cptmohog

Hello, my name is Sean and this is my first post. I have dual optima yellow tops (2nd is in rear cargo area) The guy that installed it for me talked me into a soelinoid rather than the isolator. The cable running the 2nd is 2ga. Today I had a mechanic friend of mine install a new mean green HO alternator. My question is this: I had read some threads here mentioning upgrading the main cables and adding some sort of fuse or breaker from the Alt to the first battery. This mechanic told me he could not see the reason for this and since I am not all that knowlagable, I did not want to argue with him. It seems to be working fine right now, but to those who have done this to their XJ, can you give me some insight into the cable/fuse situation and reasons for upgrading? Thank you in advance. BTW, currently running 3000w stereo, 2 kc's and a ARB compressor with 6 more KC's, winch, and invertor soon to come (setting up infastructure first)

5-90

Whenever you upgrade your alternator, it's usually done with the intention of using the increased output. (NB: An alternator doesn't always generate full output - it will generate what the regulator tells it to. The voltage regulator indirectly controls current output - just trust me. I don't know how much theory you know, but it doesn't sound like much - and it would take some explaining.)

The OEM lead is usually "just enough" for the OEM alternator, and that is assuming a full-output duty cycle of down around 35-40% (and a duty cycle at 70% output of only 60-70%, from what I've been able to determine.) And that's assuming the OEM alternator - which your Mean Green certainly is not. You don't say what year your rig is, so I can't tell you what the difference is between your OEM and the 200A-rated Mean Green - but 200A is 170-285% of the OEM rating, depending on model year and options.

Your 2AWG to the rear battery should be fine - but what's the rating on your solenoid? Most constant-duty solenoids (nothing wrong with using them!) are rated for either 85A or 200A - an 85A unit will get burned out if you use the second battery extensively and route a good deal of charging current to it (figure that the first 25-40A - again, depending on year - from your alternator goes into engine management. The rest is available for accessories.)

The alternator output lead is fused from the factory - either using a short segment of fusible link wire (RENIX and OBD-II,) or a pair of MAXI60 fuses in the PDC (OBD-I.) Either way - 200A full output will blow the fuse.

Yah, if you've clicked the link in my sig, you'll note that I sell wiring kids and such. For your Mean Green unit, I'd not go with 4AWG wiring - I'd use 1AWG. I carry fuses up to 200A on hand, and that will work neatly with your 200A alternator. The ANL format fuse I offer is easy to work with and rather rugged, and the fuse block is reasonably compact and mounts on the fender liner near the battery.

Go ahead and peruse the site - I'll answer any questions you have afterwards, if you hit me backchannel.

RRXJeeper71

pics?

XJwonders

to the OP, I ll vouch for this guy and his products, no doubts at all.

macgyver35

I'll second the vote of confidence. This guy knows his electrical systems. I just received a kit from him, and while I haven't yet installed it (planning to do that this weekend) I've inspected what he sent me and everything is top-notch.

While your 3000 watt stereo will not push a full 3000 watts for sustained periods (if ever), if you assume it did from time to time, that alone is a 250 amp load. One thing I can tell you is that if you dropped that stereo system down to 1500 watts, you'll have a much lighter amperage load, and not much of a difference in volume. You have to double the power to a speaker to get a 3.1 decibel increase in volume. So the only only difference between 1500 watts and 3000 to a speaker is, you guessed it, 3.1 decibels. Multi-driver set-ups differ, but that's too complex for this post. To put that in perspective, it requires a 10 decibel increase for it to sound to your ears to be twice as loud. In other words, 3.1 db is not much of a difference in volume, but can be a big difference in power draw and the costs of supporting it. You can also think of it this way... If a speaker produces 100 decibels of sound at 100 watts, you'd have to push 800 watts to it for it to sound twice as loud! You have to double the power for each 3.1 db increase, and it takes a 10db increase for it to sound twice as loud. Use the chart below for reference. If you want to know what you specific speakers do at certain wattages, start with the speaker's SPL rating (decibels produced at 1 watt and at 1 meter of distance form the speaker) and keep doubling the power from the previous level and add 3.1 db each time you do.

100 watts = 100db
200 watts = 103.1db
400 watts = 106.2db
800 watts = 109.3db

A real-world example of a typical subwoofer with an SPL rating of 87:

1 watt (.083 amps @ 12 volts = 87db (vacuum cleaner)
2 watts (.167 amps) = 90.1db
4 watts ( .307 amps) = 93.2db
8 watts (.667 amps) = 96.3db
16 watts (1.33 amps) = 99.4db
32 watts (2.67 amps) = 102.5db
64 watts (5.33 amps) = 105.6db
128 watts (10.67 amps) = 108.7db
256 watts (21.33 amps) = 111.8db
512 watts (42.67 amps) = 114.9db (rock concert levels)
1024 watts (85.33 amps)= 118db
2048 watts (170.67 amps) = 121.1db (permanent hearing damage can occur)

Notice that to get a bit LESS THAN a doubling of volume between 128 watts and 1024 watts, the amperage load jumps from 11 amps to 85!! 85 amps is like running ten 100 watt KC lights at the same time.

So, you can see that your power requirements ramp up exponentially compared to volume output.

Another thing you can do to lighten the load is, if those KCs are the traditional kind, they pull anywhere from 50 to 120 watts each depending on which model you have. Switch to LED lighting. You'll get the same amount of light output from a decent 20 watt LED as you will a 100 watt halogen KC. A 100 watt LED light bar can put out the same lumens as five 100 watt KC lights. With LED you'll also have lighting that does not have bulbs that burn out. Most LEDs on the market are rated at a minimal of 50,000 hours of use at full tilt. That's nearly 6 years running 24/7.

Even if you just had the winch and the ARB compressor, I'd still recommend you get a wiring kit from Jon (Kellyswip.com). But with dual batteries and the Mean Green, it's pretty much a must-have. If you have all the power in the world, great, but I'm also for smart use of power and conserving where I can, thus the stereo and light suggestions.