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Bitsyncmaster
09-20-2016, 06:53 AM
I'm holding sales of my electronic fused fan fail unit. Using it with OEM fans that draw high start current can cause the "fuse" to trip. I have been prototyping new circuitry for a few months and now have a prototype unit I'm happy with. But one of the new IC's I'm using has not been released in production quantities. It is expected in 26 weeks. I'm using an alternate part in my prototype but it has less accuracy than the one not available yet.

I have designed a new current sensor used to monitor each fan current. I was using a hall effect IC rated for 20 amps continuous and 100 amps for 100 ms. But I have had a few of those components fail with customer units. My new design uses a one watt 0.001 ohm resistor and an op-amp to give me current reading up to 50 amps and should be able to run continuous at 100 amps without damage.

So I needed to be able to read more current and the software now does the following. I tested a 20 amp fuse in my car with the fan connector shorted and peak current was 120 amps for 41 ms then the fuse popped. A 30 amp fuse held for 134 ms before it popped.

1) When a fan is turned on no trip current is checked for 40 ms.
2) Then the fan trip current is set to 45 amps for 200 ms.
3) Then the fan trip current is set to 40 amps for the next 400 ms.
4) Then the fan trip current is set to 30 amps for the next 800 ms.
5) Then the fan trip current is set to the final current of 20 amps.

I chose those currents which should keep OEM fans (even older high current fans) from tripping the fuse. The whole point of fusing the fans is to prevent damage or fire to the wiring in the harness and I feel those short overload currents of the fan starting current will not overheat any wiring.

Another added benefit to my new circuit is less current draw by the new current sensing which helps the unit running cooler.

I also monitor the input voltage (power from the fan relay) and will shut off the fans if that voltage drops below 8.0 volts. If the voltage rises above 9.0 volts it will start up the fans with the same current trip setting as a normal power up. When the voltage has dropped to 8.0 volts the fan fail light will stay on continuous however the voltage driving the fan fail light will be that 8 volts or less..

I still keep the flashing fan fail warning if either fan draws less than 4 amps or greater than 18 amps. The second fan turn on delay is now 2.44 seconds.

DavidProehl
09-20-2016, 12:50 PM
There is no concern or risk with using your old module with updated low draw fans correct? I've been very happy with your module, running it for close to 4 years now.

Bitsyncmaster
09-20-2016, 01:08 PM
There is no concern or risk with using your old module with updated low draw fans correct? I've been very happy with your module, running it for close to 4 years now.

No problems with low current fans. I'm still using the electronic fused unit in my car with Toby's fans. The fused unit never had the problem because the fuses don't react to fan starting current.

Bitsyncmaster
09-26-2016, 04:44 PM
I went ahead and ordered new circuit boards which will arrive in about 4 weeks. I plan to make up 10 units and mesure the accuracy using the op-amps that are available now. I was just looking for the best accuracy but susspect these now available parts will work fine.

FYI:
Three parts affect the accuracy of my measurement of the fan currents. First is the current sense resistor which is a 0.001 ohm 1%. Then is the op-amp gain which is specified as 1.5% on the now available part and 1% on the part not released yet. Then is the reference voltage for my analog to digital converter which is typical at 0.4% but specified to be within 2%.

There could also be some circuit board affects but those I can adjust for in software.

I could also make a calibration routine in my software if I find it necessary.

Bitsyncmaster
10-02-2016, 06:39 PM
While waiting for my new circuit boards, I set up a test using 20 amp ATC fuses to measure the time it took to pop at the following over loads.

; Fuse test, 20 amp fuse at 45 amps took 332 ms to pop
; Fuse test, 20 amp fuse at 40 amps took 470 ms to pop
; Fuse test, 20 amp fuse at 35 amps took 800 ms to pop
; Fuse test, 20 amp fuse at 30 amps took 9 seconds to pop

My new fan fail will follow the overloading time down to 35 amps but after that, above 20 amps will "pop" my electronic fuse.

Bitsyncmaster
10-28-2016, 11:11 AM
I was able to purchase the ICs I was waiting for from Texas instruments. Got my new circuit boards yesterday. Now I'm in the process of building up 10 units. But I had to order and inspection microscope to check my soldering on the little (SC70) op-amps.

Bitsyncmaster
10-31-2016, 01:42 PM
Got the first board set done and the results look better than I expected. I was concerned with accuracy since my new circuit has a 50 amp full scale current reading. The typical component tolerances are so much better than using the maximum specifications. With my software using calculated values for the currents I got the following with the first unit.

Low current flash on fan #1, 4.0 amps. No error on that one.
Low current flash on fan #2, 4.0 amps. No error on that one.

High current flash on fan #1, 18.3 amps. I wanted 18.0 amps.
High current flash on fan #2, 18.2 amps. I wanted 18.0 amps.

High current trip on fan #1, 20.4 amps. I wanted 20.0 amps.
High current trip on fan #2, 20.3 amps. I wanted 20.0 amps.

I'm waiting on my inspection microscope to finish up the other 9 board sets. I plan to average the readings on the 10 units to adjust the software for best current results.

Horsebox
10-31-2016, 03:15 PM
I love work like this [emoji1360]

The whole fan circuit seems to depend on the Otterstat working tho. Failed Otterstat >> no fans, no matter how robust Bitsyncmaster's systems are.

My Otterstat packed up a few weeks ago and I ended up boiling the coolant tank before I shut it off, even tho temp gauge was nowhere near the Red. A lot hinges on that $10 part [emoji15]

Bitsyncmaster
10-31-2016, 05:04 PM
I love work like this [emoji1360]

The whole fan circuit seems to depend on the Otterstat working tho. Failed Otterstat >> no fans, no matter how robust Bitsyncmaster's systems are.

My Otterstat packed up a few weeks ago and I ended up boiling the coolant tank before I shut it off, even tho temp gauge was nowhere near the Red. A lot hinges on that $10 part [emoji15]

Yes the otterstat and it's wiring are critical. I need to do some changed to my engine harness and I was thinking of changing those two wires with new pins.

Bitsyncmaster
11-05-2016, 06:46 PM
Got my microscope and am very pleased with the quality for $400. After the kids played with it, I inspected my boards and found two solder connections on those very small op-amps needing rework.

I tested four units and out of the 8 op-amps (two on each board) 5 were bad. So I installed two of the other manufactures op-amps I was using and those tested good and a little better accuracy then the "TI" parts. I have another 4 of the old ones and will replace the TI parts and test.

After having the high failures I don't trust how long the TI parts will work even if they test good. It may be the parts are getting overheated when I solder them on but I solder the old ones on the same way and non have failed.

My plan is to trash the TI parts and order the alternate parts.

Horsebox
11-05-2016, 08:09 PM
Yes the otterstat and it's wiring are critical. I need to do some changed to my engine harness and I was thinking of changing those two wires with new pins.

Definitely worth doing. My otterstat connectors were pretty much new but the otterstat itself had packed up. I proved it by removing it from the car and boiling it in a saucepan whilst it was connected to a DVM set to measure resistance. Open circuit all day long.

I think there is a lot to be said for running wires into the cabin and having a separate switch to manually override the otterstat in the event that the temp gauge starts increasing and the fans don't come on automatically.

Bitsyncmaster
11-25-2016, 08:27 AM
The op-amps I was using on the prototype all worked 100% replacing the 20 TI parts on the build of the first 10 units. I may have just got a bad lot of TI parts but now I don't think I will ever use those TI parts again.

Anyway, I kept the calculated current values because testing the lot of 10 units proved the accuracy was very good.

Here is the recorded current results of those first 10 units. I measured three currents, the 4 amp minimum current for fan fail flash, the 18 amp maximum current for fan fail flash and the 20 amps "fuse" trip current.

#1 pin 85 = 4.1, 18.1, 20.2
pin 86 = 4.1, 18.2, 20.1
#2 pin 85 = 4.1, 18.3, 20.4
pin 86 = 4.1, 18.1, 19.8
#3 pin 85 = 3.9, 17.9, 20.0
pin 86 = 3.9, 18.1, ??.?
#4 pin 85 = 4.0, 17.9, 19.9
pin 86 = 4.0, 18.1, 20.1
#5 pin 85 = 4.2, 18.2, 20.4
pin 86 = 4.0, 18.0, 19.9
#6 pin 85 = 4.1, 18.3, 20.4
pin 86 = 4.1, 18.2, 20.2
#7 pin 85 = 4.1, 18.1, 20.2
pin 86 = 4.2, 18.5, 20.4
#8 pin 85 = 3.9, 18.0, 20.1
pin 86 = 4.1, 18.3, 20.3
#9 pin 85 = 3.9, 18.0, 20.0
pin 86 = 3.9, 17.9, 19.8
#10 pin 85 = 4.0, 18.1, 20.1
pin 86 = 4.1, 18.2, 20.1

Voltage drop over each leg at 15 amps is 0.050 volts. Very little change in voltage drop after running the double 15 amp loads for 30 min. The current sensing value did not change at all after the 30 min. run.

Bitsyncmaster
03-06-2017, 07:23 AM
The relay ground failing is really a larger problem then I thought. It's not really something you can test with an ohmmeter. A marginal ground connection will show up when a current is drawing after that bad connection. The fan relay is at the end of that daisy chained ground buss so when the fan relay turns on current flows in the ground and a bad connection makes the ground voltage rise. Probably a good test is to have the AC running and to measure the voltage on the fan fail ground pin.

My electronic fused fan fail uses MOSFETs to turn each fan on and off and without a solid ground the gate voltage can be to low which overheats those MOSFETs.

The old fused fan fail did not have MOSFETs so if the ground was lost it only upset the fan fail light circuit. I dropped the fused unit but it did have that advantage. The fused jumpers also don't use the ground on the fan fail socket. I wonder if the OEM fan fail would fail with a bad ground.

So I may require using my electronic fused fan fail the user has to also install my front relay ground buss.