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what wattage resistor


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mrcllusb 
Copper - Posts: 489
Copper spacespace
Joined: September 06, 2005
Location: Georgia, United States
Posted: July 09, 2006 at 5:24 PM / IP Logged  
I need to add resistors for my lock unlock hook up with my clifford arrow alarm.Do i use 1/2 watt or 1 watt resistors?
"ole blake"
bmwpwner 
Copper - Posts: 174
Copper spacespace
Joined: January 28, 2006
Location: United States
Posted: July 09, 2006 at 5:54 PM / IP Logged  
i use 1/2 watt resistors and have for years. to be honest i'm not sure what the difference is though. i really should do some searching on that. but for sure 1/2 watt will work. good luck and hope this helps.
"I cannot teach anybody anything, I can only make them think."
-Socrates-
meltingplastic 
Copper - Posts: 225
Copper spacespace
Joined: November 08, 2004
Location: United States
Posted: July 10, 2006 at 7:43 PM / IP Logged  
if you dont know what difference between different wattage resistors is.. im quite scared..
yes half wat will work fine.. most remote start systems put out mAs so u dont have to worry about them overheating and blowing them
Driving a Bagged, Caddied 02 s10
bmwpwner 
Copper - Posts: 174
Copper spacespace
Joined: January 28, 2006
Location: United States
Posted: July 10, 2006 at 10:18 PM / IP Logged  
so what is the difference? i have never claimed to know everything and i'm always willing to learn.
"I cannot teach anybody anything, I can only make them think."
-Socrates-
meltingplastic 
Copper - Posts: 225
Copper spacespace
Joined: November 08, 2004
Location: United States
Posted: July 11, 2006 at 12:13 PM / IP Logged  
the wattage means how much power through the resistor it can handle before it blows.. like if u have a 1 watt resistor.. take the current output and multiply it by the voltage through it.. so typically in car its 12v(or 14.4 u wanna be more exact) and most outputs in alarms are like 500mA so uve got (12)*(0.5A) = 6 watts. now even though your going over the wattage its not long enough for it to blow the resistor due to it not being on that long. i dont remember how long there is until itll blow but basically it heats up and burns..
Driving a Bagged, Caddied 02 s10
meltingplastic 
Copper - Posts: 225
Copper spacespace
Joined: November 08, 2004
Location: United States
Posted: July 11, 2006 at 8:49 PM / IP Logged  
well the main reason i need to know about the power rating of resistors is cause im going to school for electronics engineering and am in an Analog Electronics class and we build power s upplies and amplifiers and if our load resistors recieve a power greatre then their spec'd wattage we have to split the load into multiple resistances as to not blow them
Driving a Bagged, Caddied 02 s10
texxasaudio 
Member - Posts: 5
Member spacespace
Joined: February 18, 2005
Location: United States
Posted: July 11, 2006 at 9:31 PM / IP Logged  
when you split the load in varios resistors also you are bringing the wattege capacity up
texxasaudio
meltingplastic 
Copper - Posts: 225
Copper spacespace
Joined: November 08, 2004
Location: United States
Posted: July 11, 2006 at 11:29 PM / IP Logged  
bingo! simple KCL!
Driving a Bagged, Caddied 02 s10
dualsport 
Silver - Posts: 983
Silver spacespace
Joined: September 27, 2005
Location: United States
Posted: July 12, 2006 at 9:15 AM / IP Logged  
About the calculation of the power dissipation from the example, if the resistor is used as a dropping resistor, the voltage across it isn't going to be 12V, so you wouldn't end up with that large a wattage rating.
Being in series, the voltage is decreased by the load (e.g. door lock actuator).
Usually wouldn't have the resistor connected from the source directly to ground in most cases, since that would just be a load, and not too useful, except for power supply testing.
In general, though, using a larger resistor is always safer. Tradeoff is that it just costs more and takes up more space.
meltingplastic 
Copper - Posts: 225
Copper spacespace
Joined: November 08, 2004
Location: United States
Posted: July 12, 2006 at 12:34 PM / IP Logged  
yea.. they are voltage dropping resistors i just didnt wanna make the calculations too much lol
Driving a Bagged, Caddied 02 s10
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