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Ni Cd Charging

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tom_pay

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Hi

I have spent the morning 'renovating' an old RC car for a friend, nothing too fancy just better wiring ect. Once I had finished all of that I had to charge the battery pack to see if it was going any better. However, I found that the charger was no good, long burnt out!!

My question is:

How do I charge Ni Cds?

The pack that I am using is 5 AA NiCds in parallel giving 6v @ 900mAh. Can I just give it a constant current (say 0.5C) at a certain voltage for a while, or is it more complicated than this.

Thanks

Tom
 
Ok,

So I should charge it at 90mA for 16 hours.

But what voltage do I do this at? The website says that a charged cell is 1.41V so 7.05V ?

Thanks

Tom
 
So I should charge it at 90mA for 16 hours.
If the battery is not completely dead then it will be overcharging. It will get fairly warm but will not be damaged.

But what voltage do I do this at? The website says that a charged cell is 1.41V so 7.05V?
The voltage must be high enough for some cells that charge to 1.5V each so I would use 7.5V to 9V.
The battery limits its own voltage and the current regulator drops the excessive voltage and limits the current.
 
So a circuit like this..

The pot would be a high value and be used to adjust the current output.

Tom
 

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That circuit will not work. Probably just burn out transistor.

The easiest way is to start with a higher voltage and put a series resistor to emulate a current source.

Full charge, each cell will reach close to 1.5 vdc. At rest they will drop to about 1.3 vdc. If you have 5 in series you have about 7.3 vdc at top of charge.

With a 15 vdc source, place a (15-7.3)/0.09 = 86 ohm resistor in series. Resistor power dissipation is 0.7 watts so needs to be 1 watt resistor. 100 ohm would be fine.

With a 12vdc source use a 50 ohm 1 watt resistor.
 
You charge NiCads (&NiMHs) with Constant-Current; not constant voltage. The battery voltage will rise as the battery charges. Do not try to clamp the voltage. When using the LM317, start with a voltage that is > n*1.45 + 3V, where n is the number of cells.

The **broken link removed** shows a simple Constant-Current source which is ideal for charging NiCads. If you are forgetful, use a timer to terminate the charging cycle after 14-16Hours. One of the 1hr/24hrs type of clock timers is ideal for this. Turn the dial so the timer clicks off 14 hr hence, and thereafter it will charge the battery for 1hr on/23hr off untill you get back to it. An ideal way of keeping NiCads/NiMhs ready to go.
 
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Hi

If I give them a constant current, the voltage across the pack will sort itself out.

I have attached a circuit, now it uses a LM317 instead of a 117, just because I have a 317.

Will this be a good circuit, I will control the time by using a power point timer, attached to my power supply.

Thanks

Tom
 

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I bought 4 Energizer 2500mAh AA Ni-MH cells that came with a cheap charger.
The charger is simply a timer that provides 500mA for 7 hours.

But the charger is stupid, it does not detect that the cells are fully charged:
1) If the 2500mAh cells are not fully discharged then it doesn't know and severely over-charges them.
2) If the power fails for a moment while charging then the timer starts again and severely over-charges the cells.
3) Low capacity Ni-Cad cells are not detected to be fully charged and are severely over-charged.
 
So if I wanted to use the charger I posted, I would have to make sure that the pack it discharged before re charging them.

Can over discharge harm the Ni Cds like the Li Po batteries.
 
If a series number of Ni-Cad or Ni-MH cells are discharged then the weakest cell goes to 0V first. If the discharge of the cells continues then the discharged cell becomes charged backwards by the remaining cells which is very bad for it.
Therefore, a battery of cells is considered to be fully discharged when the average voltage per cell is 0.9V or 1.0V.
 
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I bought 4 Energizer 2500mAh AA Ni-MH cells that came with a cheap charger.
The charger is simply a timer that provides 500mA for 7 hours.

But the charger is stupid, it does not detect that the cells are fully charged:
1) If the 2500mAh cells are not fully discharged then it doesn't know and severely over-charges them.
2) If the power fails for a moment while charging then the timer starts again and severely over-charges the cells.
3) Low capacity Ni-Cad cells are not detected to be fully charged and are severely over-charged.
Last year I bought 4 VIPOW batteries that were very good batteries with a high capacity of 2700mah. However as like ordinary NiMh batteries, it loses its charge if we kept idle for prolonged period. When we need it, it'll be dead. My charger require 20+ hours to recharge them at 150ma rate.

So last month I bought a pack of 8 limited edition Sanyo eneloop tones. They're simply cute and a fun to play around.. :). I'm searching for a good charger to use with them. If you know any then let me know.

Watch this video to find how beautiful they are. Nice music too:
YouTube - Sanyo Eneloop Tones - Limited Edition - Open box video
 
So if I wanted to use the charger I posted, I would have to make sure that the pack it discharged before re charging them.

Can over discharge harm the Ni Cds like the Li Po batteries.

Did you read the link I gave you to Powerstream? If you had you wouldn't be asking these questions.

Your 317 circuit charges at a rate of 89mA (1.25/14), which will not harm NICads even if left on for hours beyond full charge. It will take a long time to recharge 2400mAh cells, however.
 
Energizer make alkaline battery cells in the USA. Their AA Ni-MH cells are printed, "Made in Japan for for Energizer".
Their new Ni-MH cells have the same reduction in capacity as Sanyo Enloop and have the same advertising that a charge lasts almost for one year. Are they made by Sanyo?
 
Energizer make alkaline battery cells in the USA. Their AA Ni-MH cells are printed, "Made in Japan for for Energizer".
Their new Ni-MH cells have the same reduction in capacity as Sanyo Enloop and have the same advertising that a charge lasts almost for one year. Are they made by Sanyo?

I think so after reading this thread about rechargeable cells:
**broken link removed**
Are Duraloops and Eneloops the same thing?

Look at this quote. First time I'm hearing about 'duraloops' from Duracell and seems like all those battery giants have some sort of tie up like get the naked batteries and rewrapping for brandnames umm..:)
Just a side note, the current Energizer 2300 mah AA NIMH are made by Sanyo in Japan.:
 
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