Alternator-Upgrade Wiring Tips for Popular GM Charging Systems

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A popular form of performance upgrade revolves around applying current technology to old machines. Although others are focusing on four-figure LS engines with large turbochargers or superchargers, let us keep our goals more relevant and realistic.

One of the most overlooked aspects of replacing the latest engine model with an earlier Chevrolet is to upgrade the charging system. In the early 1960s, alternators replaced generators. Since then, it has been closely followed by the landslide of the charging system and the improvement of the alternator. We decided that we needed to focus on some of the more popular alternator conversions and the wiring harness modifications needed to adapt to them. We hope to get valuable advice from some professionals in the field of car charging, so we have



On the back of the GM alternator, you will find a two-wire or four-wire plug and a large output stud. The large stud is used to connect to the output wire of the battery positive terminal.

There are at least a dozen or more variants in the family tree of GM alternators, but we will simplify them to the basic four. The best way to upgrade the Chevrolet charging system in the 60s or 70s is to upgrade to the latest models such as the CS130D. Even the stock alternative CS130D offers more power than previous models at low speeds. That is just an idea. Other alternative methods are also very useful.

Before we study the details of the swap, it is useful to study the charging output figures. In almost all cases, the alternator is rated by the maximum potential ampere output. This is not the amperage provided when idle! Based on many factors (such as alternator design and pulley ratio), the idling output of the alternator may be much less than its maximum rating. The original 10-DN externally regulated alternator may not be able to provide more than 35 amperes of current in an idle state. Back in the AM radio era, this was enough to maintain the system voltage.

We talked with Mike Stasko, Marketing Manager of Tuff Stuff Performance, and he made suggestions. "Once the ampere requirements of the vehicle are determined, please check whether there is a higher ampere alternator in the same alternator series. Compared with the alternator of a different series, replace the low-current alternator with a high-current alternator. Generators are always easier."

Later models of alternators are much more efficient when idling, so a spare 100-amp alternator may have 60 to 65 amperes of current when idling. But let's take a closer look. The rated number of the alternator is usually tested using the alternator at ambient temperature. Unfortunately, when the charging system is at normal operating temperature, the internal resistance increases as the heat increases, and the output usually drops by 15% to 20%.

If your alternator is idle with a rated current of 100 amperes, its normal operating temperature may only reach about 75 to 80 amperes. If your dual electric fan and other electrical equipment can produce more than 70 amperes of current, that is a problem to consider. The end result is a loss of system voltage when idle.

These are the four most common alternator connectors. If you are not sure which alternator you are using, the shape of the connector can be a good indicator of the alternator configuration. From left to right: 10DN, 10/12SI, CS130/CS144 and CS-130D.

"If you switch to another alternator series, please make sure the belts are aligned and the wiring is in good condition," Mike said. "Due to the increase in amperage, an alternator with a higher amperage output than the ampere output requires a heavier charging cable (the line connecting the alternator to the battery)."

To evaluate your charging system, try the following simple experiment. When the engine is idling to operating temperature, turn on all electronic components at a reasonable level, such as headlights, blower motors, four-way flashlights, electric fans and stereo speakers. Then, write down the operating voltage of the electrical system. If the voltmeter reads below 13 volts, all electrical equipment, including cooling fans, will not operate at maximum efficiency. They need at least 13.5 volts.

Assuming you want to upgrade, we will take a few more common options and traverse the wiring variables. The original 1960s GM alternator used an external voltage regulator. This alternator (10-DN) uses a flat two-pin connection on the back of the alternator. The other main connection on the alternator is the output terminal for charging the battery.

The cheapest way to upgrade from 10-DN is to upgrade to 10-SI or 12-SI. The main advantage of either unit is that they use an internal voltage regulator (SI stands for system integration). But this is not a simple additional conversion. 10-SI and 12-SI units use different two-wire connector plugs on the back of the alternator. Line 1 on the 10-SI or 12-SI is connected to the charging warning light on the dashboard. Line 2 is the so-called voltage sensing line.

When converting from an external regulator to an internal voltage (such as 12-SI), many enthusiasts only connect the No. 2 voltage sensing wire directly to the output terminal. Although this shortcut is simple and practical, it does not optimize the charging system. It is best to connect the voltage sensing line close to the battery.

A high-output alternator (greater than 100 amps) requires at least a 8 or larger charging cable to reduce resistance. The bottom wire is AWG 12, the middle wire is AWG 10, and the largest wire is AWG6. The largest wire is always better (albeit clumsy in appearance) to minimize the resistance when the alternator is outputting more than 100 amps.

This is why it is wise to use a remote voltage sensing connection. The main charging cable on the back of the alternator is finally tied to the positive terminal of the battery. However, this connection is usually a long wire. The resistance generated by this cable length can be easily measured by a simple charging system efficiency test.

When the engine is idling, multiple components such as the headlights, electric cooling fan, and heater fan are all running, and the voltage reading at the alternator is compared with the voltage reading at the battery. Usually there is a slight voltage drop of about 0.50 to 0.60 volts on the battery. By placing the voltage sensing wire closer to the battery, the alternator can compensate for this slight voltage drop and keep the entire electrical system at around 14 volts. After connecting the voltage sensing line to the output terminal, the half-volt voltage drop cannot be measured, and the performance of the entire charging system will also decrease.

This is also a good place to mention single-wire alternators. These after-sales alternators eliminate all warning lights and voltage sensing wire connections used by OE alternators. Voltage sensing is done internally (as we just introduced), which is one of the reasons why single-wire alternators are not as efficient as remote sensing alternators.

Another small disadvantage of the single-wire alternator is that the rotor in the alternator must reach a certain speed to be self-excited. This usually requires the driver to restart the engine to increase the internal voltage to fully activate the alternator to start charging. This is not a big problem. However, you need to be aware of this and restart the engine after it is started to ensure that the charging system operates normally. The remote sensing alternator can be charged when the engine is started.

This is an illustration by Tuff Stuff that shows how to convert a typical mid-60s 10DN alternator into a more robust CS-130. Tuff Stuff also sells a plug-in seat belt, which can be used for this purpose depending on whether the car is equipped with warning lights.

Among the available charging system alternatives, you can choose to upgrade only to a higher output alternator with the same design as the existing alternator, or choose the latest model unit with a higher output to update. The easiest is to upgrade the current alternator. For example, Tuff material properties provide a higher output 10-DN option. For those who want to keep the original appearance (for restoration purposes), it may be a good idea to keep the 10-DN with a separate voltage regulator. If this is not important, it is usually best to improve output and efficiency by upgrading to a new type of alternator such as the CS-130 or larger CS-144.

Let us look at an example of upgrading the '67 Chevelle with a small 383ci module to a CS-130 alternator. The car retains the original 10-DN external regulator wiring.

 Just plug it in to build a replaceable headlight harness to integrate it with the new alternator. This is the cleanest upgrade method. As a cheaper alternative, Painless Wiring provides a replacement CS-130 pigtail connector that can be easily spliced ​​in place.

A common charging system problem in older cars is that the resistance between the alternator and the battery is too large. A quick test of engine idle speed is to turn on several electronic accessories, such as headlights and heater fans. Then, test the voltage on the back of the alternator and compare it with the voltage of the battery. If the voltage on the battery is within 0.5 volts of the alternator voltage, the charging cable is fine. If the drop exceeds 0.06 volts (for example, 13.97 volts here), the charging cable is too small, or there is resistance at the connection.

All the latest models of alternators use electronic voltage stabilizers. If your car is like this Chevelle and has a voltmeter or factory ammeter without a charging system warning light, you must connect the resistor to the warning light circuit. Essentially, the resistor replaces the load generated by the warning light.

We are curious about why this resistance is so important. According to Painless engineer Eric Cowden, “This resistance limits the amperage that the excitation wire can provide. In factory applications, this 1 ampere or less can be provided by a charging indicator or ECM. A switched-mode 12-volt power supply. Without this resistance, the regulator will withstand too much amperage and cause it to burn."

This painless performance description shows how the CS-130 and CS-144 alternators are wired. The "S" connection (pictured on the left) on the alternator is the larger pin on the far left, and the "L" is the second pin from the right. Note that the connector shown in this figure has a circular shape on the outside and a rectangle on the inside.

Cowden added a further explanation, “If you divide watts by volts, you can get amperes. Therefore, using this resistor, under normal charging conditions, the load on the alternator will never exceed 0.5A.” This is to support this. Mathematical formula for one point:

5 watts / 14 volts = 0.35 amps

Of course, just connecting the painless connector to the warning light can accomplish the same operation as the resistor, so only one or the other is needed. This is true for all new alternators with internal regulators, which is why Painless includes resistors in every pigtail conversion.

We point this out because you can buy replacement alternator pigtails from almost any auto parts store. These are usually cheaper, but are not packaged with resistors. If you are using a standard pigtail wire (may be pulled from a junkyard vehicle), you need to know which wire is the voltage sensing wire and which wire is the exciter wire that requires a charging indicator or resistor.

We have used these two-post terminal blocks from Jegs to install live battery power supplies and switching power supplies. When this terminal block is installed near the battery, it will be an excellent place to connect the voltage sensing line.

In order to keep this story short, we did not delve into the actual installation of these different alternators on various engines, as this may become a little complicated. To simplify as much as possible, the newer CS130 and CS144 alternators are ideal for Gen I small and large Chevrolet, while the CS-130D is usually used in factory accessory drives for LS engines.

Looking back at the differences in the wiring harness, updating the charging system shouldn't be daunting. Once you understand how the system works, it's very simple.

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