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Bad Alternator Or Regulator?

amnash

By amnash,
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amnash Enthusiast

amnash

Posted
Posted (edited)

ok so here is what i have going on. the battery hold a solid 12v its 1 year old red optima so its good. Everytime i start the car its struggles to turn the starter and then slowly picks up speed and then the engine will just barely start. today was bad as i was stuck in a parking lot for 15 minutes until it decided to start for me. no im going to fix it before it gets worse.

once the car is running here is my voltage at battery with different things turned on;

car off : 12.14v

running : 12.78v

+ two 12" electric fans wired straight to battery, those turned on : 12.00v

+ headlights on : drops to 10v then rises slowly to 11.30v

+ music : 11.30v

+ heater with blower on max : 9.96

the fuel pump is also wired to 12v constant. i haven't dealt with alternator issues before so this is a little new. isn't there supposed to be something keeping it at like 14v while running regardless of how much electronics i have turn on??? or do i just have to much electronics?

so is this just a matter of changing the alternator? or do i need to upgrade something somewhere?

Edited by amnash
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amnash Enthusiast

amnash

Posted
  • Author
Posted

i didn't check the voltage while cranking.. what should it be?

i just went ahead and changed the alternator, i had one sitting in the garage from my rb20.

after the install:

car off : 12.14v

running : 14.08v

+ two 12" electric fans wired straight to battery, those turned on : 13.81v

+ headlights on : drops to 10v then rises slowly to 13.64v

+ music : 13.59v

+ heater with blower on max : 12.80

so it is a lot better. i hope that my starting problems go away. my battery light is off now too :)

last question though.. the voltage is still dropping with all the accessories on. isn't the output supposed to constantly change to maintain a 14.7v charge???

Carbon 34 Grand Master

Carbon 34

Posted
Posted

i didn't check the voltage while cranking.. what should it be?

i just went ahead and changed the alternator, i had one sitting in the garage from my rb20.

after the install:

car off : 12.14v

running : 14.08v

+ two 12" electric fans wired straight to battery, those turned on : 13.81v

+ headlights on : drops to 10v then rises slowly to 13.64v

+ music : 13.59v

+ heater with blower on max : 12.80

so it is a lot better. i hope that my starting problems go away. my battery light is off now too :)

last question though.. the voltage is still dropping with all the accessories on. isn't the output supposed to constantly change to maintain a 14.7v charge???

no

The battery will sit around 12.5-13 volts , your redtop wont like being discharged so go for a long drive or find a charger that supplies high current to refresh it or it will fail before its time

You need to rethink your fans and fuel pump , you need upgraded wiring for a few things and relays fuses etc , upgrade grounds to engine , alternator frame bracket , not sure how powerful the rb20 alternator is but the other is most likely 80amps

Would guess its about 65-75 amps like older nissans had

voltage should never exceed 14.4 v or you will have overcharging problems and fry a few things

If your lights go superbright and stay that way more then likely the regulator is " stuck" open allowing excess voltage a dangerous problem

That will cause death to a lot of the car components and may cause battery to explode and catch fire even agm batteries can explode !!

And remember these cars were never designed to run amps, fans , extra current fuel pumps etc on top of day to day items , in bad weather you can exceed current input from alternators

amnash Enthusiast

amnash

Posted
  • Author
Posted

how do you suggest i wire in the fans then? and the fuel pump wiring is what i found on here apparently a lot of people do it.

i did notice when wiring in the neo loom, that it has a wire for the electric fan signal. right now that wire isn't hooked up to anything, could i use that to power a relay for the fans? they would still get a full 12v when the relay clicked over but that would be better right?

does anyone know if that wire is a grounding signal or a power signal?

blind_elk Grand Master

blind_elk

Posted
Posted

how do you suggest i wire in the fans then?

They are ideally wired through a thermo switch, so they only come on when the engine gets over heated. The set temp can safely be as high as 90C, sometimes even higher. Movement of the car through the air is nearly always sufficient to maintain the correct operating temperature. Wiring the fans direct to battery so they are always on basically defeats the purpose of thermo fans, namely to remove some load (engine driven fan) from the engine. Having the electric fans permanently on simply shifts the load on the engine from the water pump / fan to the alternator.
i did notice when wiring in the neo loom, that it has a wire for the electric fan signal. right now that wire isn't hooked up to anything, could i use that to power a relay for the fans? they would still get a full 12v when the relay clicked over but that would be better right?
Yes. (as above)
does anyone know if that wire is a grounding signal or a power signal?

Ordinarily, ECUs switch things to earth, rather than supply +12V.
t_revz Grand Master

t_revz

Posted
Posted

Although it wasn't making noise it could have been a slipping belt.

Also you said your alternator light isn't on now so it could be a dodgy phase within the alternator.

Sounds much better now

amnash Enthusiast

amnash

Posted
  • Author
Posted

so when i did the rb25 neo swap in my r32 i notice a wire from the ecu pin 78 (electric fan relay control signal). so i thought i could use this with a relay and rewire my fans so there was less drag on the alternator.

so with a test light hooked up between that wire and + terminal i idled the car and let it warm up. it go all the way up to 200F and i pulled the plug, turned on the fans and it dropped down to a normal 180F

so im not sure the purpose of that wire from the r34 ecu. the neo did have a clutch fan on the water pump anyways...so i dont know.. was there also an electric fan on the r34??

so tomorrow im gonna buy one of these and then just have it so that at 200F the fans turn on with full 12v. that way, the only time they are actually on is at a long red light or reall slow traffic. most of the time they will be off

lsdfghjk.png

  • 2 weeks later...
amnash Enthusiast

amnash

Posted
  • Author
Posted

the car is still really hard to start. im going to check the voltage when cranking and then change the starter with a rb20 starter i have sitting around. does anyone know a north American vehicle that has a starter that would work? would be nice to have a nice new one in there. im tired of this sluggish starting it makes my car look like it runs like shit but it doesn't...

what you the voltage be when cranking? and if the starter doesn't fix it what should i try next?

GTR_NUTZ Collaborator

GTR_NUTZ

Posted
Posted

Check for corrosion in your earth/ power lead (from your battery to starter/ car) Either change it or if you have enough length cut it and put the terminal back on.

My old mans car use to be a bit like this until he changed the leads.

If your regulator/ alternator was on the fritz your volts will drop and the battery light on your dash so come up really faintly after a few mins of running.

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