Possible Alternator Overcharging
10-24-2016, 07:09 PM
#1
Possible Alternator Overcharging Hey guys -- 1982 Volvo newly converted to LS3 power. New crate engine, PSI harness/ecu (08 Corvette). Start up was pretty painless - started on first try, all systems working, etc.
One of the things I noticed right away was that I was seeing 14.9V at the battery at idle. Seemed a bit high to me - expected 14.4-14.6V. And usually after a bit of charging at that level (to recover from starting load) they'll drop down to 13.6V or so. This stays right at 14.9V. I have a Volvo/VDO "voltage" gauge, and at 14.9V the needle sits right at the edge of the gauge 'redline' - which I'm guessing represents 15V.
Interesting occurrence - about 75 miles into the new engine (multiple short drives) I lost a driver's side brake light bulb/filament. This car has a finicky light-bulb-out indicator - so it's best to replace bulbs in pairs. I put two new bulbs in - these are dual filament - rear tail light and brake light in the same bulb. Fast forward - another 75 miles or so and BOTH rear brake lights burned out at pretty much the same time. As an aside -- I don't think I've had to replace ANY light bulbs in the 16 years I've owned the car.
Car hasn't been driven at night since the swap -- clearly the brake light bulbs have seen the most use.
Beginning to think that the high charging voltage may be the culprit.
Anyone have any relevant experience in this arena? Shouldn't my charge voltage be lower (14.4v or so) and then drop down after a bit of driving (13.6v)? How does one go about altering 'control' of alternator output voltage?
Thanks - Michael
One of the things I noticed right away was that I was seeing 14.9V at the battery at idle. Seemed a bit high to me - expected 14.4-14.6V. And usually after a bit of charging at that level (to recover from starting load) they'll drop down to 13.6V or so. This stays right at 14.9V. I have a Volvo/VDO "voltage" gauge, and at 14.9V the needle sits right at the edge of the gauge 'redline' - which I'm guessing represents 15V.
Interesting occurrence - about 75 miles into the new engine (multiple short drives) I lost a driver's side brake light bulb/filament. This car has a finicky light-bulb-out indicator - so it's best to replace bulbs in pairs. I put two new bulbs in - these are dual filament - rear tail light and brake light in the same bulb. Fast forward - another 75 miles or so and BOTH rear brake lights burned out at pretty much the same time. As an aside -- I don't think I've had to replace ANY light bulbs in the 16 years I've owned the car.
Car hasn't been driven at night since the swap -- clearly the brake light bulbs have seen the most use.
Beginning to think that the high charging voltage may be the culprit.
Anyone have any relevant experience in this arena? Shouldn't my charge voltage be lower (14.4v or so) and then drop down after a bit of driving (13.6v)? How does one go about altering 'control' of alternator output voltage?
Thanks - Michael
10-24-2016, 07:18 PM
#2
Are you running a one wire alternator? If not, where does the voltage sense wire tap into the electrical circuits? This should be the wire with the 470 ohm resistor and/or dash charge light. You did remember the resistor, right?
Also how is the power wire from the alternator hooked into the rest of the system? Most guys like to run it "straight to the battery" which can lead to overcharging.
And since crate motors typically don't come with alternators where did you get your alternator from?
Hard to believe the voltage can get high enough to burn out light bulbs, but 15V at the battery is not a good thing.
Also how is the power wire from the alternator hooked into the rest of the system? Most guys like to run it "straight to the battery" which can lead to overcharging.
And since crate motors typically don't come with alternators where did you get your alternator from?
Hard to believe the voltage can get high enough to burn out light bulbs, but 15V at the battery is not a good thing.
10-24-2016, 07:39 PM
#3
Thanks for your quick response - I appreciate it.
I'm running a brand new (not reman) Remy alternator that is listed as a replacement for a 2010 Escalade - 145A. It has a single stud output terminal, and a 4-prong plug. Of the 4 prongs - 3 are utilized. Two of the 3 wires in this 4-wire alt plug go into the harness and back to the ECU that PSI Conversions supplied. I have no idea what they do/are supposed to do or which "letters" on the plug correspond to these two wires. I'll need to do more research to answer that. The third wire in the plug is a short jumper that connects to the alternator output stud -- I believe this is the 'sensing' wire. Since the harness is aftermarket, I'm not sure if wire colors mean anything - but what I'm calling the short "sensing" wire is red.
I do have a functioning alternator charge light - it comes on with ignition on, and goes out when the alternator starts charging. PSI helped me set up this circuit on the Volvo - although some trial and error on both sides was required - their first circuit suggestion definitely didn't work. Working together, I suggested something I thought would work -- and it turned out to work just fine. A switched 12V+ wire from the fuse box connects to one side of the idiot light, and the other side ties into one of the two wires (the brown one! - if memory serves it connects to PIN 61 on the ECU, but I'm old and sometimes memory doesn't serve...) that come back to the ECU from the alternator. When not charging, the brown wire in the alt plug is grounded -- so the light (hot on one side, this ground on the other) comes on. Once the alt starts charging, this brown wire sees alternator output voltage -- which matches the voltage on the other side of the bulb, and since there's no delta V across the bulb -- the light goes out. By the way -- before we worked out the problem with the alternator light not working correctly, I still was seeing 14.9V at the battery during charging. Adding the functioning alternator light had no bearing on the charge level at the battery.
I have 4 different wires/cables attached to the output stud. One is the previously mentioned "sensing wire" which goes a whopping 2" back into the alternator plug. One goes to a power distribution block on the passenger side fender. Power goes from there to the stereo, cooling fans, ECU (which also drives fuel pump) and my starter relay. One goes to a factory/OEM power distribution block on the driver's side fender -- this provides all the "chassis" power to the car except for the aforementioned items -- so lighting, windshield wipers, rear window defog, horn, hvac, gauges etc. One cable goes to the hot side of the battery for charging which is mounted in the trunk.
I'm running a brand new (not reman) Remy alternator that is listed as a replacement for a 2010 Escalade - 145A. It has a single stud output terminal, and a 4-prong plug. Of the 4 prongs - 3 are utilized. Two of the 3 wires in this 4-wire alt plug go into the harness and back to the ECU that PSI Conversions supplied. I have no idea what they do/are supposed to do or which "letters" on the plug correspond to these two wires. I'll need to do more research to answer that. The third wire in the plug is a short jumper that connects to the alternator output stud -- I believe this is the 'sensing' wire. Since the harness is aftermarket, I'm not sure if wire colors mean anything - but what I'm calling the short "sensing" wire is red.
I do have a functioning alternator charge light - it comes on with ignition on, and goes out when the alternator starts charging. PSI helped me set up this circuit on the Volvo - although some trial and error on both sides was required - their first circuit suggestion definitely didn't work. Working together, I suggested something I thought would work -- and it turned out to work just fine. A switched 12V+ wire from the fuse box connects to one side of the idiot light, and the other side ties into one of the two wires (the brown one! - if memory serves it connects to PIN 61 on the ECU, but I'm old and sometimes memory doesn't serve...) that come back to the ECU from the alternator. When not charging, the brown wire in the alt plug is grounded -- so the light (hot on one side, this ground on the other) comes on. Once the alt starts charging, this brown wire sees alternator output voltage -- which matches the voltage on the other side of the bulb, and since there's no delta V across the bulb -- the light goes out. By the way -- before we worked out the problem with the alternator light not working correctly, I still was seeing 14.9V at the battery during charging. Adding the functioning alternator light had no bearing on the charge level at the battery.
I have 4 different wires/cables attached to the output stud. One is the previously mentioned "sensing wire" which goes a whopping 2" back into the alternator plug. One goes to a power distribution block on the passenger side fender. Power goes from there to the stereo, cooling fans, ECU (which also drives fuel pump) and my starter relay. One goes to a factory/OEM power distribution block on the driver's side fender -- this provides all the "chassis" power to the car except for the aforementioned items -- so lighting, windshield wipers, rear window defog, horn, hvac, gauges etc. One cable goes to the hot side of the battery for charging which is mounted in the trunk.
10-24-2016, 08:10 PM
#4
A bit more info -- pic of the alt plug below.
The letters on the alt case are P, L, IF and S. My red wire in the plug connects the S terminal to the alternator output stud. A light gray wire in the plug connects the IF terminal to something in the ECU - I'll have to ask PSI what that wire goes to. A brown wire connects the L terminal to the ECU - I believe this goes to pin 61, but not 100% sure. This is the circuit that also has a connection to the idiot/dash alternator light. There is no wire in the plug at all corresponding to the P terminal.
The letters on the alt case are P, L, IF and S. My red wire in the plug connects the S terminal to the alternator output stud. A light gray wire in the plug connects the IF terminal to something in the ECU - I'll have to ask PSI what that wire goes to. A brown wire connects the L terminal to the ECU - I believe this goes to pin 61, but not 100% sure. This is the circuit that also has a connection to the idiot/dash alternator light. There is no wire in the plug at all corresponding to the P terminal.
10-24-2016, 09:22 PM
#5
TECH Senior Member
iTrader: (7)
The S terminal should not be going to the output stud. The point is to run that wire to the main power distribution point in your vehicle, wherever that might be.
Andrew
Andrew
10-24-2016, 10:15 PM
#6
Hmmm.....PSI Conversion's instructions were very clear on that point....I even sent them a picture of my short pig tail to connect to the stud, and they pronounced that as correct.
More fundamentally - since the "stud" is directly connected to my 2 distinct power distribution points, I'm having a hard time understanding how connecting the "S" wire to those points is going to make any difference as those distribution points are 'seeing' exactly what the stud is seeing voltage-wise.
What am I missing Andrew?
More fundamentally - since the "stud" is directly connected to my 2 distinct power distribution points, I'm having a hard time understanding how connecting the "S" wire to those points is going to make any difference as those distribution points are 'seeing' exactly what the stud is seeing voltage-wise.
What am I missing Andrew?
10-24-2016, 10:27 PM
#7
TECH Senior Member
iTrader: (7)
Hmmm.....PSI Conversion's instructions were very clear on that point....I even sent them a picture of my short pig tail to connect to the stud, and they pronounced that as correct.
More fundamentally - since the "stud" is directly connected to my 2 distinct power distribution points, I'm having a hard time understanding how connecting the "S" wire to those points is going to make any difference as those distribution points are 'seeing' exactly what the stud is seeing voltage-wise.
What am I missing Andrew?
More fundamentally - since the "stud" is directly connected to my 2 distinct power distribution points, I'm having a hard time understanding how connecting the "S" wire to those points is going to make any difference as those distribution points are 'seeing' exactly what the stud is seeing voltage-wise.
What am I missing Andrew?
http://www.pirate4x4.com/tech/billavista/Wiring/Part2/
Scroll down to voltage sensing.
Where is your gauge connected?
Andrew
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10-24-2016, 11:18 PM
#8
Oh yeah - read through the 4x4 wiring site many times; the challenge is that one can find other sources that disagree, so it's hard to know who to believe. And of course, their counsel on where to connect the sensing wire (my batt is in the trunk) is in direct conflict with the builder of my harness. Not doubting you -- just frustrated that there seems to be so much conflicting counsel on this issue.
Not sure where the car's gauge is measuring voltage -- gauge was already in the car when I got it. Suspect it's sensing at the fuse box inside the passenger compartment.
I'll fire the car up tomorrow and take some sample voltages. Given that I'm getting 14.9V at the battery in the back, I don't think I'm going to see much less than that anywhere. But I'll check the batt, the OEM harness at the back (brake light bulbs), the fuse box, the alt. output stud, and the 2 distribution blocks -- and report back.
And yes - in direct conflict with 4x4's counsel, I'm running a 1/0 cable from the alt output to the positive terminal of the battery......not much drop there.
Not sure where the car's gauge is measuring voltage -- gauge was already in the car when I got it. Suspect it's sensing at the fuse box inside the passenger compartment.
I'll fire the car up tomorrow and take some sample voltages. Given that I'm getting 14.9V at the battery in the back, I don't think I'm going to see much less than that anywhere. But I'll check the batt, the OEM harness at the back (brake light bulbs), the fuse box, the alt. output stud, and the 2 distribution blocks -- and report back.
And yes - in direct conflict with 4x4's counsel, I'm running a 1/0 cable from the alt output to the positive terminal of the battery......not much drop there.
Last edited by Michael Yount; 10-25-2016 at 07:38 AM.
10-24-2016, 11:38 PM
#9
TECH Addict
You need the voltage drop from the harness between the pin and output stud, its so the alternator compensates for all the draw and voltage drop in the harness, I've fixed the charging system on several jeeps by routing that wire to the output side of the ignition switch at the switched main on the fuse box.
YMMV...
YMMV...
10-25-2016, 07:17 AM
#11
You need the voltage drop from the harness between the pin and output stud, its so the alternator compensates for all the draw and voltage drop in the harness, I've fixed the charging system on several jeeps by routing that wire to the output side of the ignition switch at the switched main on the fuse box.
YMMV...
YMMV...
I understand conceptually the need to sense voltage for regulator feedback somewhere further 'downstream' on the system. What I don't understand is this - typically, the symptom for a set up like mine (sensing at the output stud) is voltages that are TOO LOW elsewhere on the system, due to the drop in the harness and draw from other components along the way. Trunk mounted batteries are often UNDERCHARGED in that circumstance. I'm having the opposite symptom -- TOO MUCH voltage downstream. While charging the A/C -- idling for an hour or so with twin 11" cooling fans, 7" oil cooler fan and HVAC fan all on high - I was still seeing 14.9V at the back of the system.
Why would the regulator tell the alt to put out 15V if the sensing wire was sensing 15V? As I understand it -- if the sensing wire were, for example, connected to the fusebox inside the car and seeing a lower voltage - say 12V, that 12V 'signal' would be interpreted by the alt as a sign to increase output to drive the voltage higher. pdxmotorhead - what were the symptoms/problems being displayed on the Jeeps you fixed?
I understand what ya'll are pointing at - but given my symptoms (high charging voltage all the way at the back of the car all the time), I can't see how making that change is going to make a difference. In any event I/we need some more data. Let me get some system voltages at various places on the car with it running and all warmed up. We'll see if that helps enlighten the dumb mechanic.
Andrew - before I go disconnecting something without understanding all the implications -- what would you expect to happen/what should happen if the alternator is seeing 0V at the sensing wire?
10-25-2016, 08:28 AM
#12
TECH Senior Member
iTrader: (7)
Take this as a datum point in making your decision. On my GTO the only pin that is connected on the alternator is the L terminal. It goes to the ECU. When running I get a constant 13.6-.9 volts on my gauge. As accessories come on, I start to see the voltage drop. For example, when the cooling fan kicks on, there is a drop to about 13 volts. When I raise my power window, another voltage drop. As the sub woofer thumps hard, I see the voltage bounce.
On my Cougar, I experience none of those symptoms, because I have the S terminal wired to the hot side on my starter relay. This is also the point where a lot of other heavy accessories draw their power. When the car starts, I get a solid 14.2-14.4 at the battery. As accessories come one, there is never a drop I voltage at the battery.
I realize that you're suspecting a high voltage condition, which seems contrary to what we're suggesting. If you want to play it safe, take the alternator off and have it tested. Personally, I'm a gambling man, and I'm pretty sure that unhooking the S terminal wire from the output post can't break anything, so I'd try it.
Alternatively, you can go around to various points on the car and take voltage readings and see what you find.
Andrew
On my Cougar, I experience none of those symptoms, because I have the S terminal wired to the hot side on my starter relay. This is also the point where a lot of other heavy accessories draw their power. When the car starts, I get a solid 14.2-14.4 at the battery. As accessories come one, there is never a drop I voltage at the battery.
I realize that you're suspecting a high voltage condition, which seems contrary to what we're suggesting. If you want to play it safe, take the alternator off and have it tested. Personally, I'm a gambling man, and I'm pretty sure that unhooking the S terminal wire from the output post can't break anything, so I'd try it.
Alternatively, you can go around to various points on the car and take voltage readings and see what you find.
Andrew
10-25-2016, 09:06 AM
#13
I too am not seeing a drop as accessories come on....voltage gauge is steady as a rock always in the same location on the gauge and when measured at the battery. But at a higher voltage than you're seeing. And I'd expect to see some variation in voltage as big accessories come and go.
I'm not a gambling man - so, with all due respect, 'pretty sure' isn't good enough for me. After a few measurements there are two changes I'd like to explore -- and they've come from this dialogue with you and pdx, so thanks for that, and hang with me!
1) Connect the sensing wire to some location out on "the system" -- I think I'll opt for the Volvo OEM fusebox inside the car. That's the source of power distribution for the lighting system and it also comprises the largest bit of stuff that's wired with OEM wiring size choices -- which are generally smaller for a given load than what I choose when I wire up something I've added.
2) Run the voltage input of my volts gauge to the output stud of the alternator. This will be the highest voltage in the system and if I have a variation in output voltage as I'd expect to from time to time, I'll see it on the gauge.
I'll report back with more data....
I'm not a gambling man - so, with all due respect, 'pretty sure' isn't good enough for me. After a few measurements there are two changes I'd like to explore -- and they've come from this dialogue with you and pdx, so thanks for that, and hang with me!
1) Connect the sensing wire to some location out on "the system" -- I think I'll opt for the Volvo OEM fusebox inside the car. That's the source of power distribution for the lighting system and it also comprises the largest bit of stuff that's wired with OEM wiring size choices -- which are generally smaller for a given load than what I choose when I wire up something I've added.
2) Run the voltage input of my volts gauge to the output stud of the alternator. This will be the highest voltage in the system and if I have a variation in output voltage as I'd expect to from time to time, I'll see it on the gauge.
I'll report back with more data....
10-25-2016, 03:42 PM
#15
Won't leave you hanging. Going out to check voltages in a moment.
This is interesting though. Picked up 2 new light bulbs. These are a standard #1154 two-filament bulb that fit into a plastic housing which 'screws' into the lighting fixture. When I put the two bulbs in place, grounded the ground term and put 12.70V to the other two 'hot' terminals - one filament glowed brightly as you'd expect. The other filament instantly burned out - on both bulbs. Same filament that burned out on the other two bulbs. When I put my one remaining good bulb in the housing (I still had one good bulb from the very first time a brake light went out) - the filament that burned out in the other 4 bulbs glowed brightly, no problems. The other filament (which burned brightly in the other 4 bulbs) glowed, but noticeably dimmer.
So - I'm concluding there's something special about the bulb that's needed for this application -- more research required.
This is interesting though. Picked up 2 new light bulbs. These are a standard #1154 two-filament bulb that fit into a plastic housing which 'screws' into the lighting fixture. When I put the two bulbs in place, grounded the ground term and put 12.70V to the other two 'hot' terminals - one filament glowed brightly as you'd expect. The other filament instantly burned out - on both bulbs. Same filament that burned out on the other two bulbs. When I put my one remaining good bulb in the housing (I still had one good bulb from the very first time a brake light went out) - the filament that burned out in the other 4 bulbs glowed brightly, no problems. The other filament (which burned brightly in the other 4 bulbs) glowed, but noticeably dimmer.
So - I'm concluding there's something special about the bulb that's needed for this application -- more research required.
10-25-2016, 04:23 PM
#17
Have to agree with the OP. If the sense wire is connected to the output of the alternator than that should be the highest voltage seen in the car. All other points will be lower. You essentially have a one wire alternator. Unless of course you have a floating ground.
Battery in the trunk, how did you wire in the negative terminal? Hopefully you also used the same gauge wire from the negative terminal to the engine block? If you just grounded it to sheet metal than you nailed pretty much every point I think people shouldn't do, trunk mounted battery, no negative battery cable to the block, alternator "straight to the battery".
Is the alternator mount powder coated and/or painted? That can cause a bad ground and floating voltages.
Damn, long *** thread already. Too much to read
By the way one bulb bright and another dim can be bad connections or a partial short somewhere.
One last thing, it is not unheard of to get a brand new alternator with a bad voltage regulator. Might consider getting it checked at a parts store.
Battery in the trunk, how did you wire in the negative terminal? Hopefully you also used the same gauge wire from the negative terminal to the engine block? If you just grounded it to sheet metal than you nailed pretty much every point I think people shouldn't do, trunk mounted battery, no negative battery cable to the block, alternator "straight to the battery".
Is the alternator mount powder coated and/or painted? That can cause a bad ground and floating voltages.
Damn, long *** thread already. Too much to read
By the way one bulb bright and another dim can be bad connections or a partial short somewhere.
One last thing, it is not unheard of to get a brand new alternator with a bad voltage regulator. Might consider getting it checked at a parts store.
10-25-2016, 05:34 PM
#18
As a comparison, I took similar measurements on two vehicles - one on my 2015 Honda Fit and the other on the Volvo.
I checked resistance between the neg terminal of the battery and the ground point that I used to take the voltage measurements from to be sure I had a good ground. Essentially 0 ohms resistance (nothing that would show up on the DVM) on both cars. I then used that same ground measurement point for all measurements to take a bad 'ground' out of the picture. For load - I turned a/c on to high (which also hits the cooling fan), lights on bright, rear window defroster on, stereo on w/volume up, etc.).
Not running (the Volvo had just come off the Battery Tender)
Honda batt - 12.70v Alt Stud - 12.70V Dist bus - 12.70V Fuse box - 12.70V
Volvo Batt - 12.81v Alt Stud - 12.80V Dist bus - 12.80V Fuse Box - 12.78V
Running
Honda batt - 14.20v Alt Stud - 14.33V Dist bus - 14.18V Fuse box - 14.18V
Volvo Batt - 14.70v Alt Stud - 14.71V Dist bus - 14.69V Fuse Box - 14.68V
Running w/load
Honda batt - 14.2v Alt Stud - 14.3V Dist bus - 14.2V Fuse box - 14.2V
Volvo Batt - 14.74v Alt Stud - 14.74V Dist bus - 14.55V Fuse Box - 14.55V
So, about .5V more on the Volvo than the Honda -- assume the GM regulator controls to a bit higher set point, probably because we're dealing with a LOT more load in the typical GM application than the Honda Fit application (tiny accessories, tiny battery, etc.). The Honda shows a much bigger 'hit' when the big accessories come on - when the cooling fan cycles on, I'd see voltages drop from the 14.2v range down to 13.0v and then in just a second or two, the regulator would pick it back up to 14.2. Not as much variation in the Volvo -- seeing the benefit of my cooling fan controller's soft starts (PWM variable speed controller). When load hit the Volvo, I'd only see a drop of .3-.5v - and then the regulator would pick it back up into the 14.5-14.7 range. I didn't see anything here that causes me concern - with the possible exception of the impact on battery life if the GM system consistently sends 14.7V the battery's way especially when it's fully charged. Guessing an 8 hour highway run with little load on the electrical system might be trying to overcharge the battery. But, not sure how to change that as it's the internal regulator that's in control.
Oh - checked the tail light grounds - again, no measurable resistance on the DVM between the neg battery terminal and the tail light grounds. They're within a couple of feet of each other with a lot of steel body electrically in between. And PSI Conversions indicates (they attached PDF's) that with my type of alternator, the 4-pin, and no body control module, GM recommends that the sensing line be attached to the output stud of the alternator. Based on their recommendation, that's what I did. Believe I'll leave it that way based on the measurements I got.
With my most embarrassed face on -- I believe this is a bulb issue. Yeah - I said it out loud. The bulb is a two filament bulb with offset tangs. I thought they were all created equal. Turns out they aren't. Spec calls for a #1157 with offset tangs. Turns out the 1157 comes with both offset and non-offset tangs. My first two local parts stores didn't have any 1157's with offset tangs; the non-offset units won't fit in the bulb holder. They did have a two filament bulb with offset tangs - #1154. I just assumed the O'Reillys/Advance Auto computer system was wrong about the proper bulb. Wouldn't be the first time.... Well, they were right. There is some sort of resistor or different filament built into the 1157 that isn't present in the 1154. That's what allows one filament to glow more dimly (that's the regular tail light filament) and the other to glow much more brightly (that's the brake light filament) when the brakes are applied. You apply voltage to one of those filaments in the 1154 - and it immediately burns it out. It only took me 4 bulbs to believe it. I suppose the 1154 is for applications where there is resistance built into the circuit of that one filament so it doesn't see 12V-14V. LOL..... I need 1157 bulbs with offset tangs. Turns out NAPA has them. Headed there in a bit.
As for this "...than (sic) you nailed pretty much every point I think people shouldn't do, trunk mounted battery, no negative battery cable to the block, alternator "straight to the battery"." --- well, opinions vary. This is a bit like people's belief in our ability to significantly help or hurt the climate change equation. I can easily find multiple sources that want a trunk mounted battery set up like Pop 'N Wood does, and multiple sources that say 'don't do it like that' -- do it like I have done on my car. What I do know is that I mimicked the set up that was working just fine in year 19 of its beta test with the 5.0L motor in the car. Battery in the back with a sound ground to the unibody. Block with a sound ground to the unibody in the front. And everything that needs a ground gets grounded to the unibody to avoid ground loops. With some ohm measurements (which need to be done for confirmation), it's clear on my set up that grounding the block back to the negative terminal of the battery with a separate cable won't net me any more effective ground than I already have. And the alternator output is directly connected to 3 different power distribution points and back to the battery. All connections that I made (ground and hot) are tested before I put things in service. I shoot for as little drop as I can get for anything that should be supplied with full system voltage. Hasn't let me down in 5 decades of playing with this stuff.
But I learned something about bulbs, that's for sure.
Thanks for the help everyone. That's what makes a forum work.
edit - oh, no powder coating on the alternator -- and all three 10mm x 1.5 bolts that hold it in place screw directly into the block. And when I checked two or three different hot sources against a ground point on the chassis vs. a ground point on the block -- exactly the same DVM readings - at least within the two figures to the right of the decimal that I get on the 20V setting. My block and alternator case are seeing the same ground as the battery is in the back.
I checked resistance between the neg terminal of the battery and the ground point that I used to take the voltage measurements from to be sure I had a good ground. Essentially 0 ohms resistance (nothing that would show up on the DVM) on both cars. I then used that same ground measurement point for all measurements to take a bad 'ground' out of the picture. For load - I turned a/c on to high (which also hits the cooling fan), lights on bright, rear window defroster on, stereo on w/volume up, etc.).
Not running (the Volvo had just come off the Battery Tender)
Honda batt - 12.70v Alt Stud - 12.70V Dist bus - 12.70V Fuse box - 12.70V
Volvo Batt - 12.81v Alt Stud - 12.80V Dist bus - 12.80V Fuse Box - 12.78V
Running
Honda batt - 14.20v Alt Stud - 14.33V Dist bus - 14.18V Fuse box - 14.18V
Volvo Batt - 14.70v Alt Stud - 14.71V Dist bus - 14.69V Fuse Box - 14.68V
Running w/load
Honda batt - 14.2v Alt Stud - 14.3V Dist bus - 14.2V Fuse box - 14.2V
Volvo Batt - 14.74v Alt Stud - 14.74V Dist bus - 14.55V Fuse Box - 14.55V
So, about .5V more on the Volvo than the Honda -- assume the GM regulator controls to a bit higher set point, probably because we're dealing with a LOT more load in the typical GM application than the Honda Fit application (tiny accessories, tiny battery, etc.). The Honda shows a much bigger 'hit' when the big accessories come on - when the cooling fan cycles on, I'd see voltages drop from the 14.2v range down to 13.0v and then in just a second or two, the regulator would pick it back up to 14.2. Not as much variation in the Volvo -- seeing the benefit of my cooling fan controller's soft starts (PWM variable speed controller). When load hit the Volvo, I'd only see a drop of .3-.5v - and then the regulator would pick it back up into the 14.5-14.7 range. I didn't see anything here that causes me concern - with the possible exception of the impact on battery life if the GM system consistently sends 14.7V the battery's way especially when it's fully charged. Guessing an 8 hour highway run with little load on the electrical system might be trying to overcharge the battery. But, not sure how to change that as it's the internal regulator that's in control.
Oh - checked the tail light grounds - again, no measurable resistance on the DVM between the neg battery terminal and the tail light grounds. They're within a couple of feet of each other with a lot of steel body electrically in between. And PSI Conversions indicates (they attached PDF's) that with my type of alternator, the 4-pin, and no body control module, GM recommends that the sensing line be attached to the output stud of the alternator. Based on their recommendation, that's what I did. Believe I'll leave it that way based on the measurements I got.
With my most embarrassed face on -- I believe this is a bulb issue. Yeah - I said it out loud. The bulb is a two filament bulb with offset tangs. I thought they were all created equal. Turns out they aren't. Spec calls for a #1157 with offset tangs. Turns out the 1157 comes with both offset and non-offset tangs. My first two local parts stores didn't have any 1157's with offset tangs; the non-offset units won't fit in the bulb holder. They did have a two filament bulb with offset tangs - #1154. I just assumed the O'Reillys/Advance Auto computer system was wrong about the proper bulb. Wouldn't be the first time.... Well, they were right. There is some sort of resistor or different filament built into the 1157 that isn't present in the 1154. That's what allows one filament to glow more dimly (that's the regular tail light filament) and the other to glow much more brightly (that's the brake light filament) when the brakes are applied. You apply voltage to one of those filaments in the 1154 - and it immediately burns it out. It only took me 4 bulbs to believe it. I suppose the 1154 is for applications where there is resistance built into the circuit of that one filament so it doesn't see 12V-14V. LOL..... I need 1157 bulbs with offset tangs. Turns out NAPA has them. Headed there in a bit.
As for this "...than (sic) you nailed pretty much every point I think people shouldn't do, trunk mounted battery, no negative battery cable to the block, alternator "straight to the battery"." --- well, opinions vary. This is a bit like people's belief in our ability to significantly help or hurt the climate change equation. I can easily find multiple sources that want a trunk mounted battery set up like Pop 'N Wood does, and multiple sources that say 'don't do it like that' -- do it like I have done on my car. What I do know is that I mimicked the set up that was working just fine in year 19 of its beta test with the 5.0L motor in the car. Battery in the back with a sound ground to the unibody. Block with a sound ground to the unibody in the front. And everything that needs a ground gets grounded to the unibody to avoid ground loops. With some ohm measurements (which need to be done for confirmation), it's clear on my set up that grounding the block back to the negative terminal of the battery with a separate cable won't net me any more effective ground than I already have. And the alternator output is directly connected to 3 different power distribution points and back to the battery. All connections that I made (ground and hot) are tested before I put things in service. I shoot for as little drop as I can get for anything that should be supplied with full system voltage. Hasn't let me down in 5 decades of playing with this stuff.
But I learned something about bulbs, that's for sure.
Thanks for the help everyone. That's what makes a forum work.
edit - oh, no powder coating on the alternator -- and all three 10mm x 1.5 bolts that hold it in place screw directly into the block. And when I checked two or three different hot sources against a ground point on the chassis vs. a ground point on the block -- exactly the same DVM readings - at least within the two figures to the right of the decimal that I get on the 20V setting. My block and alternator case are seeing the same ground as the battery is in the back.
Last edited by Michael Yount; 10-25-2016 at 05:41 PM.