Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need Help Wiring a load Fault Indicator

Status
Not open for further replies.

Trent W

New Member
Currently wiring a custom Electric cooling fans for my Truck. I have the Relay's override and Operation lights figured out. My problem is I want to have two LED's that will indicate if the fan is bad. I have LED's indicating if the fan's have power but that only indicates if the relay's/thermostats are functioning. Ive messed around with some diodes but cant figure out how to make it work. Ive exhausted my knowledge of electrical at this point and ran into a dead end. Ive attached a one-line drawing i did in paint. I have basic electronics knowledge as in diodes resistors etc what they do and what the symbol looks like on a one line but much past that i'm at a loss. Any help would be GREATLY appreciated. Oh and as always if you have any tips or advice on the way I have my relay's or wiring let me know. Currently I have it set up to have low speed run the fans in series (6v-10v) and on high speed (12v-14.5v) with an override switch as a safety to manually bypass the entire system in case of relay or thermostat failure.

Oh BTW the fans are 15amp fans (40amp relays FYI)
 

Attachments

  • Electric Fan one line.png
    Electric Fan one line.png
    41.9 KB · Views: 465
In reality, I think you have one choice and that is detect RPM. You have optical methods) both reflective and interruptive) and you have magnetic (hall effect). Anything you add to the rotating fan, needs to be balanced (added 180 degrees apart)

Another detection scheme is current, but it won't be 100% reliable. Search for "allergro hall effect current sensor"
 
Welcome, Trent W!

With all due respect to KISS ;),

A reasonably reliable test of whether a fan is actually turning, in this case, is to monitor its current flow.

12 gauge copper wire has a resistance of about 0.0016 Ohms (1.6m ohm) per foot. The voltage generated across that resistance, at 15A (the stated fan's current draw), would be about 24 mV. Pretty small value. But we can work with that.

Using an OpAmp as a comparator, properly configured, we can take the absence of that 24mV signal to "trigger" the OpAmp to light up an LED, confirming that the fan is NOT drawing current.

I'll post a workable schematic, if you like.

<EDIT>Got it done. Might as well post it:
Fan-OpAmp Comparator.JPG

The 12ga. 1 ft wire loop above is in series with fan power lead. Observe polarities.
 
Last edited:
If you used the forward voltage drop from two 15 amp diodes in series then you could light a LED but you would also loose that voltage to the fan.
 
Welcome, Trent W!

With all due respect to KISS ;),

A reasonably reliable test of whether a fan is actually turning, in this case, is to monitor its current flow.

12 gauge copper wire has a resistance of about 0.0016 Ohms (1.6m ohm) per foot. The voltage generated across that resistance, at 15A (the stated fan's current draw), would be about 24 mV. Pretty small value. But we can work with that.

Using an OpAmp as a comparator, properly configured, we can take the absence of that 24mV signal to "trigger" the OpAmp to light up an LED, confirming that the fan is NOT drawing current.

I'll post a workable schematic, if you like.

<EDIT>Got it done. Might as well post it:
View attachment 84542
The 12ga. 1 ft wire loop above is in series with fan power lead. Observe polarities.

Thanks for the replies guys you're are awesome! Been scratching my head over this for days.
So from what I understand from your post and correct me if I'm wrong, First I need a Comparator from Radioshack. Unfortunately I live in salt lake and that's really the only option for me as far as electronics parts go. I assume i wont be running the load through the device so instead of writing a long winded description from what i understand how to wire this I'll just attach a one-line. Now will it be an issue when these fans are relayed to run in parallel? The second fan/OpAmp wont have its full voltage will that trigger the comparator?
 

Attachments

  • Electric Fan one line.png
    Electric Fan one line.png
    44.4 KB · Views: 256
Another option if the setup allows is the use of a simple air flow switch. This tells you if in fact the fan(s) are actually moving air. They are found in various shapes and sizes and used to detect air flow in large ovens or home heating systems. You can even easily fabricate your own. You start with a lever actuated Micro=Switch like those available from sellers like McMaster Carr or Grainger Supply. Then you just glue a paddle on the lever. You size the paddle for the air flow minimum you can accept. Not much to it really and if conditions allow the merit is a switch like this tells you if in fact you have air flow. Since I can't see your setup I can't say if it is a viable solution for your case.

If you have any Heating and Cooling places around you then you may want to talk to them. There are commercial flavors or as I mentioned you can roll your own.

Ron
 
Thanks for the replies guys you're are awesome! Been scratching my head over this for days.
So from what I understand from your post and correct me if I'm wrong, First I need a Comparator from Radioshack. ...
Yes. For instance, this one ( a "dual" opamp chip - one for each comparator. All other components also available at RS):
https://www.radioshack.com/product/index.jsp?productId=2062594
I'd also recommend this LED:
https://www.radioshack.com/product/index.jsp?productId=3096133&filterName=Type&filterValue=&gt;7 mm lens
... I assume i wont be running the load through the device...
Correct: only enough to power the TL082 and the LED (<100ma).
... i understand how to wire this I'll just attach a one-line. ...
No. One 12ga "line" for each fan AND IN THE GROUND LEG!!; I inadvertently misled you on its placement in my original post.
Like so:
Sensor Ckt.JPG

... Now will it be an issue when these fans are relayed to run in parallel?...
No. Each "failure" circuit operates independently (hence the seperate sensor lines).
<EDIT> You will need a seperate, complete "failure" ckt for each fan.
... The second fan/OpAmp wont have its full voltage will that trigger the comparator?
That's the point of using the LM7805 (5 VDC regulator) so that variations on the 12 VDC line won't affect the operation of the comparator(s).
Here is a modified schematic to accommodate the TL082 dual OpAmp chip that Radio Shack sells (note that R3 has been changed to 270 ohms):
Fan-OpAmp Comparator.JPG

Probably the best way to arrange the 1 ft 12ga "resistor" is to make a coil (like a spring) of it.
 
Last edited:
I got to looking at your drawing. Now I am not sure what this project is all about but will take a guess. You are using a pair of thermal switches to control a few fans. Looks like at 180 F. you want low speed and when (if) the temperature reaches 210 F. you want high speed on the fans. Depending on the layout and setup there are a few ways to go about this. One method is to have a single fan turn on at 180F. and the second turn on at 210 F. as needed. The method you have chosen is to run both fans at 180 F. low speed and at 210 F. go to high speed. You are doing this using a matrix of relays. While this should work I think there is a better more simple way to go about it than six relays.

Take a look at the below image. This is a rough drawing of how I would likely go about it. The concept is similar to how the fan speed (heater & A/C) works on my truck.

12 Volt Auto Fans.png


When thermal switch S1 reaches 180 F. it closes and energizes Relay K1. The normally open contacts of K1 close (30 & 87) powering both fans through resistor R1. I labeled R1 as .5 Ohm and that is approximate. Based on these motors being 12 VDC 15 Amp motors their DC resistance would be about .8 Ohm and two motors in parallel would be about .4 Ohm. Therefore if we use about a .5 Ohm resistance in series with the fans they will see a little less than 1/2 their rated voltage. Fan speed control using fans in series or resistance in series with fans is not an exacting science, as long as the fans can start rotation at the lower applied voltage. When and if the temperature reaches 210 F. the normally open contacts of K2 (30 & 87) will close and bypass the K1 closed contacts applying the full 12 Volt power to both fans. Matters not that K1 is closed. Finally as the Ultimate bypass SW1 simply applies full power to both fans.

Resistor R1 at .5 Ohm will obviously be a very high power resistor. What I suggest here is several turns of nichrome wire wrapped over a pencil and the pencil removed leaving an air core. It will look like the heating element in an electric hair dryer. Actually several years ago my own truck lost low speed on the blower. OK, no big deal I still have 3 speeds left. Then a few years ago I lost the next speed but lived with it. Finally a few weeks ago I lost the third speed leaving only the two highest remaining speeds. Had to keep turning the CD player volume up! My truck is an older GMC Yukon XL so I just replaced the resistor matrix for the fan speed control. Damn, that sucker was loud! :) Not much to the resistor matrix in those units. Just turns of nichrome wire used for three resistors.

The above drawing omits additional fusing and I didn't call out the wire gauges. The main wire for both fans should be AWG 10 since two fans running full power will draw 30 Amps. You need to give consideration to the wire gauges used. Anyway, if this isn't built yet you may want to consider the above method.

Ron
 
Last edited:
I got to looking at your drawing. Now I am not sure what this project is all about but will take a guess. You are using a pair of thermal switches to control a few fans. Looks like at 180 F. you want low speed and when (if) the temperature reaches 210 F. you want high speed on the fans. Depending on the layout and setup there are a few ways to go about this. One method is to have a single fan turn on at 180F. and the second turn on at 210 F. as needed. The method you have chosen is to run both fans at 180 F. low speed and at 210 F. go to high speed. You are doing this using a matrix of relays. While this should work I think there is a better more simple way to go about it than six relays.

Take a look at the below image. This is a rough drawing of how I would likely go about it. The concept is similar to how the fan speed (heater & A/C) works on my truck.

View attachment 84580

When thermal switch S1 reaches 180 F. it closes and energizes Relay K1. The normally open contacts of K1 close (30 & 87) powering both fans through resistor R1. I labeled R1 as .5 Ohm and that is approximate. Based on these motors being 12 VDC 15 Amp motors their DC resistance would be about .8 Ohm and two motors in parallel would be about .4 Ohm. Therefore if we use about a .5 Ohm resistance in series with the fans they will see a little less than 1/2 their rated voltage. Fan speed control using fans in series or resistance in series with fans is not an exacting science, as long as the fans can start rotation at the lower applied voltage. When and if the temperature reaches 210 F. the normally open contacts of K2 (30 & 87) will close and bypass the K1 closed contacts applying the full 12 Volt power to both fans. Matters not that K1 is closed. Finally as the Ultimate bypass SW1 simply applies full power to both fans.

Resistor R1 at .5 Ohm will obviously be a very high power resistor. What I suggest here is several turns of nichrome wire wrapped over a pencil and the pencil removed leaving an air core. It will look like the heating element in an electric hair dryer. Actually several years ago my own truck lost low speed on the blower. OK, no big deal I still have 3 speeds left. Then a few years ago I lost the next speed but lived with it. Finally a few weeks ago I lost the third speed leaving only the two highest remaining speeds. Had to keep turning the CD player volume up! My truck is an older GMC Yukon XL so I just replaced the resistor matrix for the fan speed control. Damn, that sucker was loud! :) Not much to the resistor matrix in those units. Just turns of nichrome wire used for three resistors.

The above drawing omits additional fusing and I didn't call out the wire gauges. The main wire for both fans should be AWG 10 since two fans running full power will draw 30 Amps. You need to give consideration to the wire gauges used. Anyway, if this isn't built yet you may want to consider the above method.

Ron

Ron thanks for looking at it, and no I was about to attempt to build this setup in the next few hours. I went and got all my parts today. I appreciate the tip I wasn't looking forward to wiring that rats nest of relays! Where would you get the nichrome wire? I was trying to keep everything redundant as possible so no single point of failure existed and using your method I can eliminate a lot of them especially keeping both fans running parallel. I would need 1 more relay for a total # of 3 because my bank of switches which one would be used for the override switch mounted in my dash are only rated at 10 amps.
 
Yes. For instance, this one ( a "dual" opamp chip - one for each comparator. All other components also available at RS):
https://www.radioshack.com/product/index.jsp?productId=2062594
I'd also recommend this LED:
https://www.radioshack.com/product/index.jsp?productId=3096133&filterName=Type&filterValue=&gt;7 mm lens

Correct: only enough to power the TL082 and the LED (<100ma).

No. One 12ga "line" for each fan AND IN THE GROUND LEG!!; I inadvertently misled you on its placement in my original post.
Like so:
View attachment 84570

No. Each "failure" circuit operates independently (hence the seperate sensor lines).
<EDIT> You will need a seperate, complete "failure" ckt for each fan.

That's the point of using the LM7805 (5 VDC regulator) so that variations on the 12 VDC line won't affect the operation of the comparator(s).
Here is a modified schematic to accommodate the TL082 dual OpAmp chip that Radio Shack sells (note that R3 has been changed to 270 ohms):
View attachment 84567
Probably the best way to arrange the 1 ft 12ga "resistor" is to make a coil (like a spring) of it.

A bit of a side question how do you guys come up with your resistor ratings? I was wondering when i was getting the different rated resistors at the store today for my setup how did you or anyone for that matter come up with those numbers? Just in case i have any more of these projects in the future I'm not bothering you guys with simple questions like that. I do plan on getting a basic/intermediate electronics book here soon, do you guys recommend any one in particular? This kind of stuff has become a fun little hobby of mine for some time now and would like to educate myself more on this subject.
 
Resistors are rated by their ability to handle power (Watts). The circuit I posted would only really need resistors with micro watt capacity, which, of course, is not a realistic or even available size. 1/8 watt capacity is a practical size for the comparator ckt.

To answer your question, Using the formula for Ohms law: Voltage (E)=Current(I) times Resistance (R), oe E=IR.
OhmsLaw.JPG


Example: this circuit has a total R=72 ohms and I=0.1667A, therefore voltage across each resistor is 36 x 0.1667, which equals 6V. And variations on that theme.

To determine wattage you multiply volts times amps. In the above case, the wattage of the circuit would equal (across each resistor) 6 x 0.1667 which equals 1 watt (and 2 watts for the whole ckt). It is generally a good rule, especially for automotive circuits, to simply double the wattage capacity of resistors to be on the safe side.

There's tons of stuff out there to help you learn the basics of electronics. I've read and heard some very good feed back about this offering (which includes a lot of hands-on examples):
 
Last edited:
Ron thanks for looking at it, and no I was about to attempt to build this setup in the next few hours. I went and got all my parts today. I appreciate the tip I wasn't looking forward to wiring that rats nest of relays! Where would you get the nichrome wire? I was trying to keep everything redundant as possible so no single point of failure existed and using your method I can eliminate a lot of them especially keeping both fans running parallel. I would need 1 more relay for a total # of 3 because my bank of switches which one would be used for the override switch mounted in my dash are only rated at 10 amps.

You can build it using your drawing since you grabbed the parts. Nichrome (nickel chromium) wire can be had from a number of sources like McMaster Carr Supply. However, you only need a few inches of the stuff thus I suggested an old hair dryer or it could be salvaged from an old hot plate, any heating element. A good source would be the resistor blower motor speed control modules from an automotive junk yard. Making the resistor is a trial and error affair.

The idea I had in mind was to reduce parts count. Not so much for cost but the simpler a design like this is the less there is to go wrong or fail. Like I said, my truck is an older Yukon XL and uses a resistor module to control blower speed. My wife has a Yukon Denali with a fancy vari speed blower motor control. Hope that thing never fails. :) Anyway, there is any number of ways to make the resistor.

As to the switch? Yes, that would be a large switch. Another bypass relay could be added but that doesn't help reduce parts. However, if things work correctly hopefully it would never be used. It's a backup.

A few things to consider with the comparator circuit. Automotive power is real clean DC right till we start the engine. Then automotive power becomes extremely dirty. Where the LM7805 regulator is used I would place a .1 uF cap at the input and the output of the LM7805 regulator. I would also place a 450 or so uF cap at the output. The .1 uF caps will help filter out high frequency noise and the 450 uF cap will provide DC smoothing. I have no clue how much noise if any will be induced by what I assume is a brushless DC fan motor on the lines going to the comparator. Never looked at one. If there is motor generated noise it may cause problems with the comparator. Additionally, I would use a decoupling cap (.1 uF) at the power pin of the comparator to ground.

Again, still not sure what this project is all about? Sometimes when people understand the final goal or objective it becomes easier to come up with ideas.

Ron
 
Last edited:
Ron, you've got a point with the fan noise and its effect on the comparator input (power filtering caps also - forgot to put those in. Thanks).

I'll sim the comparator ckt with some noise on that line and see what happens. Since, however, the ckt only trips "on" at a reduction to around 8 - 10 mV, I'm thinking the noise will have a negligible effect. We'll see.

CBB
 
Motors Series.png


Ron, you've got a point with the fan noise and its effect on the comparator input (power filtering caps also - forgot to put those in. Thanks).

I'll sim the comparator ckt with some noise on that line and see what happens. Since, however, the ckt only trips "on" at a reduction to around 8 - 10 mV, I'm thinking the noise will have a negligible effect. We'll see.

CBB

I was just curious about it. Something else I am not getting is the shunts. Using the shunt to sense the current through the motors I am fine with. When the motors run on high speed all well and fine as each motor has its low side to ground and each shunt will produce a voltage proportional to the motor current. That voltage will be referenced to ground and the op amp comparator will work. However, and here is where I may be wrong, when the motors switch to low speed the motors are placed in series as I understand it. Now if I am correct this far things will look like the above less the relay contacts ect. Each motor will see about 6 volts less the preceding shunt drops. The first motor's shunt is fine referenced to ground. However, the shunt for the second motor low side is about 6 volts with the high side being 6.012 volts. Am I looking at this correctly? :wideyed:

Ron
 
View attachment 84588
I was just curious about it. Something else I am not getting is the shunts. Using the shunt to sense the current through the motors I am fine with. When the motors run on high speed all well and fine as each motor has its low side to ground and each shunt will produce a voltage proportional to the motor current. That voltage will be referenced to ground and the op amp comparator will work. However, and here is where I may be wrong, when the motors switch to low speed the motors are placed in series as I understand it. Now if I am correct this far things will look like the above less the relay contacts ect. Each motor will see about 6 volts less the preceding shunt drops. The first motor's shunt is fine referenced to ground. However, the shunt for the second motor low side is about 6 volts with the high side being 6.012 volts. Am I looking at this correctly? :wideyed:

Ron
Yes. And a salient point.

I hadn't considered that the half speed condition was the result of a series fan configuration.

What would happen (ideally) would be the lead (positive side) fan's shunt generates 6.01v, more than enough to keep the first comparator off. The downstream fan shunt would generate 12mv, which is still high enough to keep that comparator in the "off" state (anything >8mv).

Now, with the fans in series, if either or both fan motors fail, the entire circuit will cease to draw current. As a result, both comparators will go high, lighting up both LEDs, a pretty obvious failure indication. It would not, of course, indicate which fan failed.

If need be, the comparator circuits could be modified for a slightly lower trigger voltage by reducing R3.

Noise tests in SIM (12V [24v P-P] sine, triangle and square waves, sweeping 1 to 1kHz over 1s, injected at sensor input to comparator input) had no significant discernable effect on comparator function. Only the negative going transitions had marginal effect and were generally too low to trigger an LED response. I think that this largely due to the shunt(s) essentially shorting the noise to ground. This may not reflect real-world conditions.
 
Yes. And a salient point.

I hadn't considered that the half speed condition was the result of a series fan configuration.

What would happen (ideally) would be the lead (positive side) fan's shunt generates 6.01v, more than enough to keep the first comparator off. The downstream fan shunt would generate 12mv, which is still high enough to keep that comparator in the "off" state (anything >8mv).

Now, with the fans in series, if either or both fan motors fail, the entire circuit will cease to draw current. As a result, both comparators will go high, lighting up both LEDs, a pretty obvious failure indication. It would not, of course, indicate which fan failed.

If need be, the comparator circuits could be modified for a slightly lower trigger voltage by reducing R3.

Noise tests in SIM (12V [24v P-P] sine, triangle and square waves, sweeping 1 to 1kHz over 1s, injected at sensor input to comparator input) had no significant discernable effect on comparator function. Only the negative going transitions had marginal effect and were generally too low to trigger an LED response. I think that this largely due to the shunt(s) essentially shorting the noise to ground. This may not reflect real-world conditions.

I wish I could see the fans and the overall configuration. While I like using current sense in some cases it isn't practical. If for example a fan gets gunked up and stops causing a locked or slowed rotor the current will likely increase but still be there above a set point. With a locked rotor it should take out a fuse. Also, while it doesn't apply here in the case of belt driven fans if a belt breaks you are screwed. This is where I like using an airflow sensor. Either there is air flow of not.

On a side note where is James Island? Going to Raleigh area (Carey) next week then on to the Carribean for a few weeks. Right now it is 14 degrees F. and snowing up here. At least I am finally retired and not driving to work in this crap. I need a break from the winter! :)

Ron
 
Back to:

1) Reflective object sensor: https://www.digikey.com/product-detail/en/QRB1134/QRB1134-ND/187533 You mount reflective tape on shaft.
2) Photo interrupter - https://www.digikey.com/product-detail/en/QVB11134/QVB11134-ND/187515 You place something between the slots.
3) Hall effect - https://www.digikey.com/product-search/en?vendor=0&keywords=365-1567-ND Place a magnet so it activates the sensor
4) Inductive and capacitive proximity sensors - https://www.digikey.com/product-detail/en/E2K-F10MC1/Z3191-ND/770024 Can work with ferous and non ferrous objects like the fan blade.

Unfortunately, my xtal ball is broke and have no way of determining if any style can be fitted. Jaycar, sells a frequency to voltage converter which you can compare. If you can arrange your lamps such that they "flicker", maybe a divide by counter, might be all you need.

Rotating/nonrotaing is just one mechanism. If you actually want an alarm, you have to know when the fan is powered and if it should be rotating and incorporate some delay in that comparison mechanism.

I did pick some non-available types and sensors of the same type don't mount thee same way.

Velocity sensors such as vane (probably won't work here) and neither will pressure differential.
 
Ron,

James Island (home of Fort Johnson, where the Cilvil War got started) is butt up against (actually across the Ashley river and Charleston harbour) from Charleston, SC. We are our own town, though, and claim no kinship. 62 F here.

Carey's a nice area. My stepson lived there when he worked for IBM at the Triangle.

Carribean ain't bad, either... :woot:.

CBB
 
KISS,

I just couldn't see a way to use a "fan not rotating" scheme for a failure indicator since the stupid fan(s) would continue to rotate if the vehicle was still moving because of air flowing across the blades. There may be a way to utilize such a method but durned if I see it.
 
But they won't rotate that fast, hence frequency switch. so, we need current, rotating pulse and a fuse with a blown pin in it for NASA quality "Fan doesn't work"? Let's not forget the temperature idiot light.

Or wire a "Fan speed doesn't increase" when power applied switch?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top