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NiCd battery charger design assumptions-

Y

yashwant

Jan 1, 1970
0
Dear Folks,

I have seen a NiCd battery charger design in Elector magzine. It is
a simple series charger which receives dc voltage from a adapter and
the dc is given to the battery through a series resistor. The author
of the article has some design principles for a good battery charger

1. The output of the adapter should be 1.17 of the nominal battery
votlage

2. Charging current should be 1/4 of the battery capacity. That is
if the battery is of 1Ah then the charging current should be 250mA.

The series resistor is valued accordingly.


Any comments on these assumptions.


Thank you,

Yashwant.
 
I

Ian Stirling

Jan 1, 1970
0
yashwant said:
Dear Folks,

I have seen a NiCd battery charger design in Elector magzine. It is
a simple series charger which receives dc voltage from a adapter and
the dc is given to the battery through a series resistor. The author
of the article has some design principles for a good battery charger

1. The output of the adapter should be 1.17 of the nominal battery
votlage

NiCd cells should be charged from a constant current source.
2. Charging current should be 1/4 of the battery capacity. That is
if the battery is of 1Ah then the charging current should be 250mA.

Unless it's timed, C/4 is a bit high, and can cause damage in a few hours
of overcharge.
 
Y

yashwant

Jan 1, 1970
0
Hello Ian,

Can you please suggest me a simple constant current source for such
an application? Also suggest me correct assumptions for such a
charger.

Thank you,
 
I

Ian Stirling

Jan 1, 1970
0
yashwant said:
Hello Ian,

Can you please suggest me a simple constant current source for such
an application? Also suggest me correct assumptions for such a
charger.

http://www.maxim-ic.com/ look at the charger chip datasheets for NiCd.

Basically, if you want to charge them in a dumb charger, one tenth
of the capacity (C/10, 70ma for a 700mah cell) is around the right rate
to charge.
This will result in a cell that is fully charged in 14 hours, and
essentially no effect if you accidentally leave the cells in the charger
for a few days.
If you time the charge, C/4 or C/5 won't do much harm to the cell if you
try to charge a full cell.
Much more than this, and you have to monitor cell temperature and delta-v
to charge it.

Why do you want a battery charger, they are very available.
Is it for a specialised battery?
 
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