Fuse and wire size

[DT86]

So are those LED Lights the ones you are going to use ?

If so, what is the manufacturer's requirements for amperage for each light ?

Do you have a manufacturer for these LEDs ?

Yes, these are the ones I plan to use. They are some cheap-O lights that are probably Chinese and do not list anything other than being 27w. The first four I bought were from Tuff LED, an American company. When I bought the case of ten they were not branded but are the exact same, as far as I can tell.

 

[CobyRupert]

It's s lot harder to switch off (i.e. extinguish/break the arc) of DC current than AC current because there is no zero voltage crossing (or zero current crossing) that a 60 hz (sine) wave has every second. That's why the DC rating of a switch is usually lower than its AC rating.

Interesting question as to whether a 27 watt at 12 V light draws less current if the voltage is 14v. Why would the wattage stay constant? It's not like a mechanical load that stays steady.
Not sure about LEDs, but with other lamps one would expect the resistance (R) of the filament to stay constant. We know R=V/I, or I=V/R; and from before power: P=VxI, so substituting V/R for I, P=V^2/R. If R is constant, the power goes up by the square of the increase. So for a 27Watt at 12v lamp, 27W=12^2/R, solving for R= 12V^2/27watts=5.33 ohms.
At 14 volts the power is 14^2/5.33ohms=36.75 watts, which at 14volts is (36.75W/14V=) 2.62 amps.
So.... Question is : are LEDS constant power, or do they get brighter (use more power/watts) when the voltage increases like an incandescent does?

 

[skyhook]

Another stupid question. Why are switches like this rated for AC when most would be used for DC??

I think what I'll end up doing is installing solenoids near the lights and using the hot wire (hot with key) provided by Kubota for a work light to power the switches. That way I can eliminate the fuses at the switches (except for the power socket), not have to worry about over taxing the switches, only have to run one big hit wire to where the lights are and not have to worry about leaving the lights on when the tractor is off.

Anything wrong with this plan?

There are plenty of DC rated switches, do a search on google.
Yes, you could add a solenoid but I would also leave the fuses attached, as a safety feature.
Unless the "work light" circuit is protected by the same type fuse, don't forget, if you go this route, you will only have "one" fuse protecting your switches now, something to think about.
Heat from excessive current is what you need to worry about on those ac switches.
You should be fine with 2 lights per switch, I personally don't see a need for relays on this set-up,
the load is just not big enough.

 

[Scrambler82]

As sky hook said power wires to any device should be fused.

Here is a write up I did a while back.
A little wordy as most of my stuff is.
Sorry if it is confusing.

http://www.tractorbynet.com/forums/customization/196430-aux-lights-wiring-how.html

 

[xtn]

Thanks guys. I have a little bit better understanding now.

The only question I have is about one recommendation of four lights per 15a fuse vs another of 7. Using the provided formula, and the fact that all seem to agree on 2a per light, it seems that 7 lights on each fuse is correct.

Should have mentioned the plan was to run four lights on one switch and two on another. The third would be empty for now.

Seven per fuse is possible, but not recommended. It is advisable (in fact it's a code requirement for building construction) not to run lighting circuits at more than 80% of their rated protection. I calculate a quantity of 5 of your 27-watt lamps will squeak in under 80% of your 15-amp capacity.

xtn

 

[Scrambler82]

If you do decide to run five incandescent lights drawing 12 amps on a 15 amp circuit you need to run a relay and at least 14 gauge wire.

Now if you are running LEDs... First you need to determine the actual load, the current requirements. The you can determine the rating of the circuit components.

DO NOT ATTEMPT TO RUN the 12 amps thought a switch and the main power wire needs to be fused as close to the battery as possible.

 

[Mace Canute]

On DC circuits do not forget voltage drop. You cannot use the tables set up for house wiring. I do not have the info handy but it is all on the internet. Also your friendly auto supply house can keep you out of trouble. Trailers are especially bad as you have to calculate from the battery to the last device. As the distance goes up the voltage goes down and the amps on that wire/fuse go up. The wire is a big resister in the circuit if not large enough. The weak link may be the contacts in the switches. You did not mention their amp rating.

Ron

It doesn't work that way. The voltage is constant at whatever the charging system is putting out (ideally between 13.8 and 14.2 volts) so increasing the total resistance in the circuit lowers the amperage draw.

 

[tman1020]

Where did you get that fused switch panel that is very cool.

 

[DT86]

Where did you get that fused switch panel that is very cool.

Amazon. I was looking for just the rubberized switches and came across this panel for about $25. Search for "3 gang switch panel".

 

[tman1020]

Thanks