15 replies to this topic

[blue cobra]

Any suggestions are appreciated. 

 

I have been racing a 93 miata for five years in chump.  I have never had a problem with the alternator until recently.

 

Starting in late 2014 though now, I have lost an alternator in every race I have run in.  When I take them to the parts store they say the regulator failed. (not sure their machines can even tell, I think it is just a pass/fail test)

 

I have replace every crimped battery and ground connection with new ones, and soldered them.  I swapped batteries, went through almost every inch of wiring loom looking for frayed wires, and even removed every wire I could find that was not feeding anything.

 

I added an extra ground to the engine block from the frame.  At my last race I fabricated a duct to blow cool air directly on the alternator, but it still failed after five hours of racing.  Most of the time they last about 5 or 6 hours.

 

Not running any kind of special pulleys, all stock engine and accessories.

 

At my wits end.  Anyone have any ideas? 

[Bench Racer]

Might be something within this thread.

 

http://forum.specmia...=3;t=000244;p=0

[davew]

Find a used alternator that appears to have never been rebuilt. Then find your local alternator shop. If you can not find one, ask someone in the big truck/construction business. They will know where the right guy is located. Have the used alternator rebuilt with only the highest quality parts available. Tell the rebuilder you have the time and are willing to pay the extra few dollars for the quality bearings, diodes, regulator etc. Then find a second alt and have it rebuilt as a spare.

 

Rebuilt electrical parts are terrible. Import stuff is even worse. The parts stores expect a 40% failure rate! I have been using the same shop for 25 years, Grove DC Auto Electric in Fox Lake Illinois. Yes, the police shooting last week was a few hundred feet from his front door, and his roof is on the CNN helicopter shots.

 

The parts stores only test if the alt is working or not. No way to diagnose without disassembly, and I am sure the parts looker-upper has no idea how to take an alt apart. But he is probably right, that the regulator is failing. Even the best electrical parts are crapppy.

 

Dave

[blue cobra]

Thanks Dave, your suggestion is backed up by the very good thread Bench racer pointed me to.  

 

See y'all at the track!

[RazerX]

I have also experience the same issue with a 99.  

 

I have a new kill switch. 

Have professionally rebuilt OEM alternator ready to go in 

Plan to measure resistance from alternator to ground (with the battery disconnected)

Check for ground faults in the field wires which are run from the connector in the back corner of the trunk to the secondary posts on the 4 post kill switch.  (this is how the car was wired when i purchased it)

The battery seems fine will hold 12 volts.  Is there a better battery test other than looking a voltage when off, idle and at RPM? 

 

Am i missing anything?  

[RazerX]

 I have disconnected the battery, the kill switch and the alternator. 

 

So should there be any grounding from main harness?   If I put on ohm meter from where the main harness would connect to the positive terminal on the battery, i get 36.8 ohms resistance to ground.   It is exactly the same resistance if I measure from the "white" cable that connects to the alternator to ground.  Is this normal?  Or do i have a fault somewhere?  I have a wiring diagram but it doesn't really indicated or measure any resistance. 

[RazerX]

Tomorrow is Friday, If someone has access to a 99 can you please… disconnect your battery both positive and negative terminals.  And do resistance measurement between the cables.  I.e.  a probe on the negative cable and positive cable, key off, but you likely need your master switch on.   With your master switch off you should get an infinite reading, open circuit, but with it closed I am wondering if you get an ohm resistance reading because I do.  I am wondering if it normal or I have a short.  No point going on an electrical witch hunt if there is no witch.

[RazerX]

Wow, surprised no posts on this and it isn't even secret like "plunge cuts"... 

 

So for anyone with a 99.  If you pull the main cable off the starter (the large white wire that bolts to the side) off and use a volt/test meter to check the resistant between that wire and ground with the kill switch off, do you A) get an infinite resistance, or some resistance.   Everything else makes sense on the car, mine measures a resistance but that may be by design.  

[Chad Martin]

If your L terminal, AKA charge indicator light is not wired properly it will blow your regulator.  Sometimes when people pull the dash insturment/warning light cluster out of the car the don't realize they are telling the alternator not to turn on.  SO then they think they need to go directly to power or battery with the charge indicator wire.  Which ALWAYS blows the internal regulator.....

 

Make sure you have a incandescent indicator bulb in your charge indicator light circuit (and a diode) or put the stock dash back in....that circuit needs the specified amount of resistance for the alternator to work properly.

[Mark]

Chad,

 

I have done many cars where the cluster was removed to install a data system and have never had an issue with the alternator not charging or being damaged on either the NA or NB cars. 

[davew]

On an NA car, you have 3 wires. One small wire has battery voltage, the other small wire has a little less than battery voltage as it goes through the warning light bulb. The larger charge wire goes indirectly to the battery in stock form. If you are using my master switch wiring, it goes directly to the battery positive. Through the master switch connection. The system does not need the dash to function properly.

 

On an NB car, the dash cluster and ECU are important to the charging system. The dash can be removed and the charge system still operates normally. BUT, the dash can cause a no-charge condition if it fails internally. I even had one car that would not shut off (turn key, remove key and walk away with car still running) due to a bad dash cluster.

 

dAVE

[Mark]

Good info Dave. Thanks.

[RazerX]

If your L terminal, AKA charge indicator light is not wired properly it will blow your regulator.  Sometimes when people pull the dash insturment/warning light cluster out of the car the don't realize they are telling the alternator not to turn on.  SO then they think they need to go directly to power or battery with the charge indicator wire.  Which ALWAYS blows the internal regulator.....

 

Make sure you have a incandescent indicator bulb in your charge indicator light circuit (and a diode) or put the stock dash back in....that circuit needs the specified amount of resistance for the alternator to work properly.

 

Hi Chad, my dash is still in... but i don't recall seeing a charge light come on when the battery was dying and alternator was fried...

[RazerX]

On an NA car, you have 3 wires. One small wire has battery voltage, the other small wire has a little less than battery voltage as it goes through the warning light bulb. The larger charge wire goes indirectly to the battery in stock form. If you are using my master switch wiring, it goes directly to the battery positive. Through the master switch connection. The system does not need the dash to function properly.

 

On an NB car, the dash cluster and ECU are important to the charging system. The dash can be removed and the charge system still operates normally. BUT, the dash can cause a no-charge condition if it fails internally. I even had one car that would not shut off (turn key, remove key and walk away with car still running) due to a bad dash cluster.

 

dAVE

HI Dave,

 

Thanks for the reply.  After the race weekend, where I got to compare to other cars.  I have realized that my master switch may not be wired as desired.  The large charge wire still goes to the main fuse panel in engine bay over the passenger wheel, not to the battery side of the kill switch.   That is creating the resistance reading, and i need to fix that.  I do have a new kill switch and did not roast another alternator last weekend.  I also now suspect that my battery may not be 100%, while it does hold 12.2 volts for a couple weeks and it does show 14+ during a charge, it drops to 11v after pumping just a 2 gallons out of the tank.  

 

So those are my next steps, rewire my kill switch and get a new battery. 

[alangj]

I have a 1990 NA car. Had a period 2 seasons ago when I was going thru an alternator every race or two. Tried everything - used stock/rebuilt/OEM alternators - all crapped out within hours of race/track time. Finally, pulled a power takeoff out of my cigarette lighter that I was using to power my TraqMate unit and unwired the lighter outlet & the problem resolved. Hasn't recurred since. Not sure whether that was the cure or completely unrelated, but just sayin'. 

[Chad Martin]

The light wont always come on when an alternator fails internally.   It may only if current is created in one direction by the alternator not running via a specific difference in battery vs alternator voltage.  And the light isnt burnt out or the circuit isnt damaged etc.

 

Likewise i didn't say the alternator won't work if you pull the dash in all cases, although that is true for RX-7s because both the bulb and the parallel resistor for the excite wire are in the dash, so i assumed it was true for miatas.  My point was simply some people have alternator issues and/or try to modify the alternator wiring and end up blowing alternators' regulators if they wire the charge light without any resistance and a diode....then wonder why their alternators constantly blow.

 

If dave is saying that you don't need the dash there must be some other inherent excite path on the miatas else the alternator would not turn on.  If that circuit is gone or damaged and the dash is also damaged it would not turn the alternator on.   So perhaps just rewiring the excite wire with a incandescent bulb and diode or an LED with a proper resistor, bypassing damaged excite circuit(s) would resolve your issue.

 

I work on RX-7s more than miatas but most all 3-wire alternators work the same.  This is info i posted years ago on the rx-7 forums after having trouble rewiring my rx-7 (FULL REWIRE).

 

"B terminal is the obvious part. That's the charge wire. It...um...charges the battery...min 4 gauge IMO.

 

S terminal needs direct battery signal, can't go through a relay or any switch. It can go through a fuse or breaker. This is the "sense" wire. It tells the internal alternator voltage regulator what the battery voltage is and thus how much "charge" to put into the system. The closer you connect this to the battery the better your alternator will work. If you just jumper it to the charge post it really wont fluctuate voltage output to adapt to battery state and load conditions.

 

The L terminal which is where the excite wire connects. Yes it does power the idiot light. It does this because current flows if there is a substantial difference between the system or batt voltage and the alternator charge voltage. This terminal/wire must be connected in some systems because it is in effect what "turns on" the alternator. BUT and this is a big but. YOU CANNOT JUST CONNECT IT TO A HOT WIRE OR THE BATTERY. It must have resistance or you will destroy the alternator voltage regulator and the alternator will need to be rebuilt because it will not regulate voltage, the voltage will just rise with RPM up to 16-17 volts. I don't have to tell you that is bad. SO, the factory dash has two parallel sources of internal resistance. One is a light, the other is a standard resistor. You CAN NOT skip the resistor because if you just use a light and the bulb burns out, guess what, your alternator shuts off. So, you have to wire this terminal back to +12v (again no relays upstream for this one too) but you must also put a roughly 120-150 ohm resistor on this wire. Up to you if you want a charge light in parallel. It appears in some cases (3rd gen rx-7 and other cars) the factory dashes just use multiple idiot lights as the redundant sources of resistance for this. So if one bulb burns out the alternator does not just quit working. If you do put a charge light in parallel you need to put a diode in also or the light will be on all the time. The diode should only allow current flow TO the alternator. It needs to BLOCK current flow back from the L terminal.

 

I think in your case your alternator may be damaged or isnt charging because it isnt turned on. But your assumption that the alternator "stays on" when the engine is not running is incorrect. This isn't actually possible. Without the little wheel spinning on the front of the alt it's basically a paper weight, it cant be on without being driven. But, if you damaged the voltage regulator it may create a bleed. If i recall correctly when i blew one trying different things to get it to work properly (read just put unresisted +12v to the excite terminal) it self excited after that and would not regulate voltage at all."

 

Thus it could also be in the case of miatas that the alternators will self excite?  I dont know as i have not fully rewired a miata.

 

For some reason it wont let me link the image but perhaps this link will work:  http://www.rx7club.c...cratch-1048705/