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Thread: Why is my car killing alternators?

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Posts: 11-20 of 28
2015-07-21 18:35:21
#11
Yup... Kill switch was wired completely wrong in our former 200sx SE-R when we had it too (amazing things didn't fry out before we got it to be honest).

Proper wiring of kill switch is key so the alternator doesn't get bad feed from an improper setup.
2015-07-21 20:09:30
#12
Ok Ben i saw and went through the pics you posted thanks, does the same applies to me even if im not running a kill switch ? Why do we need to add a 80-120 relay? Does the relocation of the battery makes the need of the relay? Why is the alt thinking it needs to over work and fried itself? Im tired its not fun to run dried-dead car on the middle of a busy/dangerous intersection specially when all the cars are trying to take off from a weekend car meet , and to top it off the street was incline so had to push car over the hill is scary and lame knowing that I've replace all battery and alt to be "safe"
2015-07-21 20:12:45
#13
I found this image by doing a search for 'Sentra battery charge circuit', just in case the link stops working...



So, looking at this, the SR alternator is bottom-right. There are a total of 5 connections, Ground (through engine block, so no separate wire), White, on separate lug (the 14v output that charges the battery and supplies power to the car while the engine is running), Yellow/Red to turn on the battery light on the instrument console (lights when battery isn't being charged and car is running), a Black/White wire (I'm guessing, but this line is probably there so the alternator knows what voltage it is currently outputting?), and finally, the line I referred to as the 'Sense' line, the White wire on the connector that has 4 wires on it.

Looking at the drawing, you can see this W wire going up to the fuse box, then to the battery. This line is an input to the alternator so it can tell what the battery voltage is. The obvious question is, if the output of the alternator is going to the battery, then why don't they just feed that back into the alternator to begin with at the factory?

The answer is because of the voltage drop from the wiring harness, if the alternator is putting out 14.5 volts, you may only read 14.3v at the battery, depending on the length and size of cable involved. A longer run may only see 14v at the battery. So, the regulator inside the alternator checks what the battery is seeing, and adjusts the output accordingly to whatever voltage it was designed to charge to.

So, say you hit the kill switch, and power from the battery is cut. The White wire is run to the fuse box, which now has zero volts. Alternator, being stupid, does the math, sees that it's already outputting 14.5 volts, and then burns itself out trying to raise the voltage on a non-existent battery.

So, two answers present themselves. Either cut that white wire at the harness, and run this line to where the battery is, and leave it attached to the positive terminal. For most racing series, you can get by with this, because the car will still shut off and not run when hitting the kill switch, but it does mean that you have an active 12v line going to the engine bay after hitting the kill, and in the event of a crash or other mishap, you've got a 12v line possibly sparking around inside the engine bay.

The second option would be to run that White wire over to the lug that provides the output, so that it will always see voltage while the alternator is running. This means that your battery won't charge quite as high as it did before (guessing 14.2v instead of 14.4), which may not be a big deal. A workaround would be to stick a resistor inline between these two so that the sense line sees a slightly lower voltage, but I don't have an easy way to give a good working value for such a resistor at this point, so save that for another day.
2015-07-21 20:16:17
#14
Just to add one more piece I forgot from earlier. When we were having problems, were were ONLY killing the car with the kill switch. The ignition key had broken, so this was the only way we had to shut the car off properly. Turning the ignition off at the key would have kept the sense voltage present while the alternator spun down.
2015-07-21 20:21:00
#15
Originally Posted by ztunedsr20
does the same applies to me even if im not running a kill switch ?
No, if you don't have a kill switch then you're not likely to run into any of these weird problems with wiring.
What class are you racing in that doesn't require an external kill switch if you've moved the battery from the stock location? Just kind of curious there...


I know you said you've gotten some junk yard alternators and then one re-manufactured unit. Was that an OEM reman, or one of those parts store remans? Have they at least been honoring the warranty?


When I first read the title of this thread, I assumed it would be parts store alternators one after another. Those things will last a year on a babied car at best. I wouldn't be surprised if a race car killed dozens of them...
2015-07-21 20:26:24
#16
Originally Posted by metro_se-r
Poor ground is possible, we noticed the ground wire has been making contact with the fan blade.
That is not the ground. The alternator grounds through it's own metal chasis, through the engine block. Your engine-to-chassis grounds could be the cause of this. They fail like clock work after about 8 years and you may find that you have extremely poor grounds that need replacing.

Originally Posted by metro_se-r
Also, our clip that plugs into the alternator is somewhat melted and doesn't properly clip in, although we had that issue when we built the car.
Obviously, make sure all contacts are good ones.

Originally Posted by metro_se-r
How does one check the voltage regulator to see if it's functional?
Take the alternator to a parts store and have them test it for free.

Originally Posted by metro_se-r
Also, should mention that all three alternators were Duralast (Autozone), albeit their more expensive 'heavy duty' ones. Still rated for 80 amps though. I know their re-manufactured stuff is crap, but I don't think all three would be bad and go so fast.
Yep, there it is. That's your problem right there. You need to go with an OEM unit. 99% sure that's your problem.


Originally Posted by metro_se-r
At this time we're trying to find an OEM alternator, but those are almost impossible to come by, even at junkyards. You figure even the latest year SR20 models are 13 years old.
They are super easy to come by. Get a new one from @GregV: [url]www.gspec.com[/url] Or maybe a used one from @Andreas Miko.
Last edited by BenFenner on 2015-07-21 at 20-28-27.
2015-07-21 20:48:34
#17
What class are you racing in that doesn't require an external kill switch if you've moved the battery from the stock location? Just kind of curious there...

I've never raced the car at any track , only street purposes and a cleaner/more space @ engine bay


I know you said you've gotten some junk yard alternators and then one re-manufactured unit. Was that an OEM reman, or one of those parts store remans? Have they at least been honoring the warranty?
At the moment car still starts without any noticeable issues so no need for warranty yet

When I first read the title of this thread, I assumed it would be parts store alternators one after another. Those things will last a year on a babied car at best. I wouldn't be surprised if a race car killed dozens of them...

I replaced with all oem nx one i had a p10i also had oem one and 2 2002 90 amp ones i took from wrecked p11s all worked fine for few days and got brake/battery lights so i also grabbed bigger battery and still did it so then i bought 180$ 90amp one from vatozone and this is what im working with at the moment
2015-07-23 19:25:06
#18
Originally Posted by ztunedsr20

I replaced with all oem nx one i had a p10i also had oem one and 2 2002 90 amp ones i took from wrecked p11s all worked fine for few days and got brake/battery lights so i also grabbed bigger battery and still did it so then i bought 180$ 90amp one from vatozone and this is what im working with at the moment


Not to be the forum police, but it might be better to start a separate thread for your particular issues, as it's an entirely different situation from what metro_se-r was posting about, and we're getting some confusion in here. I don't see an 'Electrical' forum, so I guess posting in General SR20 would be the right place.

On your particular issue, when did these problems start? Was it right after you relocated the battery, or sometime later? What changed prior to the problems? Personally, I've never had a problem with remanufactured alternators, Duralast or otherwise, so I'm not sure why some are having issues there.

You had mentioned the connection on your alternator had melted, this can cause all sorts of problems. Best thing would be to head to the junk yard, clip off a connector with as much extra cable as you can, and splice it securely into your harness, and tuck it away from any sources of heat. Sounds like you've tried to move your alternator a bit to get less heat there, that should help.

But you need to walk us through the original problem, step by step, to understand this.
2015-07-23 19:41:38
#19
Im no police too but at the time it did related to my issues i was having, so somewhere along the time my alternators/battery were bad, after replacing my battery and an 90amp rated alternator from vat ozone i guess it was working great but yes the red cover connection melted from being hella close prob 1" away from mani runner so i put another good platic conection i had from all the cores i had from junkyard and replaced my belt that brought down alt few more inches away, so far i havent had any issues i just wanted to update everyone and hopefully helping somebody with same issues ,no thread jacking ,no throwing anybody offtopic
2015-09-17 03:56:57
#20
Re-energizing this thread...

Why hasn't anyone considered HEAT as being the culprit? Look where the alt sits, next to a header pipe.
There are threads on the topic of cooking alternators.
I have a heat shield built w/ $30 in materials from H.D. Works wonders on reliability. (I race with SCCA and NASA.)

Relocating the alt in place of the PS pump is an option to low-port engines, but I can't see many folks traveling this path.
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