Edwardgp

I want to be able to have indicator lights in my driving compartment to make sure cooling fans are running. I have a two speed cooling fan behind the radiator on my 83 Camaro. Have install LED's in the cabin and have ran wires out to the relays. Have separate relays for low and high speed.Want to wire it so the lights are on, one for low speed and one for high speed. These need to be on the power side to the fan motor for high and low speeds. Now here is the problem, all wired up and when fan is on low speed both high and low speed indicator lights are on. Same for the high speed. Do I need to install a diode some where inline to keep power from bleeding through and lighting both indicator lights at the same time?

Jonesyfxr

iTrader: (2)

If you grounded both lights to the same point, they're probably back feeding each other.

Edwardgp

I have so many grounds on my car that I am afraid where ever I ground them I will get feedback. Hay that gives me an idea though. What kind of diode could I put inline on the ground to stop this?

Jonesyfxr

iTrader: (2)

I'd have to do some digging to figure it out.

Maybe Tuned Performance could help you out.

Edwardgp

Working on this project today, has anyone ran into this problem before?

Joe Tag

iTrader: (4)

Did you wire them to the trigger wires for the relay instead of the hot wires for the fan? It won't tell you if the fan is getting power that way, only that they should be.

Edwardgp

They are wired to the power wire for the fan motor itself. This will let me know that the fan motor is getting power and should be running unless the fan motor itself goes bad.

Joe Tag

iTrader: (4)

Wiring to the trigger wires will do the same thing, just won't tell you if the relay is not working. Maybe hook one LED up to the supply to the fan, and the other to the trigger wire for the other relay. That should keep the circuits separate and still assure you the fan is getting power.

Edwardgp

Joe I can give that a shot but my idea was to be able to tell that both the low and high speed relays were sending power to the fan, depending on demand of engine temperature. I am going to head out to my shop and I will make a jumper wire and try out your idea. Thanks for your input.

Joe Tag

iTrader: (4)

Well my thought on the diodes is the bottleneck that is created by the smaller wire. It no doubt is feeding back through the hot not the ground. Possibly several diodes in parallel will work and not have much resistance.

Jonesyfxr

iTrader: (2)

An LED is polarity specific. I guess I missed that on the original thread.

You've got something wired up wrong or something.

LED = light emitting diode

A diode will only work right if the polarity is correct.

Are you sure it's not a bulb I that light? I've seen things at Radio Shack labeled wrong.

Not saying you're wrong, just saying sometimes things are mislabeled.

Six_Shooter

iTrader: (2)

I doubt it's wired wrong, this is pretty normal for a light (LED or incandescent), when connected to a motor.

I bet you'll find that the LEDs will indicate the fans are on, even when the relays are off and you're driving above 40 MPH or so. A motor not only takes in electricpower and converts it to kinetic energy, but can also take kinetic energy and turn it into electric power. This is why both LEDs come on even when only one relay is triggered. The motion of the fan is acting upon the windings and producing electric power, that is being transferred to the LED via the wired connection to the fan. The only way to stop that from happening is to isolate the fan from the LED connection. I don't recommend it, but a large diode that can pass several tens or hundreds of amps could be used. The problem here is that regardless of the size of diode, you will get a .6 to .7 volt drop across the diode (Silicon) or .3V (Germanium), though I'm not sure I've seen a germanium diode that would fit the application.

The best you can really hope for here is that you will have an indicator that will tell you if the fan is spinning (not necessarily powered), because of how electrical energy is produced is in this set-up. You could install those diodes, though they will be pricey to be large enough, and you will get that voltage drop, that would do exactly what you want, with degraded performance of the fan(s).

I can't think of a simple way to make this work without having the voltage drop, I do have an idea, but would need to test before I would be comfortable suggesting that it will work without messing with the control part of the circuit.

Edwardgp

I agree with the wire size on a single diode being a huge bottle neck.

Edwardgp

I believe the polarity on the LED'S is correct.

Edwardgp

Six shooter is on the mark on this project. The motor is indeed generating enough electrical current to light both LED'S Sooooooo I just got back in from the shop and have rewired to the trigger wire on the solenoids. I guess this will have to do. At least I will know the solenoids are getting voltage. Thanks to all for your input.

Six_Shooter

iTrader: (2)

It's not the connector or wire size on the diode dropping the voltage, it's the silicon properties that requires a Vf (Forward Voltage) of .6 to .7V in order for the diode to "turn on", and allow voltage to pass. This is what causes the .6 to .7V drop across a silicon diode.

Edwardgp

Oh alright then, learn something every day. Thanks for the help.

Jonesyfxr

iTrader: (2)

What about tapping into the feed on the relay instead of the output on the relay. I know this would mean that only the relay is getting power, but that would isolate the LED from the fan.

You could also wire in a relay using the fan output, as wired, to feed a relay to trigger the indicators. There wouldn't be enough feed back current from the fan to trip the relay.

I'd like to tackle this wiring job. This would be a fun one to figure out for sure.

MoJoe

iTrader: (5)

I am used to two fans and two relays, that operate independent of each other, so it took me a moment to figure out what you were asking. But, what you are describing is this:


When the low speed relay kicks in, the power is back feeding through the high speed windings in the fan motor (12V and only enough current to illuminate the diode ... milli Volts). Or the fan motion is inducing a current through the high speed windings.
When the high speed relay kicks in, obvious the high LED lights, and the low LED will get ~50% Voltage from the middle of the motor windings, which is enough to light.

You can put a high power diode between the high speed relay and the high speed fan wire, with the LED on the relay side of the diode. This will block the back flow from the motor, and allow forward (high) current to run the motor.

Edwardgp

Where might I be able to find one of these diodes and how will I be able to identify it? Would there be I.D. numbers or what? Thanks for your input.

MoJoe

iTrader: (5)

A quick look at Mouser.com, I filtered on 40A forward current, and the lowest Voltage drop is 2.7V, which will significantly reduce power to the fan.

I think this is a bad solution.

Edwardgp

I agree, I do not like this solution either. I need the fan running at peak performance with the rat motor stuffed in there.

NINÅ

thunderstick

i put indicator lites on my dash years ago and simply ran the "+" (for the light) to a key on source and the grounds to the fan circuits so once the circuit is grounded to turn the fan(s) on, it also completes the circuit to the light on the dash. simple. no diodes or anything else - just a bit of wire and connectors...