Car is killing alternators

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519
Location
Australia
Thread starter
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?
 
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824
Location
Upper midwest
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.
 
Messages
2,708
Location
USA
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.
 
Messages
519
Location
Australia
Thread starter
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
 
Messages
71
Location
NM, USA
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 /
 
Messages
519
Location
Australia
Thread starter
The engine runs at around 8,000rpm. So it is pretty high, however this is the standard redline of the engine
 
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2,026
Location
CA
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?
 
Messages
519
Location
Australia
Thread starter
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.
 

LvR

Messages
85
Location
SA
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?
 
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47
Location
Eastern PA
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 <span style="font-style: italic">that</span> guy in mind.
 
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3,899
Location
Canada
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.
 
Messages
1,862
Location
missouri
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
 
Messages
2,026
Location
CA
Originally Posted by benjayman227
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.
+1 This This newbie nailed it. Need more members like this.
 
Messages
2,026
Location
CA
Originally Posted by Lolvoguy
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.
And this. Kudos
 
Messages
4,299
Location
Southeast
would help to know how they are failing. Lots of talk about electrical, grasping in the dark. Not that I can do any more - first thing i heard is track car / small battery (reduced load), and 8000 engine RPM (20,000 alt RPM). Do these alts run overrun clutches? snappy downshifts with a jammed overrun clutch will stress the alt and risk throwing the drive belt / stress the tensioner pulley.
 
Messages
1,862
Location
missouri
In a previous job used to do explosion tests on china alternators. You should hear one let go at 20k rpm. Most just seize. Not all. Steel scatter shield on table jumps a few inches sounds like explosion. Rod
 
Messages
2,708
Location
USA
I have to wonder how much has been done to truly diagnose this situation. Many racing teams fit an alternator that wasn't stock for the car at all, if it is allowed by the rules. Then you have a unit that is lightweight, low drag, and readily available new.
 
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