Wiring in a larger alternator

[Rich69shortfleet]

Given all the things I've added to my truck (stereo, amplified subwoofer, AC, backup camera, DRL halogen headlights, factory gauges include a tach, HEI) I've kind of exceeded the capacity of the original 37amp alternator. It does fine when the RPMs are up (14 volts at the battery) but at idle with lots of things running, it drops to 12.5 volts to the battery. I have installed LED lights throughout the entire truck other than the headlights, so I have reduced some of the system burden.

First of all, I will state that the truck has the original external voltage regulator system and I intend to keep it and NOT convert it to a one wire alternator set up. I will be installing a solid state regulator made by and recommended by the same company that makes the alternator.

I have a new alternator on the way, a Tuff Stuff 80 amp unit. Tuff Stuff alternators are made to have high output at idle and lower RPMs which is just what I need.

The truck has a stock wiring harness which means it has a 10 gauge alternator wire. Tuff Stuff recommends at least an 8 gauge wire from the alternator to the battery, which leads to my questions:

-Instead of hacking up the wiring harness, can I just piggyback a second 10 gauge wire from the alternator to the junction block on the fender to satisfy the need for more capacity?

-Also, the junction block to the battery has a 14 gauge wire with a fusible link in it, wouldn't I need to make that wire bigger too? If so, what size of a fusible link wire should I add to run from the battery to the junction block and where would I find such a thing? I want to retain the fusible link to maintain protection of the wiring and electrical system.

TIA

[weq92f]

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Those TuffStuff units are very nice. Running one myself at 140A.

I believe you can add more leads from Alt to Bat in leu of swapping 10 for 8 but others here will confirm. I would rather see you leave the current 10AWG and add a dedicated 8AWG Alt to Bat wire as well. Some harnesses send the Alt lead to the starter solenoid I believe and if that's the case, adding an additional 10 wouldn't be enough.

14AWG to your block from Bat seems very weak. I'd make that 8AWG and protect it with a 12AWG FL (That's 4 numerical steps smaller which is the norm). When I install FL, I crimp it onto the the lead going to the power user and attach it (the FL) to my distribution block. I use a length of about 6 inches of FL wire.

Myself, I ran 6AWG Alt to Dist Block and 4AWG from Dist Block to Bat just to be certain all the loads got feed directly from Alt rather than indirectly from Alt to Bat to Dist Block.

Hth,

-Kevin

[72c20customcamper]

Not on my truck but I put a 100 amp alternator on my Chevelle added an 8awg wire in parallel to to factory 10 . It’s worked fine for 10 years

[pjmoreland]

Adding a heavier gauge wire from the alternator to the battery is only part of the puzzle. If you have all of your add-ons connected to the fuse panel under the dash, then they are still only being powered by the 10-gauge wire that runs from the alternator to the junction in the harness near the voltage regulator and then on to the fuse panel. One common solution is to add a bus or a fuse panel in the engine bay somewhere for the add-ons that is fed by a large wire from the alternator.

One side effect of augmenting the factory wiring is that the stock BATTERY gauge will no longer be accurate. One solution is to replace it with a voltage gauge. American Autowire makes one that installs in the stock location.

[54blackhornet]

Rich go to the website Mad Electrical . Com , you will find a incredible amount of knowledge for what you’re trying to accomplish…Jack

[HO455]

It is my understanding that when the factory upgraded the charging system to the 63 amp alternator they left the standard 37 amp harness in place and added harness that consisted of a second 10 guage wire from the alternator that went to an insulated terminal on the core support near the horn and additional wires for the voltage regulator.

There was second terminal near the one from the output of the alternator that tied the voltage regulator into the circuit. GM expected that all of the additional loads added to the system be hooked up to the insulated terminal and not to the regular harness.

The regulator harness still only charged the battery at a maximum of 37 amps but allowed the system to handle high amperage loads like VHF radios or a rear heater in a Burban when the engine was running.

There is little information about the higher amperage alternators that were available from the factory. Although you might make a post in the Heavy Haulers section as I believe the high amperage systems were more common in the C40's and larger trucks.

[72c20customcamper]

Originally Posted by pjmoreland

Adding a heavier gauge wire from the alternator to the battery is only part of the puzzle. If you have all of your add-ons connected to the fuse panel under the dash, then they are still only being powered by the 10-gauge wire that runs from the alternator to the junction in the harness near the voltage regulator and then on to the fuse panel. One common solution is to add a bus or a fuse panel in the engine bay somewhere for the add-ons that is fed by a large wire from the alternator.

One side effect of augmenting the factory wiring is that the stock BATTERY gauge will no longer be accurate. One solution is to replace it with a voltage gauge. American Autowire makes one that installs in the stock location.

I put a battery bus bar for my fans and a couple of other electrical devices that draw moderate power

[Greasey Harley]

Have you read through these faqs?
Electrical forum faqs by vettevet:
https://67-72chevytrucks.com/vboard/...d.php?t=815300
This is where I started when I upgraded my alternator.

[Rich69shortfleet]

Originally Posted by 54blackhornet

Rich go to the website Mad Electrical . Com , you will find a incredible amount of knowledge for what you’re trying to accomplish…Jack

There is some very useful stuff there.

Originally Posted by Greasey Harley

Have you read through these faqs?
Electrical forum faqs by vettevet:
https://67-72chevytrucks.com/vboard/...d.php?t=815300
This is where I started when I upgraded my alternator.

Yes, but none of those sections really cover what I need to know. Informative, but not a lot there for my current situation.

I have a local friend who really knows these electrical systems. Once the holidays are over maybe he can help me out a bit to make sure I don't overlook something.

[RichardJ]

You guys are over thinking this.

If the 37 amp alternator is capable of carrying the load from the accessories, at say of 1500 RPM, the load doesn't change when the engine drops back to idle. Only the output of the alternator has changed. If you change the alternator to one that puts out more current at idle that takes care of the idle problem that you were talking about.

An 80 amp alternator Isn't gonna put out more current than the 37 amp alternator was at 1500 RPM, when I was able to maintain the 14 volts. The load remains the same. The alternator output will be the same whether it's the 37 amp or the new 80 amp. That 80 amp won't exist unless you drastically increase the load on the battery with many more accessories.

All alternators have low output at idle. The first images shows the 34 and 37 amp 10dn alternators. Notice that it is showing engine RPM. The last image shows SI alternators but take note that's alternator RPM not engine RPM. Alternators run about 5X engine rpm.

If the wiring size was adequate for the 37 amp alternator with the existing load when the engine is running at the 1500 RPM, there isn't an increased need for larger wiring when the alt is delivering the current needed for the load at idle. Nothing has changed as far as the wiring or the load.

>>stereo, amplified subwoofer, AC, backup camera, DRL halogen headlights, factory gauges include a tach, HEI<<

If this load remains the same, the 80 amp alt will charge the battery at the same rate. The current on the fusible link, battery to junction block will remain the same.

If you increase the size of the charge wire between the alt and battery, it will increase the charge rate of the battery.

Increasing the charge rate on the battery will reduce the LIFE of the battery.

If you have a battery charger with multiple charge rates, check the instructions. They will tell you to only use the higher charging rates to get enough life in the battery to start the engine, but to fully charge a battery you should always pick the lowest charge rate and they will explain that you will help the life of the battery to charging at a slower rate.

[Rich69shortfleet]

My truck idles in gear at about 650-700 and at that point I'm only getting 12.5 volts at the battery. Not good enough, thus the desire for an alternator that puts out more at idle. That's what the Tuff Stuff alternators claim to do. I don't need the 80 amps, I need better performance at low idle speeds. But the alternator manufacturer DOES recommend a bigger alternator-to-battery wire. That's easily solved, my biggest question is if I need to upsize the fusible link battery charging wire. Maybe not?

[Steeveedee]

You can increase charging voltage at idle simply by adjusting the voltage regulator. Try that first, if the system is otherwise keeping the battery charged.

[franken]

I might ask how much time the truck spends idling. Similarly, is the battery discharging over time while running the new accessories? What is the problem that needs to be solved, or is this a solution in search of a problem?
Alternators are rated at what current they can produce not what is needed.

[Steeveedee]

I'd also note that the bigger cars with a lot of accessories of this era generally have smaller pulleys on the alternator. This compensates for the load, keeping the voltage up. Just another thing to consider.