Voltage drop with H.O. alternator

[528hz 10+ year member]

Alright guys this is killing me...first tiime I've ever had an issue with a voltage drop after everything proper is installed. Now to start off, I'm not going to name the company, because I don't want this thread going the wrong direction. The problem may in fact be my error...

This may be a lengthy post, but I'll try to hit the high points...

I'm running an RF 2500bdcp for my sub, an RF 600.4 for my highs. My electrical consists of 300a H.O. alt running directly to 2 Die Hard Platinum group 31a (exact batts as the Odyssey 2150s). One run of 1/0 grounded directly to the alternator bracket at the engine and grounded to one of the batts in the rear. Power from the alt is running to the other battery. Both batteries are wired parallel...here's the issues:

-So my voltage idles at about 13.8-13.9v.

-When I come to stops at times, my voltage will drop down into the 12s (12.5-12.7)

-When I play at 3/4 volume, I stay within 13.7v, but once I go full tilt it will drop quickly down into the 12.5-12.2v range. This will happen at idle as well when I'm driving. Thing is though, my sub won't even really get too warm after 30 sec of playing it like this...

My lights don't dim at all...

I was thinking something to do with the regulator, which is internal. No external regulator. The alt does have the smaller pulley on it, and I have installed a smaller belt to compensate. From what I can tell there is NO belt slippage...

Alright audio engineers...give me some light...

Click to read more...

 

[sexy 10+ year member]

The only way someone could tell you what is happening is if they were able to be there and test with a DMM. What I can tell you without seeing you set up in person is that although there are quite a few companies that claim their alts will do 300 amps they have no proof of it. The highest output alternators on the market are also the ones that require the most RPMs. If an alternator bench tests at 300amps cold then it will only do about 240amps at best under the hood of a car due to heat loss.

12.5/12.7 drops can come from lag time also. That means that your alternator has to react to a large demand in thousands of a second like when the bass hits. Once the alternator sees the demand it ramps up to that demand and that can easily explain the drop you are seeing.

You will have to test with real test equipment while playing test tones to see if an alternator is keeping up or not. Music and no test equipment means nothing to people who know their electrical platforms.

 

[sbarber82 10+ year member]

Are you using a digital volt meter or the stock one that came in the car. Sometimes the stock meter will not show the correct voltage after electrical upgrades. If your lights aren't dimming I would suspect you meter is not telling you the truth. Also what kind of car is it? Most newer cars have a internal regulator that cuts the alts output to save gas...

 

[528hz 10+ year member]

The only way someone could tell you what is happening is if they were able to be there and test with a DMM. What I can tell you without seeing you set up in person is that although there are quite a few companies that claim their alts will do 300 amps they have no proof of it. The highest output alternators on the market are also the ones that require the most RPMs. If an alternator bench tests at 300amps cold then it will only do about 240amps at best under the hood of a car due to heat loss. 12.5/12.7 drops can come from lag time also. That means that your alternator has to react to a large demand in thousands of a second like when the bass hits. Once the alternator sees the demand it ramps up to that demand and that can easily explain the drop you are seeing.

You will have to test with real test equipment while playing test tones to see if an alternator is keeping up or not. Music and no test equipment means nothing to people who know their electrical platforms.

I definitely hear what you're saying and that most companies claim this or that, and they really don't do what they're suppose to do. One thing to note as well that just discovered, is that my front, stock battery is **** wet cell! My stupid mistake for not checking it before hand...

Are you using a digital volt meter or the stock one that came in the car. Sometimes the stock meter will not show the correct voltage after electrical upgrades. If your lights aren't dimming I would suspect you meter is not telling you the truth. Also what kind of car is it? Most newer cars have a internal regulator that cuts the alts output to save gas...

It's an aftermarket voltmeter on my fuse block, which still could be a possibility of inaccurate readings. I drive an '09 4runner, and you may be right about the cutoff. My voltage meter will periodically turn off at times while driving...

 

[gckless 5,000+ posts]

What vehicle is this? Some of the newer vehicles that are hybrid or have the economy features do exactly what you are describing.

 

[RoYALbLUE08 10+ year member]

@keep_hope_alive did testing on this on his Honda accord. I believe it was something with ECM that cuts out power which was mentioned above. he figured out a way to bypass it to keep amps up and voltage up

 

[LosIsATool 5,000+ posts]

Clipping will cause it also. A little bit will pull a lot of current and it pulls more and clips more as it happens

 

[528hz 10+ year member]

So...

I went to my good friend's shop and tested the alt. We used this:

So at idle my voltage is still sitting at 13.7-13.9 and I'm getting about 90 amps from the alt. At 2000 RPM I'm only getting 150 amps and the RF is wanting 350 on 0db tones...hence why the alt is having to dig down into the batteries. It will hold 12.6-13.0v at idle hitting on it hard.

All-in-all, my alt is not putting out what it should be, but it is working. I'm not sure if I'll mess with it or not. I don't compete, but still. It would be nice to have everything to full capability. But the good thing is I won't hurt anything.

I did get to meter though. This is SEALED on the dash.

I did get to a 48.7, when I should have snapped the pic, but after messing around too much in the end I only got this one. With my driver window down she'll do a 51.3. Not bad from one 18" SP4, RF 2500bdcp...7 cu. ft net tuned to 36 hz.

I gotta thank Bumpin Buick for all the help and suggestions!