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Discussion Starter · #1 ·
Hi,

Hoping someone can provide some insight or point me towards some troubleshooting to find an answer regarding an intermittent electrical system issue. My 2010 Pro 4x has an aftermarket HO (250 AMP) alternator, installed two years ago, along with upgraded/thicker cabling and an Optima Yellow-Top battery. About two weeks ago I noticed that sometimes when I use my turn signals, my headlights seemed to flicker briefly, usually when the turn signal turned off automatically from completing the turn. The issue got more noticeable and I now see flickering without doing or changing anything, just driving along. I have a ScanGauge installed, set to monitor voltage and it has started registering wide voltage swings, again, I don't have to be doing anything or changing anything. It can happen sitting at idle or driving. Previously, the voltage would show 14.6 to 14.8, regardless of what was turned on or if I was driving 15 MPH or 70. When you turn off the engine, the ScanGauge briefly reads battery voltage before it turns off. That voltage is consistently in the 13.0 to 13.2 range. It still is.

I've checked cables to see if something is loose and not found anything. So, is it likely / possible that this is the voltage regulator going bad or something else, and if something else, what might cause such an intermittent problem, albeit one that seems to be gradually getting worse?

Any suggestions / advice is appreciated.
 

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I won't hazard a guess as to the cause of the problem, but 14.6 - 14.8 volts sounds excessive.

Normally, it might get that high while the battery is being recharged, but should settle down into the low-to-mid 13's after the battery becomes fully charged.

Constantly exposing a sealed battery (like your Optima) to 14.6 - 14.8 volts can't be good for it.
 

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Discussion Starter · #3 ·
I don't think this alternator has ever normally (until now) shown less voltage than that. In the winter time, it actually goes higher and can hit 15.0. I've read/heard somewhere that anything over that can be potentially dangerous, but I didn't know that high 14's was bad. I've never seen the voltage in the 13's with this alternator running. I'll try swapping out the battery and see if that changes anything.

Is there a specific test that can be run on the Optima to tell if it's prematurely aged?
 

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just about any place that sells batteries can perform a load test on it - for free, in most cases.
 

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14.6-14.8 volts is normal charging system voltage for a Nissan. Anything from 13.2v to 15.5v is considered good. Make sure you don't have any accessories grounded after the voltage sensor in the negative battery cable (meaning "between the sensor and the negative battery post"). An electronic battery tester can tell you if your battery is good. Wide voltage variation could be a sign of a faulty voltage regulator.
 

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14.6-14.8 volts is normal charging system voltage for a Nissan. Anything from 13.2v to 15.5v is considered good.
If your charging system was producing 15.5 volts all the time, you'd be replacing a toasted battery in short order. There's nothing "normal" or "good" about a voltage that high on a constant basis.

As a point of reference, my charging system voltage drops down into the very low 13's after the battery is fully charged.
 

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Frontier original alternators vary voltage depending on load, this is sensed by ring around ground cable. When battery cables were replaced with heavy gauge were they run through ring or around it. I don't know how after market alternators work with our setup, but may be a cause of your trouble
 

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Originally my voltage after startup was about 14.1, and settled at 13.1 after
the truck ran for a few minutes.

I replaced the alternator with a HO, to get better amperage at idle and now
the voltage runs about 14.9 at startup and settles to 13.9/14.1 after a while.

The aftermarket alternator spec sheet says that it's "voltage set point" is
14.8. I've been meaning to look into this some more but ... finding time. Does
that mean that the voltage regulator is integrated into the alternator?

I'll been wanting to do some tests on it's output at various loads with and
without the current sensor attached. I'll let you know what I find out.
 

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Yes, the voltage regulator is inside the alternator.

It sounds like your aftermarket alternator has a regulator with a higher-than-stock voltage setting.

(This would be a desirable feature to car audio guys, because a higher battery voltage allows audio gear to deliver more power to the speakers. It's not good for battery longevity, however - which is one reason why Nissan engineers chose the voltage setting they did).
 

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Discussion Starter · #10 ·
Yeah, the voltage regulator is definitely internal to the alternator. According to the info on it from DC Electronics, Inc. , the set point output voltage is also 14.8, like Little Bulls. I did some testing at the terminals and the "resting" voltage, after about 10 hours of sitting was 12.6, which seems about perfect for a fully charged battery. At idle, I read 14.81 volts, which again, based on the manufacturer info, is right on. I have read some information that corresponds to Skillbane's comments about voltage over 14.4 or so not being good for the battery. I've also read that Yellow Top Optimas don't age very well anyway, so I'm wondering if the battery is going, even though it tested okay. Since it's an intermittent problem, I may not have "caught" it when it was failing. I wasn't able to get the old battery to charge, so I haven't been able to test a different battery to see what happens.

The tech rep from DC Electronics also mentioned checking the belt and idler / tensioners. My understanding is that if the idler or tensioner is going bad, it would be making noise. Haven't been able to verify if that "understanding" is correct or not, but it isn't making a sound. Very smooth. Belt doesn't appear worn, but kind of hard to tell without taking parts off to really get to it.

One thing it does do, that I thought was unrelated, but perhaps not, is sometimes when the cooling fan and / or thermostat or something kicks on that turns on the fan, I get a big voltage drop, down to 13 or so and the whole truck kind of stutters for a second. Doesn't happen a lot and doesn't happen when I experienced the light dimming thing. I've only ever noticed this while idling at a stop light. Very brief and everything recovers- voltage returns to normal almost immediately, possibly/likely due to that big alternator's voltage regulator sensing the drop and spinning up the alternator higher. This is an issue that I've noticed for quite a while, doesn't seem to get worse, so I discounted it, but it may also be aging the electrical system.

Little Bull- concerning your questions about cabling. The original cabling is still installed and used, but I also had something done called a "Big 3" cable upgrade. Won't go into detail here, lots of interweb info on it. It's additional cabling, added in parallel to the original, so it could be causing some issues, but no one (alternator rep, audio equipment rep and audio install guys) mentioned any potential problems with it and it's a fairly common procedure for audio installs. Still, doesn't mean that it isn't something unique to a Frontier, so I'm going to explore that some more.

If anyone can verify "tells" of when idler / tensioner are starting to fail, if there are any, I'd appreciate it. Also, wanted to say "thanks" for the input so far. This is a great forum.
 

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From what I understand, the Battery Current Sensor overrides the voltage regulator to reduce engine
load for low current draw and increase voltage beyond regulator settings for high loads.

If that's the case, having a "Big Three" upgrade, if the ground bypass' the Current Sensor, could
interfere with the trucks charge rate.

I upgraded the ground to 1/0, but had to strip the sheathing for the cable so that it would pass
through the current sensor's opening, in order to ensure that ALL current was read. Like I said,
I haven't had a chance to test the system yet, but plan to do so as soon a I can.
 
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