Moparts Tech Archive

Elec Topics

solved the common Mopa low voltage at idle problem

I picked up a Denso alternator in the wrecking yard (Toyota 4Runner unit) and fabricated a mount to hang it from my motor plate. (I'm not selling these motor plate mounts so this isn't a for sale ad.) For the first time ever, the lights do not dim at idle. The Denso alternator is a 60 amp unit and it puts out a lot of amps at idle. My amp gauge showed 10 amps of output at 850 rpm (motor rpm). Voltage is 14.4 volts at idle with the headlights off, 14.2 with the lights on, 14.2 with high beams on.

The Denso alternator is 6 lbs lighter than the Mopar unit and is internally regulated. So one more thing gone from the firewall. I just ran the 12 volt source line that used to go the voltage regulator all the way to the alternator. Had to add one sense line so the alternator can "see" what hte voltage bus is at. This line I ran to the starter relay stud since that is where the BAT connects to as well as several other 12V sources.

AndyF

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The alternator is from '85 to '92 Toyota 4Runner and pickup trucks....

AndyF/ARengineering already manufactures kits to mount this alternator to both small blocks and big blocks in the stock location.

Andy, i found the same thing with the smaller 50 amp Powermaster alternator. The amp gauge stays on the + side now at stoplights.

I looked in the tech archives and saw the mounting for this alternator, but not how to wire it in. Does anyone have a schematic?

You can hook it up with only two wires IF the bat charge line is short and low resistance. I don't recommend it but it is possible if the electrical system is well designed. Mark has some excellent tech on his website at www.madelectrical.com on this subject.

Basically the issue is around one-wire alternators that don't work very well when they are put into stock wiring harnesses. The problem is that they cannot correctly compensate for the voltage drops in the harness since they are sensing only the output of the alternator.

So if you're going to run one of these Denso units, make sure you fully understand Mark's technical papers before you wire it differently than recommended.

One other advantage to the Denso unit over the stock Mopar unit is the fact that you can underdrive the Denso unit and still get amps at idle. When you underdrive the Mopar unit it basically stops providing amps at idle. On my car with the March pulleys, the stock Mopar unit didn't output any significant amps at idle while the Denso unit reads around 10 amps. I haven't loaded it any further so I'm not sure what the max amps at idle it can produce.

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