Never ending voltage issue I can't figure out!

[stvrob]

I understand what you mean. Batteries in series vs parallel and all. But the battery is only discharging current when the engine is not running, When starting the vehicle, the battery delivers an enormous current, much more than even the powerful audio amplifier system. When the engine is running (assuming the alternator is capable of the task), the battery is always charging. A smart charging system is always trying to taper off the charge and not needlessly heating up the battery (at 14+ volts) when its already fully charged.
When running, all the battery contributes to the system is to act as a giant capacitor. It certainly smooths out what would otherwise be a pulsing voltage from the alternator, but even a single battery is overkill for that sole task. A second battery would certainly help you run the audio system for a longer period of time if the engine is not running, perhaps that is the reason for the second battery? But if the audio system is using as much power as he described earlier, it is going to need a jump start after just a few minutes of use anyway, so he'd be better off with one of the batteries isolated.
I think he ought to look into a DC/DC converter and step it up to 24-28 v for the amp.

 

[Mounce]

Have you ever seen a video of someone's systems running? I've seen some that with just a few seconds of a bass note the battery drops 3 or 4 volts because one battery doesn't have enough capacity to handle that kind of a draw and the alternator can't keep up. Since you keep referring to the battery as a capacitor in this sense, let's use actual capacitors as an example. Let's say you had a charge going into one capacitor and you have a lead coming off of each connector on the capacitor. If you were to create an arc between the two leads even with a charge going into the capacitor, the voltage is going to drop significantly and the arc won't be as strong.

Now let's say you had two capacitors wired together and in the same set up with a charge going into them. You create another arc, but now the arc will stay strong for twice as long as the single capacitor but will still lose voltage but it won't be as significant as the single capacitor due to the larger reserve of power.

So more capacitors, or batteries, will have a larger reserve than one and even while getting a charge applied to them, they will still drop in voltage if a big enough load is drawn from them.

 

[stvrob]

To be honest, I've never seen a video like that. If such a system is drawing enough current to pull a battery down 3 or 4 volts with the alternator running, thats got to be pushing 200 amps! Maybe more. Im not sure a human could survive inside a vehicle without some serious ear protection! I would think the best way to run such a system in that case is to run a separate alternator, with the field coils configured to at least 96 volts to get the current down to a manageable 20 amps or so.

 

[shepherd92683]

The system I have uses about 200a of current and a total of around 2800 watts. It's not an insane build you may see other audio junkies run but it does have some power. Extra batteries reserve current for the amps to keep better voltage to the amps during high demand. The goal later on is upgrading to a another amp that is going to draw another 150 amps on top if what I have now (another g31 battery will be added at that time along with another 1/0 power run to the rear) but I need to make this run at a high voltage to help prevent damaging my equipment. The problem lies within finding what causes the system to drop. There is no consistency in the voltage. With all things the same day in and out, it fluctuates and I don't know what's causing it. I run the ac on and headlights on one day and it's 14.2, the next day it's 13.5. Why? Here is a video I made a couple years ago before a few upgrades of what it can do.

 

[coolasice]

The problem the OP is having is that he wants to maximize the output of his stereo system which would be when the altenator is able to output at 14.4v (which amps usually have a max of 16v input). His vehicle is equipped with a RVC system (which is running as it is designed to) and lowering the voltage (12.6v) to keep from "overcharging" his batteries. In large stereo systems this can be a great loss. If you have 1500W of power at 14.4v, you only get 1312W output at 12.6v. (with even larger systems the difference is huge, especially for competition.)

His only options at this point are
1.) convert to a old style altenator and live with the charging system errors/warning lights
2.) modify the light sensor/switch to turn on lights whenever the vehicle is turned on.

 

[stvrob]

Now that I see how much power your system is using, how do you know that your stereo system is not the component drawing down your voltage. Are you just assuming the alternator is NOT at 100% excitation when the stereo is on?
Also, with the battery issue, anytime the system voltage is above about 12.6 volts, the battery is consuming current, not delivering it. At 14.5 volts its consuming a good bit of current and a second battery it's twice as bad. I'm still having difficulty understanding how a second battery helps, you can't draw from a battery unless you pull the voltage below 12.5 volts, otherwise its a current sink.

 

[stvrob]

If you throw a magazine over the light sensor on the dash, would your daytime running lights go to full voltage lights?

 

[coolasice]

Now that I see how much power your system is using, how do you know that your stereo system is not the component drawing down your voltage. Are you just assuming the alternator is NOT at 100% excitation when the stereo is on?
Also, with the battery issue, anytime the system voltage is above about 12.6 volts, the battery is consuming current, not delivering it. At 14.5 volts its consuming a good bit of current and a second battery it's twice as bad. I'm still having difficulty understanding how a second battery helps, you can't draw from a battery unless you pull the voltage below 12.5 volts, otherwise its a current sink.

He already has a high output alternator, but the rvc is not allowing full excitation, it is doing what it is supposed to be doing, regulating the voltage to save battery life and fuel economy. The second battery is being used as a high drain backup, whereas on extreme heavy use the stereo can drain enough current from a single battery to essentially discharge it before the alternator can recharge it, with two batteries you have double that capacity.

 

[stvrob]

Ok...what you are saying is true, but only during periods when the load on the system pulls the voltage below 12 or 12.5 volts. If the amp does that with regularity, the 2nd battery could be beneficial. It just seemed from reading through the thread that wasn't an issue at all.

 

[bobdec]

+1 on post #85 option number 1. This is not a normal setup for the RVC to handle. The RVC system in the vehicle was not engineered to hold a consistent 14+ volts, the voltage is lowered for emissions mileage gains. Bottom line it does keep the batteries charged, for what it was designed for, but does not consistently supply 14+ volts. It can be re-engineered with some testing and sophisticated equipment. However IMO the easiest way would be to put a high power, internally or an externally adjustable regulation, old school alternator in the system and then pay (about $100.00) get the RVC SES light DTC's tuned off..

 

[coolasice]

The main issue he is seeing is that the rvc is not predictable, his voltage can be anywhere from 12.6-14.5 at any time. With heavy hits from the stereo the voltage can actually be drawn down 2-4v. He wants to have the old fashioned way of charging, 14.4v constant so when the bass gets heavy it won't dip as low.

 

[The_Roadie]

Rip out the advanced tech, put in an old school high output alternator and profit. Jeez, 90 posts on how advanced tech does unexpected things out of the owner's control. ☺

 

[BlazingTrails]

Rip out the advanced tech, put in an old school high output alternator and profit. Jeez, 90 posts on how advanced tech does unexpected things out of the owner's control. ☺

In a bad mood today?

 

[The_Roadie]

Nah, but just spent $10K of company's money to solve a problem caused by the customer's choice of a $3 Chinese lamp.

 

[BlazingTrails]

Sounds like a fun day. I fixed a security camera today (of all things) 32' up on the side of Columbus engine centers building. Apparently it has been down for over a year and no one could figure it out. Amazing what a dead 24v mini transformer can cause. Dmm anyone? Lmao

 

[shepherd92683]

+1 on post #85 option number 1. This is not a normal setup for the RVC to handle. The RVC system in the vehicle was not engineered to hold a consistent 14+ volts, the voltage is lowered for emissions mileage gains. Bottom line it does keep the batteries charged, for what it was designed for, but does not consistently supply 14+ volts. It can be re-engineered with some testing and sophisticated equipment. However IMO the easiest way would be to put a high power, internally or an externally adjustable regulation, old school alternator in the system and then pay (about $100.00) get the RVC SES light DTC's tuned off..

The alt is internally regulated to 14.7. They told me I could make it external for another $150 and the light would stay on. What the difference to just buying an XS Power VCM so it's fully adjustable on the fly and deslodering the battery light on the cluster?? But to vcm's harm the battery's more from sustaining a strady 14+ voltage?

 

[bobdec]

Give me time to look it up on the '08.. Need to see what lights the battery light. If the light is being turned on via the class 2 data bus after the PCM sees an alternator/regulation DTC then you may be able to tune it out. The DTC may also illuminate the SES , I don't know at this point.
Lots of older systems with fixed voltage regulators run a consistent 13-14 volts. My merc outboard engine runs a starter and a house battery at 14.2 volts w/o any problems. My '94 Camaro Z28 runs 13.8. Both have fixed voltage non-adjustable regulators.
If you go w/adjustable regulation I would set it at 13.8-14 volts, Voltage may still drop at idle depending on how much current capacity buffer is stored in you batteries. Think of it as your batteries acting like a water tank supplying the variable Hi/Lo load to the amp, base is a killer, capacitors* help w/instantaneous power demands. And the alternator as a pipe trying to keep that tank filled. Keeping voltage at 14 is like forcing more water into the tank. However once the tank is empty the alternator pipe can't supply the load alone, and voltage will drop.. . Bottom it all has to work together, big alternator, higher voltage, capacitor if needed*, batteries. Each play a part of the system.

 

[IllogicTC]

Give me time to look it up on the '08.. Need to see what lights the battery light. If the light is being turned on via the class 2 data bus after the PCM sees an alternator/regulation DTC then you may be able to tune it out. The DTC may also illuminate the SES , I don't know at this point.

Everything as far as I know is fed via data bus except the tach, speedometer, MIL (controlled directly by the PCM), turn indicators, and low washer fluid signal.

 

[bobdec]

Back a few years ago "DC Power Engineering" had a dual alternator kit for 4.2 L engine. What's nice about the dual setup for RVC (PCM controlled) is you can leave the stock alternator/battery 12 volt system untouched and intact. Then use the second alternator (can be any power) to feed a completely separate 12 volt system and battery(s) for the audio. Two isolated 12 volt power systems, one stock for the vehicle and the second jacked up to any acceptable voltage you want for the audio equipment., best of two worlds.
They only have the GM V6/V8 engines listed on their website, no 4.2 L is listed, but it might be worth a call, they may still have the plasma cutter setup around. Not cheap, cost was about $400.00 for the kit back then less the second alternator.

 

[06TrailblazerLSS]

Hey Sheperd, did you use deadener on the roof and whatnot?

 

[shepherd92683]

Yes a whole dynamat bulk pack and several pieces of flat steel to reinforce as well.

And no, my wife would kill me if I spent over $400 for a 'bracket' lol! She's not into upgrading vehicles and doesn't like extreme car audio. At this point turning my headlights on while driving looks to be the only answer that's reasonable. Not a big deal to me to turn a switch for extra voltage

 

[06TrailblazerLSS]

Yes a whole dynamat bulk pack and several pieces of flat steel to reinforce as well.

And no, my wife would kill me if I spent over $400 for a 'bracket' lol! She's not into upgrading vehicles and doesn't like extreme car audio. At this point turning my headlights on while driving looks to be the only answer that's reasonable. Not a big deal to me to turn a switch for extra voltage .

Would you give me any pointers? any heads ups? what kind of tools?

Thinking about deadening as much of the roof as possible pretty quick, maybe double layers?


How hard is it dropping the headliner?

 

[shepherd92683]

Dropping the headliner isn't too bad but it only drops unless you take a lot of things apart and that was going to be too much of a pita for me. When you drop the h/l there are sections of flat roof in between the bracing that goes across. I used jb weld epoxy for applying flat steel to the roof and dynamatted over it. Took a few hours to do everything but mad a big difference. The rattling got so bad from my roof I didn't even want to turn it up anymore. No the worst part that rattles is the liftgate, which I used the remaining dynamat on it I had and it is still terrible IMO.

 

[06TrailblazerLSS]

Thanks, Im going to have to do that soon! Sounds like a pain

 

[shepherd92683]

Just a few new notes to add... Voltage does not always stay at 14.2-14.4 with lights on, most of the time stays at 13.6. Also for no reason will run at 14.4 without lights, defrost etc on. Also noticed at highway speeds will run in 13's then when parked will go up to 14.4 and back down when driving resumes.

Bottom line is there is something we all don't know that is interacting causing the drop and also increase. For the lights or nothing on the last few days and staying at 14.4 really threw me off as to what made it do that. No changes have been made since I did the rewiring mentioned prior.

 

[bobdec]

Scroll down this link to 'Fuel Economy Mode' http://www.agcoauto.com/content/news/p2_articleid/350 . Could be the second negative wire you added of larger gauge wire will carry more current. With two ground (negative battery wires) the current will take least resistance. This MAY be putting a lower current flow on the OEM negative wire going through the current detector loop. Again just a guess. Or could be the battery(s) are charged and you are entering economy mode correctly and lowering the voltage. They made this system hard to outguess and bypass. .

 

[wiredawg]

Most of us have the old alternators with built-in voltage regulators, and only two control wires going to it. One goes FROM the alternator to the PCM to report back the field coil duty cycle so the PCM knows how hard the alternator is working. If it sees the alternator working as hard as it can, and the voltage measured at the PCM is continues to go down, it starts shedding load starting with the stock head unit audio system then the HVAC system, then lights, all in an attempt to save the last battery energy for the engine. I'm not sure how the 2008 alternator works, not having a shop manual for the later years.

The other single control wire goes from the PCM to the alternator, and is a simple suppression wire to hold off the alternator from starting to recharge a battery under frigid conditions, where the engine is cold, the battery is cold, and by holding off the alternator from starting up for 10-30 seconds, it gives the engine a few seconds to stabilize its RPM before its also asked to send 2-3 HP through the belt to the alternator. That's the only condition I know about where the engine is running, but the alternator won't be putting out 13.8+ volts.

Hello Roadie, (2003 Envoy XL 4.2L) I replaced my alternator and battery (both are new), but still not getting a proper charge. My question is regarding the two control wires. I read that one should have a constant 12VDC or so(red lead/right side with clip down) and the other pin (grey wire) should only see a reading when the key is in the "on" position. In my case, I checked the pins and I have 12.66VDC on the red lead and 12.56VDC on the other lead while my vehicle is in the "off" position (no key). I take it, this is a malfunction??? Basically, I cannot get my my charging system to function properly after getting my "battery light" indication on dash along the the message "battery not charging". And not battery is not registry 14.5VDC while running, just the 12.6 or so. Also, not 100% sure about this fact will need to verify tomorrow. But, was getting very loud squealing and thought this was a belt alignment problem shot some water on it just to narrow down the squeal to no avail, no change in squeal at all. For some reason I decided to remove my 2-wire plug from the alternator and about 15 sec later the squealing stop completely gone. Will have to test this theory to be sure this is the cause. Have you ever heard of such a symptom. Also, had this new alternator tested 3 times and it was report as good. So my next logical guess is the wiring harness and the 12VDC constant on both pins...at this point I'm stuck, not very familiar with the PCM and not sure how to open to check...any help is much appreciated.

 

[Blckshdw]

Roadie is semi retired from the site and isn't on much like he used to be. Hopefully one of our other experienced members can help you out though.

 

[Texan]

Was the "new" alternator a rebuilt one? Not unusual to be
faultily out of the box. The voltage reading could possible
be ignition switch.

 

[Mooseman]

All I can suggest is download the manuals and check the wiring schematics. I do know that when it's really cold (below 0), the PCM will wait about 10 seconds after starting the engine to let the belt and stuff get limber before dumping the alternator load on it. So the grey wire may not show anything until the engine is actually running.

Check all the fuses. Not sure if there is a fusible link somewhere but the schematics should tell you.

 

[budwich]

wiredawg.... just quickly looking at the references, you need to do some "rechecks" as your "test results" aren't quite aligning with the descriptions in the reference. So first, my reference shows 3 wire connection which has two together in a connector and the third (main - red). With your vehicle off, you need to disconnect the "main red) and measure its voltage.... its suppose to go back to battery thru a fuse. Make sure you are seeing an expected voltage. Next, disconnect the "two wire connector".... turn the key "ON" (DO NOT START), and then measure voltage on the red lead in the connector to a KNOWN ground. What is the reading? This will potentially determine if the "drive circuit" of the "ON" signal is "functional".... to a small degree. Of course, if you had scan tool, you could do a bit more easier. This is where it gets "tricky". You then need to check / watch the same lead with the plug connected (and the main red lead connected) and engine running. You need to use a "pin probe" to monitor the voltage on the same lead to see what values you are seeing.