Resistor Size

phile · 2 Mar 2006

Could anybody advise on what size resistor should be used

I am wanting to use a sounder to be wire in with a 24v DC output.

The sounder is a 12v DC with a current of 8mA

Spark123 · 2 Mar 2006

You need to drop 12v with a current of 8mA. R=V/I so R = 12/0.008 = 1500, or 1K5.
Watts = I²R, hence 0.008² x 1500 = 0.096w so a 0.25W resistor should be fine.

phile · 2 Mar 2006

Thanks very much, will get on and order!

plugwash · 2 Mar 2006

if you have a local maplin try there first especially if you aren't after any other electronic components.

note that maplins standard resistors are rated at 0.6W but this should still be fine.

Lectrician · 2 Mar 2006

Talking resistors - what value and current rating would be best to stop these CFL lamps flickering when fed via a PIR, or when fed via a 2way cct?

plugwash · 2 Mar 2006

resistance: experiment and select one as high value as you can get away with. The lower the value the more power you waste. i'd start with 100K and work down

power rating: sufficiant to handle the current that the mains will dump through them. the lower the resistance the higher the power rating will need to be. for a 100K a metal film 0.6W like maplin sell as thier standard range would be fine. for lower resistances you'd need higher power rating i think you can get 2W metal film and beyond that your into wirewounds.

Adam_151 · 2 Mar 2006

LEC: See the post here: http://www.iee.org/Forums/forum/mes...did=3909&highlight_key=y&keyword1=capacitance by Mapj1

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Resistor Size

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