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Alternator 101 What You Need To Know

Posted on 8/16/17 with No comments


Most alternators look about the their really much difference besides the price? 

Fifth Avenue Invented the 6-volt alternator in 1985. Since then there have been a few knockoffs sold but they do not work as good and are not as reliable as the Fifth Avenue alternator. Here is why...

In the case of 6-volt alternators the easiest way to build a 6-volt alternator is to simply swap out the 12-volt voltage regulator with a 6-volt regulator. As with most things the easy way out is not always the best. In this case, when you install a 6-volt regulator inside of a 12-volt alternator, not only does the voltage get reduced by 50 percent...the amperage output (the part that does the actual electrical work) is also reduced by half. So if you start out with a 60 amp 12-volt alternator, swap the regulator out for a 6-volt version, you will end up with a 6-volt alternator with a maximum output of 30 amps.

Keep in mind that most alternators only develop their maximum output at highway speeds and will only deliver 30 percent of their rated output at idle and low rpms. In this example that would be 18 amps output.

Another thing to keep in mind... is that when alternators were introduced in the late 1960's, the idle speed of most engines was 1200 rpms or greater, so that was the rpms that modern alternators were designed to begin charging.

Using a 1950 Chevrolet car as an example, the ignition requires 1.6 amps, the headlights (pair) 14 amps, taillights 2.3 amps, dash and instrument cluster 2.5 amps, heater blower motor 8 amps, tube type radio 7 amps, for a total of 35.4 amps. That does not include any modern extras like electric fuel pumps and electric radiator cooling fans.

Lastly you need to consider the idle speed of your engine. If your idle speed is below 1200 rpms, that will reduce a modern alternator's output even further. We know for example, that a 1950 Chevrolet has an idle speed of about 700-800 rpms.

In the case of a 12-volt applications much of this wisdom also applies. If your idle speed is below 1200 rpms you will experience reduced output from a modern 12-volt alternator as well. The maximum rated output will still occur at highway speeds and even with 12-volt applications most alternators will deliver about 30 percent of their rated output at idle speeds of (1200 rpms) or about 18 amps.

Taking all of this into consideration, when I was working on my 6-volt alternator design back in 1984, I knew my alternator had to overcome these basic faults if my alternator was going to be successful.

A Fifth Avenue 89/90 series alternator, (both the 6-volt and the 12-volt versions) begin charging at 300 engine rpms as compared to the 1200 rpms of a modern alternator.

That is possible because Fifth Avenue uses specially wound rotors and stators. Fifth Avenue alternators are a built from scratch as special purpose alternators, and are not a converted modern 12-volt alternator.

One of the key differences is in the stator (the heavy windings inside of the alternator). Fifth Avenue uses a "Delta" design stator. In this advanced design, current is allowed to flow from all three stator windings which results in a stronger more reliable output at engine idle and low rpms, with less chance of damage from excess heat.

The more common and less expensive "Y" design stators allow current to flow in only two of the windings at any given time and are less resistant to excessive heat. As you might suspect the Delta wound stators cost more than the common "Y" design stators but in antique vehicle applications the cost difference is worth it to insure a strong current output at low idle speeds and low engine rpms.

The end result is that Fifth Avenue 89/90 series alternators begin to charge at 300 engine rpms and will deliver 30 amps output 300 rpms idle speeds. That will insure you will always have bright headlights and easier starting and your battery will always be fully charged.

An internal regulator is also very important. Its about communication. It is a lot easier to talk to someone face to face... than to yell at them two blocks down the street. With the increased distance the message is not always clear and understood.

In the case of an alternator an internal regulator means instant results and good communication between the regulator and the alternator. And all Fifth Avenue alternators are build using solid-state regulators which means no mechanical moving parts to wear out. Again...simple is good!

If you still have a generator charging system, chances are you will have to replace the battery at least every other year and in many cases every year. That is because the generator cannot keep the battery fully charged and the more times a battery is cycled (charged and discharged) the shorter its life span will be.

When you install an 89/ 90 series alternator from Fifth Avenue it is not uncommon for batteries to last 6-7 years or longer because they remain fully charged just like in a modern car. That means less maintenance for you.

Machined Steel Pulleys Are Lifetime Guaranteed

Next up is alternator pulleys. When alternators were introduced all engine driven fan belts were 3/8" wide. As we know... most antique vehicles came with much wider belts, some as wide as 3/4" in width. Fifth Avenue includes the pulley of your choice to match your belt width at no extra charge when you buy an alternator from us. While most places charge extra for a pulley we say it is like selling you tennis shoes and making you pay extra for the shoe strings... Plain and simple... a pulley should be included, otherwise how are you supposed to get any benefit from the alternator?

All of Fifth Avenue pulleys are made of machined steel and come with a lifetime warranty. The less expensive pressed tin pulleys tend to wear deep in the groove where the belt rubs against the spot welds. Eventually the two pulley haves will separate and it will get ugly and expensive from there. I have seen pressed tin pulleys go thru radiators, and it is not a pretty sight!

Another important detail is pulley offset. In order to make the fan belt line up, you can either offset the pulley or move the alternator mounting bracket rearward to make the pulleys line up. We offset all of our pulleys so everything lines up and you do not have to move the alternator mounting bracket.

Most of our customers never notice this important detail, but that is the way it should be. If you have ever tried to adjust an alternator mounting bracket to make a pulley line up, you will appreciate this detail.

DA Plug Alternator Wiring Harness

Lastly is the alternator wiring. Because an alternator delivers an output at idle and low engine rpms where the old generator did not... the output from the alternator will travel back thru the wiring harness and feed current to the ignition coil even if the ignition switch is in the"off" position. That will keep the engine running with the ignition key in the "off" position

This first happened in the late 1960's which is how we got the "accessory" type of ignition switch. The alternator field or "exciter" wire was connected to the accessory post of the ignition switch which was a separate terminal from the rest of the ignition terminals, and that stopped the flow of current to the ignition coil.

The alternator uses a field or "exciter" wire to send a very small amount of current from the ignition switch to "turn on the alternator" to help it begin charging as soon as the engine is started. That is a good thing. That is partly how an alternator can guarantee a current output at engine idle and low rpms. It is not good when you try and shut off the engine with the ignition key, and the engine still keeps running.

Most "experts" will tell you to change out your ignition switch to a modern accessory type ignition switch to fix this problem. At Fifth Avenue we believe "simple is good" so we fixed the problem for you. You will receive a "DA Plug" wiring harness with your alternator that allows you to keep your original ignition switch and your vehicle will turn on an off with the original key just like it always did. A DA plug wiring harness is included with your alternator at no charge.

A note about 1-wire alternators...1-wire alternators were originally designed for racing applications that ran only ignition and not much else. Because those engines ran at high rpms most of the time, the output of a 1-wire alternator is minimal and is designed to start charging at 1200 rpms or greater engine rpms, and will often "drop out" or quit charging completly when the engine rpms drop below 1200 rpms.

Many of these alternator are being sold to antique vehicle owners with the idea of the simple one wire installation. Like your dad always warned you... you don't get something for nothing! In this case you get little or no current output in exchange for a simple wiring installation. I talk to many frustrated antique vehicle owners on a weekly basis who complain that their 1-wire won't charge.

An 89/ 90 series Fifth Avenue 3-wire alternator is easy to wire. One wire goes to the output stud of the alternator from the "Battery" terminal of the old voltage regulator (same as a 1-wire setup).

Next snap the DA plug into the top of the alternator, the red wire with the ring terminal goes to the same output stud on the back of the alternator  that the battery wire is connected too (from the old voltage regulator) and (that tells the internal voltage regulator what to do).

The yellow exciter wire that is left goes to the (+) terminal of the ignition coil and will turn on the alternator as soon as you turn the key on. Again...Simple is Good!

The idea here is to help you get things right the first time. Then you can go drive and enjoy your antique vehicle...after all that is why you have it in the first place!


About Me

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Since 1987, Fifth Avenue owner, Randy Rundle, has been making antique, classic and special interest vehicles more reliable and fun to drive.