New Fan Fail relay

[Bitsyncmaster]

I've got one of my new REV C relays working and want to get any comments on the operation I have decided to program into the software.

I designed a new fan fail unit because I found the fuses and fuses holders were producing a lot of heat. The condition is more pronounced when running OEM high current fans. It does not seem to cause failures since a lot of users run my original fan fail with their OEM fans.

To reduce the heating, I designed solid state fuses within the unit. That circuit is a MOSFET and the driver circuitry on each fan output that I can turn on or off when my software detects an over current condition. If I had another pin available, this new fan fail could eliminate the fan relay by connecting that fan relay signal circuit to the fan fail unit. But I’ve found most owners do not want to do wiring changes to the stock harness.

I have eliminated the fan current compare failure. I decided to show a failure (flashing the fan fail light) for either fan drawing less than 4 amps or more than 15 amps. I have set the electronic fuse to open each fan circuit if 18 amps is exceeded. The electronic fuse is reset when power (the fan relay shuts power off) to the fan fail is removed. I set the stagger fan turn on to 2 seconds. Let me know if you can think of any reason to change those values I chose. As with the first unit, once they get potted, there is no way to reprogram the software. So sorry that I can not update older REV units to this new fuseless design.


The bad:

1) If you loose the ground connection on the fan fail sockets, your fans will turn off.
2) Higher cost, more components and more time to assemble.

The good:

1) Runs cooler. Should have no heat problems even running OEM fans..
2) Electronic fuses precisely cut off excessive current much faster than any fuse for the bad fan.
3) Can stagger the fans turning on. Not able to stagger turn off because power from fan relay cuts power to fans.
4) Less problems for me potting the units without the fuse sockets.
5) Single flashing sequence shows you one fan has a problem, less than 4 amps, (electronic fuse could be tripped) or more than 15 amps
6) Double flash sequence shows both fans have the problem shown in #5.
7) Works down to 8.8 volts from fan relay. If you have my LED AC panel, I turn the green fan running LED off below 8.8 volts.

[Morpheus]

I really love how you keep making improvements on your products, Dave!

Once I am done with my exhaust project, I will be sorting out my electrics. You will be hearing from me soon!

[SS Spoiler]

How come Houston hasn't hired you?

[BABIS]

great news! all the values seem to be very appropriate..

[Bitsyncmaster]

great news! all the values seem to be very appropriate..

Thanks for your thoughts. I chose 4 amps for the low value just in case someone develops a super efficient motor design. Our low current fans are now around 7 or 8 amps each.

OEM fans seem to run 9.5 to 13.5 amps each but my original fans were closer to 15 amps each. We want the fan fail light to give the owners an early warning of a fan nearing a problem so I figured to fuse the fans a little above the 15 amp warning light.

Two second fan on sequence should let the engine idle ECU recover from the alternator load easily.

[DMC5180]

I wonder if the, essentially continuous, running of the OEM high current fans is a contributing factor to heat being generated in the previous version as opposed to cycling with the A/C clutch.

[Bitsyncmaster]

I wonder if the, essentially continuous, running of the OEM high current fans is a contributing factor to heat being generated in the previous version as opposed to cycling with the A/C clutch.

On a hot summer day I don't think your AC will cycle anyway. I know mine will only cycle on a cool day if the sun is not shining.

But yes, running the fans or any electric loads will generate more heat in the relay compartment. It's just a matter of watts generated and the thermal conductance of the relay compartment.

[DMC5180]

Do I understand this correctly, This new multi-function FAN FAIL RELAY combines the stagger start and 20 second delay off features of your current FAN RELAY essentially eliminating the need for it?

[Bitsyncmaster]

Do I understand this correctly, This new multi-function FAN FAIL RELAY combines the stagger start and 20 second delay off features of your current FAN RELAY essentially eliminating the need for it?

It could do that if I had another pin (the fan relay signal pin) and the relays sockets were rewired. But as it stands now, the unit is plug and play and uses the fan relay to turn power on and off to the fan fail. So you can use a standard fan relay or my solid state fan relay. With my fan relay that adds the one second delay from the fan starting and holds the 20 seconds of running.

[DMC5180]

It could do that if I had another pin (the fan relay signal pin) and the relays sockets were rewired. But as it stands now, the unit is plug and play and uses the fan relay to turn power on and off to the fan fail. So you can use a standard fan relay or my solid state fan relay. With my fan relay that adds the one second delay from the fan starting and holds the 20 seconds of running.

I get it now, your FAN RELAY delays power to the FAN FAIL 1 second from when the A/C clutch engages. Your New FAN FAIL splits the delayed the power input between the fans with a 2 second stagger for both to be ON. Now you have a total of 3 seconds of transition time to full power load on the charging circuit.

[Bitsyncmaster]

I get it now, your FAN RELAY delays power to the FAN FAIL 1 second from when the A/C clutch engages. Your New FAN FAIL splits the delayed the power input between the fans with a 2 second stagger for both to be ON. Now you have a total of 3 seconds of transition time to full power load on the charging circuit.

That's correct.

[Bitsyncmaster]

Here are some photos of the new fan fail boards. I'm putting this first one into potting tonight so I can do the same testing for temperature and the same testing I did for fuse blow time with a shorted fan.

Note one MOSFET sits higher than the other because I ran out of board space and had to put an IC under that MOSFET.

[DMC5180]

What's the blob in the last photo?


Dennis

[Bitsyncmaster]

What's the blob in the last photo?


Dennis

There is a 1/4 amp PTC fuse that drives the fan fail lamp output under that blob of RTV. Since I pot the units, I coat it with RTV so it can expand and contract if it heats driving an incandescent bulb or someone short circuits the lamp wire.

[Bitsyncmaster]

Did a temperature test of the REV C and REV B at 30 amps (15 amps each fan) and results were almost the same.:what_the:

The hot unit voltage drop on the REV C is 0.0987 volts on one fan and 0.0931 volts on the other. The REV B hot unit drop is 0.1383 volts on one fan and 0.1395 volts on the other. So the REV C is producing less heat via the loads. Now the REV C draws 6 ma. more on it's internal 5 volt power but that would not produce that much heat.

Here is my thought. Since the REV B fuses are not potted into the unit, all that heat does not get into my measurement of temp of the unit.

Still more testing to do.

[davidc89]

I have no clue what you are talking about, but I am definitely interested on this topic. Keep up the good work!

[DMC5180]

I have no clue what you are talking about, but I am definitely interested on this topic. Keep up the good work!

Dave is working on a New cold fusion circuit for his fan fail relay.😜

[Bitsyncmaster]

I have no clue what you are talking about, but I am definitely interested on this topic. Keep up the good work!

It was my goal to reduce how hot the fan fail unit gets running high current (OEM) fans. I did reduce the power (total heat generated) but I did not take into account some of heat on the old fan fail unit was in the fuses and not getting transferred to the fan fail unit.

Old fan fail generates 4.17 watts of heat at 30 amps (15 amps each fan). Case temp peaks at 141.4 deg. F

New fan fail generates 2.88 watts of heat at 30 amps (15 amps each fan). Case temp peaks at 140.9 deg. F

Not that the unit running at those temps will make if fail since all my components are rated to work above 185 deg. F. But assuming that 64 deg rise above ambient, if the relay compartment is above 120 deg. F that would bring the unit close to that 185 rating with a worst case of 15 amps on each fan.

[Bitsyncmaster]

I tested the new and old units at 20 amps (10 amps each fan) and the new REV C peaked at 111.3 deg. F and the old peaked at 110.6 deg. F. I also ran the new one at 16 amps (8 amps each fan) which is the typical low power fan current. It peaked at 102.2 deg. F.

I tested the unit in my car and made up a shorting plug to install into the harness at the fan connector.

Passenger side pumped 125 amps for 14.5 ms.
Drivers side pumped 125 amps for 15.0 ms.

So as expected my solid state fuses are much faster than a standard fuse. They are also precise for the tripping. They will trip in well under one second at 18.2 amps.

The fan on sequence was just a "freebee" since I had to install MOSFETs for the solid state fuses.

I will be driving to a tech session in a few weeks and that 6 hours of driving will show bugs if there are any bugs in the "fan fail" light. I did not put any filters in the software for fan fail light driving but the current sensors have a pretty large capacitor filter on them. I have Toby fans in my car.

It's a shame I did not get them to run cooler. I could get a little cooler if I go with 4 oz. copper on the circuit boards but that may never get done.

[Bitsyncmaster]

I installed a parallel jumper on the longest circuit board trace to reduce power (heat). What generates heat is the resistance of my current sensor (1.2 mil/ohm), MOSFET (1.0 mil/ohm) and the circuit board traces.

So now the old REV B board generates 4.185 watts of heat and the new REV C board generates 2.43 watts of heat if each fan is drawing 15 amps (probably worst case). The potted side of the REV B unit stabilizes at 62.1 deg F above ambient. The potted side of the REV C unit stabilizes at 63.6 deg F above ambient. This just proves the fuses are dissipating a lot of heat and not transferring a lot of that heat into the unit.

I'm going to start offering the REV C units for sale at $20 above the price of REV B units to cover the cost of the additional components. I've run the first unit for 6 hours driving my car with Toby fans. Only thing in question is if the other fans may produce more noise and may cause a random fan fail light flash. I hardware filtered the current sensors pretty heavy and have not added any software filtering.

So the REV C units:
1) Produce less heat
2) Are not user programmable
3) Have fixed 18 amp electronic fuses
4) Will sequence the fans turning on with a 2 second delay on the second fan.

[Bitsyncmaster]

I forgot to add the circuit power to the load power on my heat calculations.

REV B heat = 4.54 watts.

REV C heat = 2.88 watts.

Just wanted to have accurate documentation for any future testing. The REV C draws a little more circuit power for the additional components.

[iflights]

I've got the OEM fan motors. From the outside they are in excellent physical condition, compared to what I've seen in other photos. Both are working, no immediate need to replace I would assume, given some competing repair opportunities.

But I would like to get the jumpers and inline fuses out of the relay area and replace with some proper device.

Should I wait on ordering your recent REV until your testing is complete, or will the previous REV be fine?

[Bitsyncmaster]

I've got the OEM fan motors. From the outside they are in excellent physical condition, compared to what I've seen in other photos. Both are working, no immediate need to replace I would assume, given some competing repair opportunities.

But I would like to get the jumpers and inline fuses out of the relay area and replace with some proper device.

Should I wait on ordering your recent REV until your testing is complete, or will the previous REV be fine?

I've finished testing with my car running Toby fans. I just painted 5 of the new REV C units today. The new unit and old unit will run about the same temperature with the same loads. I have both units for sale. The new REV C produces less heat since the external fuses are not used and it will sequence your fans on. I still need to document the new unit on my web site.

[iflights]

I've finished testing with my car running Toby fans. I just painted 5 of the new REV C units today. The new unit and old unit will run about the same temperature with the same loads. I have both units for sale. The new REV C produces less heat since the external fuses are not used and it will sequence your fans on. I still need to document the new unit on my web site.

Thanks. I have your email address and will paypal you tomorrow.

[Morpheus]

Dave, are the prices for your products on your website? I can't seem to find them.

I'm definitely interested in a few of your items.

[Bitsyncmaster]

Dave, are the prices for your products on your website? I can't seem to find them.

I'm definitely interested in a few of your items.

I have not set up buying on my web site. Just email or PM me to buy.

Fan Fail, $94
Electronic fused Fan Fail, $114
Dome unit, $88
RPM relay, $83 with your old unit
Fan relay, $77
Blower relay, $72
Head Light relay, $72
Hot Start relay, $66
Pair of window switch LED boards, $20, $25 installed, requires the new DMCH switches.
Idle ECU, $138 with your old unit. I have 11 pin units also for $150 with your 9 pin unit returned.
LED AC panel, $110. Your choice of blue or green backlighting.
Front Relay Bank Ground Buss, $15. $10 if combined with another product.

Prices include shipping to lower 48 states

[Bitsyncmaster]

Got my first order for the new "ELECTRONICALLY FUSED FAN FAIL UNIT".

So had to do a quick write up of installation. Boy this guide is simple since the new unit is not user programmable.

Only problem would be testing that your fan fail light is working. Old unit you just removed a fuse. New unit you will have to pull one of the fan connectors (near the fans) off to verify your fan fail light is working. If you have my LED AC panel board you know the connection is there seeing the fan on indicator LED lights.

[BABIS]

I am longing to install this new unit in my car ;)

[Bitsyncmaster]

I've decided to stop sales of my electronically fused fan fail unit. I designed this unit because the fuses produced so much heat when an owner was still using OEM fans. But after many sales it turns out the fan start and run currents are just so unpredictable that I can not guarantee all users will be happy with the unit.

I have not decided if I will produce a fused unit again. I could produce a cheap fused unit with a simple circuit to drive the fan fail light if a fuse blows.

[Bitsyncmaster]

I've been giving the fan fail a lot of thought. The problem with checking low current is it shows problems with marginal connections which most users don't have the ability to fix. The OEM fans do have high current problems but again the users don't know this because the 20 amp fuses don't blow. The 20 amp fuse takes 12 seconds to blow with 30 amps of current. Then currents less than 30 amps can still work for up to an hour without blowing the fuse.

So my thought now is to go back to using fuses. I will flash the fan fail if the load side of a fuse drops below 10 volts. I will also keep my fan on driver (-5 volts) when the fans are powered so my AC LED board will still light the fan running LED. This saves me a lot of components and built time so I should be able to offer these at a lower price than the units that did test fan currents.

[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.

[Bitsyncmaster]

I ran the same test with my external sensor attached to the cooler side (away from the power in pin "40 amps"). As expected that side did not heat very fast. The temp stabilized at 59 deg. C in the same 15 minuets. I was expecting this side to keep heating for a longer time.

So my internal temp sensor is probably accurate with the designed value put back into my software.

I ordered some thermally conductive potting epoxy and will post that result when I get one built with that. But I'm wondering if that will gain anything as far as better results. I'm guessing it will reduce the high side temp and increase the low side temp. So not sure what that buys me.

[DMC-81]

Hmm. I wonder if you can incorporate a mini Peltier plate (TEC- thermoelectric cooler) into the relay to keep temps down?

https://www.kitsandsets.com/set-of-5-peltier-cooler-thermoelectric-coolers-module-device-cell-12v-200010.html

(I'm just spitballing...not sure if this is a valid use of these or how long they last)

[Bitsyncmaster]

Hmm. I wonder if you can incorporate a mini Peltier plate (TEC- thermoelectric cooler) into the relay to keep temps down?

https://www.kitsandsets.com/set-of-5-peltier-cooler-thermoelectric-coolers-module-device-cell-12v-200010.html

(I'm just spitballing...not sure if this is a valid use of these or how long they last)

I played with one of those when they first came out. It's just a heat pump (much less efficient than a compressor). Takes a lot of current to run it.

I'm thinking my unit will be fine running that hot but remember most owners their OEM fans run 15 amps or less and low current fans run around 8 amps each.

[DMC-81]

I played with one of those when they first came out. It's just a heat pump (much less efficient than a compressor). Takes a lot of current to run it.

I'm thinking my unit will be fine running that hot but remember most owners their OEM fans run 15 amps or less and low current fans run around 8 amps each.

Cool. Now I’m curious about what amperage my fans are running at. I’ll measure this weekend.

[Bitsyncmaster]

Cool. Now I’m curious about what amperage my fans are running at. I’ll measure this weekend.


It's a good thing to check. Best to use a clamp on DC current meter that you just clip over the jumper wire. Make sure your engine is running.

FYI

My friend had his fused jumper catch fire and I tested his fan current before I installed a set of low power fans. His fans each showed about 14 amps. of current but only one fused wire showed the damage.

[Bitsyncmaster]

I got my thermal conductive epoxy today. This epoxy has a filler and is really messy to prepare since you have to mix each jar (the filler settles). It's also much thicker than my T88 epoxy. Anyway I did get the center of a new unit filled with it and will fill the top of the unit tomorrow. Not sure if I can work with this stuff. It also cost twice what the T88 cost. I will try heating it to see if it works better filling the top.

Anyway I was thinking maybe the T88 would be better since it keeps the high heat on one side and my one component rated at 85 C is on the cool side. My internal temp sensor is also on the cool side. I did keep the sensor set for 85 C.

[Bitsyncmaster]

I poured the top side today with the new epoxy. I found heating the epoxy to 115 deg F made it thin enough to pour. It's still more work than the T88. My testing when it all hardens will convince me if I will use the new or old epoxy for production units.

I could also add a metal plate on the hot side (heat sink) but I'm trying to keep my cost and build times down. I don't think the unit will overheat with normal fan currents without the heat sink.

[Bitsyncmaster]

I'm still waiting for the new epoxy top to harden so I went back to the old epoxy unit and finished the testing on the cold side.

At 40 amps, 20 amps each fan the cold side peaked at 59.8 deg. C.

At 30 amps, 15 amps each fan the cold side peaked at 43.4 deg. C

At 20 amps, 10 amps each fan the cold side peaked at 30.4 deg. C

All those test are done at 70 deg F room temp so I'm guessing if your relay compartment is 100 deg. F then my test values would be 17 deg. C higher. So I'm guessing I would flash an over temp warning if your fans are drawing above 35 amps to 40 amps with the relay compartment covered.

[Bitsyncmaster]

Ran the test on the new thermal conductive epoxy at 40 amps. As I expected the cold side temp was higher. It peaked at 73.7 deg C where as the old epoxy peaked at 59.8 deg C.

So I expect the hot side testing will run cooler about the same difference.

Now it did take longer to stabilize, taking 26 min. where as the old epoxy only took 19 min.

I moved the sensor to the hot side and will test that later after the glue dries.

[Bitsyncmaster]

I ran the 40 amp test on the hot side with the new thermal conducting epoxy. To my surprise it ran just about as hot as the T88 epoxy test ran. The new test heat peaked at 90.9 deg. C and the old test it peaked at 91.0 deg. C.

I don't know how to explain that result. Only thing I can think of is the thermal epoxy is less effective dissipating from the surface area to the air. Unless something in my testing introduced some error.

So with that result I will use T88 epoxy in production units since that will keep may one 85 deg. C rated component cooler.

[Bitsyncmaster]

The new fused fan fail unit is now ready for sale. I did a bench test with two OEM fans and a static car test in my car with Toby fans. My car is still down waiting for a new clutch so no driving testing yet. Fans get directly powered via a 20 amp fuse on each fan so the only thing I was really testing is that the fan fail light worked without any glitch.

I have four units with the paint dry now but I had promised 3 of those to customers. I will paint another four today and have started another build of 10.

I've priced the unit at $84 including USA shipping. By the way USPS just increased prices again.

I've updated my web site. I have not removed the electronic fused NLA info yet in case some users still need the instructions.

History:
Revision A fused fan fails running 40 amps. (20 amps each fan) dissipate 9.68 watts.
Revision K fused fan fails running 40 amps. (20 amps each fan) dissipate 5.45 watts.
Revision I electronic fused fan fails running 39 amps. (19.5 amps each fan) dissipate 2.58 watts. Had to drop the test current since these fuse at 20 amps.

So you can see why I tried to use electronic fused fan fails but each owner's fans are so different it just caused to many problems. Now no one should keep running fans that draw 40 amps of power because the stock wiring is just not designed for that current.

[Bitsyncmaster]

I ran a temperature test on my latest fan fail unit (REV M). My "hot plate" maxed out at 200 deg. F but the air temp maxed out at 171 deg. F. So I was running 10 amps through each fan output and after 15 minuets it flashed the overheat (three flash sequence). I shut of the hot plate and 7 minutes later the overheat warning shut off, air temp was 147 deg. F.

My temp sensor is rated at one deg. C accuracy and software turns the overtemp warning on at 85 deg. C and above.

One thing some customers are getting is a double flash which indicates both fans have 10 volts or less on the outputs to the fans. Some are confusing this as the overtemp warning but it's a warning of a connection problem that the fan fail is getting 10 volts or less on the input power. It could also indicate both fuses have blown but everyone says both fan are running.

Now due to the fuse generating heat if your fans draw more than 10 amps each the overheat warning will come on at a lower fuse box temperature. I can run that test later with 15 amps each which is what the OEM fans can run at.

I plan to order some heat sinks for my test bed so it brings the air temp up closer to the hot plate temperature.

I can load test now any relay up to 60 amps. I run a fan on my resistor loads when doing extended high current testing.

[Bitsyncmaster]

I tested another REV M fan fail.

I got a massive heat sink to sit on my hot plate. It still only brought the air temp up to 180 deg. F (82 deg. C). That is still a little shy of my 85 deg.C trigger and the overtemp did not kick on till I ran 10 amps on each fan load for 11 min. Now it did cool down a lot slower and the overtemp turned off at 156 deg. F.

I was just thinking what could be different in that temp testing as seen in the relay compartment. I thought of one thing in that the wires going to fan fail socket are only a few inches long in the heat box so maybe some heat is dissipated though the wires exiting the box. Also the fan fail unit is upside down but I would think that would be worse testing since the fuses are what generate the most heat and heat rises.

I'm thinking the turn off temp is the point that you may get a fan fail overtemp warning after a very long drive with the AC on.

[Bitsyncmaster]

I mounted a vertical plate on my heat sink so I could bolt the relay test socket pointing up an leave 12 inches of the wiring to that socket in my heat box. Big change in that the overheating fan fail would not shut off the warning until the air temp dropped to 131 deg. F. I'm assuming with my first tests the fact the wiring was exiting the box very near the socket made a heat sink removing heat from the fan fail unit. Now my test closely resembles what the unit sees in the DeLorean fuse box.

My hot plate maxed out at 207 deg. F
The air temp at that max was 190 deg. F Still did not turn on my overheat warning.
Turned on the dual 10 amp loads and the overheat warning came on in 60 seconds at 192 deg. F air temp.
Overheat stayed flashing until the air temp dropped to 131 deg. F

Note it took my hot plate 2 hours and 15 minuets to reach the max temp so the fan fail must have been very close to the 190 deg. F air temp.

I think I can improve my hot plate by placing some insulator under the top plate so the box with the electronics does not heatup the same as the hot plate. I'm thinking that will speed up the heating and also increase the max temp.

[Bitsyncmaster]

Well I got a customers returned fan fail that was giving him the overheat warning. After much testing I did find it overheating so I measured the voltage drop. One "fan" was dropping over 3 times the normal drop and the other was 2 times the normal. All I did was pull the fuses and stick them back in and both drops when to normal.

So his unit was dissipating 4.2 watts and the normal is 1.7 watts with 10 amps load on each output.

I modified my "heat box" test setup and it's working much improved now. I tested the trip value of that customers fan fail and it was 186 deg. F good and 187 deg. F was an overheat warning so the sensor is pretty close to 1 deg C accuracy which I set for 85 deg. C I also learned I need to let the unit "heat soak" so the fan fail unit gets to the air temp reading. My hot plate runs about 10 deg. F higher than the air temp in my insulated box which I read with a thermocouple.

So if your getting an overheat warning with my fan fail. Pull and re-seat the fuses.

[Bitsyncmaster]

So this peaked my interest in fuses. It's not just my fan fail but we have seen other overheating of fuses in our fuse block and the fused fan fail jumpers. I see I can order fuses that are silver plated rated to 125 deg. C where as the zinc plated are rated at 105 deg. C. I can't see why the plating would change much with the operation of the fuse. Yes silver is the best electrical conductor but the plating would be so thin I can't see how that would change anything.

I will order some silver plated fuses and do some testing. All I can think of testing is to measure voltage drop with multiple remove and insert into the fuse holder for repeatable voltage drop. Maybe all our fuse block fuses would benefit from silver plated fuses.

[mhanch]

Dang. That's an interesting question. it would be nice to do something like that to offer just an extra bit of protection.

[David T]

Besides zinc not being as good a conductor as silver, zinc can develop an oxide layer that impedes electrical conductivity, silver's oxide doesn't do that as much. Especially under high heat. Gold is an even better conductor and it doesn't develop an oxide at "normal" temperatures. That is why you see gold plated contacts in computers and aerospace devices. Too bad it is so expensive! A fuse that is handling too much current fails prematurely. That is why you are supposed to use only 80% of it's rated current carrying capacity in continuous applications. Fuses are intentionally designed to not be able to dissipate heat (energy). That energy is what causes it to fail like it is supposed to. If a fuse is in a hot place (high ambient temperature) you are supposed to derate it. Just like wire and insulation. If they are in a hot area they cannot carry the full rated current and must be oversized or derated.

[Bitsyncmaster]

Silver plating gives the best contact resistance. I guess that is why the silver plated fuses are rated to a higher temperature.

I'm doing a test moving my temperature sensor from the middle of the top circuit board (right between the fuses) to under the microprocessor which brings it closer to the two components on the bottom board rated to 85 deg. C. The top board components are all rated to 125 deg. C.

[Chris 16409]

Dave how about using gold plated fuses?

[Bitsyncmaster]

Dave how about using gold plated fuses?

I did some testing of the silver plated fuses and did not find any advantage with the testing. Actually the voltage drop was a little higher but I'm assuming voltage drop is just a matter of the lot of when the fuses were made. I did some reading on silver plating and it seems it reduces contact resistance. Since I did have one customer return his overheating fan fail unit and it did turn out to be the contact resistance (removing the fuse and reinstalling it) fixed the problem, I think I will start shipping the fan fail units with silver plated fuses.

The part number marked on the fuses is the same and the only difference I saw is the "20" amp number is underscored on the non-silver fuses. Not sure if that is how they mark them of just a manufacturing change.

Gold has the advantage of not growing a tarnish which could help with aging. But you still have the sockets not gold plated. It looks like the audio customers are the only ones thinking gold provides better audio results. They do use gold plating on circuit board edge connectors but those are not really high current circuits.