# reducing current output

V

#### vjm

Jan 1, 1970
0
Hi,

I have a power supply that will output 30 VDC @ 1000mA. Is there a
way to limit the current output of this supply to the 25-30mA range?
What components would I need to use? Will they generate heat?

Any help would be appreciated.

vjm

T

#### Terry

Jan 1, 1970
0
vjm said:
Hi,

I have a power supply that will output 30 VDC @ 1000mA. Is there a
way to limit the current output of this supply to the 25-30mA range?
What components would I need to use? Will they generate heat?

Any help would be appreciated.

vjm

At 30 volts a load designed for 30 volts will take only as much
current as it requires; up to the maximum capability of the power
supply, 1000 milliamps.
For example if you had a 30 volt lamp that consumed 100 milliamps
you could connect ten such lamps at the same time for a total of
10 X 100 = 1000 ma.
If you connected 11 such lamps you would be overloading the power
supply by 100 ma.

To go further you need to explain what you are trying to do and
need to learn Ohms Law. It sounds as though the circuit you wish
to operate from that supply may need less than 30 volts?

An example.

Today I adjusted the output voltage of our bench supply to 5
volts in order to test some lamps of unknown voltage and also to
see if they were 'good'. They each took about 40 milliamps. I
then discovered that they were 12 volt lamps and adjusted the
output to to around 10 or 12 volts. Each lamp then took a bit
less than 100 milliamps.
Each bulb/lamp therefore is consuming approx. 95 ma at a normal
voltage and brightness of 12 volts.

Using Ohm's Law the resistance in ohms of each lamp (when working
normally) is Voltage divide by Current;
That is 12/0.095 = 121 Ohms.

If I had increased the voltage to 30 volts the lamps would have
taken way too much current (almost three times as much) and would
have 'blown' their filaments!

Have fun. Terry.

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