C1142 diagnosis (SLIP, VDC, & BRAKE lights on) - Page 4 - Nissan Armada Forum: Armada & Infiniti QX56 Forums
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post #31 of 32 Old 03-30-2017, 11:02 AM
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Originally Posted by KingRJ View Post
Ehilde, you are correct...not really sure where all the alternator\defective parts\known failure info is coming from but some smoke is going to come out of something! Do not remove the limiting device!
Especially with today's electrically-commutated alternators. OEM alternators are designed with lower current limits in the exciter armature so they will produce less heat and last longer. Aftermarket high-amperage alternators basically are just OEM alternators designed with these limits removed, so the AVR will pump large amounts of current into the exciter field.

Sure, they produce more current, but they produce extra heat. The "270 amp" alternator can certainly produce 270 amps, but not for very long before the rectifier diodes exceed their junction temperature and fail. A typical schottky rectifier will have a forward voltage drop of about 0.5V at rated current. So, at 270 amps rms, each one is dissipating 67.5 watts (and there are four of them). That's a lot of energy do dissipate in a small package under the hood. I doubt they would last more than about 30-60 seconds pushing that current continuously into a dead AGM battery, and that's if whomever slapped together the aftermarket Brawndo(TM) Alternator knew what they were doing.

Then, there's the wire. Just think about this logically for a second. An alternator is typically wound with #14 or maybe #12 wire. How long do you think you can push 270 amps through a #14 wire before it burns off the insulating varnish? Not long.

There is precisely nothing wrong with limiting battery charge current to 30A, and doing so does not affect other vehicle electrical systems in any way. It's also the safe thing to do.

I'll also add that most AGM battery manufacturers recommend a 0.25C initial charge rate. A group 34 Optima Red Top has a C20 capacity of 50Ah, which means it should be charged at no greater than 12.5 amps for maximum battery life. If you dump 270 amps into it (which it will happily take, at least for a short time) who knows what will happen?

Engineer, cyclist, pilot, geek.

Last edited by ehidle; 03-30-2017 at 11:07 AM.
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post #32 of 32 Old 05-02-2017, 10:36 PM
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The Hitachi oem alternators were the subject of a court battle. Nissan lost, but instead of replacing them with Mitsubishi alternators, they shipped them to Mexico and rebranded them. Go to any professional alternator shop and ask them to rebuild the oem Hitachi alternator. They won't! The oem alternator has a max steady state rating of 65 amps. (130 amp surge capability). My Armada requires 65 amps without AC or headlights turned on. If you research how much amperage the individual components in the charging system can pass, it's down around 30 amps. If you consider the rate of degradation of crimped bimetal system components and connections, the benefits of soldered connections, and large gauge wires will be obvious. The Mechman 270 amp alternator has a constant steady state rating of 135 amps. So at 65 amps, it is running much cooler than the oem alternator and wiring. It will last much longer than the oem alternator, and provides a much more stable current to the system.
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