Wiring in a larger alternator
 

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

Re: Wiring in a larger alternator
 

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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

Re: Wiring in a larger alternator
 

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

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

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

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

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

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

There is some very useful stuff there.

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.

Re: Wiring in a larger alternator
 

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 3X 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.

Re: Wiring in a larger alternator
 

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?

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

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.

Re: Wiring in a larger alternator
 

Definitely sub'ed this thread, I know it has been a few days but... Any progress? This is the exact issue I'm now having. My Alt(10si) is outputting 60-62 amps and 13.3v at roughly 1300 rpm +(engine) 12.4v and 38 amps @ idle, but keeping the battery charged isn't the issue, my issue is at idle every thing dims considerably. To the point that I have head lights (standard sealed beam) flickering like improperly wired LEDs. Probably just gonna get a new 80-100 amp alt... Idk

Re: Wiring in a larger alternator
 

x2

Re: Wiring in a larger alternator
 

Regarding posts 15 and 16, so what if things get dim? You're pushing a solution in search of a problem.
The current statements in post 15 don't appear to be based on fact but on ratings. What the system draws and what can be delivered aren't the same.
My point is maybe the system is marginal at idle but it may not be an issue since it doesn't idle that much.

Re: Wiring in a larger alternator
 

Not sure exactly what you are alluding to and no need to be rude... But my issue is I do not have a large stereo or subs or anything that draws alot of power except the lights and when I'm stopped, idling at night with them on (say at a stop light), my headlights are in " seizure mode" they dim to the point of flashing on/off rapidly... I stated my voltages at idle and approximately 1300 rpms on the engine... I'm personally not sure where else to look... I have enough amperage and voltage to keep the truck running and the battery charged so... *shrugs* "No solution, looking for a problem"... My problem = flashing lights, either not enough voltage or amperage (12.4v @ approx 38A, at 800 rpms,idle) but 60A+ and roughly 13.8v past 1300 rpms on the engine.. Pretty clear to me... *thinking* I'm pretty "new" to these older trucks, and for some reason generally speaking "internet hide and seek" is not my strong point... Besides that 90% on the "information" on the internet is either porn or fake... So... I come here to find real people that have the actual knowledge from real world experience....

Re: Wiring in a larger alternator
 

I could be mistaken but lights at idle dimming considerably does not sound like an alternator problem to me. Sounds like a wiring problem with resistance in some of the connections. Top suspect I suggest looking into is emergency repair battery terminals if you have them, poor ground connections to engine and to headlights, then check other connections going into the cab to the headlight switch and out of the switch, through the dimmer switch and back towards the headlights. Post pictures here of your connections at the battery and ground wiring if you have questions or want some more help or better yet start a separate thread. Use alligator clip test wires to bypass connections and switches that may be suspect. You can also use a multimeter to check for voltage drops at each connector and switch.

Re: Wiring in a larger alternator
 

The oscillating brightness of the lights puts me in mind of a weak diode. Many mechanics have an oscilloscope and can determine if this is the case. I recommended a smaller pulley and a voltage regulator adjustment before, but neither of these will correct flickering. Guess I missed that the first time through. The brightness will only diminish, not flicker in either case.

Re: Wiring in a larger alternator
 

An oscilloscope makes detecting bad alternator diodes really easy but, you can also detecting diode failure with a regular multimeter.

The diode bank in the alternator charges the 3 phase AC voltage the rotor and stator make into DC voltage.

If you have a failing or failed diode you will be getting AC voltage output from the alternator. This can cause several different symptoms like flickering lights and humming from stereo. If you check for voltage with a multimeter but put the scale to AC volts instead of DC if there is a diode problem your meter will show AC voltage. Do the voltage test while changing the RPM of the engine.

Taking your alternator to the local generic parts store for testing may not reveal this problem as the alternator may still be capable of rated output.

Re: Wiring in a larger alternator
 

Good input! I hadn't thought of that. I worked in a parts store many years ago, but we didn't test alternators, we just sold rebuilt or new, as then the customer was expected to be the knowledgeable one. We didn't have equipment for it back then. But when I worked as a mechanic, we had the diagnostic tools. If an alternator had a bad diode, we'd change out the whole thing, anyway. It was more expensive to the customer to dismantle the thing and replace the bad diode...and then all those other worn parts may or may not have been replaced.

Re: Wiring in a larger alternator
 

Yeah, a larger alternator won't fix your problem. As already suggested, the easiest and least expensive fix is to first look at the quality of the connections, especially grounds. It is not uncommon for the plugs on the headlights themselves to get corroded and cause a lot of resistance and thus causing issues like yours.

Re: Wiring in a larger alternator
 

So I actually started with checking the headlight pigtails and grounds. One of the nice things about living (I say that loosely during the summer) in a desert is they all look pretty dang good. Most had old dielectric grease on them that I cleaned off and reapplied. I even cleaned all the contacts for everything in my dash... What pain in the "cheeks" that was. Checked all my factory grounds, body/engine/battery/ alternator... Cleaned the ends/connections up... Still same problem. Does the 10si have an internal regulator? If so... I still have an external one also, mounted to the radiator support...big chunk of a black box... Seems pretty old still has a Delco stamp on it but no part number... I wonder if there in lays my problem... I've been checking voltages and amps at the battery and back of the alternator.... *thinking*I'm definitely going to run the AC vs DC voltage test too... See if I get anything there. Sry I high jacked this thread... But thanks everyone who chimed in.

Re: Wiring in a larger alternator
 

A 10si is a one wire alternator with an internal regulator.