Is there anywhere I can get a high output alternator? In upwards of 300 amps? The highest I can find as a direct fit is 160.

 

jarrod, I know there was a member that just had one custom built for him, but I also know he seems to be having issues with it too as it is not playing nice with the rest of the car.

I think the big thing that you are going to need to figure out is the field control module that works on a pulse width modulation setup vice a varying DC signal like 99% of vehicles out there do. If you want me to go into more detail about how alternators work, I can do that for you. Working in the power generation field, I get to learn more about alternators than I care to admit to.

 

You can have a 160 rewound for perhaps 180-190. Anything over that, you will start cooking things unless you start rewiring with larger gauge wires. For that extra current, you'll get a significant loss of regulation.


The battery will suck back perhaps 80 amps at a bit over 15 volts, and it tends to be self-limiting due to its internal resistance.


The extra current really goes nowhere in our systems. The electrical system in out cars is a bit unusual; a higher than normal voltage is sent to the battery after starting for a period of time (several minutes) which will top the battery up very quickly, but is also rough as hell on it. It is also not very friendly to the rest of the electronics in the car. Our factory stereo system and nav boxes are designed to deal with it (except for the lighting, which WILL eventually burn out), aftermarket gear not so much.


If you have gear that draws heavy current, your better bet may be a large capacitive storage device to smooth out the demand on the battery.

 

Thermo,
What kind of troubles exactly? I know kind of how they work. Feel free to elaborate if you will.

Wa3ra,
I'm not saying you're wrong, just curious. How do other cars deal with 300 amp alternators? Is it something with a different kind of regulator?

The reason I'm asking is because at max power, my system can draw about 170 amps. Or at least try to. And I plan on upgrading sometime in the future, so it'll draw even more power.
And yea I do plan on a wiring upgrade soon, even before a new alternator.
I have a voltmeter, the lowest it'll ever show at idle, with my radio all the way up, it's around 11.9 volts. Which I'm pretty impressed with, considering most cars would drop below 10 with what I'm running. But I want to keep it above 12.5.
I'm still fairly new to this car. Would a 190 amp alternator and a large capacitor (3 farad) work?

 

jarrod, as for the problems that I am hearing about from other members with a high output alternator is that the car will sometimes regulate a good voltage and then other times the voltage will be all screwy and give numerous battery light indications. The voltage regulation in the car is all over the place.

As for how an alternator works, it is fairly basic. You have 2 loops that you need to think about and know how they interact with each other. The first loop is fairly straight forward in that it is the static windings in the alternator that then feed to a rectifier that converts the output of the static windings to a pulsating DC voltage. This voltage then goes over to the battery which is what helps smooth out the voltage to something more like a good DC signal (ie, very constant voltage even when looking at it in the millisecond range of change). In short, the voltage that the static windings puts out is relative to how fast the alternator is turning (which is related to the engine RPM) and the strength of the magnetic field (the number of wraps of this winding comes in to play, but more on this later). This is where we move on to the second loop.

The second loop runs from an electrical point inside the cabin of the car to the ECU. The ECU looks at this voltage and then compares it to a reference voltage (which is your ideal 13.7 VDC alternator output in 99% of the cases). It then sends out a signal from the ECU to the alternator to feed power to the field windings. The field winding then generates a magnetic field inside the alternator which is relative to the signal from the ECU. As stated before, the output of the alternator is a function of magnetic field strength and the speed of the alternator. So, as you speed up the engine, the magnetic field can be weaker, yet result in the same voltage output of the alternator.

Now, for what regulates the maximum current output of the alternator. This is a "what came first, the chicken or the egg" question. This is really a balance between all the components of the alternator. Normally what takes the most abuse is the rectifier. Keep in mind that the rectifier is nothing more than a series of diodes. Diodes will normally drop 0.6 VDC when operating. When you are passing 300 amps through them, they are going to get rather hot as the power that they are dropping is a function of the voltage across the diode and the current passing through it. In this case, you are looking at 0.6 VDC times 300 amps, or 180 watts of power, or 180 watts of heat being generated. If there is something that is a killer of electronics, it is heat. So, you can see where the rectifier sees a lot of "abuse", especially when you are running a high current alternator.

The second part of an alternator that is a limiter is the gauge of wire in the static winding. I liken this to trying to fill a swimming pool with a hose. Do you want to use a garden hose or a fire hose? I think anyone with even half a brain will say the fire hose. The same is true for electricity. You want to flow more current, you need a bigger wire. Where this becomes limiting and where the voltage regulation gets affected is that as you use a bigger gauge wire, you get fewer windings as you have a finite amount of space to run the wiring for the static winding. The voltage that the static winding can output is a function of the speed of the engine, the strength of the magnetic field, and the number of windings. Assuming that you are keeping the same speed, you are now trying to get a stronger magnetic field due to having fewer windings. This leads to limiting problem #3.

Where the field winding becomes a limiter is that you can only get but so much magnetic field out of a set of windings without changing something. Sure, you can add more wiring to have more field generated, but now you are limited by the amount of space for the field windings. The other solution is to use a bigger wire to pass more current through the wiring which will create a larger magnetic field (to a certain point). But, like with the diodes, the field windings are a power loss. So, if you are applying say 30 amps to the field to make it generate this monster magnetic field, the field is dropping 14 VDC (rounded for simple math), you are looking at the field winding dropping 420 watts of heat. Think about that. Think about the heat that comes off of a 60W incandescent bulb. You are now putting 7 of those bulbs inside your alternator and essentially cooking it. Keep in mind that your rectifier is adding more heat and you are making it more difficult to keep the rectifier cool too. As you can see, this is a fine balance of how much power can you get out without cooking something. This is why you will notice that higher current alternators are almost always bigger in size to help dissipate the heat due to more surface area.

There is a 4th "upgrade" that you can do, but you will find that most people do not recommend it. This is simply putting a smaller pulley on the alternator. This will get the alternator up to its maximum output at a lower engine RPM since the alternator is now turning more times for each engine turn. The problem comes when you start winding the engine up. A standard alternator turns at about 3 times the speed of the engine. So, if you rev the engine up to 6,000 RPM, that means the alternator is turning at 18,000 RPM. If you raise this to say 4 times what the engine is, that would mean at the same 6,000 RPM, the alternator is up at 24,000 RPM. At some point, the alternator is not going to be able to take this rotational speed and as you can imagine, when it lets go, it is not going to be pretty.

If there is something that you don't get, just ask. As you can see, I will try and break things down to something that you can understand. The generators that I work around output in the neighborhood of 25,000 volts and just under 1,000 megawatts, each. They use the same principles as the car alternator, but as you can imagine, things are just a little bigger and way more complex as the need for regulation is very high.

 

Jarrod, those big regulators have voltage regulators that are designed to use ONE voltage, 13.8 volts at full output.


Jag uses a sense circuit to vary the output voltage; 15.2 right after startup to top the battery back up fast, 13.8 afterwards.


Most electronic equipment has a voltage regulator built in that will let it look at up to 16 volts for a brief period of time, and most non-critical circuits (lighting for example) can take the abuse for some time.


There is a circuit in our cars that is before the VRs, by the way...it powers the info center display lighting and the radio lighting. Apparently Jag theory is that nobody runs the dash lights up full, and they actually use a PWM (pulse-width modulation) circuit as a dimmer, which will offer some protection. Some of us DO run them up full...which in Jag's case bypasses the PWM and sends full juice to them. Just a little bit of extra heat. They will survive for years, but eventually, the little bit of excess voltage will dim the displays, and eventually they'll fail...all from a few minutes of higher voltage every time you start the car.


Now take that handful of milliamps, and multiply it by 140,000...all that excess heat has to go somewhere...which is into the alternator case, and the diode bridges, and the regulators. (assuming 160 amp to 300 amp)


As long as the alternator has the oomph to keep the battery topped off, anything excess is overkill. Better idea, boost the alternator current slightly, and add a second battery and a charge regulator so it doesn't discharge one battery into the other.


My experience comes from running BIG RF installations under portable and mobile conditions...makes any car stereo install look like a Walkman!

 

Thanks for that thermo. It's really detailed. I get it, I understand electricity pretty well.

Wa3ra,
What would you suggest? Would a big 3 wiring upgrade allow enough current flow so my amps won't suck all the cars voltage? I really want to avoid a second battery.

 

jarrod, a second battery in your car is only going to mask the real problem. A second battery is only useful (assuming it is properly wired) if you plan on running the stereo with the car off. With the car running, 100% of the load should be on the alternator. If you are sucking from the battery, then you are going to end up on the side of the road with a dead battery and a car that won't start to recharge the battery.

Unfortunately, because of the amps that you are running, it is sucking up around 150 amps with the stereo turned all the way up. If you are listening to it at normal volume, then you shouldn't need to upgrade anything. If you are wanting to play it loud a lot, not even a simple "Big 3 Wiring upgrade" is going to correct things. It may make the problem not quite as obvious, but it is still there. You will definitely need to upgrade to a bigger alternator or figure out how to power the stereo with a second alternator. That is up to you.

 

That's what I figured. So a 190 amp, was suggested by wa3ra, seems to be the best option. Am I correct with this assumption?

Also, once I get the money for this, be prepared to help me with an alternator swap. I hate paying labor costs.

 

That is a good bet; the mild upgrade on the alternator...any decent shop can rewind for the extra 20%... update the big wires...and add a few decent sized capacitors for both filtering and holding up the voltage for those brief peaks when you exceed the alternator.

 

Sounds good to me. Now just to check on how much that'll cost me. I appreciate the help guys.

Is there any way to regulate the alternator to where it doesn't spike the voltage upon startup? So it stays at a constant, or is that just one of those 4 hinges that could cause problems?

 

jarrod, because the alternator is controlled by the ecu, you would have to have a custom "tune" put into the factory ECU to make that happen. The trick is finding a shop that will go in and make an adjustment like that.

 

Am I right in assuming that will be quite expensive?

 

jarrod, I am not sure what it would cost, but I know for a normal engine tune to be purchased, you are looking at about $300. I am sure you will be in that same range. Granted, you may also be able to get rid of the PWM control of the alternator and make your current one work. But, that would be up to the internals of the ECU and what converts the amount of control to the PWM control (is it done in the program or is there a circuit that converts a DC signal into a PWM signal).

 

I would add a second alternator and a second Lithium ion battery dedicated to the stereo equipment only and isolated from the rest of the electrical system. The only reason not to do it this way is lack of room on the engine to add the extra belt, brackets and pulley. I would look up from the bottom of the car as there is no way it will fit from above. If deleting the air conditioning compressor is an option that real estate would work fairly easily.

However, I do not think the OP has the resources to accomplish this modification at this time. I also question his asssption that the stereo system will draw 150 amps. It won't at least not continuously. Peak demands are usually met with banks of capacitors in high powered "show" systems such as he may be contemplating. Be careful - the capacitors can give a nasty shock, possibly dangerously so.

 

Haven't been on here in a while.
I did have to replace a leaking water pump, though that was simple.

Anyway, I guess that's not such a bad price. Seems about right. I'm not sure what exactly pwm is..

Nookieman, no way I could ditch the ac. My system at max power of everything would draw 173.
This car is just a pain for what I want to do, since more common vehicles have high output alternators that will just bolt right on and work.

I just don't want to be limited to only a 190 amp alternator, but oh well. Not like I need much more of a system for an everyday driver anyhow.
It's hard enough to drive a manual with the whole car vibrating as it is.

 

jarrod, pwm is Pulse Width Modulation. So, in short you have to look at things as an average over time. Instead of having a signal that is variable and ranges between say 0 and 14 VDC (like most alternators use), you have a circuit that switches the 14 VDC on and off very quickly. So, what happens is if you want say a "1 VDC" signal, you would turn on the DC voltage for 1/14th of a second and then leave it off for the other 13/14th of a second. So, the average over that second is 1 VDC. In reality, it would be doing something similar to this, but turning it on for say 1/1000th of a second and then off for 13/1000th of a second. This would be occurring so fast that to the eye and a multimeter, it would appear to be a constant voltage. If you wanted a higher voltage, you would simply turn the DC voltage on longer and have it off less. You can then make what ever voltage you want by simply turning on and off the voltage vice trying to regulate it to a specific voltage.

 

Ok. So then that's why my volt meter sometimes will go up when the amps are drawing power, because it's putting out more when needed?

 

jarrod, yes. You can think of the voltage on the multimeter as the percent of the possible output that the alternator can do. This isn't a simple "at 5 VDC it is 30% of max output and at 14 VDC it is 100%". The max output of an alternator is also based on the speed the alternator is spinning. At idle, you can have the field at 8 VDC and it will only be outputting say 20% of the rated (max) current. Where you get the engine up to highway speed (2500 engine RPM), that same 8 VDC input will allow the alternator to output 70% of max. This is where a detailed understanding of how a generator works will explain this. This effect is why a lot of people with large stereos have no problems at highway speed with their lights flashing with the beat of the music, but they get to a stop light and their car looks like a disco dance floor. In this case, the alternator is seeing 14 VDC on its input so it is outputting its maximum current, but with the low RPMs, the alternator can only output say 50% of its max.

 

So I’ve read this thread many many times. Thermo: I appreciate your knowledge greatly! Anyway... I’m running a 1800 watt RMS amp in my 03 X type and it’s pulling 180 amps roughly. So I had a custom alternator built for my car and it should be done soon. The company I ordered from actually had a x type in the driveway so that was promising! He was able to measure the distance from the battery to alternator for my big 3 upgrade so I was sold. They are a competitive audio company so wish me luck...