Charging Ni-MH
06-26-2003, 04:57 AM
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Charging Ni-MH
Hi,
I was wondering how are you supposed to charge a 4 or 5 cell Ni-MH properly. I have a 1450 4 cell and a 1500 5 cell. Would it be easier to use a wall charger for a day or am I better off purchasing a Ni-MH charger? Also, do I need to worry about discharging??? Any help would be much appreciated.
Brad
I was wondering how are you supposed to charge a 4 or 5 cell Ni-MH properly. I have a 1450 4 cell and a 1500 5 cell. Would it be easier to use a wall charger for a day or am I better off purchasing a Ni-MH charger? Also, do I need to worry about discharging??? Any help would be much appreciated.
Brad
06-26-2003, 05:42 AM
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Charging Ni-MH
If they are new packs, you will want to cycle them a few times at the C/10 rate to stabilize them. If the wall wart is 50mah then it will take a WHILE to bring them up. I use this formula (we'll use your 1450mah battery):
1450x1.4=2030mah (you do this because the battery doesn't take all of the current supplied to it)
now 2030mah/50mah=40.6 hours... a long time.
This is the first charge for a new pack, obviously if you don't drain the pack then it will be shorter. You're better off getting a charger/cycler that handles NiMH's, but you can do it with the wall wart too, I have. As far as cycling, you don't "have" to, but it is recommended occasionally as to keep watch on the life of the pack. Hope this helps.
IronZ
1450x1.4=2030mah (you do this because the battery doesn't take all of the current supplied to it)
now 2030mah/50mah=40.6 hours... a long time.
This is the first charge for a new pack, obviously if you don't drain the pack then it will be shorter. You're better off getting a charger/cycler that handles NiMH's, but you can do it with the wall wart too, I have. As far as cycling, you don't "have" to, but it is recommended occasionally as to keep watch on the life of the pack. Hope this helps.
IronZ
06-26-2003, 03:03 PM
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Charging Ni-MH
Also, I have read that if the charge rate is to low, the pack will never reach full charge. I believe it was said if the charge rate is less then C/40, this will happen.
If that is correct, a 50mA charger will never fully charge anything larger than a 2000mAh pack.
If that is correct, a 50mA charger will never fully charge anything larger than a 2000mAh pack.
06-26-2003, 04:03 PM
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Charging Ni-MH
And don't forget about the inefficiency of the charger.. and that NimH has a higher self-dishcharge rate than NiCd. If I recall correctly, it's around 3% per day.
As the pack approaches a full charge, the charging capabilities of a standard wallwart become even more inefficient. Try hooking an ammeter to the circuit while trying to charge a 2400mAh pack with a 50mAh wallwart... Then run it through a cycler to see how much charge it actually took.
As I said earlier, I don't remember the exact cut-off charge rate, but I think it was C/40 or C/50. Remember, a wallwart isn't a true "constant current source".
As the pack approaches a full charge, the charging capabilities of a standard wallwart become even more inefficient. Try hooking an ammeter to the circuit while trying to charge a 2400mAh pack with a 50mAh wallwart... Then run it through a cycler to see how much charge it actually took.
As I said earlier, I don't remember the exact cut-off charge rate, but I think it was C/40 or C/50. Remember, a wallwart isn't a true "constant current source".
06-26-2003, 07:23 PM
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Charging Ni-MH
BDFlyinHigh,
If these packs are going to be used in electric planes then I would suggest getting the correct charger. Last year I got a Durtrax intelliPeak AC/DC charger that can charge and discharge both NiCad and Nimh batteries my only regret is that I didn't get one that could handle Lion batteries.
When fast charging these packs general rule is don't exceed 2C where C is the Capacity of the pack expressed in milliamps
formula to calculte charge rate in Amps for a 300Mah pack is
2 * 300 = 600 That gives C
Now Divide 1000 Mah = 1 Amp
So charger should be set at 0.6 Amps
If these packs are going to be used in electric planes then I would suggest getting the correct charger. Last year I got a Durtrax intelliPeak AC/DC charger that can charge and discharge both NiCad and Nimh batteries my only regret is that I didn't get one that could handle Lion batteries.
When fast charging these packs general rule is don't exceed 2C where C is the Capacity of the pack expressed in milliamps
formula to calculte charge rate in Amps for a 300Mah pack is
2 * 300 = 600 That gives C
Now Divide 1000 Mah = 1 Amp
So charger should be set at 0.6 Amps
06-26-2003, 09:50 PM
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Charging Ni-MH
===
I was wondering how are you supposed to charge a 4 or 5 cell Ni-MH properly. I have a 1450 4 cell and a 1500 5 cell. Would it be easier to use a wall charger for a day or am I better off purchasing a Ni-MH charger? Also, do I need to worry about discharging??? Any help would be much appreciated.
===
For brand new packs of any size it is suggested that the packs be 'slow charged' at a rate that is one tenth their capacity, for about 16 hours or so. In your case the 1450 mah cells would be charged at 145 milliamps for about 16 hours and the 1500 mah cells would be charged at 150 milliamps for about 16 hours. That should bring all cells within each pack up to full or near full capacity using a charge that will not harm the cells that reach full capacity first. Hopefully ALL the cells will reach full capacity on this first charge. They can be described as 'fully charged' and also 'balanced'.
After that the charge can be a 'fast charge' suggested at a rate of '1C'. For the 1450 mah cells this would be 1.450 amps for about 1 hour and for the 1500 mah cells this would be 1.500 amps for about an hour. When you perform fast charges it is wise to use a charger that is 'smart' enough to know when to change back to a 'slow charge' so that excessive heating does not take place in any pack after 'full charge' is reached.
Some suggest that a rate of 1.5C is safe if a proper cutoff sensing circuit is used. These rates would be:
1450 x 1.5 = 2.175 amps for about 45 minutes
1500 x 1.5 = 2.250 amps for about 45 minutes
And some people suggest with proper cutoff sensing circuits you can go to 2C which would work out to:
1450 x 2 = 2.900 amps for about 30 minutes
1500 x 2 = 3.000 amps for about 30 minutes
One benefit of using an intelligent charger is that you can just plug it in and trust it will put in just the right amount of charge needed by the cells and then adjust to a charge that will not harm the cells.
Discharging would always be recommended from time to time to determine if the packs are still providing acceptable discharge times (also, and this is very important, this gives you confidence the charger is performing correctly).
Also, 'slow' charges are suggested from time to time so that each cell is allowed to reach full capacity. At the 'slow charge' rate any cell that reached full capacity before another cell will not be harmed. This 'balancing' of cells could be of interest maybe once every month if the cells are actively used.
I think this points out that for hassle free battery management it would be prudent to obtain a quality charger/discharger made for the types of cells that are in use. This is especially true when they are used in aircraft.
I was wondering how are you supposed to charge a 4 or 5 cell Ni-MH properly. I have a 1450 4 cell and a 1500 5 cell. Would it be easier to use a wall charger for a day or am I better off purchasing a Ni-MH charger? Also, do I need to worry about discharging??? Any help would be much appreciated.
===
For brand new packs of any size it is suggested that the packs be 'slow charged' at a rate that is one tenth their capacity, for about 16 hours or so. In your case the 1450 mah cells would be charged at 145 milliamps for about 16 hours and the 1500 mah cells would be charged at 150 milliamps for about 16 hours. That should bring all cells within each pack up to full or near full capacity using a charge that will not harm the cells that reach full capacity first. Hopefully ALL the cells will reach full capacity on this first charge. They can be described as 'fully charged' and also 'balanced'.
After that the charge can be a 'fast charge' suggested at a rate of '1C'. For the 1450 mah cells this would be 1.450 amps for about 1 hour and for the 1500 mah cells this would be 1.500 amps for about an hour. When you perform fast charges it is wise to use a charger that is 'smart' enough to know when to change back to a 'slow charge' so that excessive heating does not take place in any pack after 'full charge' is reached.
Some suggest that a rate of 1.5C is safe if a proper cutoff sensing circuit is used. These rates would be:
1450 x 1.5 = 2.175 amps for about 45 minutes
1500 x 1.5 = 2.250 amps for about 45 minutes
And some people suggest with proper cutoff sensing circuits you can go to 2C which would work out to:
1450 x 2 = 2.900 amps for about 30 minutes
1500 x 2 = 3.000 amps for about 30 minutes
One benefit of using an intelligent charger is that you can just plug it in and trust it will put in just the right amount of charge needed by the cells and then adjust to a charge that will not harm the cells.
Discharging would always be recommended from time to time to determine if the packs are still providing acceptable discharge times (also, and this is very important, this gives you confidence the charger is performing correctly).
Also, 'slow' charges are suggested from time to time so that each cell is allowed to reach full capacity. At the 'slow charge' rate any cell that reached full capacity before another cell will not be harmed. This 'balancing' of cells could be of interest maybe once every month if the cells are actively used.
I think this points out that for hassle free battery management it would be prudent to obtain a quality charger/discharger made for the types of cells that are in use. This is especially true when they are used in aircraft.
