Alternator ratings...

[ice745]

My stock alternator is rated for 80 amps.
I can get a remanufactured one, with a better stator and other parts they say, that is rated 160 amps. They say at idle it will give out 80 amps.

My question is the rating printed on the stock alternator, is that idle output or the max? I.E. Will a "160 amp at 1200 RPM, 80 amp at idle" actually be an improvement over the 80 amp stock. Or is it really not a standard rating system, so there's no sure answer?

Thanks

[vgames33]

I think the rating is the maximum load that can be supplied by the alternator. If you have it rewound, the output should rise regardless of RPMs.

What do you want a beefy alternator for?

[ice745]

I have a stereo system that shouldn't really need a beefed up alternator. But the battery is not being charged nicely. I had a wet-cell that had to keep being charged every few weeks, and sometimes every week at times, til it didn't hold a charge at all. I replaced with Optima Yellowtop, now the battery just needs to be charged every few months, or every month sometimes. Probably a reman 80 amp will do, because my alt is probably just worn out; but I want to beef it up just to be safe. And the beefed up one is not much more than a regular reman one.

[vgames33]

As long as you don't need any special brackets, I don't see why the bigger one would be a bad idea.

If your stereo drains your battery like that, I think you might have another problem. How many watts are you pushing? My 200 watt head unit has never drained my battery to the point where it needed charged, but then again, I don't blast it all the time.

[UncleBob]

high output stereo systems (very high output) have a very large draw, but it comes in phases. The problem is not so much the output of the alternator, but the "buffer" the battery offers. Too small of a battery will cause the voltage to spike downward.

The answer is to increase battery capacity. Super serious stereo's such as stereo competitions, will have DOZENS of batteries in parallel because of this. I assume your system isn't that severe though. Start with one extra battery and see how it does, add more as necessary.

This doesn't mean you couldn't use a higher amperage alternator, but that depends on how often you run your stereo at levels that surpass output of the alternator. Shortish use at peak output, there no real advantage to increasing the size of the alternator. IMO, if your battery still starts the car every morning (assuming the battery is in good condition of course) then there's no point on changing out the alternator.

[ice745]

Ya it's not a crazy system. It's just 900 watts. But I do have it pretty loud for most of the time. The yellowtop battery is working a lot better with it, althought I do have to charge it every few months. I charge it to keep the voltage up. The old battery I had to charge to start the car.

The reason I want to change the alternator is for voltage swings that occur now. People in stereo and camry forums tell me it's normal. But my alternator for the past 3 years until now has always stayed above 14.2 and never swung. It usually ran 14.5, high beams could bring it down to 14.2, but it stayed at 14.2 until I turned high beams off. Stereo would of course swing the voltage between battery level and the 14.5. This part seems normal to me.

The abnormal, which people tell me is in fact normal is now headlights swing between 13.3 and 14.5, highbeams between 12.9 and 13.2, wipers 12.9 and 14.4. Some burts go to 14.8, but rarely and shortly. And this is all with the stereo off. Maybe it's just so different from my normal alternator's operation that I see this as drastically bad, because at least 5 people have told me this is ok, and nobody agrees it is bad. Even if it is ok, I still want to replace it so I can have my own peace of mind.

I am going to run 4 gauge wire between the alternator and battery and remove the stock connection. I am planning on having 2 fuses, one close to the alt, and one close the the battery.

[UncleBob]

so the voltage at the headlights is different than the voltage at the battery?

That is called a "voltage drop" and has nothing to do with the alternator. Has to do with the amount of wattage of a component, and the amount of resistance between the power supply (mainly the battery, because its the buffer for the entire system)

Dirty connectors, deteriating wires, too small wires, too many connections/contacts, or too small connections/contacts, or corroded/dirty connections/contacts, will all add up together to increase voltage drop for a component.

Some voltage drop is quite normal. I think you probably don't have a real problem here

[ice745]

Nope... I use a digital multimeter, but lets pretend I use an analog one with the needle for illustrative sakes.

I hook it up to the battery and the needle goes back and forth pretty wildly. Used to stay at 14.5 and move slightly to a new position if I turned on more electrical stuff. Now it can stay at 13.3 if I'm lucky, but usually turning on anythign causes the needle to go into it's wild frenzy.

[UncleBob]

you need to check the diodes, if you have severe oscillation....but I doubt the truth of the meter, honestly.

Diodes in the rectifier of the alternator (interally regulated), called the "diode bridge" convert the AC output to DC. When the diodes start failing, it causes some AC output, which can cause voltage fluxuation.

But....13.3V with everything turned on at idle, isn't bad at all. There are cars out there that will drop way lower than that with eveyrthing on

[ice745]

Oh no, 13.3 is with everything off at idle. It used to do 14.5 a few months ago. Now 13.3 is with everything off. And then it starts swinging crazy when I turn things on. With a low of 12.7 and a high of 14.8. Never did the crazy swinging before

Shouldn't be the multimeter, it's one of the fancy electronic engineering ones that's pretty spensive. It does voltage, amps, capacitance, resistance, temperature, infared temperature, and frequency. And it's not even a year old I think. Plus I double checked with an old rinky dink one that was laying around.

[UncleBob]

simply find a shop to test the diodes. It requires a tool designed for the job (VAT45, for example) that any monkey can hook up, push a button, and it spits out a result.....or find someone with an expensive oscilliscope that can see AC bleeding in the system voltage

Or, you could take apart the alternator and measure the diodes directly. But first two options are much simpler

[ice745]

True. But not to get away form the original post. I know something is wrong. And since I am replacing the alternator, I don't entirely care what. I am going to put the higher output alternator in. I just wanted to know how they were rated to be sure it was actually an upgrade.

I could spend the time and determine if the rectifier is failing or if the regulator is failing. Being that it gets worse as it gets hotter, it leads me to think more that the rectifiers are failing. Since both forward voltage drop and reverse voltage is affected by temperature. While the regulator could be failing to give a constant proper voltage to the rotor, this would more affect the amperage output of the alternator. Which would only reflect on voltage if it was too low for the open paths of resistance. In this case it should be too low to keep the battery charged at all. But being that I only have to charge the battery every month, I would say the amperage output is decent.

Why do I want to replace the alternator? Because I'd rather maintain a 160 amp alternator than an 80 amp. I know how the stator and rotors are wound to give higher amperage, I just wanted to see how stock alternators and rated so I know if the data the supplier gave me actually represents a higher output alternator. I am convinced it does, so I want to replace.

[UncleBob]

all alternators are rated by peak output.

[KiwiBacon]

For reference the alternator on my nissan is rated at (I think) 80 amps. I have measured 50 amps coming out of it at idle.

Some alternator companies make special units for show cars. Usually with a polished body (wank factor) and a smaller pulley to put out more current at idle.

[curtis73]

On alternator ratings... I recommend only what you need. The alternator will only charge as much as you are using. If you're running the headlights and the A/C and they're drawing 10 amps, the alternator only produces 10 amps regardless of what its max rating is.

If 80 is enough and you give it 160, it will be totally wasted, and if you ever run the battery dead and have to get a jump, the alternator defaults to full 160 amps until its charged again, probably 20 minutes. In 20 minutes of 160 amps, chances are your fancy alternator might be a puddle of molten plastic, copper, and aluminum.

An alternator case design is no different from wire gauges. You could run a car using a 8ga battery wire. If you have short cranking times, don't have a crazy stereo, etc, it will be fine, but that one time you have to crank the engine for more than 10 seconds, you have a fire on your hands. Asking your stock alternator style to handle double the amperage is a recipe for a dead alternator. Think of it like this: you could double the power of your engine, then never use it because you'd break the transmission and axle. You'd have to drive around all day with a light foot, but that one time you let er rip, you'll destroy the driveline and break a crankshaft because its not designed to handle it.

Only get what you need. Save your money, and you won't have to worry about things. More is not better.