# charging NIMH and NICAD batteries

M

#### Mark

Jan 1, 1970
0
say i want to charge a 2000mAH battery at 1C from a 4A current source. is it
acceptable to do this with a 50% duty cycle or will this f*** the battery in
the long run.??

This seems to me like the eaasiest way to make a variable constant current
charger and the battery voltage could be monitored during the off time.

Thanks

M

#### mike

Jan 1, 1970
0
Mark said:
say i want to charge a 2000mAH battery at 1C from a 4A current source. is it
acceptable to do this with a 50% duty cycle or will this f*** the battery in
the long run.??

This seems to me like the eaasiest way to make a variable constant current
charger and the battery voltage could be monitored during the off time.

Thanks

With a little L and a diode, you can "average the current".

I tried to measure the voltage during the off time with a processor.
The voltage reading is VERY sensitive to how long you wait. The
variation in interrupt latency of the processor caused the readings
to change way more than the actual battery voltage changed. If you
try this, use a hardware timer to precisely sample the voltage
before feeding it to the A/D.
mike

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R

#### R.Legg

Jan 1, 1970
0
Mark said:
say i want to charge a 2000mAH battery at 1C from a 4A current source. is it
acceptable to do this with a 50% duty cycle or will this f*** the battery in
the long run.??

This seems to me like the eaasiest way to make a variable constant current
charger and the battery voltage could be monitored during the off time.

Thanks

It may be easier for you, unfortunately it wasn't for the guy's who
have originally collected relevent data that allows you, now, to
intelligently charge the cells.

The open circuit cell voltage is not likely correlated to any
published data, though the difference between voltages (off and on
charge) can be an indicator of cell health and SOC - this information
is not guaranteed to be available for the specific cells you are
using.

You would have to use blind time or temperature-terminated charging
techniques, if the cells are capable of accepting the elevated charge
current.

You should consult the specific battery mfr's advice on this.

When data is collected for a 1C charging rate, they are not fooling
around, and do not expect you to be, either. 4A is 2C, regardless of
duty, unless averaged externally before entering the battery
terminals. The differences between charging efficiency at the two
rates will depend on the battery.

If you have the ability to control charging duty cycle, you no doubt
have the ability also to to control the actual charging rate, and
should do so, if you want predictable results. If you have the ability
to monitor cell voltage, then monitor it under the conditions that
correlate to the published data, to obtain predictable results

RL

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