What to look for in a High Output alternator.

[Tirefryr 1,742]

Figured I'd post some stuff up seeing as how it has been a hot topic as of late.

The biggest problem with rewinding a stock alternator is the fact that most winders do nothing more than rewind the stator for additional output. This does nothing but increase upper RPM output and decreases the cut-in RPM. This is the RPM in which the alternator begins charging. This can be controlled with a lower cut-in regulator, but that is just a band-aid. The alternator will still produce nothing more than stock output at a low RPM.

When looking for a GOOD unit, make sure to ask the manufacturer how the alternator was built. You want to look for one that has had a rewound rotor as well. This will increase the voltage in the AC wave during low RPM in conjunction with the rewound stator. It allows for a lower cut-in and greater output in the lower RPM levels. It also allows you to rotate the alternator at proper speeds alleviating the need for a smaller pulley (another band-aid to assist with a lower cut-in).

The rectifier and regulator: Another shortcut used by some manufacturers is using a stock or replacement equivalent rectifier and regulator. The aftermarket for replacement parts for alternators is just as vast as the car audio market and there is NO shortage of high quality parts and supplies for these units which are specifically designed to handle high output and demanding loads. Your main focus here should be a rectifier that will cool efficiently and has higher amperage diodes. Some rectifiers will have an Avalanche type diode. This is far superior to a normal diode in terms of voltage spikes. When the alternator is under a full or heavy load and suddenly the load is decreased, this will cause a voltage spike as the alternator is still trying to supply that high voltage and current demand, even though it has been suddenly removed. Avalanche diodes handle these spikes better than conventional diodes.

As for the regulator, you want something to keep your voltage stable and quite high. Voltage loss will occur no matter what. Try to find something that will regulate to 14.9 and no higher. As the engine warms up and the alternator does more work, more heat is generated. A high quality, purpose-built regulator will handle this with no problem. One drawback is many cars are now being switched to a computer controlled regulating system. It's becoming more and more common and the only way to change it is through tuning. The plus side to this, is you take the heat away from the internal regulator and the computer is more efficient at regulation versus the standard solid-state internal regulator.

Now, obviously, the best alternatives would be external rectifiers and regulators, but these are expensive, hard to implement, and can take up space that is already in short supply. IF you're looking into external regulation and rectification, do your homework and make sure you can implement the components before buying, and make sure they will interface with your ignition and electrical system. Regulators may look the same, but electronically, they don't all function the same.

Bearings, IMO are the weakest point of the alternator. MAny builders are using cheap bearings. AVOID THIS!!! A good quality bearing will hold up to heat, vibration and harmonics. The alternator is spinning at a very high RPM, sometimes three times the engine speed and a good quality bearing is a necessity.

The enemy in the whole situation is HEAT. YOu want to remove, or keep out as much as possible. MAny newer units have internal fans which are part of the rotor assembly. Aftermarket units may have a different fan style which will aid in cooling. This is a good feature to look for. With an external fan, your choices are pretty much limited to a stock fan as there are not many alternatives on the market. IF you have the time, skill and resources, I suggest a forced cooling system for the alternator. This is very common on Bosch and VAleo units on BMW and is quite effective. Simply supply some fresh air from a fenderwell, or somewhere outside of the engine compartment can decrease temps dramatically and help prolong the alternator.

The main thing is, to not buy cheap! IT may be a deal, but it won't last. You may spend $3-400 on a decent unit and have to replace it in 3-5 years, where if you spend a couple hundred more, you'll be able to double the lifespan of your alternator and increase durability.

[Eldorado 0]

No sense in buying something that is the heart of the system thats built like crap

[Chevy350TPI 12]

Great info. Learned a few things, too ... thanks Ryan

I agree with Elias ... why bother skimping? Do it right.

[Acidburn 10]

thanks Ryan, definitely a good read

[Hayabusa 0]

Would Mean Green or Ohio Generators be classified as quality high out put alternators???

Edited May 19, 2006 by Hayabusa

[Tirefryr 1,742]

Would Mean Green or Ohio Generators be classified as quality high out put alternators???

Both have made a good name for themselves, especially Ohio. I cannot really comment on them without knowing the build aspects of the alternator. I was fortunate enough to work next to a man whom had 30+ years of experience and has used just about every product on the market, therefore, I know what to ask and what to look for.

I suggest when shopping for an alt, ask them if they use the type of parts I have layed out in the thread. If so, you should be good to go, assuming they are competent in the assembly process, which is a rather simple process. If they are using quality parts, they should be more than willing to let you know, and if not, stay away. Some even go to the extent of having their own R&D team and developing custom parts for their own use.