Need Help Wiring a load Fault Indicator

[cowboybob]

Maybe just a playing card clothespinned to the fan blade shroud: no noise = no fan...

 

[4pyros]

This is where I like using an airflow sensor. Either there is air flow of not.

The car moving can possibly trigger this as well.
Can you use back EMF?
Would the wind tuning the fan blades make Back EMF?

 

[cowboybob]

The car moving can possibly trigger this as well.
Can you use back EMF?
Would the wind tuning the fan blades make Back EMF?

They could (and here I'm assuming they are not brushless motors) if the fan circuit was complete, but it would be of little consequence against the 12 VDC driving them.

With the relays "off" though, there'd be no complete circuit for the wind generated current to flow through.

 

[Reloadron]

I just want to know where the fans are and what they do? Then worry about it.

Ron

 

[Trent W]

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

These are the exact fans I have if you were still curious as to what I was using. the description didn't actually specify exact motor specs but its should be very close

**broken link removed**

 

[Trent W]

So I got it wired I attached a one line so you guys can see if i got this right. Still have to go install it, going to bench test first before I start screwing into my engine bay (waterproof enclosure)

 

[cowboybob]

Looks good, Trent.

Don't forget the various capacitors that Ron suggested:

... 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. ...

Like so. Keep the caps soldered real close to the pins of the ICs.

<EDIT>!! Also, the 12ga shunt resistive value is for a single strand wire. NOT multistrand. Bascially, house wire.

 

[Trent W]

Ok got this thing wired and bench tested it. I have LED's on when the fans are not running/not powered. When i turn the fan on I get a 36amp inrush and a running DC amperage of 9a. While running i get 25.6mv between the fan negative thru the coil to ground. The LED still is on even with the fan running. Do i need a bigger resistor? The only thing I wired different from my one line is on the negative from BOTH LED's to ground I only used one resistor. So they don't have there own resistor to ground. While bench testing I only turned on Fan 1 full speed Fan 2 wasn't wired. Would that be the cause of that or am I missing something else?

 

[Trent W]

Looks good, Trent.

Don't forget the various capacitors that Ron suggested:

Like so. Keep the caps soldered real close to the pins of the ICs.
View attachment 84603

<EDIT>!! Also, the 12ga shunt resistive value is for a single strand wire. NOT multistrand. Bascially, house wire.

The 12ga coil of SOLID copper is about 1.5 feet long and it was folded in half twice and ran to there corresponding locations on the one line i drew. Its not an actual "coil" but still produces 25.6mv. Don't know if that is an issue or not

 

[cowboybob]

With power applied to the comparator circuit, but both fans OFF, what is the bias voltage on the non-inverting (+) inputs of the comparators (should be about 7mV)?

Then check for those voltages with one or both fans ON.

We might need to add a 100 ohm resistor to the inverting (-) leg of each comparator to bias it to ground when the fan(s) are OFF. Sometimes "floating" inputs cause erratic behavior.

 

[Trent W]

fans off 3.1mv from non-inverting (+) to ground. I was getting nothing from all other test points. With a fan on testing non-inverting to ground i got 3.4mv

 

[cowboybob]

See next post.

 

[cowboybob]

Ok got this thing wired and bench tested it. I have LED's on when the fans are not running/not powered. ...

Is the 7805 being powered as you had shown in this schematic? (I missed this in a previous post):

If so, it needs to be powered from this line

When i turn the fan on I get a 36amp inrush and a running DC amperage of 9a. While running i get 25.6mv between the fan negative thru the coil to ground. The LED still is on even with the fan running. Do i need a bigger resistor? ...

Perhaps R3 needs to be 330 ohms.

But for the moment, if you will, please post ALL the LM386 pin values when the comparator is powered (from the thermostat switch) and the fan is ON.

And then again when the fan is OFF (but comparator still powered).

 

[Trent W]

Voltage measurements from all points are as follows. power is being fed from an external battery on my work bench and the op-amp is being fed from the thermostat 180F but jumpered from the battery. this is not yet installed in the vehicle yet its all on my workbench temporarily set up. Also I put the .1uf ceramic disk cap from the LM7805c input to ground 470uf electrolytic cap from the output to ground and a .1uf ceramic disk cap from pin 1 on tl082 to ground.
Battery to ground 13.89vdc (battery is being float charged, readings i gave before were just being fed from battery and was around 10vdc with fan on)
7805 +5vdc Regulator to ground. fan on LED still lit
1Input to 13.89vdc
2Ground pin 0
3Output 12.82vdc
Op-amp measurements to ground fan on
1. 4.71vdc
2. 43mv
3. 7.2mv
4. 0.9mv
5. 7.2mv
6. 0 (fan is not wired)
7. 4.74vdc
8. 12.77vdc

Same readings without fan running LED still lit
LM7805C (was extremely warm for only running the 2-3 min while testing) Mounted to aluminum plate
1.14.30vdc
2. 0vdc 12.6 ohms
3. 12.88
comparator
1. 4.79vdc
2. 0
3. 6.4mv
4. 0.9mv
5. 6.4mv
6. -0.1mv
7. 4.74vdc
8. 12.9vdc

 

[Trent W]

Is the 7805 being powered as you had shown in this schematic? (I missed this in a previous post):
View attachment 84676
If so, it needs to be powered from this line
View attachment 84677



Perhaps R3 needs to be 330 ohms.

But for the moment, if you will, please post ALL the LM386 pin values when the comparator is powered (from the thermostat switch) and the fan is ON.

And then again when the fan is OFF (but comparator still powered).

Also the readings i was getting before that was 3.1mv was because of a low battery

 

[cowboybob]

Ok. Thanks, Trent.

First things first:

...
7805 +5vdc Regulator to ground. fan on LED still lit
1Input to 13.89vdc
2Ground pin 0
3Output 12.82vdc...

Pin3 (output) of the 7805 should be 5 Vdc. Anything else indicates either no load on the regulator or a defective 7805 (or, less likely, it's wired backwards).

This elevated source voltage (12.82Vdc) to the comparator circuit puts all of the biasing and functional outputs of the TL082 way out of range for the circuit to operate as designed.

If it were me, I would:

1. ALL power OFF
2. isolate the output of the 7805 from the comparator circuit
3. put a, say, 1K ohm (1/4 watt) resistor across the 7805's output to ground (this is a temporary load, necessary for the proper regulation features of the device to function)
4. briefly power it up (using the same source as previously) while taking a reading of the output voltage
5. it should be 5 Vdc, give or take a few mVdc.
6. remove power from the 7805

Please let us know your results.

 

[Trent W]

Ok. Thanks, Trent.

First things first:



Pin3 (output) of the 7805 should be 5 Vdc. Anything else indicates either no load on the regulator or a defective 7805 (or, less likely, it's wired backwards).

This elevated source voltage (12.82Vdc) to the comparator circuit puts all of the biasing and functional outputs of the TL082 way out of range for the circuit to operate as designed.

If it were me, I would:

1. ALL power OFF
2. isolate the output of the 7805 from the comparator circuit
3. put a, say, 1K ohm (1/4 watt) resistor across the 7805's output to ground (this is a temporary load, necessary for the proper regulation features of the device to function)
4. briefly power it up (using the same source as previously) while taking a reading of the output voltage
5. it should be 5 Vdc, give or take a few mVdc.
6. remove power from the 7805

Please let us know your results.

Tested the 7805 and was replaced it was indeed faulty but the same problem persists. I also pulled the caps out still nothing. then i completely disconnected the B side of the op amp and tested still no change other than the second led would not come on

 

[cowboybob]

Ok.

But still, with the replacement 7805, would you please re-do the pin voltages?

 

[4pyros]

Tested the 7805 and was replaced it was indeed faulty but the same problem persists. I also pulled the caps out still nothing. then i completely disconnected the B side of the op amp and tested still no change other than the second led would not come on

Are you getting 5 volts now?

 

[Trent W]

Are you getting 5 volts now?

Yes I thought you meant all my voltages but here they are anyways
7805
1. 14.02vdc
2. 0
3. 4.94vdc
Opamp
1. 2.5vdc
2. 43.9mv
3. 3.4mv
4. 0
5. 3.5mv
6. -0.2mv
7. 2.5vdc
8. 4.97vdc