I posted a note in the pictures section regarding a compressor that is capable of filling a 3 gallon air tank to 120 psi in 2 minutes 5 seconds. This compressor is a Blow Jax unit that is designed to run at a 100% duty cycle. At max psi (165), the compressor draws a whopping 100 amps of raw current. As the pressures drop, so drops the current. The typical off-roader will want to maintain a 90 - 120 psi level at the tank. What this means is that at that level, the compressor will be drawing some 90 amps of juice. The average duty cycle for the typical four wheel drive with no leaks in the system should be in the 20 - 30% range.

My conclusions are as follows. When that sucker kicks on, it will suck every ounce of juice it can get its hot little hands on. I would NOT run something of this caliber on a factory battery only. The million dollar question is, how long can it run on a yellow top Optima before it wipes it out?

The second problem comes back to the alternator. At 90 amps, it is a wuss. When that compressor engages and pumps up to 120 psi, how will it load the alternator and how will it affect it during the brief time period it runs? Running an alternator at max output is never a good thing, but is the time frame short enough where the effect won't be detrimental?

These are all rhetorical questions, but some out here may have some thoughts that may lead me in the right direction in my research. If anyone has a little input and a few suggestions (besides not putting it in), post them here and open it up to discussion. Just for the sake of argument, I am installing a switchable isolator with an Optima red top as the primary battery and an Optima yellow top as the auxillary battery which will run the winch, lights and compressor.

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Gordon "The Warmonger" White
Silver Ice SE 4X4