I am having some issues with my charging system. I’ll tryand describe the issue as best I can.

I’ll start with the set up and then the issue at hand.

I have a swapped REW and I’m running an FD alternator inplace of an 8 alternator. I have my battery relocated to the trunk.

The issue I’m having is the voltage will drop and the carwill not idle as well. When I start the car, voltage sits at around 14.9 V to 15.1V. during this time the car will run nice and smooth, idle will hold withoutany encouragement from the right foot.

After driving, SOMETIMES the alternator light willilluminate. When the alternator light illuminates, the voltage tends to besitting around 14.2 V to 14.4 V. Once this happens, the car gets a littleerratic at idle, and will die off every now and then. Length of time for thelight to come is varied, however, the warmer the car, the quicker the lightwill come on. It won’t come on until after the car has reached operatingtemperature, sometimes right after it reaches operating temp, sometimes a whileafter reaching operating temperature.

This weekend, the alternator light stopped appearing asfrequently. Example, today was the first day I was able to drive to work (45minutes with some traffic) without the alternator light. When I got to work,car idled beautifully.

I can’t decipher if the alternator light comes on and thevoltage drops, or if the voltage drops first.

1) What causes the alternator light to illuminate?From my research I understand the lights illuminates anytime the voltage drops below14.5 V. is that correct?

2) What sensors / equipment combines to completethe charging system? Battery and alternator are obvious answers. I’ve readsomewhere the MAF is tied into the charging system, is this true? How does thisimpact the system if so? Are there any other sensors tied to the chargingsystem?

3) I’ve read that non OEM alternators can cause thelight to illuminate, I don’t fully understand why this is the case. Is it dueto the aftermarket alternators not charging at the right rate?

4) Does anyone have access to the operatingspecifications for the Renesis Alternator and the FD alternator? Is it possiblethe pulleys on the alternators are different sizes causing the charge rate notto be sufficient?

My thoughts for remediating the situation has led me to twodifferent options so far, and neither seem like great ideas, but band aids.

1) Install a capacitor between the battery and themain power supply. Theory is the stored energy in the capacitor will preventthe volts from dropping below the point where the alternator light illuminates.Similar to a capacitor in a sound system.

2) Change the pulley size on the alternator toensure the FD alternator runs/charges at the same/a similar charge rate to the Renesis.

I apologize in advance for my **** poor understanding of theelectrical system, but electrical is my biggest weak point.

I’ll answer any questions that help get to the bottom ofthis.

Thanks in advance!

 

If I recall it's below 12V. Certainly a lot lower than 14.5V. Anything above 13.5V is certainly good. With a race pulley setup at idle I only see 13.5V or so and no light. Before I ran a high idle it was down in the low 12V range with no light that I can recall.

If you're using the FD alternator then you also need to be using the FD voltage regulator. This is all handled electronically on the RX8 by the PCM. The FD3 was not. You haven't stated if you have one or not.

 

I was under the impression the voltage regulator for a FD alternator was internal to the unit.

 

Could be. I'm not an expert but knew it had to have one somewhere.

Did you have the alternator tested somewhere to be sure it doesn't have a problem?

Also might depend on how you have it wired since it can't just be plugged into the RX8 harness like the RX8 alternator.

 

I'm going to perform a load test on it this weekend.
I've had it verfied as working by an autozone, but i can only trust those results so much.
I'll have to take another look and see how the wiring sits, it's been a minute since i looked at it.

I'm also starting to wonder if an aftermarket votltage stabilizer is an effective thing to use.
I've heard mixed reviews.

 

Bump.. Did you ever get this sorted? Been doing some reading and it reminded me of this issue. Are you running rx8 MAF sensor?

You may need to as it reads intake air temps and if there isn't any temps being logged it cuts charge to the battery. Assuming its too hot and being overcharged. It may or may not be your problem. But if im not mistaken with Adaptronic you can do away with the MAF and run a MAP based system... I think.

Edit: RX-8 13B-RE conversion! - Page 5 - RX7Club.com <--- Source (post 102).