New Fan Fail relay

[dmcnc]

Sounds like a good compromise. Thank you for working around our Fan issues Dave!

[Bitsyncmaster]

I've been working on the new fan fail unit. I thought of another warning flash I can do for those owners that insist on using OEM fans. From the many melted fused jumpers some owners have found, it can't just be bad connections on all those fuses, but just proves my thought that OEM fans can draw close to 20 amps each. A 20 amp fuse can still work for a long time even running 25 amps through it.

Anyway my thought is to put a temperature measuring device inside my unit and warn the user via the fan fail light if my unit gets to hot. What the user should do then is remove the cover from the relay compartment until he has a chance to replace the fans with low current units.

I will do a short flash of the fan fail light one time a second if one fan voltage is below 10 volts (fuse has blown). A double flash one time a second when both fans are below 10 volts (both fuses blown). And a triple flash one time a second if the unit is overheating.

The new unit uses regular 20 amp fuses so I have no control of turning the fans on or off. Hence no power on sequence like my electronic fused unit did.

[DMC-81]

I've been working on the new fan fail unit. I thought of another warning flash I can do for those owners that insist on using OEM fans. From the many melted fused jumpers some owners have found, it can't just be bad connections on all those fuses, but just proves my thought that OEM fans can draw close to 20 amps each. A 20 amp fuse can still work for a long time even running 25 amps through it.

Anyway my thought is to put a temperature measuring device inside my unit and warn the user via the fan fail light if my unit gets to hot. What the user should do then is remove the cover from the relay compartment until he has a chance to replace the fans with low current units.

I will do a short flash of the fan fail light one time a second if one fan voltage is below 10 volts (fuse has blown). A double flash one time a second when both fans are below 10 volts (both fuses blown). And a triple flash one time a second if the unit is overheating.

The new unit uses regular 20 amp fuses so I have no control of turning the fans on or off. Hence no power on sequence like my electronic fused unit did.

I like this idea Dave. It's too bad that you can't do the sequencing as well. Drat!

As an owner with OEM fans and still running the fuse jumpers, I might put this new version on my short list. I've already been following this thread.

Thanks for all your insightful work! I really like my solid state RPM relay.

[Bitsyncmaster]

I like this idea Dave. It's too bad that you can't do the sequencing as well. Drat!

As an owner with OEM fans and still running the fuse jumpers, I might put this new version on my short list. I've already been following this thread.

Thanks for all your insightful work! I really like my solid state RPM relay.

The unit will sell for less money than previously. Saves me a lot of components not measuring currents. Still time consuming potting the units since it's a two step process.

[BladeBronson]

Anyway my thought is to put a temperature measuring device inside my unit and warn the user via the fan fail light if my unit gets to hot. What the user should do then is remove the cover from the relay compartment until he has a chance to replace the fans with low current units.

Couldn’t you just add a fan to your fan fail relay to keep it cool?

[Bitsyncmaster]

Couldn’t you just add a fan to your fan fail relay to keep it cool?

It's just the heat produced by the fuses, fuse sockets and little by the traces to those components. My electronics inside the unit only draw a few milliamps of current. I have to do a lot of testing when I get my first unit finished as to how much heat those fuses produce at the ambient temps inside the relay compartment. I had tested my relay compartment heat on a long drive and it only got to 95 deg. F but I'm guessing mine runs a lot cooler since I have all sold state relays.

[Bitsyncmaster]

I've built one unit. This unit has a connector in it so I can modify the software. The unit is potted so I can do temperature testing.
My unit has one component rated at 85 deg. C and most other components are rated to 125 deg. C. Fuses are rated to 105 deg. C.

So right now I plan to set my overtemp warning to around 85 deg. C but I need to test if anything like my potting will fail at or below that temp.

I have finished the software. I set the warning flash to 300 ms. on, 300 ms. off and 2 second off between the flash code. That seems to result in the easiest timing for the user to read the flash code. Software checks each failure twice (again after 500 ms. delay) to filter any noise from an erroneous flash error. I need to have the software tested before I start producing these units because I'm not able to change software after it is potted.

My first test will heat the unit in water to verify my sensor flashes at 85 deg. C.

My next testing will be how hot the unit gets with 15 and 20 amp fan currents for long time runs. That test will be at room temp. I'm assuming if your relay compartment is 100 deg F and my room temp at 70 deg. F testing your result will be 30 deg. higher for the unit test. Now I may find a way to test the unit at elevated room temps.

[Bitsyncmaster]

I glued a thermocouple to one side of my fan fail and ran a test driving 40 amps (20 amps each fan). The unit heated up to 91 deg. C in about 15 minutes and stabilized at that temp with the room temp at 72 deg. F. My internal temp sensor needed an 11 deg C lower setting than theory than expected. The sensor specs say 2 deg. C typical accuracy with 6 deg C max error. So I have to find out why I have that large error. I'm thinking the internal sensor is in a cooler location than where I mounted my external sensor.

So I will move my external sensor and try testing again.

Nothing looks like any damage running at 91 deg. C (you would not want to touch the unit at that temp). I may also try testing higher temps until something fails.

[DMC-81]

I glued a thermocouple to one side of my fan fail and ran a test driving 40 amps (20 amps each fan). The unit heated up to 91 deg. C in about 15 minutes and stabilized at that temp with the room temp at 72 deg. F. My internal temp sensor needed an 11 deg C lower setting than theory than expected. The sensor specs say 2 deg. C typical accuracy with 6 deg C max error. So I have to find out why I have that large error. I'm thinking the internal sensor is in a cooler location than where I mounted my external sensor.

So I will move my external sensor and try testing again.

Nothing looks like any damage running at 91 deg. C (you would not want to touch the unit at that temp). I may also try testing higher temps until something fails.

Interesting. Dave, is 91 Degrees Celsius (196 Degrees F ?) a relatively normal temperature for any version of a fan fail relay? I'm thinking if they tend to run hot because of the fuses, would it make sense to incorporate some kind of Heat Sink in the unit.... or would that mask potential problems elsewhere?

[Bitsyncmaster]

Interesting. Dave, is 91 Degrees Celsius (196 Degrees F ?) a relatively normal temperature for any version of a fan fail relay? I'm thinking if they tend to run hot because of the fuses, would it make sense to incorporate some kind of Heat Sink in the unit.... or would that mask potential problems elsewhere?

Heat is mostly produced by the fuses which run 3.38 milliohm cold. As the fuse heats the resistance increases. The wiring to the fuses and the fuse socket also add a little heat as do the "relay" socket pins and wires. The wiring was never intended to run 20 amp fan currents each.

I think my epoxy is not good enough thermally for conducting the heat. I moved my external heat sensor from the hottest side (where the power pin "40 amps") enters the unit to the opposite side (where my internal sensor and micro is). When the glue dries I will test again and that will tell me if the T88 epoxy needs to be changed. My testing is done with 40 amps right now to get the unit to heat quickly, if your fans are drawing that much current you need to replace them.

I'm guessing my unit will remain under 85 C if your fans are under 15 amps each. Defiantly should have no problems with low power fans.

Yes the 91 deg. C temps I was getting is 196 deg F. I don't usually use C but since most component specifications are listed in C I decided to stay with C.