A123 batteries with just a charge cord and digital voltmeter.  It is all over in 15 minutes. 

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RE: Are 2 Batteries worth it? - 9/7/2012 8:02 PM   
acdii


 

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quote:

ORIGINAL: jester_s1

acdii- tTsting LiFe's with a loaded voltmeter is not reliable. Their discharge is so flat and their ability to keep voltage up under load is so good that you won't see much change at all until they are almost completely gone. It's much better to do some cycle testing and calculate an average mah used per flight and just do the math.




I took your advice and pulled the pack out last night. It is easy to put in and take out. I hooked it up to my charger and did a .5A discharge. After 20 minutes the voltage was down to 6.35 volts.  I flipped to charge at 1.9 A as spec'd on the pack and it took 20 minutes to fully charge. Didnt mark down the mah, but it was less than 300. 

I have a TT AC680 charger which does a pretty good job at cycling my Nimh packs, and charging the Lipo's.  I used it to cycle that 5cell nimh, and my venom packs, the mah on that one pack thats rated at 2000mah is more like 600mah.  It has been in my plane at a friend house and was charged 2 weeks ago, so will check it again on Tuesday when I am out there, and see if it has discharged, if it has, its pretty much a bad pack, and I will replace it with a different pack. 



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RE: Are 2 Batteries worth it? - 9/8/2012 4:02 AM   
acdii


 

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Status: offline 		I did some research, the charger discharges down to 4 volts for the 2 cell. Not good, the minimum discharge is 2.5 volts, so 5 should be the lowest.  So I sat back and watched it discharge at 1 amp. It took 75 minutes to burn up 1200mah and the pack was still at 6.17 volts. I stopped it at that point and just recharged it.  Quite satisfied with the results, I should get at least 2 hours of flight time out of this pack before recharging. 


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RE: Are 2 Batteries worth it? - 9/29/2012 1:29 PM   
ronwc



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ORIGINAL: ronwc

I have a couple of those GP Cherokee's I fly, they are really good flying planes and fun with the flaps. The 600 mah was fine years ago when we all ran 4 servos, back in the 60's and 70 we used to run 400mah Gates packs which were really bad, but best we had in the day. Nowdays with 2.4 radios and more servos, get the most mah you can for the money - nimh packs are cheap - this 2300mah 5 cell one under $10 with shipping - http://www.ebay.com/itm/6V-2300mAh-Ni-MH-AA-Rechargerable-Receiver-Battery-Pack-/370530538202?pt=Radio_Control_Parts_Accessories&hash=item56455752da


I ordered some of the cheap batteries off ebay from two different places (one mentioned above), and they turned out to be junk. Both claimed well over 2000mah, and neither got over 800mah in actual testing (Accu-cycle Elite). However, I did find the place to get great battery packs, all-batteries off ebay - http://www.ebay.com/itm/140853483130?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 - these were rated at 2200mah and actually came out to 2260mah, over rated capacity - and the 5 cell packs were $8 each - highly recommend this company.


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RE: Are 2 Batteries worth it? - 9/29/2012 3:11 PM   
bogbeagle


 

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Status: offline 		Years ago, we used to fly all day with a 500 mAh pack ... .40 -sized models, with 4 standard servos.

Nowadays, I generally use two AAA packs (800 mAh is the smallest I can get). I rig these in parallel. Each pack has a diode on its output, such that, if one pack fails, the other pack is not affected. Been using this system for about 20 years, now. Usually, each pack has a separate switch ... but sometimes I feed them both into a Y-lead and then through a single switch. On smaller models, a single 5-cell pack of 800 mAh is plenty, imo.

There is a voltage drop across the diodes, of about .7 Volts. So, a 6V pack has a nominal output voltage of about 5.3V.

In that time, I have ONCE experienced a pack failure. On that occasion, one cell failed completely. The battery system worked fine and the model was not lost. So, in my opinion, a dual-battery system is worth the hassle and complexity. I reckon that the loss of that one aeroplane would have cost me about £700... probably 10 times as much as I ever spent on extra batteries. Then, there is the labour involved in building a decent model.

Anyway, recharging at the field is pretty easy, nowadays.

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RE: Are 2 Batteries worth it? - 9/29/2012 7:30 PM   
Gray Beard


 

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Status: online 		I have made up a couple packs with Eneloops and love them. Charge them today and fly with a full powered pack next month without having to recharge. I pick them up at the camera store. Sometimes they are on sale and I can get them for a good price.

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RE: Are 2 Batteries worth it? - 9/29/2012 8:28 PM   
bogbeagle


 

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Status: offline 		Same here. Eneloops are now the only cells that I buy.

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