selecting a charge current for NiMH

[mccririck]

I just got an Accupower IQ328 charger and you can select a variety of different charge rates (200, 500, 700, 1000, 1500, 1800mA)

Is it correct that you should select a charge rate between 50% and 100% of the capacity (ie for 1000mAh battery between 500 and 1000mA) or 20% or less than total capacity, but not between 20% and 50%?

 

[Shadowww]

That's partially correct.
For fast charge, you'd want to use 0.5C - 1.0C charge rate, indeed.
But for slow charge, you need to charge at 0.1C, timed at 16 hours. Delta-V termination (and termination by temperature, etc) won't work at current so low.

 

[mccririck]

Thanks. So really you're best charging at 0.5C to 1.0C and only charge at 0.1C if you know the actual capacity and you charger can provide 0.1C?

 

[marcham]

You should find the answer in the owner's manual for the charger. Some will not properly peak detect if charging slower than 0.25C

Sent from my GT-I9100M using Tapatalk 2

 

[mccririck]

You should find the answer in the owner's manual for the charger. Some will not properly peak detect if charging slower than 0.25C

Mine doesnt mention it.

Also why shouldnt you use less than 0.5C (eg 0.4C or 0.3C)?

 

[tatasal]

Mine doesnt mention it.

Also why shouldnt you use less than 0.5C (eg 0.4C or 0.3C)?

Rechargeable cells/batteries has been around for a number years already. The engineers/designers of such products, including the recent smart chargers (where rates are adjustable) must have determined, after years of actual user feedbacks and laboratory tests, that 0.5C would be the OPTIMUM rate, putting into consideration cell life, charging times and other factors.

 

[SilverFox]

Hello Mccririck,

Within reason, the charge rate doesn't matter. The important thing is how the charger terminates the charge.

For example if your charger uses an increase in temperature to signal the charge termination, you need to charge at a rate high enough to produce a change in temperature. Along the same lines, if your charger uses a drop in voltage to signal the charge termination (-dV), you need to charge at a rate high enough to produce the signal.

New cells work great even at lower charging rates, but as cells age the termination signal looses strength.

A 1.0C charge rate produces a strong end of charge termination signal. A 0.5C charge rate produces a reasonable termination signal. A 0.25C charge rate produces a weak termination signal.

That's the basics. From here things get a little more complex.

Charger manufacturers have had single termination charges fail and ended up with melted chargers and some fires. As a result they put in some additional charge termination parameters. One of the most common is a timer. The charger will only put so many mAh into a cell then it will shut off. In this case the primary termination signal was missed and it terminated on a secondary signal.

So before you start charging ask yourself how your charger terminates and adjust the current to produce a strong charge termination signal. Once you have decided on a charging current, start the charge and set a timer. If the timer goes off and the charge hasn't terminated, the termination signal may have been missed and you may have to terminate the charge by removing the cells from the charger.

Tom

 

[Phil828]

The Maha 9000 has a default charge rate of 1000mA. At least for AA batteries this seems to be a reasonable rate, around .5C for Eneloops. It works well and I find no reason to tweak it. I do reduce the rate for AAA batteries.
Experiment with your particular charger and batteries and find a setup that you are comfortable with.