24 V to 5V

7

7frank7

New Member

• Oct 4, 2009

• #1

Hi,

I need an easy way of converting 24vdc to 5vdc.

I have an omron plc which i'm going to connect a panel mounted encoder http://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/03584638_2.pdf
i run everything on 24Vdc but these encoders seem to only be available in 5V versions.
so if anyone has an easy way of doing this please share..
Thanks,

Frank

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 4, 2009

• #2

Its current is only 0.5mA so a resistor and a 5.1V zener diode or a 5V little 78L05 regulator with two capacitors will make 5V for it.

 

7

7frank7

New Member

• Oct 5, 2009

• #3

thanks fro replying,

any pointers on how to determine the size of the resistor?

Frank

 

D

Diver300

Well-Known Member

Most Helpful Member

• Oct 5, 2009

• #4

There are two outputs, so you need 1 mA for each encoder.

(24 - 5) / 0.001 = 19000 ohm

Use an 18k resistor with the 5.1 V zener.

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 5, 2009

• #5

Many zener diodes do not work properly when their current is almost nothing.
Many 5.1V "400mW" zener diodes are tested at 45mA.
Use 1.8k for about 10mA in the zener diode.

 

Arkham00

Member

• Oct 5, 2009

• #6

The device you are trying to interface is not an "active encoder" that needs to be powered. It's just a double rotary switch mostly used on microcontroller boards (at 5Vdc) but it can be safely used at 24Vdc.

Just connect it to two standard inputs of your Omron PLC as if they were two standard pushbuttons.

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 5, 2009

• #7

Why were we trying to power a mechanical switch?
Its max allowed current is 5mA but its spec's are measured when its current is only 0.5mA.

 

7

7frank7

New Member

• Oct 5, 2009

• #8

Arkham, if that is indeed so, that would be a relief, i suppose i could just test it.

it was brought to my attention that i needed an open collector encoder and not a line driver,to be able to use it with the regular inputs. but i couldn't find that information in the datasheets.
if it is indeed a double rotary switch, i suppose there wouldn't be any info whether it's a line driver output or open collector.
can anyone confirm if this is so?

thanks,

frank

 

7

7frank7

New Member

• Oct 5, 2009

• #9

Ok, so it is just a mechanical switch?

somehow i got hung up on the idea that it was an encoder that needed to be powered.

in case you didn't read my reputation it says NEWBIE.
thanks for putting up with me.

frank

 

B

bountyhunter

Well-Known Member

• Oct 5, 2009

• #10

7frank7 said:

Hi,

I need an easy way of converting 24vdc to 5vdc.

Click to expand...

Just connect the 24V to the input of a 7805 regulator. They are dirt cheap and require no other parts.

 

Last edited: Oct 5, 2009

A

arunb

Member

• Oct 6, 2009

• #11

Just connect the 24V to the input of a 7805 regulator. They are dirt cheap and require no other parts.

Click to expand...

that may work but the 7805 will get hot...

 

B

bountyhunter

Well-Known Member

• Oct 6, 2009

• #12

arunb said:

that may work but the 7805 will get hot...

Click to expand...

Nope, read the above posts where it says:

There are two outputs, so you need 1 mA for each encoder.

Click to expand...

If you only need 2mA of load current, the power dissipation in the 7805 or 78L05 will be negligible.