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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> When and how
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When and how - 4/14/2003 6:43:04 PM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Gidday fellow fliers, I have a JR 631 Tx with a 9.6 v 600 mAh ni cad pack and the Rx has a 4.8 v 600 mAh pack. The charger is the standard wall type, Tx DC11.6v 50mA and the Rx Dc5.8v 120mA ( I'm just writing down whats written on em ). I've had the system for about 6 months, flying most weekends. When I get home I charge them for about 16 hours and again the night before flying. My questions are when should I cycle these batteries and how could I do it? Is it ok to leave the Rx and Tx on overnight to discharge em? What voltage should the Tx battery indicator read when it's discharged enough to cycle? Any input would be appreciated. Thanks, regards John.
       Post #: 1

No takers - 4/16/2003 8:49:46 AM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Gidday again, I see there have been no takers on answering my questions. Perhaps they are not clear enough. I've looked for past threads that would explain em, but I've had no luck. Please help.

(in reply to john flynn)
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How and when - 4/16/2003 12:01:37 PM   
elderair



Posts: 317
Joined: 1/16/2002
From: Plattsburg, MO, USA
Status: offline 		Hello John. Since no one else has answered your question I'll tell you what I have done in the past. I have been into R/C for about seventeen years and always remove the tx battery to cycle it. This not only prevents unnecessary heat build up of the RF module if you were to leave it on over night, but also allows you to sense peak charge without going through the built in reverse current circiutry in the tx. Also with the Rx pack there is very little drain on the system without working the servos. I only cycle my packs every six months to test their condition based on minutes to discharge a fully charged pack to a predetermined safe voltage with a comercially available cycler of your liking. I have used Hobbico accucyler in the past but have not heard too many words of praise about their accuracy from the factory. I have recently switch to Powerflite Lion packs in my transmitter and all receiver packs. No more cycling! No more 16 hour charge times. Go fly all day and then charge at home or in the field for a couple hours with their smart charger and you are ready for another day of fun. Also my voltage doesn't drop sitting around week to week like my nicads used to do. Figure on spending about $100.00 to convert your Tx. pack and then another $180.00 for a four port smart charger. I like them though. My two cents worth.

A great source of cycling information can be found on the Radical R/C web site. [url]www.radicalrc.com[/url] Kent.

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When and how - 4/16/2003 1:21:57 PM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Thanks for your reply Elderair, the smart charger and batteries you mentioned sounds like the go. I guess with the value of the Aussie dollar I'll be paying around $340 for the charger. I'll have to start saving. It's not a poor mans sport is it? Just another question, would a multi-meter be ok to test the voltages of batteries and there condition. Thanks again for your info.

(in reply to john flynn)
       Post #: 4

When and how - 4/16/2003 4:14:15 PM   
Ross Kean



Posts: 686
Joined: 6/4/2002
From: Fredericton, NB, CANADA
Status: offline 		A multimeter will give you some idea about the extent of charge but make sure you take any measurements with a load on the system. A 20 ohm resistor across the meter leads will place a ~250mA load on the battery and this will provide a much more accurate assessment of capacity. Be careful, because of the discharge curve shape, there may not be a big voltage difference between 80% capacity and 20% capacity!! Know your batteries and after a couple of flights, make sure you check them for every flight - err on the side of caution.

Ross

(in reply to john flynn)
       Post #: 5

When and how - 4/16/2003 8:11:53 PM   
foxx


 

Posts: 594
Joined: 10/28/2002
From: Somewhere in the west, USA
Status: offline 		John most experts say you need to cycle your batteries twice a year. NiCds have very strange discharge curve, that is a steep initial drop in voltage then constant for a long period (1.2 V) then another steep drop to 1.1 V. There are a lot of inexpensive cycler in the market now that you don't have do it manually. Interesting to know that a large group of experts believe NiCd memory is a myth and there is no need to cycle. Here is a link that would answer all your questions.

http://www.rcbatteryclinic.com

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One of the senior members

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When and how - 4/16/2003 8:21:48 PM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Thanks Foxx, lots of handy info on that sight.

(in reply to john flynn)
       Post #: 7

When and how - 4/26/2003 5:24:06 PM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Gidday again fellas,
well I got myself a multi-meter (I could'nt afford the smart charger, Elderair) and a 22 ohm resistor ( they did'nt have 20 ohm, but my new multi-meter say's it's a 19) I plugged the resistor into the Rx pack, it read 5.21 volts. I left it that way and watched the voltage slowly drop. I see what Foxx and Ross were saying about the discharge curve. It dropped at a fair rate at the start until about 4.9 then slowed way up until 4.5. I left it until 4.4. It took about 40 minutes. It's now on the charger. When it's fully charged, can it be then considered cycled? What load would the 22 ohm resistor have put on the pack? and what load does a standard servo pull under operating conditions? Is it ok for me to take out my Tx pack and cycle it in same way? One more question how low should I discharge the Tx pack? 8.8? Thanks for your help. Regards, John

(in reply to john flynn)
       Post #: 8

When and how - 4/26/2003 5:40:06 PM   
Ross Kean



Posts: 686
Joined: 6/4/2002
From: Fredericton, NB, CANADA
Status: offline 		V = I * R where V is the voltage of the pack, I is the current draw and R is the resistance. If you rearrange the equation you get
I=V/R

If we assume a nominal 5 V for the pack (a little high) we would get a current draw of 263 mA with a 19 ohm resistor and 227 mA with a 22 ohm resistor. Not a big difference.

The higher the resistance, the lower the current draw.

Now, if we assume an average voltage during the test of 4.7V (probably a good guess) and exactly 40 minutes to draw the pack down, this will give you a rough estimate of the pack's capacity:

Average current would be 4.7V/19ohm= .247 A or 247 mA
this is 247 mA * 0.66 hr = 163 mA.hr. Not much capacity for a Rx pack if you started out with it fully charged!. You might extend the test to 1.0 or 0.9 V per cell for the discharge. Make sure it is fully charged when you begin if you are planning to test the pack's capacity.

Have fun

Ross

(in reply to john flynn)
       Post #: 9

When and how - 4/27/2003 8:54:57 AM   
john flynn



Posts: 217
Joined: 10/22/2002
From: CardwellQueensland , AUSTRALIA
Status: offline 		Righto Foxx, the Rx pack has been on the Wall Wart for 18 hours and the Multi-meter reads 5.62 v or 5.38v under load with the 22 ohm resistor. Is this the norm and is the pack now considered cycled? Thanks for your help. Regards, John.

(in reply to john flynn)
       Post #: 10

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