Outer Limits 4x4 Board

Two 30 amp fuses feeding power to elec fans melted. What would case this? I replaced them and fans are working again?

First of all my car has a rear mounted radiator so fans run a lot

Cooling system works well as long as fans are working

Has ford twin elec fans i think AU?

Both fans are wired seperatly through a relay each just the cheap square ones you see every where

Both relays are switched together by the one factory style sensor the sort that screw into the block or thermostat housing

power runs direct from battery to a pirana fuse box two seperate 30amp fuses run power to each of the above mentioned relays.

Why would the fuses melt?

any help very much appreciated cheers Daz

how many amps are the fans drawing

ledgend80 wrote:how many amps are the fans drawing

I dont know not sure how to find out. They are the standard ford ones some one might know what they draw?

anyone?

Check the fuse connections for corrosion.

Check what voltage is at the fuse with the fans going

STIKA wrote:Check the fuse connections for corrosion.

Check what voltage is at the fuse with the fans going

no corrosion all like new

both fuses to melt at same time i think seems odd. A mate i just called said for me to check if i have wired a common earth and that it is big enough with good connections etc.

also if the fuses are not big enough would they melt should i up size to 40 amp?

thanks guys all help appreciated big trip this weekend grrrr

The fuses are to protect the wiring. They are there to melt & fail before the insulation on the wires burst into flames (or suffers other problems, but you get the idea.)

Larger fuses may fix the problem, but this may also mean that the wires will be damaged if something goes wrong (i.e. dodgy bearings increases drag, motor turns slower, draws more current).

Before anybody can tell you if larger fuses are appropriate we need to know the size of the wire you have used.

you realy need to measure the load. the earth should be the same size as the combined supply wire ie if you have 2 x 6mm supply wire you should have 2 x 6mm earths

What is the size of fuses you are using, mini or standard size?

STIKA wrote:you realy need to measure the load. the earth should be the same size as the combined supply wire ie if you have 2 x 6mm supply wire you should have 2 x 6mm earths

What is the size of fuses you are using, mini or standard size?

Standard blade fuse. Earth is good size looks like twin 6mm. wire from relay to fans are good size each look 6mm. wires from fuse to relay look smaller ill look into them better tomorrow at a quick look seems as though i have doubled up standard wires that were spare in the rear 80 series loom i used.

grrrr i hate electrical grrrrr thanks so much for feed back keep it coming

cheers Daz

reply from mate on another forum thoughts? Sorry i dont have the gear to measure amp and volt draw will try and borrow somthing tomorrow

cheers Daz

MUD000 wrote:2 reasons
1 your fans are drawing too much power like mine were
2 cheap realy are a bit dodgey
Have you tried seeing how much power they draw ???
Mine were rated at 22amp on run but were drawing 35amps :yikes hence why I melted 2 fans on the Simpson trip because they ran most of the time. We had to use a 50amp C/B to keep them running as they just blew the 30amp fuses
My new ones only draw 20amps :thumb
I have a set of AU ones here if you need to borrow them for the weekend but the spal fans keep the car cooler
Cheers Dan

DAZ wrote: thoughts?

I'm surprised that the fans were drawing that much more than nominal, but I can (sort of) understand it? The nominal rating probably involves free air - no restriction on either side of the fan. Installed in a vehicle, there will be resistance to the air flow, which means that the blades are working harder, spinning slower, so the DC (?) motor is probably drawing more current.

When you say "6mm" - is that "automotive 6mm" or real 6sqmm?

What's the largest fuse you can fit into your holder? 40A?

If you don't have time to find, fit etc new fans, I'd find some quality 8ga cable (try a high end car sound installer) to re-wire each fan (i.e. separate 8ga run for each fan) and stick in 40A fuses. If you can find suitable holders, I'd consider 50A fuses (or circuit breakers) for each fan.

Thanks to all for your help.

I think the problem was the wire between the fuse and the relay was to small.

I need a reliable cooling system so, A mate and i rewired the whole thing tonight
all wired in 6mm wire (fits in yellow connectors not in blue)

Wired both fans 100% individual circuts
40 amp good quality water tight fuses mounted close to battery for each fan
40amp relay close to the fans one for each
same size earth wire to chassie one for each

only fitted 30amp fuses for now but will upgrade to 40amp if required

took for a good test drive tonight and fingers crossed all looks good.

Thanks again to all the helped

time to start packing head off Friday arvo cheers Daz

When i was running Au thermos i was using 30 amp fuses on each one no probs. I tried 20 but blew on start up.

I found the best solution was to strip out the wiring from a falcon and use as much of it as i could inc relays,etc. Fans then seemed to pull more air and were noisier as if they were working harder. Off the top of my head i cant tell you what the ford fuses were, can look when i remember for you.

-Scott- wrote:I'm surprised that the fans were drawing that much more than nominal, but I can (sort of) understand it? The nominal rating probably involves free air - no restriction on either side of the fan. Installed in a vehicle, there will be resistance to the air flow, which means that the blades are working harder, spinning slower, so the DC (?) motor is probably drawing more current.

In theory, restriction on the intake side of a fan reduces current draw, it doesn't increase it. So I've been told anyway, and I can almost make sense of it. I am not sure whether the logic extends to restriction on the outbound side of the fan as well though, to be honest I have a bit of trouble getting my head around what is really going on in these cases.

chimpboy wrote:

-Scott- wrote:I'm surprised that the fans were drawing that much more than nominal, but I can (sort of) understand it? The nominal rating probably involves free air - no restriction on either side of the fan. Installed in a vehicle, there will be resistance to the air flow, which means that the blades are working harder, spinning slower, so the DC (?) motor is probably drawing more current.

In theory, restriction on the intake side of a fan reduces current draw, it doesn't increase it. So I've been told anyway, and I can almost make sense of it. I am not sure whether the logic extends to restriction on the outbound side of the fan as well though, to be honest I have a bit of trouble getting my head around what is really going on in these cases.

what theory o_O

Shadow wrote:

chimpboy wrote:

-Scott- wrote:I'm surprised that the fans were drawing that much more than nominal, but I can (sort of) understand it? The nominal rating probably involves free air - no restriction on either side of the fan. Installed in a vehicle, there will be resistance to the air flow, which means that the blades are working harder, spinning slower, so the DC (?) motor is probably drawing more current.

In theory, restriction on the intake side of a fan reduces current draw, it doesn't increase it. So I've been told anyway, and I can almost make sense of it. I am not sure whether the logic extends to restriction on the outbound side of the fan as well though, to be honest I have a bit of trouble getting my head around what is really going on in these cases.

what theory o_O

Okay... the context was a restriction on the pulling side, a cabin blower with a blocked filter. Instinctively you think the restriction from the blocked filter makes the fan work harder, in reality (according to the engineer who said it), the fan motor sucks less current, not more.

To me this makes some possible sense since (a) the motor is simply moving less air and hence doing less work and (b) while there is more resistance to airflow, there is less resistance to the motion of the fan blades.

I am not claiming this is true, it is just something that came up in a conversation. I would be interested in hearing what an engineer like -Scott- thinks... or even an engineer who is not like Scott

It would be pretty easy to test actually, I might even give it a go at some stage. Sit a 12V PC fan upright (ie unrestricted), measure current, then lie it down on the table and see if it draws more or less with the restriction.

Makes sense in a way because you would create a vacuum in the intake side, which would make the air around the fan blades 'thinner'

tehekho wrote:Makes sense in a way because you would create a vacuum in the intake side, which would make the air around the fan blades 'thinner'

It sort of makes sense both ways so I don't know what to believe

tehekho wrote:Makes sense in a way because you would create a vacuum in the intake side, which would make the air around the fan blades 'thinner'

Take your average vacuum cleaner and tell me what happens when you block the suction nozzle? The motor speed increases, implying less load is being placed on the motor.....

DAMKIA wrote:

tehekho wrote:Makes sense in a way because you would create a vacuum in the intake side, which would make the air around the fan blades 'thinner'

Take your average vacuum cleaner and tell me what happens when you block the suction nozzle? The motor speed increases, implying less load is being placed on the motor.....

And then it smells like burning because it uses the airflow to cool itself

chimpboy wrote:

Shadow wrote:what theory o_O

Okay... the context was a restriction on the pulling side, a cabin blower with a blocked filter. Instinctively you think the restriction from the blocked filter makes the fan work harder, in reality (according to the engineer who said it), the fan motor sucks less current, not more.

To me this makes some possible sense since (a) the motor is simply moving less air and hence doing less work and (b) while there is more resistance to airflow, there is less resistance to the motion of the fan blades.

I am not claiming this is true, it is just something that came up in a conversation. I would be interested in hearing what an engineer like -Scott- thinks... or even an engineer who is not like Scott

It would be pretty easy to test actually, I might even give it a go at some stage. Sit a 12V PC fan upright (ie unrestricted), measure current, then lie it down on the table and see if it draws more or less with the restriction.

In this context, with a supply side restriction, I can accept that the fan isn't working as hard (I believe it would create its own vacuum, so less resistance to the blades), and current should drop.

I was thinking of a blow-through fan (like the kind I see in front of my radiator - I don't often see the one behind my radiator). In this instance, a blockage downstream is creating backpressure, which makes it harder for the fan to do its thing. Slower motor (DC motor, slower due to increased load), less back EMF, current goes up.

That's my theory. Fire away.

Edit: Jason, when you do your test, make sure it's a traditional brush motor and not brushless. And measure with the fan lying both ways - intake restriction and discharge restriction.

-Scott- wrote:Edit: Jason, when you do your test, make sure it's a traditional brush motor and not brushless. And measure with the fan lying both ways - intake restriction and discharge restriction.

On reflection, I was thinking I would do it standing up and block it with a piece of wood or whatever, rather than lying it down, as lying it down could change the way the bearings sit or whatever... but as for brushed/brushless... how come? I am not sure I have anything brushless around as all the PC fans are brushless (I think, from memory).

On the overarching theory, I am iffy on the "low pressure" or "vacuum" concept, since that cuts both ways - it means you have a higher pressure zone outside the blades that is trying to "push back in", so in theory that's a load on the blades.

With the downstream vs upstream blockage, I think the same way you do Scott when I try to picture it in my mind... but then when I stop trying to think it through, the idea that the outcome is opposite depending on where the restriction is just feels a bit off.

Damn I really want to know now.

chimpboy wrote:as for brushed/brushless... how come? I am not sure I have anything brushless around as all the PC fans are brushless (I think, from memory).

Because I don't understand brushless fans that well, and I'm not too interested in doing the research.

I expect (without really knowing) that brush and brushless fans will behave differently in this situation (but could be wrong). I also presumed that radiator fans would be brush type, but I guess that many of them could be brushless these days.

I've also been comparing our theories here with (my understanding of) how turbos behave. I've heard/read that a turbo downstream of a butterfly (throttle) can over-speed to destruction if the throttle is snapped shut at the wrong time. But that could be another one of those internet myths that I detest with a passion.

Damn! I wanna know too!