# Charging rate on NiMH batteries.



## Pure (Jan 14, 2010)

So I finally got around to buying a decent battery charger, the Maha C-9000.  

On the instructions, it states to charge above .3C and but below 1.0C, C being total capacity.  I assume this means if you have lets say 2500mAh batteries to charge them at a rate above 750mAh and below a rate of 2500mAh.  Is this correct?  

However, I've heard of the .1C rule, meaning charge at a rate of 1/10 the battery's capacity.  

Also when discharging, what is the proper rate?  I can't seem to find any hard answers for this stuff.


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## Phranquey (Jan 14, 2010)

Pure said:


> I assume this means if you have lets say 2500mAh batteries to charge them at a rate above 750mAh and below a rate of 2700mAh. Is this correct?
> 
> However, I've heard of the .1C rule, meaning charge at a rate of 1/10 the battery's capacity.
> 
> Also when discharging, what is the proper rate? I can't seem to find any hard answers for this stuff.


 
You are correct on your proportions, except 1C is 2500 mAh....the capacity of your cell (unless you have 2700's & you typo'd).

You can disregard a portion of those instructions... down to .3C. If you are doing a normal, everyday charge, .3C to .5C (two to three hours) is a good place to be. If you are in a hurry, I would recommend going no higher than 1C (1 hour), and if you want to do a conditioning (top off, full discharge, and then recharge) I would do it at .1C. It will take a log time for conditioning at .1C, but I recommend doing that roughly every 20 to 30 charge cycles.


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## Pure (Jan 14, 2010)

I was using 2500mAh as a nice average number.  The cells I have are 2700mAh.

I have them charging at 500mAh for a charge/discharge/charge cycle so I can measure their capacity.  

So a fair charge rate could be anywhere from 500 to 900mAh?  Basically I want a nice middle ground thats not too slow that its a pain, but not too fast that it'll kill my batteries.  .3C of my 2700mAh is just over 800mAh.  800mAh would be about a 3.5hr charge.


Discharge rate anybody?


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## Derrel (Jan 14, 2010)

You know, my wife and I bought some rather slow 13-hour chargers a number of years ago, and those doggone things were used with some early Radio Shack brand NiCad and NiMh batteries, with the original sets of batteries lasting almost 10 years!!!! Literally, ten full years, with hundreds and hundreds of charge/discharge cycles, but a long, slow 13 hour typical charge time, and they were used mostly in Sony Discman CD players and various small cassette tape players for daily audio books on cassette tapes. Simply incredible duty cycles on 1200 then later 1600 and 1700 milliampere hour Radio Shack batteries.

Later, as we moved into 7 hour chargers, we noticed a sharp and pronounced decrease in battery duty cycle (meaning shorter overall lifespan), even with batteries that had significantly higher capacity numbers, like 2000 then 2200 then 2400 and 2500 milliampere-hour ratings.

So, I guess slow and steady wins the race...


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## Phranquey (Jan 14, 2010)

Pure said:


> I was using 2500mAh as a nice average number. The cells I have are 2700mAh.
> 
> I have them charging at 500mAh for a charge/discharge/charge cycle so I can measure their capacity.
> 
> ...


 
You'll be _very_ safe at 500 to 800mAh charge rate. You can go to 1300mAh (.5C) for normal charging and not worry about doing too much. When you start generating a lot of heat above 1C is when you really start doing damage. 

The "15 minute" chargers are what make me cringe...those are charging at 4C !! So, for a 2500mAh AA cell, you are cramming 10,000mAh (10 AMPS !!) into that little cell. Most portable car battery chargers run at 6 Amps.... think about that one.


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## Garbz (Jan 15, 2010)

Charging time is inversely proportional to the battery life. 

Charge at the rate you need to but no more. If you got home, throw your batteries in overnight at the slowest rate. If you're out in the middle of a gig toss them on a quick charger. Batteries cost next to nothing compared to the rest of your camera gear so it's not really worth worrying dearly about it. Even if you use one of those 15min quick chargers your batteries should still last a few months.


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## Brian L (Jan 15, 2010)

I have a maha charger as well. Love it. I charge my cells around 500mah or so. Sometimes more if I need to charge them faster. Although the guy above me is right not saying your wrong....lol but that charging fast does generate more heat and cells and heat don't mix. Slow charging if you have the time is better. Believe it or not but charging at a higher mah rate will also not give you as much run time out of the batteries. I learned this from racing electric 1/10 on road cars. Charging a 3300mah nmhi at 5 amps got me bout 15mins of runtime with a mod motor. charging it at 3300 or lower got me 20 to 25 mins. Little more battery info there for you.

Now you may ask why I was charging at 2 and half c's more well when charged at higher amps you actually get more burst our of the pack when acceleration is applied. So now that im off topic and brought back my days of racing im going to quick talking now. hahaha. Peace.


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## Pure (Jan 17, 2010)

I've discovered my 2700mAh cells hold a charge anywhere from 1900mAh to 2600mAh.  I'm going to do a few slow slow slow charge/discharge cycles on them to see if I can get them past there.  I've had these batteries for just over a year or so.  We'll see what happens.


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## Big Mike (Jan 18, 2010)

> I've discovered my 2700mAh cells hold a charge anywhere from 1900mAh to 2600mAh. I'm going to do a few slow slow slow charge/discharge cycles on them to see if I can get them past there. I've had these batteries for just over a year or so. We'll see what happens.


That's fairly typical.  Few batteries seem to actually be up to their rated capacity.  I just tested a set of older 2700s and they came in between 2000 & 2300.

You C-9000 has a 'break-in' mode, does it not? 
That is the mode that you can use to push that capacity back up.


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