Why does my rad fan fuse keep blowing?

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Lucky
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Why does my rad fan fuse keep blowing?

Post by Lucky » Mon Aug 03, 2015 8:37 pm

Help!

I'm hoping for some wisdom from anyone who knows more than me about vehicle electrics... and believe me, that's pretty much everyone :oops: So with this admission in mind, please work from the premise it's not possible to patronise me too much :lol:

Right, specifically, I have a problem with the electric radiator fan conversion on my FB. As you know, the car originally came with a viscous fan, which has now been deleted. I bought a Kenlowe full kit to replace it because it seemed an all-in-one solution, but with one thing or another it's been an endless PITA. First off, the little control box/thermostat thing blew up almost as soon as it was installed, so we fitted a replacement. This seemed to work fine for a few months, but the car overheated a couple of times because the fan would intermittently stop running and this was traced to what appeared to be a faulty relay... if you pushed down on the top of the relay it would fire, but as soon as pressure was released on the plastic case, it cut out again. I replaced the relay, and it worked OK for a few weeks before the same problem repeated itself. Then the new control box fried itself; not in a "it went bang" way like the first one, but more annoyingly in an intermittent way.

Soooooo, we sacked off the entire Kenlowe control box/temperature probe setup and fitted a solid-state thermo-switch into the waterpump housing. It's from a Nissan Micra, oddly, simply because it had the correct m16x1.5 thread and the right temperature range; on at 90 and off at 85 degrees. This seemed to work fine, except now the fuse blows instead. Not all the time, annoyingly. Only when it gets hot :roll: . It's a 25 amp fuse, and I tentatively tried a 30 amp but that blew as well. The irritating thing is, if you bridge the two thermo-switch wires together, the fan will come on and run happily, seemingly as many times as you want. It's only when in the stress situation of long-term stop-start traffic jams (the M25 is a good one) that at some point the fuse blows and the only way I can tell is that the temperature gauge just keeps climbing


so, if anyone's still reading, the wiring goes like this;

switched live to relay 85 terminal (from ignition feed to coils)
+12v direct feed to relay 30 terminal from battery terminal
thermo-switch goes to earth and to the relay 86 terminal
relay terminal 87 goes to the fan motor, and the fan to earth


this leaves me a few variables to ask about;

The relay has the same ratings as the one that came with the fan kit. I kinda understand (a bit) how a relay works; it basically throws when it detects demand so that it feeds battery rather than stepped-down circuit voltage to whatever it's connected to (i.e. the fan). But what effect does the amperage rating on the relay have? This one is a 40 amp, which seems quite rare compared to the common-as-muck 30 amp ones. Surely its purpose is to regulate power, not current, so why the different amp ratings? Surely the fan will draw as much current as it needs irrespective of what the relay "thinks" it should? Is this the problem, should I drop the amp rating on the relay?

Is it the fan that's the problem? Is it a case that when it's all hot, it sooner or later draws a sudden current spike at switch-on point, before the relay can actuate and this blows the fuse? If so, how can you avoid this? Or is it simply faulty? Note that I've never got it to blow the fuse when cold, no matter how many times I fired it

Because the original Kenlowe probe is no longer in the circuit, but the gubbins (fuse, relay and wiring) are all still in the location that it was originally mounted in, there is a really long run of wiring involved... basically it ruins from top/middle of the engine where the waterpump/thermoswitch is, across to the nearside where the battery mounts, then down in front of the radiator along the crossmember to end up on the offside radiator mount. Will all this length of wire have an adverse effect? Also, presumably you want the fuse as near as possible to the battery, also?

Is the thermo-switch the problem? It runs without even a relay on the Micra circuit, far as I can tell, so it's obviously intended to switch some manly voltage... but is this too much for my setup?

Could it be as obvious as am intermittent wiring fault... a chafed bit of insulation or dry joint in a connector somewhere that only shorts when heat and vibration are introduced?



Sorry for the million stupid questions, but I'm running out of ideas with my feeble knowledge of electrics. I've decided to replace the entire wiring setup and try to make it a bit more... well, organised and shorter... in the hope changing the cheap stuff is a better start than the expensive stuff (i.e. the fan) but it'd be annoying to do all that faffing about only to keep the same problem.

Help!

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DKWW2000
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Re: Why does my rad fan fuse keep blowing?

Post by DKWW2000 » Mon Aug 03, 2015 9:12 pm

The best way of working out what amp rating the relay should be is quite simple, Wattage of Fan (EG 108) divided by Voltage (12) = 9 amps, or amps x volts = watts If your fan is 200 watts you should have a 20 amp relay. The relay is only a switch operated by a circuit opening & closing.
the website below explains better than I :-

http://www.12voltplanet.co.uk/relay-guide.html

I have always found keeping it as simple as possible (KISS) & thats not coming on :lol:

I would also remove your + switch feed from the ignition coil (as high amp relays can arc back through the switch circuit) so you need a feed controlled by a fuse not in any critical circuit.

The relay should also be a resistor or diode type, this will stop them burning out.

Relay Terminals= 30 Battery 87 Fan 85 + Switch 86 - Earth
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RamoNZ
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Re: Why does my rad fan fuse keep blowing?

Post by RamoNZ » Tue Aug 04, 2015 2:58 am

Righto.. I'm a little bit lekky tekky so i'll try see if what I know can't unravel this a bit for you.

First thing - Where is the fuse located? Should be near the battery but anywhere pre-Relay on the 30 terminal should be fine.

Second - I agree with moving the Ignition trigger from the coils - I would personally put it direct to the battery - that way the fans will continue to run when the engine is off as per modern cars. This cooling in the radiator creates a siphon effect which keeps the water flowing around the engine somewhat. If you actually measure the temperature of the engine on shut down, it continues to increase when the water stops flowing as other so is a long term reliability mod to allow it to cool this way.

Anyways - Electric motors, the way they draw power (current) is not linear. On start up, at they are effectively stalled, they take a lot more power than if they are already moving. Same principal applies to moving objects - anyone who has ever pushed a car will know its far easier once it is moving. This power draw is called Inrush current and can be significantly more than the quiescent (constant) current draw.

I took a trip to the Kenlowe website and listed on the fan page, it shows the 14" fan requires 24A to run, which is basically its Max Inrush rating. Given that your fuse is 25A, there is little headroom for the poor thing to get going and not pop its fuse.

However, it apparently for the most part runs up and down fine when the car is cold - so what could cause it to pop a 30A fuse?

Possibly, as the car heats up. something metal in the fan is heating up, causing a tightening of some clearance which causes the fan to need a bit more juice to spin up - this overcomes the fuse and fan stops working. This increase in current required could well be over 30A, and just as easily pops the 30A, as it does the 25A.

Other than that I dunno - Unless the volts are dropping badly when it kicks in - since Watts = Volts x Amps, Less volts requires more amps and could also play a part? The heat/traffic thing could be a mask for the fact that heat = blower fan and traffic = stereo also competing for the limited Amps that are being requested from the stock Alternator.

Solutions?
Well for a 24A fan, I'd def stick on a 30A fuse as standard - Since it blows this as well, I would go 35A or 40A and be done with it as long as the cables running the fan circuitry are capable of handing the current - i.e not spindly twin flex wire.

Other than that, if you want to get all tricky, then you need an inline Thermistor. This basically slows the feed of current to the motor and gives it a 'soft' start. if you're not nodding off by now, it has a high resistance at low temperature, so when the current is applied it reduces the amount of current that flows, once the current starts to flow, it heats up and reduces resistance. By this stage, the motor is drawing very little and all is well in the engine bay.

Lastly, on a side note - the relay rating of 40A is its ability to flow that level of current reliably - a spark jumps across contacts and will damage it in short order if the current is too high. There is no limiting aspect to it at all - run 1-40A through it no probs.
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Lucky
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Re: Why does my rad fan fuse keep blowing?

Post by Lucky » Tue Aug 04, 2015 6:28 pm

Cheers guys, that helps!

I stripped out all the original wiring now (there's bloody miles of it). It's not quite as I remember it! What I have is;

The switched live goes to pin 85.
The thermoswitch goes to pin 86.
The fan goes to pin 30
The power wire goes to pin 87 via the fuse

The fan and the thermoswitch also go to earth, but the relay isn't directly earthed. Problem?

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DKWW2000
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Re: Why does my rad fan fuse keep blowing?

Post by DKWW2000 » Tue Aug 04, 2015 6:41 pm

Lucky wrote:Cheers guys, that helps!

I stripped out all the original wiring now (there's bloody miles of it). It's not quite as I remember it! What I have is;

The switched live goes to pin 85. CORRECT
The thermoswitch goes to pin 86. CORRECT
The fan goes to pin 30 WRONG should be BATTERY (in line FUSE)
The power wire goes to pin 87 via the fuse WRONG should be FAN

The fan and the thermoswitch also go to earth, but the relay isn't directly earthed. Problem?

RamoNZ wrote:STUFF!
I love you :lol: Where have you been? :lol:

Fan should have its own Earth -

Can please confirm this is correct RamoNZ
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Lucky
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Re: Why does my rad fan fuse keep blowing?

Post by Lucky » Tue Aug 04, 2015 7:01 pm

Sorry, Pete, I've one more errata to correct as well

I've wrestled the wiring out flat and realised the fuse is between the relay and the fan, rather than as I thought between the battery and the relay. This is wrong, too isn't it? Should be as near to the power source as possible, surely?

The fan does indeed have its own earth, though

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DKWW2000
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Re: Why does my rad fan fuse keep blowing?

Post by DKWW2000 » Tue Aug 04, 2015 11:10 pm

That is correct, the Fuse should be between the Battery - Relay in a suitable location.

The other consideration is to ensure that the wire from Battery = Relay & Relay = Fan & Fan = Earth is also the correct Amp rating for the Fan.

All might sound complicated but is not, sometimes its best to draw out the wiring diagram so when you come to fit you have a easy reference.

One other consideration is if the Fan Switch + comes from the battery & not controlled by the ignition switch is that if the Rad Switch/Sensor in the radiator becomes faulty it would allow the fan to stay on & flatten battery.

If you wanted a visual means to tell you the fan is operating a small LED (like you have with a alarm) connected to the + wire from the relay to the Fan & the other to earth would come on when Fan was running (for peace of mind).
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myatt1972
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Re: Why does my rad fan fuse keep blowing?

Post by myatt1972 » Tue Aug 04, 2015 11:13 pm

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RamoNZ
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Re: Why does my rad fan fuse keep blowing?

Post by RamoNZ » Wed Aug 05, 2015 4:01 am

DKWW2000 wrote:
Lucky wrote:Cheers guys, that helps!

I stripped out all the original wiring now (there's bloody miles of it). It's not quite as I remember it! What I have is;

The switched live goes to pin 85. CORRECT
The thermoswitch goes to pin 86. CORRECT
The fan goes to pin 30 WRONG should be BATTERY (in line FUSE)
The power wire goes to pin 87 via the fuse WRONG should be FAN

The fan and the thermoswitch also go to earth, but the relay isn't directly earthed. Problem?

RamoNZ wrote:STUFF!
I love you :lol: Where have you been? :lol:

Fan should have its own Earth -

Can please confirm this is correct RamoNZ
Generally 86 is thought to be the trigger (switched live and 85 the Earth (Grounded temp switch) but not sure it actually matters as it should pass straight through.

Fuse should be close to the battery - idea being that if the relay fused itself together and joined its Earth to the power then you have a short circuit in that section of the wiring and the fuse wont stop anything. Less wiring prior to the fuse the better.

Regarding running on after the engine is stopped personal choice, new cars obviously have timers built in and voltage monitoring to prevent this so next e-fan I run will have the same thing .
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RamoNZ
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Re: Why does my rad fan fuse keep blowing?

Post by RamoNZ » Wed Aug 05, 2015 4:05 am

Lucky wrote:Facebook Like button, Smiley & Location Request
Thanks!... I think..? :D + NZ.. Obviously.

Seems to have taken me a bit of time to settle in properly - loads of new stuff to do taking up way too much time! Going to start getting back into my cars now that I have got myself a decent man cave.... Watch this space... 0-0
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