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voltage across battery when charging ?
We're in the last phases of getting our 88GT on the road with the 331. The rolling chassis we bought had the battery moved to the trunk.
Got a PA Performance 3G 130A alt installed, we're getting 12.5v across the battery while car is idling. Is this where it should be, or should it be higher? If this is low, any ideas on what to check, I've been checking everything in sight to ensure tight connection, fuselinks are good, good grounds etc. |
Re: voltage across battery when charging ?
That's a little low. You should have 14.5 volts at idle.
I know on my power master alternator you have to rev the engine to 2500 before the field windings energize. Maybe it's the same for your pa-performance unit. Also, you're going to have some voltage drop since the battery is in the trunk. What size wire is used from the alternator to the battery? I would first have the alternator checked to eliminate that possibility and make sure the wire is heavy enough gauge they used to relocate the battery. |
Re: voltage across battery when charging ?
I'm thinking it's a little low too, but then again, it's at idle. We haven't established whether there are underdrive pullies on it, which could be causing a lower alternator output. How is the voltage over the normal operating range of the engine? Does the voltage rise to ~14V when the engine's running around 1500rpm?
I think it would be great to find out how well that cable is transferring power to the rest of the electrical system, and also how well the battery's negative connection is made, i.e. is everything crimped & bolted down, or are things soldered, shiny, and :cool:? This is one of the things that kinda scares me away from trunking my battery in the notchback: the gauge of the cables is going to have to be huge to ensure minimal voltage drop from the battery to the starter & alternator. |
Re: voltage across battery when charging ?
Thanx for the input on this issue, please keep the thoughts coming as this is the last thing from getting this beast on the road.
No underdrive pullies, can't have them as we're putting on a T-trim blower Gauge of wire to trunk #2 All ground connections are tight, clean, and free of paint |
Re: voltage across battery when charging ?
my PA performance 130Amp alternator charges my stock stang at about 14.5V at 750rpm idle with no accessories on. with just say the lights on, it will charge at around the low 13's at idle. these numbers are not across the battery but from my autometer gauge reading from my ignition switch as i wanted to get a "real feel" of what voltage the accessories are getting. any time up raise the rpm's to 1000 or more, it will always charge at 14V or over. keep in mind that this is using a march 1000 underdrive pulley kit which includes a smaller (i believe) alternator pulley.
if it matters i upgraded to the cable running from the starter selenoid (sp?) to the alternator with the "premium" one that PaPerformance seels with the inline 200A fuse. i believe that is a 4 gauge cable. i also replaced my old positive and negative wires from the battery as well as the cable running from the starter selenoid to the starter with PaPerformance 4 gauge cables. in your situation, what RPM are you idling at? what happens when you bump to 1000rpm? 1500rpm? post your stats. if that cable going to the battery is really long you may want to upgrade to a larger size to be on the safe side and it can't hurt anything. you can always try shortening it if possible. you may also want to condier changing the pulley on the alternator to a larger diameter model such as the stock size (i think it's larger than the pa performance pulley) and some manufacturers make pulleys larger than stock. |
Re: voltage across battery when charging ?
I once had a very old style (1970's) 130 amp alternator with an external voltage regulator. During my heater core swap job, I drove the car without the instrument cluster connected for about 2 days. Turns out that the alternator was excited by a charge on the same ciricuit as the cluster. Without this circuit closed, I had to blip the throttle to about 4-5000 RPMS to manually excite the alternator. I could also excite it by running a lead from the + battery terminal and touching one of the terminals on the regulator. If you're running an adequate gauge of wire and have good connections, you may have a similar problem.
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Re: voltage across battery when charging ?
I'll post the stats tonight on different idles
We're running the same PA Performance cable with the inline 200A fuse. |
Re: voltage across battery when charging ?
Here are a few more bits of info from our charging issue
1) started the car at idle voltage across the battery was 12.03 in the hatch and 12.5 at starter selenoid. 2) At 3K RMP voltage readings didn't change. 3) Under load with lights, fan etc on voltage dropped below 12volts. 4) With the car idleing, removed positive lead from battery, car still ran. Voltage at the starter selenoid was 14.3. This is where it should be with the battery hooked up. Does anyone have any other ideas or comments on this new info? Thanx in advance for your input. |
Re: voltage across battery when charging ?
I'm leaning towards a bad alternator. You should have had 14.5v across the battery at idle. I would get both the alt. and battery checked.
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Re: voltage across battery when charging ?
One more thing I had to do with the battery in the trunk and 2 gauge + cable was to run a 2 gauge ground cable all the way from the - terminal on the battery to the bolt on the starter motor. Grounding the battery to the chassis in the trunk was just not adequate, especially starting with the engine and starter motor hot.
Rev |
Re: voltage across battery when charging ?
Well, here's an update on recent troubleshooting on this problem.
1) Took the alt. off the car took to an alternator shop, it's putting out 14.6 v and 152A at peak. 2) Put another battery in the car, and didn't change the readings off 12.3v. Calling all experts - help WILL BE APPRECIATED. THIS IS THE LAST THING BEFORE WE GET OUT HOT-ROD ON THE ROAD. Thank you in advance for any help. |
Re: voltage across battery when charging ?
Are you sure you don't have underdrive pulleys? Your alternator wants to put out 14+ volts like it should but when you're hooking up your battery it's dragging it down to 12. That's what my car does normally with underdrives. Even with a fully charged battery a car with underdrive pulleys will find itself trying to play catch-up with an electric fan, ignition, fuel pump, etc. If you want to check the integrity of your system try this. By placing a voltmeter along the entire length of your positive cable (from the battery terminal to the start solenoid) while the car is running you will read the voltage drop of that part of the circuit. It should be a lot less than 1 volt with the 2 gauge wire. If that checks ok try the same with your ground cable by going from your battery negative terminal to a ground point up front (usually on the left inner fender forward of the strut) and from the negative terminal to the engine block. These couple of checks will tell if your losing voltage from the wiring.
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Re: voltage across battery when charging ?
If it was ME, at this point, that mofo battery would be back under the mofo hood!...LOL
Seriously, how many grounds do you have? You can never have too many grounds. |
Re: voltage across battery when charging ?
Have you checked voltage directly at the alt output? Any difference if you have? A voltage drop of .5vdc is normal, anything over that and it's re-wiring time. I have underdrive pulleys in my '86 and had to rewire the alt. output 2 yrs. ago when I had the same problem.....and the battery is in the stock location, not in the trunk. Just my 2¢. GL
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Re: voltage across battery when charging ?
Seriously, how many grounds do you have?
You should have your battery grounded in one place. The other "grounds" I mention are where other electrical equipment is grounded to the car. My point is, maybe his battery is grounded just fine but the ground for his alternator is not adequate or maybe the bonding strap from the engine/tranny isn't cutting it. These will cause problems that can be hard to diagnose. Good luck. Hope you get it on the road soon. |
Re: voltage across battery when charging ?
I've been running a stock alt, underdrives, and a Optima Red Top for years. The lowest my bat drops is 12.5 with all the bells and whistles. I just took a 8 hour class in starting and charging systems 2-3 weeks ago, and it seems like you have a short someware,,,,
Check the connections at the starter and your ground. hope this helps.....Good Luck |
Re: voltage across battery when charging ?
Battery is grounded in one place in the back of the car to the frame. What is the bonding strap from the eng/tranny? Are you talking about the grounding strap from the block to the frame?
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Re: voltage across battery when charging ?
There should be a ground from the block to the body(firewall) and another one from the block to the frame.
If the battery ground is all you have, then that's your problem for sure. |
Re: voltage across battery when charging ?
so the strap goes to the firewall?
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Re: voltage across battery when charging ?
yep and I would put another one from the engine to the frame.
That "should" solve your problem.....I said should. Let us know how it goes |
Re: voltage across battery when charging ?
not that it's apples to apples, but my battery on my bike w/ the key off was about 13.5-13.8
while running it was about 12.10-12.50 never checked the stang, never had charging issues. |
Re: voltage across battery when charging ?
To back up what has already been said, this sounds a lot like my charging situation. I have underdrives, but the stock pulley on my Powermaster and it barely keeps voltage above 12.5 at idle.
What is the diameter of your crankshaft pulley? That will tell us all for sure if you have/or don't have underdrives... |
Re: voltage across battery when charging ?
If the alternator checks out on the bench, there's something wrong with the wiring, but it's not the guage of cables used to remote the bat to trunk. If the wiring can deliver the battery's current to start the engine, it's good enough to charge the battery. In any case, you should have a minimum of 13.8 volts at idle.
John |
Re: voltage across battery when charging ?
We're running a stock crank pulley as once the motor is broken in, a Votech T-Trim awaiting our pony.
We put the grounding strap on - from the firewall screwed to the head on drivers side. We also put another alt. on the car and same low 12.3 volts. This clearly takes the alt out of the picture. We've also switched batteries as well no change. |
Re: voltage across battery when charging ?
Well...that only leaves the wiring. Someone already said there could be a short somewhere. If it's not the battey, alternator, gauge of wire or lack of grounds then that only leaves the wiring and/or connections.
Can you tell us exactly how it's all wired? |
Re: voltage across battery when charging ?
PA Performance 3G 130A alt, got their wiring kit with the 200A inline fuse which runs to the starter selenoid. Battery is located in the back hatch with a Morosso relocation kit, which has a 2G wire going from the starter selenoid back to the positive on battery. Negative from battery runs to a shut off switch, which is grounded to the frame in the rear. Up front, we've got an engine to frame ground, and an engine to firewall ground with the strap.
Is there a quick and easy way to check for shorts in the system? |
Re: voltage across battery when charging ?
Sounds like a short to me. If you disconnect the battery, all of a sudden it's putting out the correct voltage at the starter solenoid. That eliminates the alt. and ITS wiring right there.
Not familiar with the PAP unit, is it internally regulated, or do you have an external regulator on that? I had that exact problem, and figured out my external regulator wasn't wired correctly. Fixed that, and buddah bing, 14volts at the battery in my hatch. |
Re: voltage across battery when charging ?
yeah we disconnected the battery while the car is idling, and we saw 14.5v across the selenoid.
Are there any specific areas where a short could be, or do we need to check the whole flipping wiring in the car? |
Re: voltage across battery when charging ?
D/C the postitive lead from BOTH ends, check it with an OHM meter to ground, see if it has a short in it. With it D/C there should be NO reading on the OHM meter.
This is a tough one bro, the more I think about it, the more confused I'm getting. This just doesn't make sense. It's gonna be something "stupid" when we finally figure it out. Ahah! Are you running a disconnect switch in the rear of the car? If so, WHAT KIND? I had this freakin problem with my car too. |
Re: voltage across battery when charging ?
Yeah, if it's Summit junk, get rid of it!!
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Re: voltage across battery when charging ?
checked the + and - cables last night, no short between them. I even checked the disconnect switch it's working like it's supposed to.
We brought in an alt off a friend of my son's car. Put that alt on, still reading 12.3 volts. I told my son I'm a little concerned about the vortec supercharger bracket grounding properly to the engine block, as the block came painted from Keith Craft. So we ran another ground from one of the alt bolts to the frame. We took another reading and read about 13.3, this was very positive. Here's where it gets freaky. We took off that alt, put back the PA Performance alt on, and took another reading at idle and we're back to 12.3 volts. I was also thinking that if we had something in the car loading the system, wouldn't a fuse pop, as all electrical runs through the fuse panel right? Only difference is some circuits are switched by ignition, and some circuits are live all the time. |
Re: voltage across battery when charging ?
Now that you have a ground to the frame, is there one more alternator you can try?
That will tell for sure if the PA alternator is bad since you are now getting 13.3v with a different alt. Sometimes an alternator with a bad diode will not always show up on a test bench. I would try one more alternator, if you can, and if you get a good reading I would send the PA alternator back to them and let them test their own unit. The guilty finfer seems to be pointing at the PA alternator. It sounds like you have it pretty much narrowed down to the problem! |
Re: voltage across battery when charging ?
Just as an FYI, much below 12.3 volts, the battery probably won't have sufficient voltage to start the car.
12.4-12.6 volts is considered charged. 12.3 is pretty low, and 12.2 is discharged. Below 12.2 is pretty much dead and you shouldn't expect the engine to crank. The only place I can think to check is at the union of the main power lines off the alternator. While two positive leads run off the alternator, they merge into one 10gauge wire, if I remember right (been a long time). That connection can get severely corroded which can definitely lead to low voltage coming from the alternator. I apologize if this was already suggested, I didn't read the whole post. |
Re: voltage across battery when charging ?
Have you put a load test against it with a load tester??
Also, it isn't a good idea to disconnect the battery cable while the engine is running to check the alternator. It will burn it up, you are making an incomplete circuit. Diodes don't like that. A good tester has a diode tester built in, I'd look there. |
Re: voltage across battery when charging ?
Only load tests we've done is turning on lights, electric fan, all other accessories to drive load. What exactly is a load tester - how is it used?
We will be trying another alt this week. |
Re: voltage across battery when charging ?
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I think you're wasting your time changing the Alt. You've already proven that it works, ie bench test, and it works on the car with the battery disconnected. Would this per chance be a CHROME alternator? A buddy of mine had his brackets powder coated, and the alt no longer grounded itself through the case. Cleaned off a little powdercoat, and all was well. A friend of my Dad's had the same thing happen with a chrome alt. Just throwin shyt out there to check man. Like I said, this is gonna be something silly when we finally figure it out. |
Re: voltage across battery when charging ?
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Yeah, he did take HIS alternator to be checked and it checked out ok but I question the type of tester the place used. I say, at this point, his alternator has a bad diode and the bench test that was used couldn't check it under load or check to see if the diodes were good........or both If the other alternator worked and got the correct voltage readings, why doesn't his PA alternator do the same? |
Re: voltage across battery when charging ?
OK, I musta misread that then. I thought the PA read the correct voltage on the bench, and when he D/C the battery (WHICH may have killed the diodes right then.)
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Re: voltage across battery when charging ?
Well the mystery continues. We put on a PowerMaster alt, same voltage. Never done a load test on the battery. Do I just put it across the battery with the car not running?
If something is loading down the car when key is on, wouldn't it blow a fuse in the panel, as all circuits run through the fuse panel whether switched on/off or hot all the time? |
Re: voltage across battery when charging ?
To load test the battery. The car is off. The tester is hooked up to battery. The test puts an adjustable load on the battery so you can see what kind of reserve power it has with the load.
To test the charging system under load. You start the car and then load it up. On a Load test for starter/charging system/batteries, you take the load probe [it's a clamp that you put around the wire to read amps] and put it on the bat. wire at the alternator, while the car is running. This will tell you what kind of amps the alternator is putting out, at the alternator before it gets to the car and battery. |
Re: voltage across battery when charging ?
Even if the battery is junk, shouldn't we still get a 14v reading on the terminals when the car is running?
What's the voltage on the battery with every thing disconnected? I mean JUST the battery. I'm still thinking that damn kill switch (SMOKED mine in no time) or a short somewhere. This is killing me. Now I know how the wife feels when she watches her soap operas. I GOTTA KNOW! |
Re: voltage across battery when charging ?
This is always how I've determined whether a battery is failing or not. If 14v across the battery terminals told me the alt is doing it's thing. Then I replace the battery we've done in our stang.
My son and I decided to take the rear battery wiring out of the equation and temporally moved the battery back up front and wired it up OEM style. Same low below 13v when car is running. |
Re: voltage across battery when charging ?
Your're making this harder than what it really is dude.....your PA alternator is shot.........period.
Send it back to be repaired or replaced.....BAM....back in business!! |
Re: voltage across battery when charging ?
So...did you replace that alternator yet?
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Re: voltage across battery when charging ?
Yes we did - put a brand new Powermaster 140a alt on, same readings. We haven't touched it since then.
Here's what we've done to date: * Changed alts with same readings. * Swapped out the battery * Relocated the battery to the front, removing these things from the equation: - 2G wiring to the back of the car - Ground to the frame in the rear of the car - Kill switch located in the back of the car * Checked and cleaned all the grounds * Reconnected the ground strap to FW |
Re: voltage across battery when charging ?
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Re: voltage across battery when charging ?
Are any fuseable links invlolved in this equation? If so check/delete them.
Powermaster alts are "1 wire" type, correct? If so, where does that "1" wire connect to? I belive you said the starter solenoid, right? Check for corrosion on ALL the terminals on that solenoid post. Also, no washers between wire connections on there either. Galvanzed washers make good insulators.... I'm still going with my original theory, this is gonna be something "stoopid"....... |
Re: voltage across battery when charging ?
This is going to be one for the archives when we find the answer. :)
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Re: voltage across battery when charging ?
Jester: "Powermaster alts are "1 wire" type, correct? If so, where does that "1" wire connect to? I belive you said the starter solenoid, right? Check for corrosion on ALL the terminals on that solenoid post. Also, no washers between wire connections on there either. Galvanzed washers make good insulators...."
Powermaster one wire hookups go directly to the positive terminal on the battery. Do you have the two blade terminal hookup for the voltage regulator on your powermaster too? I have the stock green wire going to the upper blade terminal as recommended by powermaster. Nothing is conncted to the lower blade terminal. I don't want to sound redundant, but was the diameter of the pulley on the alternator ever measured? I had this problem forever, b/c I switched alternators after I had installed underdrives, so my old alternator had the underdrive pulley, Not the 140 pwermaster out of the box. I have 14.4volts at idle with a 1 7/8" alt pulley. my grounds are crappy too, I still have that worthless stock strap from the head to the firewall and nothing going to the frame. this one is going to be good... |
Re: voltage across battery when charging ?
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My powermaster has a 2 gauge wire from the alt. to the battery.....nothing else. |
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