Charging Light

[Jim Fierst]

When first starting the engine the charging on my 79 LBZ seems to require about 2500 RPM before it will go out. It charges fine and seems to work normally in later starts..What causes it to require so much RPM to go out initially and is there any way to fix it??

[Jim Keller]

my guess, :-\ Sounds like the regulator in the alternator, driving a car regularly will iron out a lot of bugs like that, lack of use causes a lot of problems! :) however, if it doesn't go away after driving it regularly for a few hundred miles, may want to consider a replacement

[SubGothius]

My '79 Zag's done the same thing as long as I can remember, prolly since I got it about 3 years/10k mi. ago, already with a newish (<13k mi. on it then) alternator courtesy of the PO; I just start'er up, wait for the oil pressure to rise, then give'er a modest throttle blip to tip the charging system out of a net-drain state. Puzzling as it is, it doesn't seem to affect anything otherwise, so I'm not really worried as long as the light does go out quickly! ;)

[Jim Keller]

Quite frankly, I would do just as you said, wait on oil pressure, blip the throttle and go on with driving it without worry till the alternator actually pukes or quits responding to the throttle blipping! ;D

[radioal]

This seems to be a fairly common issue with Bosch alternator equipped cars. Both my Beta and my X1-9 do it. The X has been doing it since new, so I think its more of a design issue than an impending failure. Blipping the throttle has become such a habit that I find myself doing it on ALL cars now. I've never noticed the issue on my Marelli or Iskra equipped cars.

Al

[Jim Keller]

I knew I had an Italian car that did that but for the life of me I couldnt' remember which one it was! your last post reminded me, it was my 86 Bertone X1/9! it always did that and had to blip it to get it charging! I never had any problems beyond that with it either! ok, I'm good now, wont' lose anymore sleep trying to remember what car it was I had that did the regulator blip thing! LOL!

[Jim Fierst]

It appears "Tis The Nature Of The Beast"..so be it.. Thanks guys.

[Will]

Tha Scorpion (Marelli) has the charge-light-glowing issue too, there has got to be a fix for this- perhaps a faiirly large value resistor across the light or a zener diode "backwards" in front of it? There's at least one EE on here, a "fix" for this issue would be nice, so maybe someone with electrical/electronics background can contribute a solution. I'm not sure what causes it-if it's cuirrent flowing backwards through the circuit maybe it can be checked with a regular diode, if it's low voltage potential triggering the light then maybe it can be clamped with a zener until the voltage gets high enough to equal the zener's breakdown voltage and trip the light.

I'm not an EE so I'm just talking out my a** wirth some suggestions, hoping to give somebody that knows more than me in this area some ideas about how we might fix this. This would IMO be a totally worthwhile pursuit since most all our cars do this.

[radioal]

If I recall correctly, the Marelli issue is a little different from the Bosch one. Is the symptom that you have a constant dim illumination of the alt light which never goes completely out?

If so, I have seen it on 124s and 128s. Its related to a difference in ground potential between the engine block (alternator case), the chassis (voltage regulator and/or battery -) and the instrument cluster (light). The easiest way to troubleshoot this is to run the car with the headlights and any other major loads you can think of switched on. Then measure the voltage between each of the 3 ground points described above (in a Scorp, you will need LONG meter leads!). My guess is that you will find a volt or so of difference between 2 or more of them. At that point, you can either trace out where the bad connection is (the right way) or add a heavy gauge jumper between the affected points (crude, but fixes the symptom). At this point, you will probably get brighter headlights and your warning light issue will clear up as well.

Al

[Will]

OK, explain this to me like I'm a 4-year-old, what do grounds have to do with it?

My impression was that the alternatore light is connected between the battery (+) and alternator (or voltage regulator)(+), in such a way that if the alternator output was lower than 12v, current flows through the light and lights it, is this not correct? (I don't have a wiring diagram handy)

I also thought (perhaps incorrectly) that the dull light was related to the alternaltor output being higher than the battery (+), i.e. current flowing the opposite way through the light. Is this not correct?

Yeah, I reckon I know just enough to be dangerous, but I figure if cuurent is flowing in the wrong direction a diode should cure it, and if it's flowing in the right direction and it just needs to be cut off below "threshold" it could be clamped with something that doesn't let current flow until it reaches 4-5V potential, although I'm not sure what that something is?

[radioal]

I think you are basically correct in your understanding of how the "hot" side of the circuit works. Unfortunately I don't own a Scorp (yet!) so I don't have a diagram handy. The thing that you must always remember when working on automotive systems- especially old Italian ones- is that most of the individual wires that you see are on the "supply" or "+" side of the circuit. In most cases, either the engine block or the car body is used for the "-" or "return" connection. This is quite different from a residential AC power system where the return (or white in the US system) is kept completely separated from the ground (or green).

As the car ages, connections corrode, crimp lugs loosen and other things happen so that instead of having a nice 0 volt return everywhere on the car, you have different voltage potentials on the battery - post, the body, the engine block, and the miscellaneous dashboard points. Even in a new car, this difference is enoough to read with a DVM, but in an older I-car, it can get dramatic. I once had a rusty 128 that "floated" by 4-5 Volts! I have actually seen Ford Crown Vic police cruisers (which surprisingly use a regulator system very similar in layout to the Marelli) boil out the battery and blow headlight bulbs and radios!

The major effect this has on the dash warning light is that in most Marelli systems, the voltage regulator is mounted externally to the alternator and therefore grounded to the car body. The alternator is of course grounded to the Engine block. The battery is probably grounded to the frame like an X1-9 or 850, but I really don't remember.

What happens is that lets say you have enough resistance in your frame to block strap and associated hardware to generate an 0.5V drop (not really a lot, but measurable). If the voltage regulator is working properly, it will try to control the field output so that it sees 13.8V across its input or feedback terminals. The problem is that while it is seeing a perfect 13.8 internally, the output of the alternator is actually 14.3V (the 13.8 that the regulator sees plus the 0.5V drop between the engine and the frame that it does not see). Therefore you are in an overcharge situation and the warning light responds accordingly.

Al

[Will]

OK- my car is not typical because I've done a lot of rewiring, with 2 disaconnects, etc- but I do have what I believe are pretty comprehensive grounds. Like you said, there may be a difference in potential between the starter ground and the instrument panel grounds, but I'm having trouble understanding how that's relevant if the "Gen" light is connected to a circuit that's hot-hot (and I'm not saying it IS, I'm just saying I thought it was)

In my case it's avery dim glow that's only visible at night. At first, I thought it was backwash illumination from the dash cluster, but subsequently found when the fuse for the dash lights (#1) blew that the "Gen" light was actually glowing by itself. Not a hughe deal, but now that I know about it I find it annoying and I'd like to conquer this poltergeist. My car isn't running at the moment but when it is, I'll try running a bonding wire between the starter and instrument grounds to see if that helps any- Thanks for the suggestion. If it works, that'll be swell.

[radioal]

Actually, I may have muddied the waters somewhat by mentioning the instrument grounds. I really suspect your drop to be between the Alternator housing and the voltage regulator as per the above scenario. Try a jumper there first.

Good luck,

Al

[Shane Taylor]

Here is a solution that worked for me and the glowing light went away ... simple ... run a length of medium shielded gauge wire from the external case of the alternator to the block of the engine.

regards, Shane

[Will]

Thanks- will give that a go!

[Jim Fierst]

I tried running a ground wire from the alternator housing to the engine block . There was no appearent change..The first start in the morning still reguires about 2500 RPM to turn out the light . On all subsequent starts on a warm enging the light goes out as it should..

[Will]

Ok, as I said before I'm no electrical engineer, but the only reason I can think of that woiuld seemingly explain this is if the battery is significantly enough discharged on the first start that enough current is flowing back to the battery through the dash light to light it, and kicking the speed up to 2500 or on subsequent starts the VR is kicked off because it thinks the battery is "full" - preventing the light from lighting. Checking to see if power to the alternator field corresponds with the behavior of the light would be the next step I'd take- and again, I'm pretty sure ther's a simple, solid-state solution to the problem, I just don't know exactly what it is.