Buss case fuse - too long and too hot?
 

My electric fan fuse gets hot quickly, and the fans won't run for more than a minute before they become intermittent. Seems that a bad fuse connection would be the most likely culprit if the fuse is hot but not blowing so I'll get that sorted.

I'm worried that the fuse is physically too large for the fuse holder. Surely it's not ideal to be able to see the fuse "legs"? The fuse holder seems too deep to fit a standard blade fuse in there. Is this something in between the standard case fuse and blade fuse sizes?

Here it is:

649df0ec.jpg picture by randompicsofstuff - Photobucket

The silver tin unit looks more like a bi-metalic thermal circuit breaker to me. When load capacity is exceeded they open the contacts and prevent current flow.
They are well known for gradually failing over thier life. May start as 30 amp then decrease over time as the metal strips weaken from moving open/ closed, plenty of cars use them on headlights and youhear reports of hi=beam going on and off when bigger wattage globes are fitted.
A replacement option could be a relay holder with the fuse built in on the side, they look tidy, are compact, cheap and use a standard blade fuse. That way the existing relay wiring could be transferred to the new case and probably only need to change the terminals on the thermal bit.

Thanks for that. As an exercise, I put a 30A blade fuse in it's place. It lasted for about a quarter of a second before blowing. Refitted the circuit breaker, and it ran for a couple of minutes before tripping and resetting.

What would cause a fuse to blow so quickly, but would allow a CB to work for a couple of minutes?

You will find the fan motor has a heavy start up current of say 40 amps then comes down to say 10 amps once it's at full speed.

In that case
a) as Gaz suggested
b) read the amps off the back of the fan then allow extra for the inertia draw, if it is in watts use the formula I=P/V where I is Amps, P is Watts and V is Volts

The conversion of Watts to Amps is governed by the equation Amps = Watts/Volts

For example 12 watts/12 volts = 1 amp
120 watts/12 volts = 10 amps etc

Circuit breakers can be good but they can also be good at damaging equipment that is half faulty as they keep kicking back in as they cool down.

If you have serious doubts about the fans integrity get a cheapo Amp gauge and hook it in line and view the actual current draw. Many a mechanics electrical box has a common round amp gauge in it for such purpose.

Thanks for that. Is there any issue with my volt meter going from 14V down to about 11.9V when I turn the fans on, or is that about right?

Where are they wired to? Alternator size? Battery size?

I'll leave that one to an expert.

JUSTIN where are youuu......

id say yr fan is fkt
30amp blade fuse to blow straight away
u must be running a fan from a house a/c unit hehehe

as a rule of thumb and most do not do this properly and to this safety spec

any fan 14inch or bigger i run

5mm wire whihc is rated at 25 to 30 amps from battery to fuse
never use a normal blade fuse even if its 30amp as it might not blow
but it will eventually melt and cause issues
i use the pink 30amp slow blow fusable links and use a female fusable link holder(2 pin)
as the 30amp pink fusable links push directly into them
make sure u use the bigger terminals too to suit the 2 pin plug and bigger terminals that the fusable link takes
its not a nice looking fuse holder but it works better than a crappy normal blade fuses they r ok on most stuff but not for big thermos

then run 5mm wire from fuse to relays and then 5mm from relay to fan power
then 5mm from fan neg to a good ground

another rule of thumb ive been told a 30 amp fuse will not blow when amp draw gets to 30 it has to be alot more so a typical 30amp fuse might blow when it gets an instant 40 amp never tested it but an old auto elect told me

unplug yr fan and if the fuse does not blow then yr fan motor is yr problem
its very common especially on davis craig fans thats y i try to only use
spal fans

Heheheh......Good to see ya still around Mate knew you couldn't desert us..We do value your advice!!!!!...:p

What is the issue with the Davies Fan?????....And what is you prefered fan???

Sorry just read your post again and it's their Motor???

ive hopefully changed my attitude
we r selling our house as of next week and moving up north hopefully
and ill be doing some mail order stuff and maybe slowly get a name again
or get a casual job doing something totally different
unfortunately between our work and our friend's work afew people have been copying our looms which everyone does anyway in many other industries
so once i start agian i will just use my stuff for my own jobs and maybe even get a
1300 number which i can help over the phone and charge 5 bucks a minute hehehehe

i wish hehehe no one will ring it

plus im also looking at have a 20 page questionaire to hand to all my customers to fill out which i go thru and decide whether to work on their cars just kidding but i did think about it hehehehehehe
as u can tell im abit over it down here in sydney

Surely it doesn't have to be that COMPREHENSIVE..:LOL:...you only need 1 question "DO YOU DRIVE A COBRA??"....:p

You've got some good ideas there......:D

:eek:.....Where you movin to?

When your talkin fans whats is spal??

i think the question will be do u drive any car hehehe
maybe a job on the beach will better depending how quick i grow it back up
and what type of work is up there maybe ill get into doing late model car diagnosing
and charge 150 bucks an hour hehehe then i can work one day and goto beach the rest
but i doubt il get back to doing full rewires unless somoene hands me 6 grand or more
they r just so time consuming and its like u r alwways going back n forth fixing the fiddly bits

my family is moving up around qld/nsw border closer to the beach than middle of sydney
,ight not make as much money but will be much less stressed and kids will love the beaches and as they grow up me and th eboys can hang out at surfers hehehe

well I hope you pop in here for a bit of insanity occasionally!!...hehehehe...:)

Spal fans

Jim, glad to get you closer to God's Own Country.

Cheers

Thanks Geoff!!!...:)