Hyundai Forums banner
1 - 12 of 12 Posts

·
Registered
Joined
·
662 Posts
Discussion Starter · #1 ·
Here is how the LED is ON and OFF. The led represents the BATTERY CHARGING LIGHT on a car. It has constant 12V and is a ground side switch. Whenever Key is ON, it STAYS ON. As soon as engine is running, it is off.

The light is control by a IC/MODULE. This module gets a signal whenever KEY IS ON and subsequently turn ON the light by grounding the negative side of the light. Again, when engine is running, it receives signal and then, subsequently turn OFF the charging light by disconnecting the ground to the charging light. So, there is 12V and 0V when battery light is OFF AND ON respectively. So, it's a computer controlled GROUND SIDE SWITCH.

Now, I want to make some modification to go in tandem with the charging light on and off. This brings to the second circuit, sharing the same power source, which consists of the resistor, Optocoupler and the diode. Resistor value is high enough so as to maintain as much minimum current as possible. Diode is for to prevent back current flow to the second circuit.

When both circuits are connected in parallel by joining both ends together, and grounded, there's 3v voltage at both the negative (A) and positive side (B) of the diode. This is really surprising. However, when the 2 circuits are separated, each circuit shows OV as opposed to 3V when connected in parallel!!!

My confusion stays why and where does the 3V comes from when the 2 circuits are connected in parallel????

Product Rectangle Slope Font Parallel
 

·
Registered
Joined
·
2,984 Posts
Re the mystery 3V, I suspect there is some wiring confusion.
Besides that, this circuit is more complicated than it needs to be.
The opto-coupler, and R2 are not needed.
I would connect the left side of R3 to point A, use a PNP transistor to switch the relay on the high side, and put the diode across the relay coil for inductive freewheeling.
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
18,639 Posts
there's 3v voltage at both the negative (A) and positive side (B) of the diode. This is really surprising.
If you understand how the charge warning light circuit really works it's not surprising.
The reason for the 3V is the resistance between point 'A' and ground. The negative side of the charge warning light IS NOT connected to ground. It's actually connected (via carbon brushes) to the positive end of the rotor winding inside the alternator. Then the ground end of the rotor winding is connected to the output of the voltage regulator. And the regulator is then connected to ground. So you have two components in series between point 'A' and ground. And each of those components has a certain amount of resistance. The 3 Volts is the voltage drop across that resistance.

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #4 · (Edited)
The reason for the 3V is the resistance between point 'A' and ground...
My confusion stays why and where does the 3V comes from when the 2 circuits are connected in parallel????
Sir, please be reminded that there are 2 circuits with 2 different cases:
1. Only One Single Circuit:
There is 0V as and only when the existing charging light circuit is ON (here the added new circuit is removed by disconnecting the common joining points at A).
And, it shows 12V when engine is running.

2. Two Circuits in Parallel:
Now (this case is interesting), when both circuits are joined together at A to form a parallel circuit, and when engine is off, there is 3V at the point A, and 12V when engine is running.
Now, I'm curious to know why there is 3V when circuits are in parallel? and only 0V for the already existing circuit?

Slope Rectangle Font Parallel Circle
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #5 ·
The opto-coupler, and R2 are not needed.
To protect and control the amount of current entering to the module, and to allow as much as extra minimum current (say 12/100000=0.00012 A) to flow to the module, I prefer to choose optocoupler with a very high resistor R1 enough to activate the optocoupler. If i'm wrong, your suggestions is always appreciated. Thanks.
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
18,639 Posts
Now, I'm curious to know why there is 3V when circuits are in parallel? and only 0V for the already existing circuit?
Ohm's Law provides the answer.
Ohm's Law tells us that the voltage dropped across a resistance is directly proportional to the current flowing through the resistance. Therefore an increase in the voltage at point 'A' has to be the result of greater current flow through the resistance within the alternator (the path to ground). Which kinda makes sense. You add an additional circuit, you increase the current flowing through the resistance, you get a greater voltage drop.

Also bear in mind that part of the ground circuit is the alternators voltage regulator. The regulator is like a variable resistor. It's job is to control the current flowing through the alternator's rotor winding. It does that by altering the resistance between the rotor winding and ground. So the resistance within the ground circuit is not constant.

That's all I can tell you about the circuit from the diagram. But if you want to prove what I'm saying for yourself use a link wire and connect point 'A' directly to battery negative (with the engine off). I'm sure you will then observe 0V on the meter with both circuits joined, because your link wire is bypassing the resistance within the alternator.

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #7 ·
... an increase in the voltage at point 'A' has to be the result of greater current flow through the resistance within the alternator (the path to ground). Which kinda makes sense. You add an additional circuit, you increase the current flowing through the resistance, you get a greater voltage drop.
Okay. Thanks for the input.
Then, 3V reading when both circuits are in parallel, is this 3V will do any harm to the existing OEM circuit? BCM Module? Alternator?
Is this 3V harmful to any parts of the car wiring? If so, what would be your best suggestions to make a new circuit for the same objective?
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #8 ·
here is another redrawn circuit. My first priority is not to disturb any changes in the OEM electrical readings as far as possible. Previously, there was 3V due to extra current.
Is this rebranded (hehe...) more safer and more appropriate design?

Rectangle Slope Font Parallel Technology
 

·
Registered
Joined
·
2,984 Posts
I prefer to choose optocoupler with a very high resistor R1 enough to activate the optocoupler.
If you use two PNP transistors configured as a darlington, you can make R3 a high value to minimise current.
You could also use a P-channel FET and reduce the parasitic current to essentially zero.
No need for optocoupler or comparator IC.
Your re-drawn circuit is far more complex than it needs to be.

The mysterious 3V could come from the diode rectifying stray noise, acting like a radio detector.
Rectangle Slope Font Parallel Circle
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #10 ·
Ohm's Law provides the answer.
... You add an additional circuit, you increase the current flowing through the resistance, you get a greater voltage drop.

Also bear in mind that part of the ground circuit is the alternators voltage regulator. The regulator is like a variable resistor. It's job is to control the current flowing through the alternator's rotor winding. It does that by altering the resistance between the rotor winding and ground. So the resistance within the ground circuit is not constant.

... the resistance within the alternator.
Really appreciate your inputs for giving the detail complete working of the charging circuit.

Now, I would like to know if that "3V" is likely to cause any issue for the charging alternator circuit in the coming future assuming that the aforementioned circuit is used.
Thanks in advance.
 

·
Registered
Joined
·
662 Posts
Discussion Starter · #12 ·
Thanks for all your inputs and help!
Finally here is my update of the accomplished project:
1. Green lights on cluster meter will only come ON in parallel with the battery charging light.
2. Door open and Hand Brake Buzzer Warning Sound if and only if Engine is Running.

Speedometer Gauge Tachometer Odometer Trip computer
 
1 - 12 of 12 Posts
Top