Topic: Where can I find a 40A fuse for my FoMoCo fan?

[Sherpa]

Being my day off, I decided today was the time to do my electric fan conversion.  I spent most of the day on it, and I'm mostly happy with how it turned out.  I found a Hayden brand adjustable thermostat controller and integrated that into my install.  Its instructions said it was good for a 30A fan, but I felt its power wires didn't look beefy enough ( I think they are 12 gauge) for running a 30A fan, let alone this monster Ford fan.  Because of that, I also installed a separate 40A relay and some 10 gauge wire to actually power the fan itself; the Hayden controller merely trips the low-powered side of the relay rather than running the fan directly.  My power wire from the battery to the relay uses the best inline fuse setup I could find; it is like this:



I inserted a 30A fuse into it (which was the largest one I had).  It uses the traditional automotive style fuse, not the mini ones.

Anyway, I buttoned everything up and started the Jeep.  After an extended period of idling, the engine warmed and the thermostat opened.  I had guessed and tried adjusting the thermostat to where I wanted it, and I may have done a fair job: just as the temp needle began cresting the 210^ mark, the controller activated... and my 30A inline fuse promptly blew.    As a reminder, my Ford fan connector only has two wires; I think I am running my fan only on the HIGH setting.

Do they make these fuses in a 40A size?  If not, what style of inline fuse arrangement have you other guys used?  Any help you can provide would be very... helpful.

[sharpxmen]

get a couple of resistive loads off some dual fan taurus shrouds and put them in series with your fan, they should be inside of the shroud so they get cooled off while the fan is running, that will lower your amps (try with one or 2, for me just 1 was still too fast). You could use a 50A fuse just like the ones in the PDU by the battery but you should match the wires for that. you should also match the relay or the contacts will be damaged in it as well if you go with a 40 AMP fuse (or 50).

[Bounty Hunter]

You're going to have to jump up to the jumbo fuse to get that kind of amperage.  Run the low side of the fan if you have it, plenty fast to cool the 2.5L engine.

[jfrabat]

You're going to have to jump up to the jumbo fuse to get that kind of amperage.  Run the low side of the fan if you have it, plenty fast to cool the 2.5L engine.

X2; I used a Jumbo 40A connected to the low side of my fan as a back up (use a relay to activate it).  The high side is connected to the DC Controler...

[dustjunkie]

The fuse and switch are just not up to par with that fan.  The DC controller is an ok unit, they fail and customer service is less than par.  A writeup I did a few years ago on pirate on it.  I wouldn't buy from him again. 
http://www.pirate4x4.com/forum/showthread.php?t=293231&highlight=ccrm

You need a relay...... 12volt guy has them cheap.  http://12voltguy.com/web/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=38&category_id=7&option=com_virtuemart&Itemid=43&vmcchk=1&Itemid=43

I have used the ford taurus CCRM and it works, I have the pinout drawing if you need it.  It has 4 relays inside.

On my jeepspeed I use this painless unit, but don't need a temp switch because when the car is on we are racing!
http://www.painlesswiring.com/webcatalog/largeview.php?SearchField=30100

[Sherpa]

You need a relay...... 12volt guy has them cheap.  http://12voltguy.com/web/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=38&category_id=7&option=com_virtuemart&Itemid=43&vmcchk=1&Itemid=43

Dude, that's a 70 amp relay.  I seriously doubt the OEM wires in the fan's connector can handle that much current.  There has got to be a better way.

I have used the ford taurus CCRM and it works, I have the pinout drawing if you need it.  It has 4 relays inside.

This sounds more promising.  Can you post that drawing?  Or email it to me?

[neale_rs]

Dude, that's a 70 amp relay.  I seriously doubt the OEM wires in the fan's connector can handle that much current.  There has got to be a better way.

Nothing wrong with using a 70 amp relay, it's not there to protect the wiring and it won't cause the circuit to pull 70 amps.  It just means it can handle that much so it will be more reliable. The fuse will protect the wiring.

[jfrabat]

Dude, that's a 70 amp relay.  I seriously doubt the OEM wires in the fan's connector can handle that much current.  There has got to be a better way.

This sounds more promising.  Can you post that drawing?  Or email it to me?

Someone here did a test on the fan and it turned out not to pull the 70A that everyone seays it pulls...  IIRC, it was 40A on high at startup.

[dustjunkie]

The CCRM's fail too, that's why there are so many Taurus's in the junk yards, CCRM fails, fan quits, motor blows.

[dustjunkie]

What they said ^^^^ about the relay, you are just trying to protect the fuse from the initial spike of the fan coming on.  With a fan that good it cools the radiator quickly so it comes on and off a lot.  I've blown 40 amp relay's in a short time with it. 

The 70 amp relays are the ones to use.  I've raced with one for 4-5 years without a failure.  The high fan wire on the fan is 10 guage.  It can handle the draw of the fan if the relay is close to the fan.  Ford put the CCRM's on the shroud!  Your controller will cook if you just increase the fuse size.  Wire the controller to the relay and let the relay handle the load.

[dustjunkie]

here's a simple diagram that uses a temp switch.

[sharpxmen]

What they said ^^^^ about the relay, you are just trying to protect the fuse from the initial spike of the fan coming on.  With a fan that good it cools the radiator quickly so it comes on and off a lot.  I've blown 40 amp relay's in a short time with it. 

The 70 amp relays are the ones to use.  I've raced with one for 4-5 years without a failure.  The high fan wire on the fan is 10 guage.  It can handle the draw of the fan if the relay is close to the fan.  Ford put the CCRM's on the shroud!  Your controller will cook if you just increase the fuse size.  Wire the controller to the relay and let the relay handle the load.

you're spot on with all the statements but i'm not sure about the relay position
the current thru the relay has nothing to do with where it is located on the wire, it's a closed DC circuit - i'm trying to understand why do you think it has to be closer to the fan?

[Mozman68]

I bought one of those monster size inline fuse holders from carquest and a 60 amp fuse to go with it....I blew 30's easily and was also blowing 40 amp fuses.  The 60 has done fine since installed.  I am also running high speed when the temps call for it.

Bought one of those fancy laser temp readers at Harbor Freight last week so I can measure the temp where the sensor is to dial it in.

[neale_rs]

I think he means it has to do with the 10 gauge fan wire, not the relay. For a given voltage and given total circuit resistance you will have a certain amount of current.  However, the voltage drops across different parts of the circuit will be different, being greater for the sections with higher resistance.  Watts = Voltage x Amps, so if the thinner fan wire has relatively higher resistance, that part of the circuit will dissipate more watts.  By making the wire shorter, it will have less resistance and will dissipate fewer watts and not heat up as much.

[sharpxmen]

I think he means it has to do with the 10 gauge fan wire, not the relay. For a given voltage and given total circuit resistance you will have a certain amount of current.  However, the voltage drops across different parts of the circuit will be different, being greater for the sections with higher resistance.  Watts = Voltage x Amps, so if the thinner fan wire has relatively higher resistance, that part of the circuit will dissipate more watts.  By making the wire shorter, it will have less resistance and will dissipate fewer watts and not heat up as much.

You're coming from the battery or PDU so i assumed we were talking the same length of cable (unless you move the battery is more or less going to result in the same overall length)

what i was saying is that in a closed DC circuit with all the components is series the current (amps) is the same thru all wires/components regardless of the combination of thinner/thicker wires (the thinner ones should be at least the size recommended for the fuse in the circuit though). What you're saying about voltage drop is more related to the loss in the circuit or the ohm/length specific resistivity for that wire if you wish which would in fact drop the amps in the circuit (not that is a good thing but will put less stress on the relay and not the other way around).

EDIT: actually you pretty much said the same thing

For a given voltage and given total circuit resistance you will have a certain amount of current.