Any 12V electrical guru's here? An E.E. mabey!

[cruiseroutfit]

I'm fairly confident around vehicle electrical systems, I've had some basic electrical engineering courses as well as plenty of experience with general auto repair and accessory installation, aux. lights, dual batteries, etc. Basically enough EE stuff to "know, that I don't know" type of deal I'm stumped... I'm literally beating my head trying to find the answer to this.

Background:
I'm installing in-cab winch controls for my Warn 9.5ti, using a power switch, and a DPDT switch to handle the "5-wire" system that warn utilizes. This is all fine and dandy, however the 9.5ti winch has an overheat sensor (they call a Thermometric Indicator). Basically the sensor causes a LED to flash in the remote when the motor reaches a temp that could begin to cause damage. Easy still right? Well the way Warn wires the LED according to their schematic diagram has me baffled.

Here is the diagram:

Where I'm confused:
So the anode side of the LED is constantly powered with 12V+ via the white wire the connects to the battery, though there is a 1k-ohm resistor inline with the input. The cathode side of the LED is constantly grounded by hooking to the red wire. So that would tell me the LED is constantly powered right? So how does the temp switch (marked TPD) on the diagram cause the LED to NOT emit light by intersection on the anode side AFTER the resistor. Furthermore, how does it cause it to flash?

Warn nor any Warn repair centers I've spoke with have every really looking into it (well not any of their customer service reps that is). I want to have the overheat LED in my in-cab controls, just as it functions on the remote. I could dissect a remote, but I don't want to ruin it just to figure out how their wiring works (especially when I have a schematic already). Thoughts???

 

[Clark White]

I'm no electronics genius, but I think that is an incomlete diagram. It would have something to do with the solenoid in the middle top, but I'm not sure how exactly its working. To be honest, I'm usually really good at reading diagrams, but I really have no idea whats going on with that one. The solenoid (I'm assuming thats what the "field" is?) would be powered all the time, when you activate the switch it would short the battery to ground, and I have no idea how you turn off or flash the LED on that diagram.

 

[eugene]

Basically the thermal sensor is in parallel with the LED. My guess would be it simply changes resistance with temperature creating a voltage divider with the 1k resistor. As the resistance changes the voltage between the resistor and the thermal sensor/led combination causing the voltage at that point to change enough to turn the led off and on.

First google hit for voltage divider http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

The 1k and the thermal resistor make up the voltage divider.

 

[pete.wilson]

Hey

Eugene has it correct in that the Thermistor (resistor that changes with temperture) is across the diode and as temperture changes so does the resistance of of the thermister which in turn changes the bias of the diode which turns it off. The 1k resister is used as a standard diode bias voltage in most LED circuits. Like Eugene stated when the 1K resistor is used with the thermister as a voltage divider which obviously changes with temperture. You could take a voltmeter and connect the ground lead and then connect red lead to the Led, heat the thermister with a heat gun slowly and actually check and see where it trips the LED, then if you ever have a problem your will know where is supposed to trip.

Thermistors are found in a lot of electrical, heat generating devices to shut down items before they burn up, most are sold by their temperture rating in degree's and mounting style which can be either axial (lead at each end) or will have a type of ring mounted to the body of the thermistor and attached with a screw to the chassis of the device.

Pete Wilson

 

[TheRoadie]

I'm in the semiconductor equipment business, and here's my guess what it does. A straight thermistor device in parallel with the LED would make it go dimmer as the sensor heats up. Or a disc thermostat like a Klixon could make the LED go from full bright to nothing, but the motor would have to cool down to reset the thermostat, which would require the user to let go of the button. And it would take minutes. And a dark LED isn't a good warning indicator.

Nothing I could find in a search told me exactly how the Thermometric Indicator actually behaves as the motor heats up before it gets to a damaging temp, but I think there's two possibilities.

1) The sensor is a thermostat in series with a flasher, that will cause the LED to flash at some fixed rate when the trip temperature is met.

2) For a few bucks more, they could have added a PWM (pulse width modulated) fan controller ICl, and the PWM chip starts shorting its output to ground and flashing the LED so its ratio of on time to off time increases as the sensor heats up. Or a simple 555-style timer can do the same thing and vary the rate of flashing. At some upper trip level, the circuit could force the motor off as a safety measure - this isn't shown in their diagram, but I bet there's some function like this in there. For warranty expense reduction if nothing else.

Have you ever driven the winch to heat up and see how the LED behaves? Or is the owner's manual more enlightening than the web sites? That would be very interesting observation for curious folks.

 

[cruiseroutfit]

...Have you ever driven the winch to heat up and see how the LED behaves? Or is the owner's manual more enlightening than the web sites? That would be very interesting observation for curious folks.

Yes, on a handful of occasion's it has started flashing, generally during extremely heavy pulls for long periods of time (one in particular was doing a vehicle removal from a forest close to home, we had to pull the car (no tires) up a 45+ degree hill for nearly 100ft. It will flash if you continue to use it, but if you let it cool down for several minutes it stops. Hard to say how long it took, we were stopping to re-rig on occasion and that would take 5-10 minutes or more at times.