Ok I need some help please! I keep having alternator failure and have replaced 2 140 amp alternators already and now that I need a new one I'm researching everything I've done since this has started. I figured out that it's happening sometime after heat cycle and dual fans come on. I have Dewitt radiator spal fan combo and everything kicks on and cycles perfect with the Holley Sniper but I hooked the power lead from relays to the back of alternator with advice from tec at Summit. In stuctions say connect to battery so after talking to spal fan tec he said it could spike to 100 amps on start up of fan and settle down at 30 or so. Power master alternator tec said he was not sure if it would spike that high but if it does it could possibly damage alternator. Please let me know what you guys think.

Thanks
Robert Edwards
USMC Retired

 

Is the radiator hose routed behind the alt?

 

I have always run the power leads for the fans off the starter. I think your correct that your alternators are failing due to the load from the fans. Most company's tell you to go direct to the battery for power. I would think the battery would buffer any spike of power from the fans.

 

Fan power should be connected to the battery. It softens the shock on the system. In the Corvette, the easiest way to do that is take power from the big stud on the starter.

I have a big terminal stud by my starter that everything is tied to and fed by an upgraded 1/0 wire from battery.

 

I know guys here claim that hooking directly to the alternator or directly to the alternator via a bus is the correct method to run the fans. I'm am of a different school of thought on that. The battery IS equipped/designed to handle large spikes in amperage draw, that's what it does every time you hit the starter.
The alternator may tolerate it up to a point or a period of time but if it's too long or too high of an amperage, something is going to fail.

I would recommend taking large start up draws from the battery at the starter cable (for underhood access) vs directly from the alternator. It's how I have mine hooked up with no problems thus far in 9 ish years or so with the spal style fans.

 

It's running right across the front of alternator.

 

Exactly-

Think of the alternator as your income- battery as your savings account- you would not want to pay your house mortgage with the paycheck - but rather the bank account.

AND take in to account when the fans kick on - usually at idle- the alternator will NOT be putting out rated power- as that'll happen around 1500-1800RPM- so try paying your mortgage when you are not getting your full pay!!!

As others have said- the battery not only starts the car- but it stabilizers the voltage AND filters the leftover AC ripple from the alternator (electronics like that).

These car were never designed to handle the load that is common now days...

Here's one way to upgrade the charging system and properly fuse-protect

 

Good advice. Also, what size is the wire going from alternator + to the battery? If it is the stock C3 wiring, you are running a big risk. Should a significant battery depletion (or a battery drain problem) occur, the alternator would TRY to send more current through that line than for what it was rated. You could fry the wire and/or cause an insulation fire.

 

While the car is running, the power for the car is being generated by the alternator. If the fans are the reason for upgrading your alternator, you haven’t upgraded your alternator wiring, and you connect fans to the starter, the stock wiring may not be able to handle the extra load. My stock wiring melted thanks to how one mechanic wired my fans.

I ran the dual SPAL fans for years with the relays getting power from the alternator. The power lead off of the alternator is connected to the starter and then the battery. Unless those connections have a lot of resistance, the fans are still essentially connected to the battery. But, with the alternator being the main source of power, that power can travel directly to the relay instead of from the alternator (through questionable stock wiring) to the starter, and then to the relays.

What alternator are you using? I’ve been using Powermaster 140 amp 12si style alternators for years. The bearings wire out on my old one, but it still functions perfectly. I did try using CS130 style alternators, but they started overheating and failing pretty quickly.

 

I dont know if this helps but this is what happened to me in the last couple of months. purchased my 81 last spring. it had a rebuilt alt. in it, it wasent long before i noticed my battery lept loosing power, so i went to Orilleys ( dont go there) paid 80 something for a rebuilt alt, got home installed it got my meter out still wasent putting out the correct out put, took it back they exchanged it, on the 3rd try finnaly got one that worked guess what that on burned up the voltage regulator also. so went to NAPA got a brand new alt. went to my mechanic and yelled help, he had my vette for 2 weeks worked on it part time, cleaned all the grounds installed a new engine to frame ground, than finally had to replace the main hot wire from the battery to the alt.the otter coating on the wire running threw the frame had wore off in a couple of spots. it works perfect now. for the alt. to work perfect the wires going from it must have no resistance, this encludes the hot wire and the ground wire, I posted here when i first had the problem, a lot of people said the engine bay is like a oven, buy a higher amp out put ect. when most of the problems are 40 year old wiring that should be up graded

 

Watt am I looking at there,?? the two red items, the double post thing looks like a fuse of some sort, but that single post thing shows no clear connection to the battery..... why that 'lid' is shown is a mystery.....and the nature of the obvious connection to the two post terminal from battery..... MY alt has been failing a lot recently, on number 3 by now, the original one lasted some years, but the two replacements only last a year or so.....and my wiring is off the alt through a 40 amp fuse and into the spal fan relay.....

 

I just wanna say- if the alternator does NOT produce enough income- money gets pulled from your bank account - that happens when the car is idling -not making full income-and the fans kick on....so that's why the factory wires melt-

"Electricity takes the path of least resistance"
HOWEVER- Electricity takes ALL paths of resistance-

I've heard way too many say- just add a bigger wire and leave the factory stuff alone-

Here's an example- the battery capable of throwing out almost TEN times what the alternator can-say a battery with 700CCA-cold cranking amps

You can see that the FULL power of the battery can make it up to the fusebox/ignition switch UNPROTECTED!!!

 

Yes -it is a fuse block with two high current fuses (available up to 250A )- Marine grade- with a protective cover

You get a battery cable that is connected to a starter lug then to a post right up the the starter on the fenderwell- that's where you mount the fuses and can connect the added wires- completely protected from torching the factory thin stuff-

AND you can use the post to jump your car-if needed

 

On an 81, the alternator output goes directly to the battery via that little binding post next to the battery. I upgraded mine to #4. Be advised, the original wire had a fusable link as it entered the battery compartment. I installed a maxi fuse there instead.
BTW, it's NOT in the book or on the schematics. All the fusable links are documented, but NOT this one. Yes, it's factory.

 

There are three diodes in the alternator....so it's the diodes that are dying...The power should come off the battery. It's a 'snubber' for the current.

Also do NOT jump start anyone's vehicle from a Corvette (or other) yes, you are helping the helpless....and in short order you will order a new diode/rectifier set! If not immediately.

Be DAMN sure the grounds are tickety boo!

What most people don't understand is ANY alternator has 14.3 volts available....into a 12V battery...so that 2.3 volts available.

Unkahal

 

The alternator is not meant to be a "real time" provider of energy. That job is supposed to be performed by your battery. The alternator is designed to replenish the charge depletion from the battery as the declining battery voltage requires. Folks who are using their alternator to supply power directly to the electric cooling fans are designing risk into their charging system UNLESS the wiring in the system can properly support it. What does that mean? Well, if you wire your fans directly to the alternator expecting 50+ amps to be fed to them whenever they come on, you should also have a very large wire running from that connection point directly to the battery. If you only have the original alternator feed wire going to the battery, very little of the demand from the fans will actually make it through that small wiring from the battery. The higher resistance in that line will minimize the current from the battery and maximize the current being required from the alternator.

Now, imagine that you are sitting at a stoplight with engine idling and the thermostat for your electric fans actuates and that 50 amp demand is immediately dumped on the alternator...which isn't putting out more than 10 amps (or so) at the time. Definitely not a good design for your power system. Battery FIRST; alternator gradually recharges it.

 

Real Time last week..
1973 383 Coupe...Electric cooling fans...Optima red Top. 70 amp alternator

From the fans running on start (heat soak into the fan switches)....The car would not start. (unrelated problem) The guy cranked on the starter an number of times....then needed to get jump started.

This is where I come in....
Alternator was RED HOT....well above 160°F
Ground wire was too hot to touch....smelled of melting vinyl.

Fans NOT wire to Battery.
Inadequate ALT

No Defeat switch on the fans.

WAY TOO MUCH DRAW!.

unkahal

 

Well, this thread has enuff guyz suggesting for the Spals to the battinator, so that's watt I did, ran a 8 ga wire to a 40 amp fuse next to the batt.......up and over engine to the relay on the shroud.....PIA taking apart all that crap in the console, dash, etc....but it's DUN!!!!

 

Why? The battery cable from the battery to the starter lug is A LOT bigger than 8 gauge, like 2 gauge.

 

It seems to me when I suggested that, everyone screamed fusable links.