[Tyler_Canada]

I had my alternator replaced yesterday per the recall. When I popped in a cd today on my way to work, the bass was too loud. I have an entirely aftermarket system consisting of a HU, amps, speakers and sub. I put all the settings on the HU back to what they had been prior to the alternator replacement, but there was just way too much bass. I have a separate sub level control on my HU, so I turned it to minimum, and even that didn't help enough.

My first thought was that some fool at the dealer had cranked the gain or the bass boost on the amp. I checked, and the bass boost was off and the gain was set exactly where it had been all along (analog controls, not affected by loss of power). I turned the gain to minimum, and now the system is listenable, but it's still much more bass than there used to be.

So my question is, is it possible the new alternator is putting out a higher voltage than the old one?

 

[ekaxel]

Measure it with a digital voltmeter and see if it is within spec. Higher voltage will usually result in shortened bulb life, among other things.

 

[andy]

Measure it with a digital voltmeter and see if it is within spec. Higher voltage will usually result in shortened bulb life, among other things.

what are the specs by the way?

 

[ekaxel]

should be between 14.1 and 14.7 Volts

 

[Tyler_Canada]

Ok, I came across some interesting specs when I looked this up. These specs relate to the old, recalled alternator. I don't have the specs for the new alternator.

Regulated output: 14.1V - 14.7V

24A @ 1300 RPM
87A @ 2500 RPM
105A @ 5000 RPM

So, from that, the alternator isn't putting out much current at all when cruising at less than 2000 RPM, which is pretty much any speed up to 120km/h (75mph).

 

[Tyler_Canada]

Is there anyone out there who has an old alternator that hasn't been swapped yet that could do a voltage test for me? I'm curious.

 

[Gonzo]

Don't hold me to it but my radar detector displays voltages... and with my old alternator it typically displayed 14.1-14.4 volts. During idle it would drop to 13.9 volts.

 

[Tyler_Canada]

Close enough for government work. I'll check out the new alternator tomorrow morning if I can. If anyone is quicker than that, please post it.

 

[zebelkhan]

Ok, I came across some interesting specs when I looked this up. These specs relate to the old, recalled alternator. I don't have the specs for the new alternator.

Regulated output: 14.1V - 14.7V

24A @ 1300 RPM
87A @ 2500 RPM
105A @ 5000 RPM

So, from that, the alternator isn't putting out much current at all when cruising at less than 2000 RPM, which is pretty much any speed up to 120km/h (75mph).

Is that engine RPM or Alternator RPM? Due to pully size, I assume the alternator RPM will be at least twice that of the Engine RPM.

 

[Kris]

I believe the data relates to alternator speed.

 

[Tyler_Canada]

Good to know.

 

[jaak]

Where do you want it measured? I've not had a chance to look into the SM as to where would be a good spot, but the alternator's not that easy to get to...

Just a quick check, I put my HP972A Multimeter on the battery and saw 12.3 volts with ignition on, but not running, it dropped to 9.86 to start the Murano and then went to 14.37 at idle. Revved it up to 4K in steps of 1,000 rpm and it sat at 14.38 (Good thing, otherwise my battery's in trouble.)

What's really needed is a current measurement as well as voltage before the regulator, but I don't know that it's possible without a lot of work.

Yup, still have the old one. I'll get it swapped out shortly.

Which reminds me... They'd have to change your battery for you to see a significant voltage increase.

 

[zebelkhan]

Just a quick check, I put my HP972A Multimeter on the battery and saw 12.3 volts with ignition on, but not running, it dropped to 9.86 to start the Murano and then went to 14.37 at idle. Revved it up to 4K in steps of 1,000 rpm and it sat at 14.38

That is quite a bit of drop during crank. No wonder my PC sometimes reboots when I crank the engine. Its PSU protects it up to 9.5 volts for 5 seconds during crank. So mine must have droped even lower than that. I need to stop working on the car with interior lights on for long times

 

[hfelknor]

"just a quick check, I put my HP972A Multimeter on the battery and saw 12.3 volts with ignition on, but not running, it dropped to 9.86 to start the Murano and then went to 14.37 at idle. Revved it up to 4K in steps of 1,000 rpm and it sat at 14.3\8 (Good thing, otherwise my battery's in trouble.)"


Sounds perfectly normal.

Measuring voltage on a start is more of a battery test than an Alternator test, tho.
There is a shop procedure that we used to use, called a "9.6 Volt Drop Test". I think it is still viable.

I'm a little rusty, but I remember some.
First of all we had Battery "testers' that had very large resistors in them to dissipate the load.
We could adjust that load.
The test (IIRC) was to look up the starting current for a particular car, and put on a "half load.
In other words, if a starter typically would draw 600 amps, we would set the load for 300 amps.
The we would measure the voltage for 10 seconds.
If the voltage dropped below 9.6 Volts, the battery was bad, or at least it was going bad.
The biggest variation?
Whether the engine was "tight" or not.


So a battery that measures 9.86 under full load is very, very good.


Homer

 

[Tyler_Canada]

Where do you want it measured? I've not had a chance to look into the SM as to where would be a good spot, but the alternator's not that easy to get to...

Just a quick check, I put my HP972A Multimeter on the battery and saw 12.3 volts with ignition on, but not running, it dropped to 9.86 to start the Murano and then went to 14.37 at idle. Revved it up to 4K in steps of 1,000 rpm and it sat at 14.38 (Good thing, otherwise my battery's in trouble.)

What's really needed is a current measurement as well as voltage before the regulator, but I don't know that it's possible without a lot of work.

Yup, still have the old one. I'll get it swapped out shortly.

Which reminds me... They'd have to change your battery for you to see a significant voltage increase.

Off the battery is good enough, that's where I'll measure it too.

I was thinking they might have replaced the battery too, but they would have told me. It's very strange that the bass would increase as much as it did. Knowing what I know about my hearing, I would say the increase is about 6dB, which is pretty substantial.

My only other guess would be that they changed what is known in the car audio world as "the big 3". The 3 wires involved in connecting the battery, alternator and chassis. I'm certain the '03 Muranos use 8 gauge wire for those, but my amp sugggests 4 gauge, which is what I ran from the battery and to the ground point.

I read in the SM that the starting voltage could be between roughly 8V and 10V depending on the temperature. I don't have the exact numbers handy.

 

[Tyler_Canada]

I got 12.7V with the engine off.
8.5V while cranking
13.7V while at idle
13.9V while revving to 2500 RPM.

I think the rad fans were running, but the stereo, HVAC and lights were all off.

I checked the water in the battery, it looked like it was down about 3/4" from the top, but I'm not sure how much should be in it.

 

[Kris]

12.9 V – engine off
?? – cranking (DVM dropped to 0 for a fraction of a second and engine was running!)
13.9 V - idle
14.1 V - > 1,000 RPM

“old alternator”.

Experiment – switched HID on while idle – voltage dropped to 12.9 V and raised back to 14.0 V after approximately 3 – 4 seconds. It shows the high current during HID start up. Interesting.

 

[jaak]

This is actually quite interesting!

However, I do have one request... Multimeter brand and model number. There can be some variation in the accuracy of the meter depending on who made it. I don't expect this to be an issue right now, but if something interesting shows up, it's good to know.

(Sheesh, these instrumentation guys....)

What I should really do, is put a scope probe on and a current probe and capture the whole sequence on a scope so you can see it all... It would be cool if we could all do this, but it's not so simple!

With a math function, we could see instantaneous power.

Anyone know how much current is drawn during the crank?

Oh, wait, just reread Homer's post... 600 AMPs... Hmmm...

Yup, I might be able to get a current probe to do that.

 

[Kris]

Sorry jaak, I do not have digital scope. It would be nice but...........I could get from our workshop though.........hm.............interesting thought.......maybe in two weeks time when I get back home....

 

[Tyler_Canada]

I don't know the model, it's a 3 year old RadioShack cheapo ($19?) model. I have the part number, but they don't sell them anymore, so I can't find out anything more. Do you think it might be off by much?