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Thread: Why is my car killing alternators?

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Posts: 1-10 of 28
2015-06-17 01:04:13
#1
Why is my car killing alternators?
Long story short, our car keeps killing alternators on the track. We typically get 4 to 5 hours out of them and then they stop charging. We start out around 14 volts, and then it drops to 8.5 volts. Any ideas?
2015-06-17 04:59:32
#2
Do you have the alternator underdriven at all? How high are you revving the motor?

Sent from my SAMSUNG-SGH-I317 using Tapatalk
2015-06-17 05:21:16
#3
loose belt ... doubtful
too tight of belt ? excessive heat ? poor ground ?... possible
battery dead cell ? try different battery ? output is 8.5v ? what are you using to determine VDC ? Gauge or multimeter ?
alternator not providing enough amps for system, overload regulator til it burnt ?
2015-06-17 13:44:15
#4
Originally Posted by ny5speed
Do you have the alternator underdriven at all? How high are you revving the motor?

Sent from my SAMSUNG-SGH-I317 using Tapatalk

Not sure what you mean by 'underdriven'. We're basically always between the 3K and 6.5K RPM range, constantly.
Originally Posted by nismo_star
loose belt ... doubtful
too tight of belt ? excessive heat ? poor ground ?... possible
battery dead cell ? try different battery ? output is 8.5v ? what are you using to determine VDC ? Gauge or multimeter ?
alternator not providing enough amps for system, overload regulator til it burnt ?

Not a loose belt, checked that. Not too tight, checked that too.
Poor ground is possible, we noticed the ground wire has been making contact with the fan blade. 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.
Not a battery issue, because when we killed ours, we borrow other teams' batteries, and it ran those out of charge as well.
Yes, output drops to 8.5v, checked by multimeter.... actually checked by two multimeters.
How does one check the voltage regulator to see if it's functional?
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.
2015-06-20 18:26:29
#5
Did you fix the ground?

you should find a pigtail to replace a melted connector, could cause high resistance @ pin

how many amps does your cooling fan(s) draw ? I can't think of anything else that would draw more power in the electrical system or possibly any other accessory electronics you may be running.

testing the voltage regulator is explained in FSM: requires disassembly of unit.
http://www.nicoclub.com/FSM/Sentra/1993_Sentra/alternator%20and%20regulator%202.pdf

have you tried to locate a good used OE or if choosing AM Denso would be a close match as they are a OE supplier, but not the Nissan OE supplier of the alternator.
2015-06-21 04:42:51
#6
Originally Posted by nismo_star
Did you fix the ground?

you should find a pigtail to replace a melted connector, could cause high resistance @ pin

how many amps does your cooling fan(s) draw ? I can't think of anything else that would draw more power in the electrical system or possibly any other accessory electronics you may be running.

testing the voltage regulator is explained in FSM: requires disassembly of unit.
http://www.nicoclub.com/FSM/Sentra/1993_Sentra/alternator%20and%20regulator%202.pdf

have you tried to locate a good used OE or if choosing AM Denso would be a close match as they are a OE supplier, but not the Nissan OE supplier of the alternator.


Yes, we're replacing the ground wire as well as the pig tail just to ensure that's not the issue.

Not sure how many amps the fan draws, but truthfully because the car is gutted there are no other electronics outside the fuel pump running, so even 80amps should not be a problem.

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.

Thanks for the reply.
2015-06-25 22:10:19
#7
I believe b15 ones can be used, but require some modifying if that helps in your search. I would also advise on maybe searching for Sr20VE alternator ? I believe they fit as well.
2015-07-21 17:53:54
#8
I dealt with this on a Toyota at the track last year. The problem there was that the alternator output was going straight to the battery, from the battery to the kill switch, and from the kill switch to everywhere else. So, when the kill switch flipped, all power was cut, INCLUDING the sense line that normally goes from the alternator to the battery. The alternator was still spinning, trying to put out power, saw the battery voltage drop, and essentially fried itself trying to boost power to the battery (which to the alternator appeared to be at 0v).

I just did a quick check on a few Nissan wiring diagrams courtesy Google, and ours appear to be the same charging scheme. So, the question is, what exactly does your wiring look like? Does the alternator have a sense line going to the battery, regardless of Kill Switch position? If not, fix that, and you'll stop killing alternators.

We went through 4 alternators in a weekend. After replacing it for the 2nd time, I realized what the problem was, but it was too late to fix properly during the race.
2015-07-21 18:13:38
#9
Can you please explain what is a senseline? I put 4 junkyard 2002 90amp alt all of em fried i bought new battery size up from required, and reman 90amp one just to be safe and still drying my battery and getting battery/ebrake lights, i have battery relocation to rear seat a thick gouge red cable that runs through my fender and connects to what i believe its a Y to feed starter and to the 75amp fuse then i believe from fuse box it runs itself to another fuse box on the passenger side and then the wiring of alternator to connect to alternator ,i cooked the black piece that connects to alternator the one that holds the red cover and since it melted the plastic it was touching the case of alternator being ground , idk what to do , since im boosted my guesss was that the alt was too close to manifold thats why it melted, i put a shorter belt dropping the alternator away from a
Manifold few more inches down and thats where im at so far car started no issues ,second start i got battery/ebrake lights only on low idle i took off and they went away, 3rd start i came home no lights on dash i will,keep posting more updates
2015-07-21 18:20:55
#10
I'm not 100% sure what a sense line is, but I posted this about 7 years ago describing how my remote battery and kill-switch are wired.
To make sure the alternator feed is cut properly, I used an 80 AMP relay (you may go with a 120 AMP relay for your higher output alternator) controlled by the cut-off switch itself.

There is even more info in the thread that might be useful: http://www.sr20-forum.com/car-entertainment-general-electronics/12464-wiring-trunk-mounted-battery.html

Originally Posted by BenFenner
Here's a diagram I made 5 years ago of my set-up. Ignore the distribution blocks for amplifiers.



I can't believe I dug this up and I can't believe you got me to post it. =P


The bottom line is that if you're going to use a remote battery kill switch, you need to make sure the alternator is prevented from trying to keep the whole system running on its own.

It's entirely possible my setup is more complicated than it needs to be. There may be a 3rd wire on the alternator that controls whether or not it charges. If so, this wire could be run to the switch to make sure the alternator doesn't try to charge when the switch is off. When I wired mine 12 years ago, I wasn't considering that possibility.



If you're not using the kill switch on race weekend, then I'm not sure if any of this is a concern for you?
Last edited by BenFenner on 2015-07-21 at 18-40-46.
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