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Old Nov 07, 2004, 06:42 AM
Just "PLANE" crazy
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what voltage to charge different bats at??

at what voltage do I charge my KAN 250 6cell pack at??
I know abt the c*1 for the amps but what about the voltage?
Is ther any mathical formula to follow??
Thanks
Ashwin
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Old Nov 07, 2004, 08:00 AM
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6 X 1.2 = 7.4 volts
The voltage will go higher than that while charging
Milton
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Old Nov 07, 2004, 08:48 AM
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How high?I know the voltage is supposed to be higer but how high? any formula?
Thanks
Ashwin
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Old Nov 07, 2004, 08:54 AM
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That will very from charger to charger, you set the voltage at 7.4 and let the charger do the work
Also you might have to set the amp rate
What charger are you charging with.
Milton
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Old Nov 07, 2004, 08:58 AM
Just "PLANE" crazy
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I rite now dont have a charger...
Trying to make one as my buget for the year is over...I have a Ac-DC transformer and i wanted to know what voltage to set up to charge them...
-Ashwin
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Old Nov 07, 2004, 09:05 AM
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The voltage isnt too critical, its the current you need to take care of........However, as a rule of thumb, take the number of cells n and multiply by 1.6 and add 2.

So for an 8 cell pack 8*1.6=12.8 + 2 comes out at 14.8v.
Your current needs to be limited to the C rate of the pack, which in your case is 250mA........so you need a constant current source capable of charging at 250ma with an output voltage in the region of 12 volts......and as KAN's are nimh chemistry you should not charge them for more than around 10 hours...any further charge put into the pack is released as heat......not good.
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Old Nov 07, 2004, 09:11 AM
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Well if you do that be carefull and don,t leave the battery or you will cook it.
Most charger have a peak cut off that will cut the charger off when the battery has reached it 's peak.
also the volts are one thing but the amps are another, How many amps you are charging will decide how long it will take to charge and if you charge at to high amp rate you could distroy tha battery.
Milton
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Old Nov 07, 2004, 09:16 AM
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Ok thanks! But then why is the the wal-mart type of charger the my old rtf came with only 9V when the batts where 8.4v??
And the mah part bit i understand!
so I can charge these bats at 9v 250mah??

thanks!
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Old Nov 07, 2004, 09:21 AM
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Look for the output on the charger and see what the mAh output is
Milton
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Old Nov 07, 2004, 09:23 AM
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That is 380 mah
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Old Nov 07, 2004, 09:24 AM
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Use of your wall wart thing depends on the battery chemistry of the pack for your rtf.......
Nimh cells have a finite charge time strictly based on their capacity, whereas nicd's can be fast charged and then allowed to trickle charge( at a greatly reduced rate I might add! ) this is why we use peak detecting chargers.......they detect the peak at some point in the charge cycle which then terminates the charge.......

If you must use your wallwart then firstly you need to determine what the voltage is across the wires.......it needs to be around the 9v mark, then you need to find out at what rate it charges, anything below 250ma will be safe.....obviously if this is lower than the 250 then its going to take longer to charge the pack, but you will need to determine how much time is needed......
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Old Nov 07, 2004, 09:27 AM
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ha missed that bit........380mah you say..........hmmm thats like 50% more............
I'd be inclined to say no, dont charge with it....you will reduce the longevity of the pack.........
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Old Nov 07, 2004, 09:28 AM
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How do you determine how much time it will take to charge??
And the rtf's batts were nihm...
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Old Nov 07, 2004, 09:30 AM
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No I wont use the 9v 380mah...I was thinking of using a 9V 100mah.. so how long will it take to charge the bats??
-ashwin
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Old Nov 07, 2004, 09:37 AM
Willis ISD 1937 SchoolBus
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Back in my early rc car days, I put a thermometer on the pack and charged till warm. I dont remember the tempature.

I would say it would take 2 1/2 hours if you use that wall wart
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Last edited by WillisTx; Nov 07, 2004 at 09:39 AM.
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