I need to run a wire that can handle 130 watts. What gauge should it be, at min?

Also - I will be switching it via a relay. Will a 12V 130amp relay do the job? The relay doesn't say anything about wattage.

Thanks! Its for the off-road lights on the front of the truck.

 

I=W/E 130 watts@12V=10.833 Amps.

I would probably use 10 ga. wire (rated at 15 Amps BTW), because 12 ga. is rated for 9.3.

The 130 Amp relay will be able to handle the load.

 

Dude - you freaking rock!

Not only did you just give me a fish, but you taught me HOW to fish!

Thank you!

 

10 AWG is slightly over kill for 11 amps.

Try 14 AWG stranded wire ( good to 15 AMP in any length you can run on a truck from NEC motor data calculator ).
This is with normal 90* C rated wire, which you should be using 105* C rated wire for an automotive application. If the wire runs past anything that gets warm, the 105* rated wire will have a higher capacity at normal operating temps, and the temperature correction factor is not as steep as 90* C rated wire.

Also you did not note if the load was linear, or non-linear.

If it is something like a motor ( such as a winch) , then the in-rush is usually 2 times the name plate amps. This would cause you to fuse the connection different to carry the in-rush current without blowing the fuse durring the short in-rush duration.

The other item to note is what is the duty cycle for the amps on the load. Some the name plate is for 100% duty cycle, others are less. Usually noted on the plate or in the directions. If normal duty cycle is 40%, and you are going to try to run it at close to 100%, then you need to over size the wire to handle the additional amps that the draw will be from running it more then is recomended.

Also when you fuse something, the normal full load should only be a maxium of 80% of the fuse ratting, so a 11 amp load would have a 15 amp fuse on it ( actually 13.75 amps, but there is no such thing ).

The other is when calcuating the amp draw, it is best to go to the low side of the operational battery voltage at 11.5 volts, rather then the norm of 12 V. If you use 11.5 then the amp draw is 11.30 amps.

10 AWG wire is good to about 30 amps of non-linear, 100% duty cycle, load.

The relay, a 20amp Bosh ( or similar ) relay will work fine for the 11 amp load.

Good luck

 

SSCULLY-

I used my copy of Handbook of Electronic Tables and Formulas for the wire rating. The maximum amps for power transmission used the 700 circular mils per amp rule which is very very conservative. You are correct to say that 14 ga. is sufficient, because the maximum amps for chassis wiring for 10 ga. is 55; provided that the wire is run in air and not bundled. Minimum wire ga. for chassis wiring of a 10 amp load would be 20, so splitting the difference to 14 ga. is acceptable. (14 ga. =32A chassis, 5.9A 700 cir mil will handle the in-rush and duty cycle nicely)

That's what I get for shooting first and asking questions later. :o

But you have to admit, 55 Amp driving lights would be killler.

 

Killer, more like kill the battery

55 amps at 12 volts, ~ 6,700 watts...ouch you might get flashed when using those in traffic

If the reflector was as big as your head, I think you might get a 1/2 mile wide beam pattern, that would reach out about 1.5 miles...

 

Well, you would have an advantage when you used "flash-to-pass", but you could find yourself in a game of chicken with a 747 that mistook Golf Road for ORD thanks to your lights.

 

That's true. Considering that I live on the South West corner of the airport, and use Irving Park Road ( runs on the south side of the airport ) quite a bit going to Edison Park in Chicago.
I could really confuse the pilots if there was fog. I'd dround out the landing strip line up lights

 

Tower:United 271 please alter your approach to line up with runway one-niner.

Pilot:I'm already lined up on one-niner.

Tower:Unless you plan on stopping at the White Castle Drive thru we suggest you wave off.

 

Another question on wire guage requirements.

I am wiring some driving lights. 2 at 55 watts each. This is 4.6 amps each, if my calculations are correct.

I will be using a DPDT- center off toggle switch to operate the lights. One input will be from the high beam headlights, the other is direct from the battery. The output will be to the relay.

The question is. What guage should I use for this? I'm not drawing hardly any amps to trigger (pin 86) the relay right? Since the relay is doing the real work providing power to the lights.

How do I find out how many amps the relay draws on the trigger input?

 

deep6blue-

Depending on the type of relay, the trigger is nothing more than a magnet (or coil of wires). Typically the amp draw is less than 1 amp. They usually are in the milli-amp range. You should be fine using 18-20 gauge. However, I would recommend 14-16 ga. Also the ground (pin 85) should be alteast the same gauge as the power.

Hope this helps

My $0.02 worth.

 

SilverStreak02

You are absolutely correct. I went over to Radio SHack and checked the specs on some of the relays. The 12 volt, 30 amp, relay uses 160mA of draw. Perfect for the 18 guage wire that I have.

Here is the link to the specs for the RadioShack standard 30A relay:
http://support.radioshack.com/suppor...oc38/38002.htm

I will also be adding 2 mini lamps to the switch. A green one for when the switch is turned on using the headlights power, and a red one for when the switch is using the battery power. Both lamps are in the mA range as well.

This should be fun!

If anyone is interested, I will draw out and post a wiring diagram for it when it's done.