Can I run a ground wire directly to the alternator case?

Long story short, I recently picked up a 2001 cherokee xj, and was doing the big 3 upgrade, battery positive to alternator positive, battery negative to chassis and engine to chassis.

I've seen a lot of guys, rather than add an additional ground to the engine block, they just grounded the alternator case directly. I picked up a new 117 amp alternator from napa along with a new battery, but did not see a dedicated lug, or area that I could ground the case to.

The issue I'm having is that I have a 500 watt RMS amp, which really shouldn't be too hard on the electrical system, but when the bass hits, it does dim the lights. I've checked and doublechecked, the grounds are good. I used a die grinder to make sure that they were totally ground down to bare shiny metal, so I'm kind of at a loss as to why the lights are continuing to dim.

One note, this is at idle. So RPM are around 700. I'm assuming that alternator output is less than 117 in this situation, could that be the entire problem?

Typically alternators don't start making usable electricity until about 1200 rpm. Or so I've heard.

There are exceptions:
https://www.youtube.com/watch?v=xHg2EgPTGs4

Alternator is already grounded through the brackets and bolts

You want three ground wires: battery-to-block, battery-to-body, body-to-block. Electrical current takes the path of least resistance, so it will use whatever is best path to ground

ehall said:

Alternator is already grounded through the brackets and bolts

Click to expand...

Yep!

And if you powdercoat a bunch of the right brackets and the alternator case you will lose that grounding. DAMHIKT.

If you are going to add electrical loads to anything, you need to familiarize yourself with Ohm's Law and various other formulas...otherwise you may overtax the system and damage one thing or another, or start a fire. https://en.wikipedia.org/wiki/Ohm%27s_law http://www.rapidtables.com/convert/electric/Watt_to_Amp.htm#dc The average alternator is putting out around 30-40 amps at idle, maybe 60 if it's cold(power output goes down as the alternator gets warmer) and there is high electrical demand. Alternators are also usually rated by the peak output, which is when they're cold and at much higher rpm than idle speed.

At 14.4 volts(approximately what voltage should be with the engine running), 500 watts is equal to roughly 35 amps. At 12 volts, it's roughly 42 amps. Your headlights are probably drawing around 20-25 amps, and the climate control fan probably draws close to the same. So, if your alternator is putting out 40 amps and you're drawing more than 40, then the extra current is being supplied by the battery and your voltage is dropping. This is why your headlights are dimming. If you want to verify this, check voltage(multimeter on the battery terminals) with the engine running, without anything on, and then do it a few more times, turning something else on each time. If you drop below 12.6 volts, then a portion of the existing load, any additional load will be supplied 100% by the battery, which is now not being recharged. At the same time, you're cooking the diodes in the alternator to death and it will live a short, miserable life...likely taking the battery with it.

You can try adding a 1 to 2 farad capacitor(maybe bigger, outside my knowledge range) on the power cable to the amp. These work sort of like a battery, although they can deliver current faster and help smooth over the short term peaks of power demand. This is really more of a bandaid than a fix though.