1 for the Alternator Gurus
 

78 SC with a later internally regulated alternator, have had charging issues for a long time, Alternator been out and bench test 3 times, always told it is good!

Finally decided today to add some idiot wire to the poles of the alternator lead to a terminal block outside the housing where I can see what is going on.

Here's what I know (think I know).

Good new earth to engine, and good new grounding strap from transmission to body.
Strong continuity on blue wire from alternator to alternator warning light by oil gauge

Here's the readings I get,

Engine & ignition off

Power Wire 11.49
Blue Light Wire 0.0004
Earth continuity

Engine off, Ignition on

Power Wire 11.21
Blue Light Wire 1.632
Earth continuity

Engine Running

Power Wire 11.21
Blue Light Wire 2.49
Earth continuity

Similar results gained with engine cold (running at 2000rpm with arr) and warm idling at 900

I am electrically stunted, know just enough to start a good fire, so the questions are

1. how does the voltage change on the blue wire effect things and what should it read, what voltage does this wire need to see for the light to go out - zero?

It has been suggested that the alt may need to see a certain voltage before it will start outputting power, is there any merit to this??

Also, I have had this alt out several times, what it the prescribed method for getting the shims back in place. My set-up is all shims to the outside and it's a major PIA to get them back in place.

Thanks all in advance,

Regards, Glen

Glen, search here for "blue wire" for a detailed explanation of how the system works.

You have a more immediate issue which is you need a new battery. 11.21 volts is so dead that nothing will bring it back, and even if you did get the system to start charging, trying to bring back a battery from that level will cause the alternator to overheat and cook things.

For reference, 12.25V = 25% state of charge. Our alternators are designed to bring the system back from a long period of cranking, like in the winter, maybe a 3-5% drop in charge. They are absolutely not designed to bring one back from deep cycle.

if you are showing 11.xx volts when running, I suspect you have a short somewhere. The best way to find it is to put your DVM across each of the fuse terminals (with fuse out) one at a time, until you see current flow. Make sure all switches are OFF (lights, fan, radio, etc). Then you have to troubleshoot that circuit to find the short.

Any history of fuses blowing ?

an alternator can not make voltage without a input voltage to make the "field" or the electromagnet. The old generators had a permanent magnet that could produce voltage with rotation. so yes you need excitation voltage to make a alternator work

Millarg,

I cannot answer the electrical questions but my setup is the same as yours (6 shims outside) and I have had my alternator on and off 3 times in the past week.

The cup washer just under the large nut is the same outside diameter as the shims so using your fingers around the cup washer and shims together you can get them to lineup as you start to tighten the nut by hand.

Its usually the last couple of shims I do this with.

Just be careful you do not trap the shims on the inside edge when you are tightening the nut.

Cheers

Bill

check to see if you have a radio noise suppressor installed they can cause all sorts of charging issues when they go bad. remove it if you do.

You have checked the grounds at the alt end and the engine to frame part..but have you also checked at the battery?
If the alt checks OK on the bench with a proper tester...then the wiring has to be the problem.
Bob

Thanks guys, swapped the battery with the one in my truck - both are Optima Reds, now have 12.4 volts on battery terminals with eng & ignition off.

So checked the voltage across the fuses, wasn't sure if this was to be done with ignition off or on, suspected it should be on, but I did both ways.

Ignition off, had full voltage across
"Total Inter Light"

With ignition on, had full power across
"Total Inter Light"
"Cig. light" - have a Voltage meter plugged in, so probably this
"back-up lights"

Guess none of this is good news, I have one of Fred Cooks new ATO fuse panels waiting to be put in, but had wanted to remove fuel tank to complete the installation as part of a wider front truck clean-up (new fuel hoses, redo vent system etc).

Kept the offending fuses out and checked alt again, no change.

With reference to the "blue wire" if I force feed it 12 volts, will I cook something???

no but something is going on. blue or field wire should have the same voltage as the battery

OK, just gave the blue wire 12.4V, direct from battery

Ignition off, red charge light on

Engine running, red light off, alternator putting out 13.1, battery charging, & ....... distinctly hot wiring smell :(,

Guess I won't be using this as my quick and dirty fix.... back to external battery charger & no driving at night.

So it would appear that I have a good alternator?
I have good connectivity from alt to light on blue wire, so am I looking at the red/black wire that runs to the other side of the charge light? seems this goes to the back up lights fuse, which is were I have power with fuse out!

Maybe an ignition switch problem? The red black is bus 15 - switched hot. It comes off the ignition switch and feeds the instruments and the alternator light unfused. It also feeds fuses 11 & 12. Do your other gauges work?

I would trace the red black back to the ignition switch and see what's going on there. If you need the wiring diagram email me and I'll send you a color scan.

How many of us "here" have gone to start out cars of a morning and found the battery COLD STONE DEAD due to a door left ajar overnight.....

Discard/junk the discharged battery...NOT!

Jump start the engine and drive off.

Starter field winding and surrounding metal core were designed to retain magnetism once "flashed", alternator rotors do not.

Re the battery, if a single cell has gone bad you will struggle to retain 12V after charging. Sometimes if an older battery is allowed to discharge (eg interior light left on) a single cell can go into reverse polarity when recharged if its internal resistance is different to the others. A lead acid battery has 6 cells each with a nominal voltage of 2.105V = 12.63V. If one cell is dead then 5 x 2.105 = 10.525V. Your 11.25V suggests one cell is on the way out if this is what it measures disconnected a few hours after charging with a known good battery charger. The new smart chargers are great and will often bring a dead flat battery back to life. I remember changing British car electrics from positive earth to negative earth to suit a new "modern" radio cassette player, we had to flash the generator by quickly closing the regulator relay contacts before starting. I do not recall any issues with starter motors trying to run in reverse, but that was a long time ago. Alternators with internal regulators are a bit fussy about the warning light specs, there a few posts about this and the need to add shunt resistors or change the bulb to get the alternator to charge correctly, maybe this is something to look at? I do not advise feeding a raw 12V to the blue wire, that warning light bulb has resistance to limit current and drops the voltage down from a full 12V for a reason. Now that you have a good battery in place its time to get back to basics and measure the voltages at idle with the warning light on and again at 2000 rpm with the warning light hopefully out to check correct alternator performance. You can also get auto multimeters with shunt current capability to check how much current your alternator can pump out. The shunt looks like a strip of metal, the meter connects to terminals at each end and calculates the current by the small voltage drop across the low resistance metal shunt.

Well, my experience is different, the alternator is in a bad place from a heat standpoint being right above the engine case, and based on that experience I don't recommend running it full-field if a battery charger is available.

As far as state of charge/percentage being "nonsense" you can google up any number of references that give the relationship between volts per cell and % of charge. Or you can search here, Wil Ferch posted a summary about a decade ago.

The fellows I know in the alternator rebuild business have stated to me that an alternator is not designed for recharging a flat battery, just maintaining a charged one. Sure, you can boost a car and it will charge but the alternator was never intended for that kind of service and could shorten it's life.

And from the recent post on Otima batteries, someone in the busines who knows the score said this:

"Since Parker suggested deeply-discharged batteries should be fully-recharged with an alternator, I want to caution everyone that any battery deeply-discharged to the point that a vehicle needs a jump-start, should be fully-recharged with a battery charger as soon as possible. Most alternators are designed to maintain batteries, not recharged deeply-discharged batteries. Asking that task of an alternator can lead to a cycle of dead batteries and jump-starts, until either the battery or alternator fails. If anyone has any questions about our products, I'll do my best to answer them.

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.
OPTIMA® Batteries (optimabatteries) on Pinterest

When I went to my local auto electrician he recommended one type of battery over another on the basis that my Porsche would sit at least a week between drives and that its older alternator would struggle to bring a "newer technology battery" back to full charge as they required a slightly higher voltage to achieve full charge. Any truth to this Jim? I think he mentioned some sort of plate coating, I was happy to go along and the battery lasts weeks with just the mechanical clock sipping current, always starts easily. I also agree that when you have a flat battery a jump start may get you going in an emergency but I prefer to use a charger asap to get back to full charge. Hitting a flat battery with 50amps from an alternator can not be as good as using a 12 amp intelligent charger that ramps off the voltage in stages as the battery voltage increases and auto adjusts for ambient temp.

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