Wiring for more power.

[GeoRoss]

I am needing abit of input on this.
Background: I don't have a 2nd battery yet, but it is something for the near future. In the mean time, the only outlet (cig lighter) is not enough. I don't need alot right now, but it would be nice to wire it with enough flexibility for future needs.

Right now, I need to power the following (but not each all the time),
CB
GPS
laptop
150W inverter (may upgrade, but there hasn't been a need yet)
iPod
phone recharger
portable DVD player for kids

Some will be better with a ACC wiring, other hot all the time. I would like to wire in a dedicated carputer for navigation and take advantage of a smaller touch screen in the future. The laptop just takes up too much room, but I do like the large screen size. I also have plans for a 2m radio as well.

Plan: 6 ga wire from the battery through the firewall w/100 amp inline fuse near the battery. Run the ground back to the battery so I don't have to mess with finding a good ground? Run through the firewall.

Inside the passenger compartment split the power feed line. One would go straight to the new aux. fuse box. The other would go via a (20 or 30A?) relay (powered by either straight from the OEM fuse block or tapping into the cig lighter) to the fuse block. This configuration would provide both constant and ACC power.

Wire both plugs and accessories as necessary.

Any comments?

Ross

 

[MaddBaggins]

Run the CB right off the battery. They draw little power, even if you forget to turn it off it would be days before it drained the battery. I should have showed you that the other night, but I think the beers got priority.
Eventually I will have a 2nd battery, then I will run the CB, stereo, fridge, winch, etc etc off the second and let the first run the truck. Of course a switch is a must, in case #1 dies.

 

[goodtimes]

Dont use a 100 amp fuse. Calculate your maximum load on your new main circuit (add up all the branch circuit loads), multiply by 1.25, then find a circuit breaker that is as close to, but not under, the number you came up with. This will preclude you from having to carry extra 100amp fuses, and will offer better protection as the device is properly sized. Be sure to use secondary protection on each branch circuit. Size each for the load on that branch circuit (max load x 1.25). If you are running anything which has a large start up amp draw, look into slow-blow or time delay fuses rather than breakers. These will allow the start up load, but will blow if the load is sustained too long (good for motors, etc).

Common advice is to run radios on a dedicated circuit, not off of a branch circuit. But if you properly size everything, you will be OK. Pay special attention to the ground, you are on the right track going back to the battery.

Be careful with tapping into any existing (OEM) wiring. The systems are engineered to perform as designed. Adding too much additional load on a circuit can result in a headache. The cigarette lighter circuit is usually safe to play with, as it is dedicated and 15 amp. Be sure to consult a factory service manual wiring diagram and verify before you start adding stuff.

Consider adding 2 bus bars inside the vehicle. One +12vdc, one ground. You can add circuits to these as your needs change. It will act just like connecting things directly to your battery, but a much cleaner install. Be sure to properly size the protection between the battery and bus bar (this is the main breaker I mentioned above), and again on each branch circuit coming off the buss. Always protect the hot side, not the ground side.

Your on the right track, but by adding the bus bars (or terminal blocks...whichever) will give you more options down the road w/o having to hack into your wiring every time. You can just add/remove the circuits as needed no cutting/splicing involved....and the circuit breakers, well, they are just cooler than fuses (that and the self resetting breakers are nice for things like air compressors, etc).

 

[GeoRoss]

Thanks GT & MB
I am trying to set this up for easy changes as things arise. The only reason I don't want to run the CB/radios off the battery is to minimize the number of wires running around the engine compartment. I'll do it if necessary, but would like to avoid it.

I have added up my current/near future load for the things I can find.
laptop 1.875A max @24V
inverter 150W (VxA), @120V=1.25A?~10.9A@13.6v, 12.5A@12v
DVD player 3A
GPS ?, not much (<1A)
iPod ?, not much (<1A)
CB 1.7A
Phone charger ? (<1A)

My math for finding out amps from watts seems too low, but it does depend on voltage right?

In the short term, the laptop is run off the inverter, but I would prefer a direct DC input as I get FM radio feed back when running the inverter. The laptop charger pulls 45W (V A), so @ 120V=.375A?

Many of the outputs will be accessory plugs, not dedicated circuits. The cig lighter is indeed a dedicated 15A circuit. This seems to be flexible with a number of accessories, so I thought I would go with that. So 3-4 15A outlets for occasionally used accessories (ie DVD player). Hard wire inverter, CB and in the future power for the GPS & laptop. This is why I thought the 100A main line fuse/breaker would be necessary. Maybe I should down grade the plug loads to 10A

My plan to either splice into the cig lighter or to a space on the OEM fuse box is only to run a relay (<.2A) so that I can have ACC/Ignition powered circuits. I do not plan on running accessories off the OEM fuse box. Is there a better place to run a relay that will operate off the ACC/ignition?

I plan on getting started today on the constant power. Adding a ground buss is a great idea. For this weekend I need to be able to run DVD, inverter, CB (if it will ever arrive), phone and the iPod at least. 3 new 12V plugs and hardwiring for the CB. If I run a 6ga main line wire(~10ft run, 50-65A safe transmission) but use a smaller fuse/breaker that will leave plenty of room to increase for loads. Right now I calculate for the inverter ~10.9A+ DVD 3A+iPod/CB/Phone 3.7A=17.6A load ~22A fuse seems small.

Am I getting closer?

Thanks Ross

 

[goodtimes]

To avoid a bunch of wires running to your battery, simply run a 6ga cable from the battery to a breaker or fuse (you already know I prefer breakers....but a fuse will work), from there to a +12v buss bar. Run all your circuits off of that buss bar....that way you only have one extra cable going to the battery. You can also feed a second buss bar off of the first, using a relay to isolate it so the 2nd only operates when the key is in the ACC or Run position. Tapping into the cig lighter for this would be acceptable as you suggested....provided the cig lighter is not constantly hot (my jeep has one of each...one constant, one keyed). Just be aware that with radios, you will lose some efficiency as you add more "stuff" between the battery and radio (stuff = relays, breakers, buss bars, wire splices, etc). The higher the output of the radio, the more pronounced the losses will be. This is due to the amount of resistance a circuit has and the increased amp load on that circuit.

Your math is off. Are you using the input volts/amps? Your input should be 12vdc, not 120vac. If you are using a 150w inverter, calculate the amp load as follows.

Amps = watts/volts
A = 150/12
A = 12.5

Of course, we all know that automotive electrical systems do not normally run at 12 vdc. A dead even charge on a 12v battery is actually 12.6v (and change). Most vehicles run around 13.8 volts when the engine is running. So this will affect the amp load of each circuit slightly. Your 150w inverter will pull closer to 10.9 amps @ 13.8 volts. Of course, on the flip side of that...once you get too much junk running at one time, the charging system cannot keep up with the demand and the voltage will drop off. In this case, your amp draw will spike in all the circuits, and bad things can happen (smoke, fire, smelly stuff like that). This is very prevelant when putting a big load on a winch, starting your engine, etc.

Ok, I'll shut up now....

 

[GeoRoss]

Thanks for the inverter clarification, I was using output volts not input, doh!
I will revise by load, again.

Ross

To avoid a bunch of wires running to your battery, simply run a 6ga cable from the battery to a breaker or fuse (you already know I prefer breakers....but a fuse will work), from there to a +12v buss bar. Run all your circuits off of that buss bar....that way you only have one extra cable going to the battery. You can also feed a second buss bar off of the first, using a relay to isolate it so the 2nd only operates when the key is in the ACC or Run position. Tapping into the cig lighter for this would be acceptable as you suggested....provided the cig lighter is not constantly hot (my jeep has one of each...one constant, one keyed). Just be aware that with radios, you will lose some efficiency as you add more "stuff" between the battery and radio (stuff = relays, breakers, buss bars, wire splices, etc). The higher the output of the radio, the more pronounced the losses will be. This is due to the amount of resistance a circuit has and the increased amp load on that circuit.

Your math is off. Are you using the input volts/amps? Your input should be 12vdc, not 120vac. If you are using a 150w inverter, calculate the amp load as follows.

Amps = watts/volts
A = 150/12
A = 12.5

Of course, we all know that automotive electrical systems do not normally run at 12 vdc. A dead even charge on a 12v battery is actually 12.6v (and change). Most vehicles run around 13.8 volts when the engine is running. So this will affect the amp load of each circuit slightly. Your 150w inverter will pull closer to 10.9 amps @ 13.8 volts. Of course, on the flip side of that...once you get too much junk running at one time, the charging system cannot keep up with the demand and the voltage will drop off. In this case, your amp draw will spike in all the circuits, and bad things can happen (smoke, fire, smelly stuff like that). This is very prevelant when putting a big load on a winch, starting your engine, etc.

Ok, I'll shut up now....

 

[Pskhaat]

Where do you find 12v breakers?

 

[njtaco]

Breakers

Any RV/Camper store should stock 20A and 30A 12V breakers. They double 20s for a 40A rating, etc. Available in automatic or manual reset.