Ive been MECP cerified (Master) also. Haven't renewed my certificate though because I dont do these kinds of things anymore.

I agree voltage at idle isn't important unless his car stalls, but I was just making a reference of how much voltage the car should be around at idle. Obviously everyone's idle is different, (Lexus references the voltage at 2000rpm).

Indeed V=IR, but we may not necessarily see an increase voltage at the battery as the RPM increase because we have a voltage regulator that guards against such thing. If you were to measure the voltage without the regulator, then yes, voltage should increase as current goes up. Mine idles ~14v and if I rev my engine to 4000rpm, i'm going to get approximately the same voltage (+/- a few tenths)

 

Just curious, are/were you on any car audio forum? I thought I remember seeing a screen name likes you.

 

No, not that I can think of off hand.

I agree voltage will be regulated at about 14v at full output but I disagree that you will get that at idle, there is a reason amplifiers are rated at 14.4 volts input and 12.6 volts input. While 14 volts is possible as the engine is reved up, 12.6 volts is considered a nominal rating most people will consistently see, such as at idle.

The OP is seeing lower than 12.6 volts at idle but remember that this is sitting stationary in-gear, quite possibly with the a/c off as it is winter which would eliminate the "high idle" compensation circuit. Basically he would be seeing a max low on voltage due to the drop of rpm with the car in gear.

Also remember that the voltage generation of the alternator is not a linear function of rpm. The voltage ramps quickly from idle to max output. At the low end of the curve you will see a more drastic difference between say 600-800 rpm compared to 4000-5000 rpm where you will see roughly no change. You don't have to have the car redlined to reach the max output of the alternator as there comes a point in the rpm range of diminishing returns for increased rpm.

 

Yeah...you have helped me out once before.

So if I'm ok with the voltage, its time for the mounts?

 

Mac, I'm getting ~14v (or even 13.5) at 800rpm, but never below 13v. All other GS i've tested were about the same. I must be lucky then. For all I know, manufacturers rate amplifiers at 14.4v to hype up their output rating. I never really look at it anyways as all the amps I buy are rated for 12.5v.

Darrell, its very possible that your mounts are done for. I find that most GS4's mount wear out by the time the car hits 100k miles. If you turn on your AC at idle and you feel a clunk, then its a sign that your mounts are worn. I had the same problem before the mounts were replaced.

 

I'll check what my car is later today when I get a chance and see what it looks like in the same scenario.

Also, it would be good to know where the voltage is being measured from and with what ( digital fluke or analog cheapie gauge etc).

 

Well if I'm dropping below 13.5 what would that be? Which is more accurate, my radar detector or the safc? Why is there a .5 discrepancy between the two? THe radar detector is hard wired into the fuse box.

*Last I checked back in december my alternator is good...my assumption was the voltage regulator.

 

I measured the voltage from the battery terminals using a Craftsman DMM (rebadged Fluke 17B). No analog meter..too much human error for me.

 

Not all meters are accurate so I wouldn't rely on the SAFC/radar detector as your main source for voltage reading. There is also a voltage drop from the battery terminals to your accessories due to resistance.

I think you are fine regarding the electrical system. If your car isn't running weird, then there is nothing to be worried about. Just have the mounts checked out.

 

Thanks...I guess I was wanting to make sure that I didnt have any major problems going on. I'll have my mounts checked out. I get a little rough idle thats pretty annoying. Yes I can feel the AC engage, mostly a smoother idle, nothing harsh, but still the shakes.


Thanks for you all's help.


So are voltage stabilizer any good for our cars? I have not seen much exposure to the topic.

 

I'll meaure my voltage at the terminals with the car at idle, but you are fortunate if you are getting 14V at idle. The typical I've seen is about 13.2-13.7 or so volts. I mysef have never seen 14+ V at idle, but perhaps the Lexus alternator puts out a higher voltage at lower RPM than typical.

As for the amps, most are regulated to output a certain consistent output given a certain input voltage range. Usually that is about 12.4-14.4V. That is simply the amps power supply. If it were an ungegulated power supply you mights see an increase in power output as input voltage rises.

As for adding large capacitors, I'm in the minority that in most cases it just causes more problems. All it does is add another load to the alternator. The alternator is the highest potential when the car is on. At that point everything including the battery is now just a load on the alternator. In order for a capacitor to work as many people believe it will, the votage drop of the alternator, as well as the battey has to drop below that of the cap and its ESR. The cap also has to be very close to the amp.

 

As for why the safc and radar detector read difderent voltages its because each is getting its readind at different points. All wiring has resistance. You have to measure the voltage at the source if posdible. Often the alternatnator is impractical, so the battery terminals is your next best point.

 

just went to lunch...voltage dropped as expected on my two devices, Engaged the AC and felt a little shimmy,

MOTOR MOUNTS! MOTOR MOUNTS! Guess I'll checking in to the labor on getting them changed. Looks like my 172k mile luck streak is over.

I'll probably still check my voltage tonight.

 

Makes sense...I assumed that each point had different amp readings but consistent voltage readings, guess I was wrong.

So should I invest in a grounding kit and or voltage stabilizer? Or a waste?

 

Chris, my 14v may have been at a higher idle ~1100rpm. I'll check on it again, but it's always at least 13.5v at 800rpm. It's never been lower than 13v no matter how low the idle is.