How do I calculate the current running through the bulbs?

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calculate current through the bulbs

I built an adaptor to test an ATX power supply. I connected Pin14 (Power Supply On (active low)) to ground, a 12V 10W bulb to +5V, and a 24V 2W bulb to +12V. The power supply swings on and everything is fine.
Now, the question is, how do I calculate the current running through the bulbs since the bulbs are PTCs?
I have no clue.
Thanks in advance, ep20k.
 

Hi,

So a search here in the EDABoard. I saw few projects on current sensing and lots of diffrent ways to do so.
Im sure you will be able to find your answer...

Good luck.
 

Re: How do I calculate the current running through the bulbs

Just put a cheap low resistance current sensing resistor in series with each of your bulb circuits, and measure the voltage drop across each of the resistors. Ohm's law will give you the current from the voltage drop. Add the individual results for total current, if you need that value.

Take a look at the following CHEAP resistors:

**broken link removed**

They are available for 42cents(US) each from Digikey. The catalog page is:

http://dkc3.digikey.com/PDF/T051/1033.pdf
 

Re: How do I calculate the current running through the bulbs

Hi guys,
The point isn't measuring! I know how to do that.
The question is, can I calculate the current with the above given parameters?
to gidimiz,
So a search here in the EDABoard.
Click to expand...
I always do that before I ask a question here on the board, like everybody should. No success. If you have a concrete link, please let me know.
Best regards, ep20k.
 

Re: How do I calculate the current running through the bulbs

No, you cannot calculate the current directly with any degree of accuracy. The hot resistance of the lamps, and the intensity of the output, is so widely variable from bulb-to-bulb that there is no reference parameter upon which to base a converted measurement.
 

Re: How do I calculate the current running through the bulbs

Hi House_Cat,
right up my alley. I don't know what's written in a spec of such bulbs. The 12V bulb is a car rear lamp. I was googleing for specs but didn't find any which would be useful.
Regards, ep20k.
 

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