Fire alarm trouble

I have a cooper notification rss 12 volts my system is putting out 27 volts and want to use a resister for the alarm how big would the resister need to be

You will not be able to use a resistor to convert 27VDC output to 12VDC. You will most likely not be able to power that alarm with your current system. You’re best off buying a 24 VDC RSS, like this one.

I don’t have an eBay account

No, you can’t with one resistor.
But you can with two!

This is a circuit schematic for a simple voltage divider.

Wire this ONLY to your RSS, do not connect any other signals to it. If you need to hook up an EOLR, DO NOT put it on the output side of the voltage divider.

I calculated the resistor values based on the wattage of a Wheelock RSS.

You’ll need two 100 ohm, 1 watt resistors. RadioShack sells these:

The 27 volts will be decreased to 13.5, which is 1.5 volts higher but won’t do any harm to the RSS. They say 12 volts but they actually mean ± 2V from 12V. (10V-14V)

Nathan, you mentioned your dad is an electrical engineer so I bet he could help you set this up.

I am not responsible for any accidental damage you do to your RSS or your panel. I am just offering a suggestion.

One last thing, can you please post your help questions in the Fire Alarm Help section? Thanks. Just helps with organization a bit.

I have an RSS for $10.00 free shipping.

Ya he is that is how I know we could do the resister I did the Calculations on a Calculator and I got 35.82089552238806

What did you do on the calculator?

The thing with this voltage divider is the two resistors are the same, so it divides the voltage by 2. What I needed to determine next was what resistors to use for the wattage of the strobe, and I determined 100 ohm and 1 watt would be best.

Ok thanks

my dad seems to thank that the sheet that came with it is wrong he knows what resister to use thank you for all your help i might buy an rss i have towo people trying to sell me a 24 volt one thank you again