Hello

I would like to build the circuit below:



I have never built a circuit before but I am quite familiar with wiring and a soldering iron. But there are just a few things I would like to clarify first and hope somebody can help.

1. Is the V In on the LED side linked to the 12v V In on the other side.
2. Is it possible to substitute the LED with a 12v bulb. would you just remove the 500R.
2. What is a 500R.
3. Do you think this circuit would be OK to link into an alternator charge wire to operate the charging / not charging warning light.

Apologies for the barage of questions and thanks for any help.

Alan

 

1. Is the V In on the LED side linked to the 12v V In on the other side.

Yes, it is.

2. Is it possible to substitute the LED with a 12v bulb. would you just remove the 500R.

No, 12v incandescent bulbs require much more current than the 741 opamp can sink or source.

2. What is a 500R.

That means 500 Ohms. 500 Ohms is not a standard value of resistance, however you could use a 510, 560, 620 or 680 Ohm resistor with not much of a noticeable difference.

3. Do you think this circuit would be OK to link into an alternator charge wire to operate the charging / not charging warning light.

Is this an automotive application? Most autos either have an alternator "idiot light" or a meter to indicate state of charge/discharge.
If you decide to build this circuit, I suggest that you set the threshold to around 13.6v; below that indicates not charging, above that indicates charging. You will need to isolate the circuit from the alternator output using a filter, otherwise the electrical noise from the alternator will quickly kill it.

 

Wow! thanks for such a quick reply. It is for an automotive application. The problem I have is that the alternator has no wiring provision for an "idiot light" and there is no meter. I was kinda hoping I could use this circuit to take it's place.

Will the 100K variable resistor be ok to set a threshold of 13.6v

Can you suggest what filter and were it would go in the circuit

Thanks again

Alan

 

Alan,
Your thread galloped off the page so fast I lost where it was.

Here you go:

Radio Shack carries a 100uH inductor that will work just fine for this.

You should connect the circuit to the ACCY or IGNITION circuit in your vehicle using a fuse of 1A or less. Do not forget to use a fuse.

Use heat shrink tubing for insulation. Don't use electrical tape, as it will get all gummy and fall off in a year, then you will have problems.

If you connect the circuit directly to the alternator or battery, you will drain the battery when the engine is off.