Dodgy otter switch?
Discussion
Got home tonight and ran the engine up again 
Engine gets up to temperature, and the fans cut in perfectly.
Engine cools and I assume all is well.
A couple of minutes later, I'm aware that the engine temperature has soared, the fans haven't cut in and there's water pouring from the header tank overflow.
Checked the fuse for the fans, and it's blown (30 Amps).
Change the fuse and the fans cut back in again, but the next 'cycle' around, they don't cut back in.
What temeprature is the standard otter switch set to come in at?
Also, where can I get a replacement? I currently have the headlight pod out, and I'm thinking it might be a good idea to change it now whilst I can.
Engine gets up to temperature, and the fans cut in perfectly.
Engine cools and I assume all is well.
A couple of minutes later, I'm aware that the engine temperature has soared, the fans haven't cut in and there's water pouring from the header tank overflow.
Checked the fuse for the fans, and it's blown (30 Amps).
Change the fuse and the fans cut back in again, but the next 'cycle' around, they don't cut back in.
What temeprature is the standard otter switch set to come in at?
Also, where can I get a replacement? I currently have the headlight pod out, and I'm thinking it might be a good idea to change it now whilst I can.
Number 7 said:
It could be that the fan motor is starting to go, causing the fuse to blow - I had one on a 350i once that completely seized due to internal corrosion. See if it spins easily by hand (you should be able to get your fingers on it to spin it).
I've just fitted these fans. They were - admittedly, off a scrap car (Audi 80 Tdi) but were in great condition, and span freely by hand and worked superbly on the bench.I'm now thinking that they may be pulling more than 30 Amps (the rated fuse which blew) on start up.
I'll get a multimeter on it tomorrow and see how many amps they're actually pulling.
I'll probably whack a 35 or a 40 Amp fuse in there.
voltage_maxx said:
I've just fitted these fans...
I'm now thinking that they may be pulling more than 30 Amps (the rated fuse which blew) on start up...
I'll get a multimeter on it tomorrow and see how many amps they're actually pulling...
That'll have to be a hell of a multimeter; most are only good for 10A...I'm now thinking that they may be pulling more than 30 Amps (the rated fuse which blew) on start up...
I'll get a multimeter on it tomorrow and see how many amps they're actually pulling...
You could measure the winding resistance with the multimeter - half an ohm equates to 28A, 0.4 and it's 33A. (At such low resistances make sure you measure the multimeter leads too) When they start spinning you get back e.m.f and the current drops.
If you find it's too low how about doing a staggered startup - e.g. use 2 relays and delay one of them a few seconds (or from a second thermostat). Also 2 relays might be needed anyway depending on your relay rating. Just thought too - if you slave the second relay off the first one (so the output of the first relay drives the coil of the second) then that might give a natural delay until the first fan spins up a bit.
If you find it's too low how about doing a staggered startup - e.g. use 2 relays and delay one of them a few seconds (or from a second thermostat). Also 2 relays might be needed anyway depending on your relay rating. Just thought too - if you slave the second relay off the first one (so the output of the first relay drives the coil of the second) then that might give a natural delay until the first fan spins up a bit.
Edited by adam quantrill on Friday 5th July 08:18
Agree with Adam re the relay setup... this is a bit like my set up for twin fans on my 500. I have made a circuit with manual over ride with a switch as awell as an indicator LED to tell me that the fans are running in auto mode (yellow) i.e. coming on and off and manual overide (red) to remind me its on!
My fans were rated at 30A each at 100% duty cycle but they would fire th fuses from time to time. When I measured with a good quality amp meter at turn on they were drawing 32A each so up rated to 35A fuses and the jobs a good un!
Picture tells a thousand words!
My fans were rated at 30A each at 100% duty cycle but they would fire th fuses from time to time. When I measured with a good quality amp meter at turn on they were drawing 32A each so up rated to 35A fuses and the jobs a good un!
Picture tells a thousand words!
Well, got the multimeter on the job (big old AVO meter), and sure enough there was a massive inrush current on start up which peaked at around 40Amps.
It then settled down to about 15Amps.
I've simply bunged a 40Amp fuse in to accomodate for the inrush current.
If the constant draw had been 40Amps I might have thought about putting a relay in.
I've had the fan cycling in and out mutliple times now without problem
It then settled down to about 15Amps.
I've simply bunged a 40Amp fuse in to accomodate for the inrush current.
If the constant draw had been 40Amps I might have thought about putting a relay in.
I've had the fan cycling in and out mutliple times now without problem
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