How do I determine the fuse amperage required for my electric fan conversion?

[97Ranger3.0]

Hey guys,

Probably 4-5 years ago I did the electric fan swap on my Ranger following the article for the Volvo cooling fan swap. At the time I couldn't find any of the correct Volvo fans in my local salvage yard, so I ended up grabbing a fan out of a 97 Thunderbird 4.6 because it looked like it would fit. It did fit with some minor trimming so I went with this fan instead, however I followed everything else in that article - using the Volvo relay, a 30 amp fuse, and the Volkswagen temp switch in my upper rad hose. Overall the setup has worked pretty well for me over the years.

However, occasionally the 30 amp fuse will blow (and by occasionally I mean probably less than once a year), and now after a few years it looks like the main fused power wire to the Volvo relay has been getting a little too hot. I've always assumed the reason my fuse has been blowing is due to the wiring job I did on it years ago, that there's probably a poor connection somewhere shorting out occasionally, but never looked into it entirely. However, I've been planning on adding an accessory fuse box to my truck to power other things, and have been thinking about rewiring the fan when I do that as well to hopefully have it be more reliable.

Anyways, I've been wondering if maybe the 30 amp fuse is incorrect for this fan. I just put a 30 amp fuse because the article said to for the Volvo fan, but obviously I'm not using that fan and should've considered that at the time of the swap lol... But I stumbled upon this fuse box diagram for a 97 Thunderbird, and I see two fuses for a fan of some sort.

#5 says radiator fan for 60 amps, and #16 for pusher fan at 30 amps. I'm confused on what the pusher fan fuse would be for. My only thought is that since the fan is 2-speeds, maybe the 30A is for low speed, 60 is for high? Or is the pusher fan for something else entirely? And if the cooling fan requires a 60A fuse on a thunderbird, how has the same fan been working on a 30A fuse for mine?

So my questions are, what size fuse would I actually need for this fan? Or, how can I know how much amperage this fan actually uses (It seems to me that the fan controlling for the Thunderbird is more complex than the Volvo relay setup, thus maybe needing a higher amperage of fuse for that reason)? And also, should I have 2 separate fuses for low and high speeds?

Thanks in advance,
Alex

 

[rubydist]

That fan takes more than 30 amps and you have been lucky that it only pops once or twice a year. I think a 40 amp fuse will be okay, especially if you get one of the slow-blow type because it is the current at startup that is the highest.

Some of those cars had a big radiator fan pulling air and a smaller fan in front of the a/c condensor that pushed air through that when the a/c was on, so that is why it shows 2 different fan fuses.

 

[Roert42]

The fuse should be sized based on the capacity of the wire you use, not the decay the end of the wire.

The way it should be done is you figure out how many amps the fan will draw, then you use wire that will handle more then that, then the fuse is set to blow at or below the capacity of the wire.

The fuse is there to keep the wiring from getting burned up if the circuit becomes over loaded.

 

[97Ranger3.0]

That fan takes more than 30 amps and you have been lucky that it only pops once or twice a year. I think a 40 amp fuse will be okay, especially if you get one of the slow-blow type because it is the current at startup that is the highest.

Some of those cars had a big radiator fan pulling air and a smaller fan in front of the a/c condensor that pushed air through that when the a/c was on, so that is why it shows 2 different fan fuses.

Ah okay that makes sense, thank you.

The fuse should be sized based on the capacity of the wire you use, not the decay the end of the wire.

The way it should be done is you figure out how many amps the fan will draw, then you use wire that will handle more then that, then the fuse is set to blow at or below the capacity of the wire.

The fuse is there to keep the wiring from getting burned up if the circuit becomes over loaded.

That all makes sense to me. However, how can I determine how many amps the fan will draw other than just using a 60A fuse because Ford did in the car the fan came from? I've tried looking the fan up on parts websites to see if any of them list the amp draw with no luck.

 

[Roert42]

That all makes sense to me. However, how can I determine how many amps the fan will draw other than just using a 60A fuse because Ford did in the car the fan came from? I've tried looking the fan up on parts websites to see if any of them list the amp draw with no luck.

Normally there is some kind of indication on the device, like a sticker or something. With something this old and used it may not be still visible.
If you have an amp meter that will read dc you could jump out the switch so the fan runs full speed and see how high of a draw you get when the fan starts up.

 

[Curious Hound]

Ah okay that makes sense, thank you.



That all makes sense to me. However, how can I determine how many amps the fan will draw other than just using a 60A fuse because Ford did in the car the fan came from? I've tried looking the fan up on parts websites to see if any of them list the amp draw with no luck.

In addition to what @Roert42 said...

Take full load rating of the fan X 125% and that is what your wire and fuse should be rated for.

Example. If fan is rated for 24 amps, 24X1.25=30amps. For the short runs used in that circuit, 12guage wire should be fine and a 30 amp fuse.

30amp fan X 1.25 = 37.5amps. So, 10guage wire and 40amp fuse.

The extra 25% capacity is to account for starting current or intermittent current spikes. I've never seen automotive fuses rated "slow blow" or "Fast blow". That is usually for other types of fuses in other machines and industry. Just use the regular, commonly available automotive fuses.

 

[97Ranger3.0]

Thanks guys

I don't have an amp meter, so I'll have to see if there's a rating on the motor somewhere or invest in one. I appreciate the advise, it'll help me a lot when I re-wire this set up properly

 

[gaz]

@97Ranger3.0 ,
If you are going to be responsible for building your own power circuit, you owe it to yourself to invest in at least a simple reliable multimeter. That way when something does go wrong, I am not left with a complete mystery, at least I know who is at fault.

 

[97Ranger3.0]

@97Ranger3.0 ,
If you are going to be responsible for building your own power circuit, you owe it to yourself to invest in at least a simple reliable multimeter. That way when something does go wrong, I am not left with a complete mystery, at least I know who is at fault.

I have a multimeter, but not an amp meter. I could be mistaken, but can't most multimeters only measure small amperages, like less than 10 amps?

 

[Curious Hound]

I have a multimeter, but not an amp meter. I could be mistaken, but can't most multimeters only measure small amperages, like less than 10 amps?

That is correct.

 

[RonD]

E-Fans often have Watt rating on them

Watts divided by volts = amps

so 200watt motor / 12v = 16.6amps
400watt /12v = 33.3amps

But that's after startup when running
Add 20% for start up

so 33.3amps x 1.20 = 39.9amps needed to get the fan motor moving to full speed from 0 rpms

You use 12volts instead of engine running voltage of 14volts because you want to calculate the highest amp draw that could happen in order to have a safe system
And if you have fan activation with key on, then when doing a restart of engine the fan can come on before engine is started if coolant is still warm enough, so its running on 12volts

 

[Josh B]

Since yours came from a vehicle, if it no longer has the information on a label you might could find info about it from the vehicle it came from

 

[Josh B]

Hey guys,

Probably 4-5 years ago I did the electric fan swap on my Ranger following the article for the Volvo cooling fan swap. At the time I couldn't find any of the correct Volvo fans in my local salvage yard, so I ended up grabbing a fan out of a 97 Thunderbird 4.6 because it looked like it would fit. It did fit with some minor trimming so I went with this fan instead, however I followed everything else in that article - using the Volvo relay, a 30 amp fuse, and the Volkswagen temp switch in my upper rad hose. Overall the setup has worked pretty well for me over the years.

However, occasionally the 30 amp fuse will blow (and by occasionally I mean probably less than once a year), and now after a few years it looks like the main fused power wire to the Volvo relay has been getting a little too hot. I've always assumed the reason my fuse has been blowing is due to the wiring job I did on it years ago, that there's probably a poor connection somewhere shorting out occasionally, but never looked into it entirely. However, I've been planning on adding an accessory fuse box to my truck to power other things, and have been thinking about rewiring the fan when I do that as well to hopefully have it be more reliable.

Anyways, I've been wondering if maybe the 30 amp fuse is incorrect for this fan. I just put a 30 amp fuse because the article said to for the Volvo fan, but obviously I'm not using that fan and should've considered that at the time of the swap lol... But I stumbled upon this fuse box diagram for a 97 Thunderbird, and I see two fuses for a fan of some sort. View attachment 99094
#5 says radiator fan for 60 amps, and #16 for pusher fan at 30 amps. I'm confused on what the pusher fan fuse would be for. My only thought is that since the fan is 2-speeds, maybe the 30A is for low speed, 60 is for high? Or is the pusher fan for something else entirely? And if the cooling fan requires a 60A fuse on a thunderbird, how has the same fan been working on a 30A fuse for mine?

So my questions are, what size fuse would I actually need for this fan? Or, how can I know how much amperage this fan actually uses (It seems to me that the fan controlling for the Thunderbird is more complex than the Volvo relay setup, thus maybe needing a higher amperage of fuse for that reason)? And also, should I have 2 separate fuses for low and high speeds?

Thanks in advance,
Alex

Yeah, these, they are the ones that should have been used in the first place