I recently installed a pair of subs and two amps along with two pairs of door speakers in my 02 X-type. The extra demand on the electrical system prompted me to upgrade the charging system and the power/ground wires.
I replaced the battery with an Optima AGM and the ground and power wire leads with 1/0 gauge SGX copper wire. I also replaced the alternator with a 210amp new unit that was a direct bolt in replacement. Since that install I have DTC's for low voltage and its gone into limp occasionally if the stereo is on and the rpm's drop below 1000-1200.

I was going to put a smaller pulley on the alternator but cant find one. Is there any proper way to raise the idle from 700rpm to 1000 ? Has anyone overcome a similar issue as this with their X-type ?

 

LVS, being a stereo guy and also an electronics tech, I can tell you almost down to a tee what your problem is.

Lets start with a little background on how an alternator works. You have a spinning field in the center (ie rotor) that is driven by the serpentine belt and how fast this spins is dependent on the engine RPM. The voltage that is outputted from the alternator is a function of how fast the rotor spins and the current going through the rotor. The ECU will regulate the current going through the rotor to maintain the output voltage since it can't control the engine RPM.

Now, in your case, what you are experiencing is as the engine RPM comes down from highway speed to near idle, the current through the rotor has to go up to maintain the output. Unfortunately, you reach a point where you have raised the voltage as high as it will go due to the current draw of the system pulling the voltage down. This can be compounded by the fact that some aftermarket alternators play with the rotor wiring to help produce higher outputs when the alternator has more speed. But, this comes at a cost of reduced output at idle even compared to the stock alternator.

No alternator that I am aware of gives you its rated output at idle. The factory alternator (160 amp unit), only outputs about 85 amps (or roughly 50%) at idle. It isn't until you hit about 1500 RPM that it finally reaches its rated 160 amp output. In the case of your aftermarket unit, even if you have a good rotor in the alternator, you are still only getting but maybe 100 amps or so out of the alternator at idle.

As for raising the engine idle, there is no way to do this other than going to a dyno shop and having them put in a custom tune to the engine. But, that will probably set you back about $300 or so. You can try a smaller pulley, but at the same time, I would also recommend that you don't rev the engine over say 6000 RPM. You are going with the smaller pulley to make the alternator spin faster for a given engine RPM. You start pushing the engine up near redline and that alternator is going to be spinning really fast. Potentially so fast that it is going to come apart on you. Know what a grenade sounds like going off? You could potentially experience that if the rotor comes apart.

As for overcoming your issue, I can only think of 2 ways to overcome it. 1) turn down the music when you are moving slowly, or 2) be the first to install a second alternator into the X-Type. I know neither one of these answers is probably what you want to hear, but that is the short of it. Lowering the volume puts less of a current pull on the alternator and therefore you won't overload it. By adding a second alternator, you can have a second unit to add that much more current to the electrical system.

I wish I had better news, but it sounds like you have one hell of a stereo in the car and unfortunately, if you plan on playing, it is going to cost you.

 

Thank you for the reply. You answered my question about raising the idle. Also I am going to add a second battery then power all the add-ons with the new circuit. The alternator I bought does not fit the needs of a cruising vehicle and does not produce below 1000rpm. I am either going to replace it with the 160amp OE unit or have the ecu tuned to raise the idle rpm. I do think that there may be another variable to the issues I am experiencing. The new alternator I bought may be to blame. I wish it was not such a pain in the *** to replace.

The stereo consists of 2 10" subs powered by an 800w RMS 2 Ch amp and then 2 pairs of 6.5" components powered by a 600w RMS 4 Ch amp. The peak output is in the 1800-2800w range when its cranked up. But even with the stereo turned down and the sub amp turned off the electrical system is showing signs of some sort of issue. When I blip the throttle the head unit's line out signal to the amps cuts out momentarily and the green lcd display on the A/C control lights up when it is off??? Then the fuel mileage went from 21 mpg to 15-16.5mpg on average as well ?

 

becafull with two batteries you can kill your alternator if hooked up wrong

 

I plan to use a proper isolator with it.

 

LVS, smart man using an isolator. I can't tell you how many horror stories I have heard with just hard wiring 2 or more batteries together thinking that it was making things better.

As for your mileage dropping, if your voltage is dropping like you are saying, then your problem is that you are not getting sufficient spark at lower RPMs. Like you mention, reconnect the factory unit and see what you have then. It could be something as simple as the alternator that you put in.

Just to put things into perspective, you are pulling about 140 amps just for the stereo. The motor requires 10 just to run. The headlights are another 10, running light are another 5. Seat heaters are 15 amps each. Dash blower (on high speed) is 20 amps. This will give you an idea of what sort of power you may need in your vehicle.

Adding a second battery is only masking the true lack of power coming out of the alternator. The second battery is only going to make it so you can drive a little farther before both batteries are dead. The main purpose behind a second battery is to allow running of the car's electrical stuff with the engine off and still giving you the ability to start the car afterwards (assuming you move the appropriate stuff to the isolated battery). This sort of thing is what I did for a living for 20 years. Granted, the battery I played with could power a small town. It powered a nuclear reactor/submarine for a few hours during emergencies.

 

I'm still trying to comprehend the noise levels from a stereo system that needs the power to have that effect on an X Type!

Is driving it an indulgent pleasure or a self inflicted punishment!!?

 

Back-up generator in the trunk? Probably would be too loud!

 

I think I am going to reconfigure the load from 2ohms to 4ohms on the sub setup. That will cut the power demand in half from that amp. I will probably use a Kinetic or Optima yellowtop deep cycle in the trunk I already have 1/0 gauge pure copper power wire running to the trunk that supplies the amps and the air compressor. I just need to pick a top shelf isolator now.

Does anyone else on here have a media sever/sound system like this in their X-type ? If so please describe your charging system setup and or the hurdles you had to get over to keep the car happy.

 

I spoke with the local alternator shop that sold me this 210amp unit. He said they could change the stator to a 160amp unit for free. He explained that my 210 unit needs 1000-1200 rpm to produce charging voltage and only outputs 198amps at 5000-6000rpm. I replied that the operating range of the unit he sold me will not work for the application. By his words, the only parts options available for this Denso alternator to produce charging voltage at 700rpm is the 160 amp stator or smaller. Not sure how accurate that information is though.

 

LVS, that is sounding about right. I mentioned what you are seeing in my initial post. Granted, I would be asking him how they can "rate" the alternator for 210 amps if it can only hit 198 amps. Just saying. ANy alternator worth anything should be at full output by 2000 RPM on the engine. Spinning it faster is just making it so the rotor won't heat up as much since its current draw will be less.

 

I bought a 200amp isolator, some extra 1/0 copper wire, and a second battery (Optima 35 Yellowtop). Just waiting on the battery tray for the trunk to arrive. I will post some pictures along with the outcome soon.