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The car moving can possibly trigger this as well.This is where I like using an airflow sensor. Either there is air flow of not.
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.The car moving can possibly trigger this as well.
Can you use back EMF?
Would the wind tuning the fan blades make Back EMF?
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
Like so. Keep the caps soldered real close to the pins of the ICs.Reloadron said:... 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. ...
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.
Is the 7805 being powered as you had shown in this schematic? (I missed this in a previous post):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? ...
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).
Trent W said:...
7805 +5vdc Regulator to ground. fan on LED still lit
1Input to 13.89vdc
2Ground pin 0
3Output 12.82vdc...
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.
Are you getting 5 volts now?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?