Charging Warning Dash Light and Battery Not Charging (Page 2/2)
GraterFang JUN 09, 03:49 AM
This is probably useless theorizing, but I'm wondering about the effects of adding a parallel circuit for the warning lamp because these are the things that keep me up at night, or more specifically the possible adverse effects. I'm not an electrical engineer, but at the risk of sounding like an idiot this is what I've put together in my head.

In theory, adding a parallel circuit for the warning lamp reduces the resistance of the circuit to the field current supply. The effects of this are that (theoretically) voltage remains the same but current increases. So, (in theory), adding a parallel circuit for the warning lamp can reduce overall resistance of the field supply circuit and increase current. This can increase the electromagnetic field and in turn increase alternator output (before the voltage regulator) which can (theoretically) increase heat generation which at a certain level can be a problem.

Now, realistically, here is what I expect is more true. I'm not sure what the usual resistance of the warning lamp circuit is, but 50 ohms is probably quite a bit more than normal. From what I can see with a quick google search, the usual field resistance of the alternator is around 5 ohms but can vary. As such, I expect that the relative decrease in resistance and increase in current is relatively small. I'm not sure where the 50 ohm recommendation came from but I'm guessing it's sufficiently high enough to not allow a significant increase in current. Furthermore, once running, the alternator is self-exciting and this circuit is playing a negligible role in alternator function compared to the role of the voltage regulator.

Thoughts? Corrections?
olejoedad JUN 09, 08:35 AM
Parallel circuits containing a resistor are very common.
GraterFang JUN 09, 10:59 AM
Of course. Not genuinely concerned in the least, just like to understand the effects of making changes to pre-existing circuits even though I know it's "okay". I like to understand how things work, how the size of a resistor is chosen in a situation like this, and also have a better idea of when things aren't going to work.

For example, what if you used a 1 ohm resistor instead? No resistor? I used the word theoretically a lot for a reason. It's meant to be an academic question for sure, even though its coming from somebody who's academics are in a different field despite having wired a large number of combination circuits before.

But hey, maybe I'm the only one.

EDIT: Edit to say that its a no-brainer that a resistor is typically chosen based upon the voltage of the system and the desired current, which is usually kept within a range that will avoid overheating the wiring or damaging sensitive devices if there are any. What I felt made this question interesting is the alternator, as a small change in field current can produce a significantly larger increase in output. I still don't think its a concern here, but that's what I thought would be interesting to discuss.


quote
Originally posted by olejoedad:

Parallel circuits containing a resistor are very common.

[This message has been edited by GraterFang (edited 06-09-2023).]

theogre JUN 09, 02:23 PM
The Dash Light has Nothing to do w/ alt's coils in GM or other brands of vehicles.

Power Generated by the Alt is a function of coil winding plan and more but Not that light.

It just used by the Regulator to try to warn you and turn on when start the car. Note that Some alts delay turn On a bit so don't think all vehicles will have 14-15v instantly using dash meter or any other meter.

Many vehicles have a light. Some don't like 84 Fiero but somewhere in the harness has ~ 10Ω resistive wire (for GM. Others may charge &ohm and very hard to see w/o tearing harness cover off.
When a vehicle have Volt and/or amp meter is not = to the light/resistor as far as the alt sees.

⚠️ Warning: If put 2 resistor in parallel will cut Ω and can kill the Regulator.
Only when the OEM light/resistor doesn't seem work... you discon the OEM part in one of a few ways like for most Fiero, unplug the light in the dash.
Then use a test light from battery to lamp pin on the alt.

OEM light bulb maybe 100% Good but wires to it goes thru many other places/plugs and maybe one area is bad. Quick Jump w/ Test Light bypass all of that. But if made such a thing, type of lamp matters. 194 and related are ok but not a brake light or others eating 1 or more amps.
GraterFang JUN 09, 05:35 PM

quote
Originally posted by theogre:

The Dash Light has Nothing to do w/ alt's coils in GM or other brands of vehicles.

Power Generated by the Alt is a function of coil winding plan and more but Not that light.

It just used by the Regulator to try to warn you and turn on when start the car. Note that Some alts delay turn On a bit so don't think all vehicles will have 14-15v instantly using dash meter or any other meter.




Ogre, you probably know better than me but this doesn't fit with my understanding of how this works. My understanding is that the 12+V that runs through the warning lamp is used to excite the coils in the alternator (even if going through the voltage regulator first). Once functioning, the alternator provides this voltage itself and is self sustaining. At the same time, the 12+V the alternator is producing for this purpose negates the voltage difference which is why the warning lamp is no longer lit.

As supporting evidence, here is quote from the link provided above by sardonyx247


quote

The regulator uses transistors to control the field current. A transistor is a device used to amplify and switch electronic signals. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. When system demand causes a voltage drop (the control voltage inputis less than nominal) the regulator senses this and a small current is sent to a transistor which amplifies it and sends it to another transistor which acts as a valve in controlling the flow of the field current input to the rotor.

The field current supply is provided from one of two different sources, depending on the state of the alternator. When the engine is not running and the alternator is not spinning and producing electricity, the field current supply comes from the vehicle's battery, via the ignition switch and alternator warning lamp (if equipped). We'll go into more detail on the warning lamp shortly. The process of supplying battery voltage to "kick-start" or "prime" the alternator is known as "exciting" the alternator, and the wire that carries the current from the alternator warning lamp to the appropriate voltage regulator terminal is known as the "exciter" wire. A few special alternators do not have this wire and are known as "self-exciting"- we'll cover this in more detail in the wiring section.

After the engine is started, and the alternator is generating electricity the diode trio feeds the alternator output back to the voltage regulator to serve as the field current supply.

Theoretically, once up to speed, the alternator is self sustaining, and the car will run without a battery until it is shut off (as long as system demand does not exceed alternator output capacity). However - you should never disconnect the battery in a running vehicle as doing so can cause voltage surges that can damage not only the voltage regulator, but also other on-board electrical equipment - particularly computer-controlled devices. Remember the diagram of the pulsed DC output from the alternator and the fact that the battery acts as a large filter or cushion in the system.

Note that the field current is much smaller than the output current produced in the stator windings. For example, to produce 70 amperes of DC, the field current required will be less than 2 amperes.




So, you're saying that the 12+V through the warning lamp is NOT used for excitation? And if so, what is occurring exactly then that prevents the alternator from functioning when this circuit has a disconnect?



quote


⚠️ Warning: If put 2 resistor in parallel will cut Ω and can kill the Regulator.
Only when the OEM light/resistor doesn't seem work... you discon the OEM part in one of a few ways like for most Fiero, unplug the light in the dash.
Then use a test light from battery to lamp pin on the alt.




I'd appreciate more information on this is as well. Are you saying that wiring in a 50 ohm resistor in a parallel with the warning lamp (if equipped -- a resistor if not) as suggested above will indeed potentially cause harm to the alternator? Is this due to an increase in current as I suggested above, and if not what is the cause? An increase in current from a parallel 50 ohm resistor should be fairly minimal (unless being amplified by the alternator due to an increase in field current). If this is what you're stating, then there is some conflicting information here that should be clarified so that people aren't making harmful changes to their electrical system.

[This message has been edited by GraterFang (edited 06-09-2023).]

sleek fiero JUN 09, 06:36 PM
This may sound off topic but I used my spare alternator on our forklift and it does not have an idiot light, only an ammeter. It has been charging just fine for several years now. I think we are all trying to make this too complicated. sorry I had to get a part number .what we used to make it all work was get a painless performance #30706 resistor plug assembly from Summit to eliminate the light circuit. What I don't understand is why you would want to eliminate the dash light on your car?

[This message has been edited by sleek fiero (edited 06-09-2023).]

GraterFang JUN 09, 06:56 PM

quote
Originally posted by sleek fiero:

This may sound off topic but I used my spare alternator on our forklift and it does not have an idiot light, only an ammeter. It has been charging just fine for several years now... what we used to make it all work was get a painless performance #30706 resistor plug assembly from Summit to eliminate the light circuit.




I think as long as the appropriate circuits are complete, the alternator will work regardless of whether or not a light is present. The light is in essence simply a resistor that lights up. There is a possibility that having the wrong resistance/current could affect the quality or longevity of the alternator's function, though, which is what I was trying to start a discussion over.


quote
Originally posted by sleek fiero:

I think we are all trying to make this too complicated.... What I don't understand is why you would want to eliminate the dash light on your car?




I certainly wouldn't, but some might. What's more likely from this thread though is that somebody might add a "backup" parallel circuit as described above so that the alternator continues to function even if the warning light goes out or if some other problem with the circuit occurs. However, if having the wrong current to the voltage regulator is harmful I think some of us would want to know that.

Personally, I just want to know because I want to know. I enjoy the details.

[This message has been edited by GraterFang (edited 06-10-2023).]