Alternator Charging Voltage question

[MikeyM73]

Hi all,

Happy Holidays. My charging voltage is around 14.1/14.2ish volts with engine running. When I apply a series of loads - headlights, voltage drops a bit to 13.5ish; windshield wipers drops it to 12.9. Auxiliary heater fan drops it even more to around 12.1-12.3.

I don't have any indications of undercharging going on but I guess my question is should the alternator maintain around 14V at idle? Or is it normal for the charging voltage to decrease as more load is added even though the alternator is charging? I ask because I notice the engine speed being affected as the voltage drops and am wondering if my alternator may not be outputting as much as it should. The charging voltage will be higher as engine RPMs increase but I guess I'm used to my 98 Jeep that pretty much stays at 14-14.5V all the time with normal load.

Thanks,
Mikey
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'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[74 Thing]

What are the readings at approx 3k rpm at idle and with the various power loads?

[SGKent]

where are you making the measurements?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[MikeyM73]

74 - I will do that and report back.

Steve - I'm taking that measurement from a VDO voltmeter wired into the fuse box and grounded to a screw connected to one of the air ducts.

Thanks,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[74 Thing]

Use a multimeter and take the reading at the battery terminals.

[SGKent]

[MikeyM73]

Will do. Part of this is trying to confirm if my voltmeter is accurate. Currently, at idle with no load i’m seeing between 14.1 and 14.3. However, with lights on, windshield wipers on, and turn signal on, at idle, it drops to 12.1. At speed, around 3000 to 4000 RPM, with the same load and accessories turned on the voltage drops to about 13.1 maybe 12.9. Just wondering if that shouldn’t be a little higher.

When we first got this bus, five years ago, one of the diode’s was loose from the back plate in the alternator so I JB welded it in and it has been running and charging, seemingly fine, ever since.

Thanks,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[SGKent]

you are saying that you want to know what the pressure is at the water well head pump but you are reading the pressure 1000' way at the hose end while you are running the bathtub. If you want to measure what is going on at the pump you will have to install a gauge at the pump. If you want a more accurate accounting of what the pressure is at the well head but you want to read it 1000' away, you will have to run a dedicated line that has no loss at the gauge end. Meaning you will have to run a dedicated line from the alternator / battery connection at the starter, and FUSE it to be safe. It will tell you what is going on back there but next you will ask why is it 12.5 V up front and 14.3 V in the back. Turn off the bathtub or improve the plumbing in between.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[telford dorr]

[Wildthings]

If you have 14volts at the battery and 12.9 at the fuse box with everything "ON" then that would be normal. Though at idle you might not be able to maintain 14v at the battery under full load, especially if the one diode is not making good contact.

[MikeyM73]

Thanks all. Telford, I dug through some old posts and turns out I posted up a couple years back about having a loose diode that you guys helped me out with (https://www.thesamba.com/vw/forum/viewtopic.php?t=728659&postdays=0&postorder=asc&start=0) - forgot about that until now. Apparently, the metal of the "lip" of the hole in the B+ plate that secures the diode in place somehow cracked just enough to loosen it and let it jiggle around. These days, as we're getting more accessories working, fixed, added, etc. I had a concern about voltage levels.

My JB Weld fix was actually a thin epoxy bead but at the time I pushed the diode back through the hole, squished that metal back together as much as possible and when I pressed the diode back in from the back, the fit was tight but I wasn't sure if it would come loose again so my epoxy application was a very thin bead on the backside only around the edge of the diode just for insurance. I did not slather it across the back because I figured there would need to be some kind of heat dissipation. If you think I should correct this, I will.

Other than that, I'll compare the voltages from front to rear but if it's considered normal to idle at 12.5V + with headlights, wipers, and turn signal on, I can live with that.

Thanks for all your help
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[sodbuster]

A word about JB Weld. it is a conductor and not an insulator. JB weld has ground metal in it. As a result it will conduct electricity.

This is why you can use it like bondo on something then powder coat it. Someting you cannot do with actual bondo.

[telford dorr]

[MikeyM73]

Thanks Telford. So what kind of issues might I see related to that?

Thanks,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[telford dorr]

[MikeyM73]

Fair enough. Thanks Telford,

Have a happy NY, all.

Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[telford dorr]

[SGKent]

from JB Weld FAQ, manufacturer's web site.

Q. Will J-B Weld conduct electricity?
A. No. J-B Weld is not considered to be a conductor. It is an insulator.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[MikeyM73]

So let's say for the sake of the conversation that all wiring is good, no electrical draws, etc. What should the minimum charging voltage be? I'm starting to see the volt meter creep to 15.1 and I believe the max should be no more than 14.5, correct? I have a couple spare voltage regulators that I will install to see if I can bring that down to around 14.5V but it's the minimum voltage I'm concerned with. I presume VW rated their alternators to run all accessories the bus came with in rainy weather so I'm curious as to what you all see with everything (or almost everything turned on) at idle. Wipers, radio at low volume, lights, aux heater fan, and let's throw in a turn signal for good measure.

My Jeep is modern day and with all of the above it charges at idle right about 13.5V, maybe a bit more. I presume this would be true of most alternators in a 12V system but I guess that's the bottom line question... what is the minimum voltage one should see under those conditions?

Damn.. 74 Thing, I haven't gotten to checking on your question but I will do that tomorrow and let you know. Thanks.

Thanks for the continued advice,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[busdaddy]

15.1 is getting up there, 14.5 is the common max voltage. If your's is going higher the VR is to blame, it may not be sensing voltage properly (bad terminal or broken wire, or terminal pushing out of the plug, bad ground), or it may have internal issues. The mechanical ones can be tweaked to limit max volts, the solid state ones can not.

A properly functioning VR keeps the volts at a set limit, if you turn on a light or some other draw it signals the alternator to work a little harder to maintain the volts it's trying to see. If it can't properly sense voltage, or the battery isn't soaking up what the alternator is putting out voltage may exceed what you hope to see.
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