# 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.

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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