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. However I'm stumped...

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???

 

[waynehartwig]

It's a pull up resistor. When there is no ground/hot signal, the light is off and there is no current draw. Once there is current flow, it's then a current limiting resistor.

In this case, when the TPD 'opens' (gets too hot) the pull down resistor pulls the LED hot and turns it on.

...As for flashing, they do make flashing LED's as well as solidly lit...

 

[cruiseroutfit]

It's a pull up resistor. When there is no ground/hot signal, the light is off and there is no current draw. Once there is current flow, it's then a current limiting resistor.

There is always a ground and always a constant 12V+ into the LED as per the diagram no? So how does potentially adding another ground (or removing depending on how the switch works) change that? I guess I don't see how the switch could "pull" the 12V through the resistor??

 

[gijohn40]

from what I am seeing the led is hooked to the green wire and the third position on the switch... when it (switch) is moved to that location it makes contact with whatever is connected to the common on the switch...

The resister is not even connected to the led...

Connections are made by the solid black dot where the wires come together... if they cross but don't have a black dot they are not connected...

 

[cruiseroutfit]

from what I am seeing the led is hooked to the green wire and the third position on the switch... when it (switch) is moved to that location it makes contact with whatever is connected to the common on the switch...

The resister is not even connected to the led...

Connections are made by the solid black dot where the wires come together... if they cross but don't have a black dot they are not connected...

Yes, and there is a solid black dot at the resistors connection with the LED (going by the actual LED schematic rather than the label). That "LED" label is a bit confusing, it is NOT that node, rather the label should have been moved down more. The other Warn diagrams I have have the label closer to the anode/cathode diagram on the schematic. Sorry for the confusion... my conundrum still stands

 

[waynehartwig]

Ok...Here's what really confuses me and I was just rolling with it, but now it's bugging me so I have to say something... That symbol is not for an LED, that is a Diode symbol. LED is a diode symbol with arrows pointing away from it and a anything that detects light has the diode symbol with arrows point towards it - all at an angle.

R is the pull up resistor for L2 (the load).

So I guess I'm trying to say are you sure that's a LED and not a diode? Maybe where it's labeled LED the LED hooks there?

But still.... The resistor is a pull up resistor if that diode is an LED instead.

Just did a google on pull up resistor and found this:
http://www.seattlerobotics.org/encoder/mar97/basics.html

"An LED (Light Emitting Diode) is a semiconductor that emits light energy when a current flows through it. Current will only flow one direction, just like a regular diode. There are a few things you need to know about an LED before you use one. First, and most importantly, is that an LED has very low internal resistance. This means that left to itself, an LED will pass so much current that it will burn up. They require an external resistor to limit the current.
Most LED's have a current rating, which determines the size of the resistor you will need. The current rating tells you what the maximum allowable current for the part is. In general, the higher the current, the brighter the LED.

Most LED's seem to handle at least 15mA. If you are using a 5 volt circuit, then Ohms law tells you what resistor value to use. R = V / I, so R = 5v / .015A = 333 ohms. "

That's better explained than my version And it can be anything, 5v or 40 or 200v.

I'll also add that the pull up reistor is goign to assign a 'value' (voltage) to the LED. But the pull up resistor is also at a high value, allowing another object (TPD) to change it's state. So maybe on each side of the LED is ground, but when TPD shows heat, it turns to a open and causes the LED to go hot. The TPD is short when there is no heat, and opens as it heats up. Doing this would also cause the LED to never light (grounds on both sides) until the heat on the TPD get's to a certain point that opens. Because keep in mind, as long as that LED is not lit, current is flowing through the TPD and that pull up resistor. Current can't flow through the LED until it reaches a certain current (called the avalanche current where the substrate finally breaks down - all of my schooling from 20 some years ago is coming back to me! lol Of which I am STILL paying on student loans for!) and that won't happen until the TPD resistance increases so that it doesn't keep pulling the resistor low and turn the LED on.

Without actually touching this and probing around, it's all speculation on what the engineers were thinking....

 

[cruiseroutfit]

Great thoughts Wayne...

LED versus diode, yes I realize they didn't use the proper schematic, but they have it labeled "LED" on all 3 Warn diagrams I have (albeit in different locations on each). I also understand the resistors purpuse. But how does the TPD itself cause a flashing at overheat? Either it acts as a capacitor, or there is a capacitor inline with the blue line (such as the rectange just before its intersection with the diode). None of the diagrams I have show a value for that capacitor if in fact it is a capacitor. If in fact it was a capacitor, that alone would answer the question. But as of now you have a 12V+ charge going into the TPD. Mabey the TPD doesn't work as a ground switch rather as you say it pulls the charge through the TPD UNLESS it senses overheat in which it acts as a capacitor??

 

[DaveB]

As I read the schematic the TPD acts like a switch that is normally closed which shorts the diode anode to ground. When the TPD is closed there is current that flows through the resistor but not the diode. When it overheats the TPD will open up allowing the current to flow through the diode causing it to turn on. The TPD will then close again and turn it off. It will repeat the action causing the blink to repeat.

 

[waynehartwig]

As I said before, they are probably using these LED's...
http://www.elexp.biz/opt_6bid.htm

...Flashing style.

This would be the most logical, since there are no external components that would be needed to create an electronic style flasher (digital circuitry, etc).

After Dave's comment, I looked at the schematic again and realized the TPD is not hooked to source voltage, so I've been backwards on my thoughts. But still, the pull up resistor is tied high and the TPD is stopping current flow to the LED (By allowing the flow to go through the resistor and to ground). Once the TPD starts warming up, the resistance increases and once it allows enough current that the LED turns on and blah blah blah...

But I think your answer is flashing LED's.

 

[dutchovendude]

I also agree with the flashing LED. I used to install alarm systems and I used to use the blinking LEDs more than the steady on type. The customers liked the blinking lights better.

 

[timpanogos]

I believe Dave is right about the TDP being normally closed, holding the point between the resistor and anode at ground. Current flow through resistor from TDP ground not via the diode. When the TDP opens up (over heat), the ground is dropped from the anode and current now flows through the diode, lighting it up.

I believe others are right in that it must be a blinking diode, if you expect a fast blink when TPD is open.

 

[bobmed]

I've seen flashers that operate on temperature in some machine controls.
If all the tpd does is flash the led it might be just a thermal flasher switch

 

[78mitsu]

it should be a solid state controller that opens the ground path to the relays and prevents the winch from applying power to the windings when it's too hot, Not a terribly complex circuit, but probabby saved a lot of winches. I believe tpd=>thermal power disconnect. the blinky light is just for notification so you don't get the tools after it.

 

[cruiseroutfit]

Bump, still looking for clarification on this. Any new thoughts?

 

[DaveB]

To repeat my last post with one modification: the TPD acts like a switch that is normally closed which shorts the diode anode to ground. When the TPD is closed there is current that flows through the resistor but not the diode. When it overheats the TPD will open up allowing the current to flow through the diode. The diode will blink if a blinking type diode is used or it will stay on if you use a normal diode (until it cools off and the TPD goes back to its initial state).

 

[cruiseroutfit]

To repeat my last post with one modification: the TPD acts like a switch that is normally closed which shorts the diode anode to ground. When the TPD is closed there is current that flows through the resistor but not the diode. When it overheats the TPD will open up allowing the current to flow through the diode. The diode will blink if a blinking type diode is used or it will stay on if you use a normal diode (until it cools off and the TPD goes back to its initial state).

That makes a bit more sense!

I have a gentleman that has a controller pulled apart right now, he's going to get me some pics of how Warn has it wired.

The square figure in the schematic, on the blue wire just before the resistor, is apparently just a splice that all of the ti/si remotes have??