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Car is killing alternators #5210460 09/11/19 08:14 PM
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Spetz Offline OP
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Hi guys,

I have an old Mitsubishi Mirage that has had a Mitsubishi FTO motor transplanted into it.

It keeps going through alternators. Some only seem to last minutes...

Some points:
1. This is a car I use on the track so the power draw is low (essentials only, nothing else)
2. The alternators I have used have been 2nd hand units (yes, they are 20+ years old) however I have gone through about 6 of them so far with a total run time of 10 hours I would say on the car
3. The last time I had the car on, it was fine. I let it sit for 2 months and started it again and the alternator is dead (battery was flat too, left connected)
4. The battery I use is a Deka AGM which is underpowered for daily use.
Specs of battery:
Voltage: 12
CCA: 325
Capacity (Ah): 19


I have been researching what to do/test.
The first thing I plan on doing is checking for resistance between the positive and negative terminals of the car to see if there is a short somewhere
Check +-ive cabling
Check for good ground

What else can it be?
What else can I check?


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 165,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Car is killing alternators [Re: Spetz] #5210477 09/11/19 08:45 PM
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redbone3 Offline
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The only time I have seen this problem is when the bonding cable between the chassis and engine was defective/


2014 Passat Wolfsburg, 1995 Miata.
Re: Car is killing alternators [Re: redbone3] #5210498 09/11/19 09:03 PM
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Mainia Offline
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Originally Posted by redbone3
The only time I have seen this problem is when the bonding cable between the chassis and engine was defective/


Even on a new car , I always add another chassis to engine connection and on new and old connections use ant-ox grease and coat the connection with Fluid Film.

Re: Car is killing alternators [Re: Spetz] #5210511 09/11/19 09:25 PM
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mk378 Offline
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You've done all this with the same battery? Battery could have a short that overloads the alternator. Or it just doesn't hold charge and you think the alternator is bad.

Also there's a wire from the ignition circuit that powers up the alternator.

Re: Car is killing alternators [Re: Spetz] #5210527 09/11/19 09:53 PM
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Spetz Offline OP
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Yes, this is all done from the same battery.
The battery was bought new...
Also, when the car is running there is no output from the alternator.
It is just running on the battery power


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 165,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Car is killing alternators [Re: Spetz] #5210553 09/11/19 10:33 PM
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StarCaller Offline
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there is one constant: the battery /
ask one of your buddies for a battery over the weekend & see what the outcome is /

on the other other hand, before you put a different battery in, you rather triple-check the alternator wiring /

Re: Car is killing alternators [Re: Spetz] #5210554 09/11/19 10:33 PM
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clinebarger Offline
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Resistance checks are absolutely useless on high amperage circuits!


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
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Re: Car is killing alternators [Re: Spetz] #5210556 09/11/19 10:38 PM
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user52165 Offline
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You say used on a track car.

What rpms are you running?

Last edited by user52165; 09/11/19 10:40 PM.
Re: Car is killing alternators [Re: Spetz] #5210575 09/11/19 11:08 PM
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Spetz Offline OP
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The engine runs at around 8,000rpm.
So it is pretty high, however this is the standard redline of the engine


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 165,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Car is killing alternators [Re: Spetz] #5210585 09/12/19 12:11 AM
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user52165 Offline
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20 year old, second hand units. 8000 rpms......................hmmm.

We would need further info to calculate the alternator rpm.

Are these units spec'd for this engine?

Do you have perfect pulley alignment?

Is this a V belt or serpentine type?

Re: Car is killing alternators [Re: Spetz] #5210592 09/12/19 12:36 AM
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Spetz Offline OP
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Yes they are old units, however I have gone through many of them.
One of which was a freshly rebuilt unit which only lasted a few minutes.

It runs off of a V belt.
Pulleys etc are all new.

Yes the unit is for this particular engine. It won't be the rpm, it was all designed for this from factory.


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 165,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Car is killing alternators [Re: Spetz] #5210601 09/12/19 01:12 AM
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LvR Offline
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If the alt has a built-in regulator then not much can go wrong electrically if its sound to start with.

You say you have an "old" vehicle ............... possible you have an external to the alternator regulator, that have funky connections on itself or bad cables running to the alternator?

Re: Car is killing alternators [Re: Spetz] #5210739 09/12/19 08:13 AM
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benjayman227 Offline
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Assuming you find the actual problem, an underdrive kit would be prudent. Your electrical needs are very different from a DD that cruises at 1500rpm around town with headlights, wipers, radio, and defogger all cranking, and the "factory" design parameters are set with that guy in mind.

Re: Car is killing alternators [Re: Spetz] #5210869 09/12/19 11:08 AM
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Lolvoguy Offline
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Originally Posted by Spetz
It won't be the rpm, it was all designed for this from factory.

You are not operating your vehicle at "factory" levels.
How can you expect to push stock parts to high performance levels?!
Surely more electrical upgrades would be required.


06 Lexus IS350- Wife
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Re: Car is killing alternators [Re: Spetz] #5210880 09/12/19 11:24 AM
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ragtoplvr Online Content
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1. Never use alternator to charge dead battery. Do you have a trickle charger . To recharge that battery you want C/10. C is,19 so charge should 1.9 amps. 2 OR 2.5 AMP trickle charger would be good. The alt can supply 40 amps to that battery which will severely shorten the life. When discharged the battery can not function as surge absorber and kill regulator.

2. Do you know what failed on the alt? Diodes, regulator?

Rod

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