Tampa 928s

I have two 40 amp relays with common switched ground 86 via coolant sensor and switched common 12v feed 85 from the CE panel. I have a fuse tap with a 10 amp fuse that blew the fuse and damaged the tap. I don't have the specs but how much current should these be pulling?

jpitman2

Lost already here - you have two relays both fed from the same source of power, and both fired by the coolant sensor (which - level , or radiator temp sensor?)? Where does the fused tap come into the picture - is it the feed to the relay switched power? Where does that power go when the coolant sensor grounds? If it goes to something like fans that pull more than 10A, you would have to expect a 10A fuse to blow...
Or have I misread?
FWIW, my twin 11" SPAL fans are wired up :- std rad temp sensor fires std relay which runs LHS fan; the RHS fan has a relay powered from a fused lead from the engine bay hot point, and is fired by a tap off the LHS fan relay's output (other side grounded). IMHO the std fan relay shouldnt be asked to run both fans. IIRC each fan pulls around 10A, so I think I have 15A fuses on them.
jp 83 Euro S AT 54k.

smiffypr

Should be about 150 mA each.
Get your ohm meter across the 85 and 86 terminals.

Tampa 928s

This was the first time I ran the fans constantly to test my cooling theory. They were on for an hour when the fuse blew With a 10 amp it was way oversized now need to track down the cause, heat related or possible wire connection seems odd that the on time caused this. For the record the ground is on pin 86 power to 85 this just engages the solenoid when ground is provided by the sensor. Main power 30 and 87 are fused with a main power off of the power post. This happened after constant running of the fans been installed for over a year with out problems.

jpitman2

If you have bullet fuses, I would look at the relevant fuse for poor contact, and a high resistance. I killed 2 fuel pump relays in much less time that I expected, and on the last event actually saw a spark on the pump fuse out of the corner of my eye while playing with a relay jumper. I now have home made blade fuse adaptors in the high drain or critical fuse positions.
jp 83 Euro S AT 54k

Tampa 928s

My thought also cheap auto zone tap allowing for two fuses off of one connection. I found the relay and a life expectancy of 1 million on life min rated at 30 min on time. I will replace the tap with a blade and in line fuse and see what happens. To test the resistance 79 ohms I need to remove my S/C piping so I will do the easy part first.

Dave928S

The constant running may have overheated the relay(s), which can happen if the main contacts become a bit resistive, which cooks the actuating coil to give you a lower resistance/dead short 85/86 circuit. Smiffy's ohm check suggestion will give you the answer.

I've had similar strange things happen in plant rooms with contactors (big relays) controlling high start current motors ... where I had to use over rated contactors, and replace them often to get reliability. Motors are harder on relays than static resistive loads.

Tampa 928s

I am not sure on this but should not the Aux fan come on when the A/C switch is activated? I have read it comes on when the temp is high I need to to run when the A/C is pressed.
Mine does not, looking at the diagram it shows Thermo-switch from radiator and temperature regulator freon which I believe is connected to the Receiver Dryer provides the ground. One other switch is pre-resistance auxiliary fan I am not sure where this is located.

WallyP

The '86 triggers the fan with (among other things) refrigerant temp at the receiver/dryer. Not a good way, in my opinion. You can tap onto the compressor clutch lead to trigger your relays, so that the fan runs when the compressor is operating. If you use multiple triggers, such as compressor operation and coolant temp, you might want to use diodes on each trigger line to prevent feedback.

Alan

The two coils shoud be about 300mA as stated above.

The relays have almost nothing to do with the current to the fans. It depends on the fan specs not the relay specs. I'd expect your fans could take more than 10A (stock S4 fans have a 30A fuse each).

There is a big difference between these two things:

- Fuse body melts OR fuse terminals look burned (but fuse element still conducts)
- Fuse element blows

These are caused by quite different things.

- Fuse melts has nothing to do with excess current - ALWAYS A CONNECTION INTEGRITY ISSUE
- Fuse blows is always excess current (seems thats what you may have here)

- I suspect you need a bigger fuse - make sure the wiring is suitable for whatever fuse you put in.

Fuse ratings have a time constant - the same current for more time is more likely to blow the fuse
However the time constant is small here measured in seconds.

Measured in minutes/hours/months is degradation from running very close to the limit (which is actually typically higher than the actual rating).

This is due to - in the short team heating of the fuse element and in the longer term electro-migration of the fuse element.

Check the fan specs and install a fuse with a margin of at least 20% above that.

And lets remember: in the general case - heat gets you less current not more - heating the coils lowers coil currents... heating the relay contact lowers fan currents ... heating the fuse element lower fan currents... heating the fan motor windings lowers the fan currents... however none of these effects are very significant in the usual ranges - only near catastrophic failure do they change things very much...

Alan

Dave928S

Alan ... I read the original post as there being a 10A fuse for the coil circuits, and that was what was blowing. Obviously that should be ample for the approx 300ma load ... but it would seem there's an issue causing over current on that circuit. I was suggesting a relay coil, for whatever reason, being cooked and going short circuit or low resistance, and therefore over current, as the possible cause for the 10 amp coil circuit fuse blowing (I've had coils fried from arcing/overheating contacts within contactors).

I don't see any mention of the fuse he has for each fan, but in post #4 the OP says they are fused separately... "Main power 30 and 87 are fused with a main power off of the power post." after mentioning the other fuse which blew (10A) was "way oversized" (which it is for 300ma).

I would think, like you, that if he has a ten amp fuse for each fan that they would be marginal.

Maybe the OP should clarify.

Tampa 928s

Dave you are correct relay pins 85 & 86 used a 10 amp fuse it blew this is a common feed to both relays. I had a tap that allows for two fuses on one CE fuse connection. I found one fuse side open on the tap after replacing the fuse. I did a direct connection and it seems to be holding up after a 15 mile drive. The coils measured 80 ohms in spec. I am working on a solution to have the fans cycle and not stay on.
As for Alan I always learn something every time he chimes in.

Dave928S

I'm not quite following what you've done. You soldered in a double fuse on the CE? ... used one of those for both relays? ... fuse blew so you put a new one in, but not sure what you mean by 'found one side open", perhaps bad connection?? .... then don't get what you mean by "did a direct connection", does that mean you soldered a fuse inline?? Be interested to know what you did.

Nevertheless, as the coils are spec ohms it seems a bit of a mystery .. and I can't see why they should draw a combined current to blow the fuse, even with sustained running.

So do I ... he's an invaluable asset to this community.

Tampa 928s

This cheap add on "think Discount Auto" allows you to insert this into the fuse slot than add an addition fuse. I use this for my air/fuel gauge and Lm-3 and never had a problem. This prevents from having to wire into the C/E panel for non factory devises. Once I ran my fans all the time the two fan relays which share the 10 amp fuse blew. The original fuse 5 amps for the factory circuit was not effected although connected to this same device. What I found was the it opened up the fan relays circuit 1 of two on this device only. This would indicate a high current surge but I am going with a failure due to the cheap nature of this product. It is rated for 10 amps so 5-amps for the factory fuse 10 amps for the primary relays pulling just over 1/2 amp so should be within the range of the device. This has been connected this way for a few years the only change was running the fans full time, both are located on the firewall and are subjected to high heat. So was it a failure of this tap or could it be the heat due to constant running under the high heat conditions?

Tampa 928s

Just looked up the specs 85 c equaled 185 degrees maybe on the high side of this relays operating range. I guess I need to test the heat after a long drive in traffic on the fire wall.