Thread: Slow Blow 30 Amp fuse

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I am not an electrical guru, so I have a question for those who are.---Is there such a thing as a slow-blow 30 Amp blade type fuse.---this is a 30 Amp fuse that will momentarily take surge loads of higher than 30 Amps without blowing? In a situation where the surge current lasts longer than 5 seconds (or thereabouts), the fuse will blow. I have an electric fan that momentarily spikes up to 60 Amps when the fan comes on, as it goes from zero RPM up to full speed, then settles in and runs at about 15 Amps. The fuse doesn't care that it runs at 15 Amps----it blows during the momentary current spike at start-up. A circuit breaker, even a self resetting one, will trip when the initial surge current passes thru it.---I know that there are slow-blow fuses for smaller amperages, but I haven't been able to find one as large as 30 Amps.

Brian, never seen one in automotive use,only house circuits,of course that doesn.t mean they don't exist.....

Hey Brian,,,, I was lookin at some Fiero wiring diagrams, Man some of em used a 2 speed cooling fan motor that used a processor to control the fan relay, but the 2 speed motors only used a 20 amp fuse and the single speed motors only need a 10 amp fuse, wonder if ya got a 2 speed motor and its hittin both speeds on start up ????? I checked with NAPA and ya can buy a brand new "value line" fan motor for about $36 bucks in the states...
Only other thig I can think of is hard as them fans worked on a Fiero your salvage motor may be flat worn out......

How about a Fusible link?

Denny---I'm trying to keep an open mind here, concerning the fan. I did wire it to the low speed side, and now the spike from zero to full speed is a very brief spike (as measured by an ammeter wired into the fuse location)---then it drops back to about 15 to 17 Amps, and runs quite smoothly. The spike lasts only about a second. The reason that I'm not anxious to run out and purchase a new fan is that I have fabricated a weldment that incorporates the fan shroud, mounting brackets, and the fan motor and blade into a "composite entity" that does not come apart. I would post a picture, but its all chassis black and doesn't show up on a digital picture. If I absolutely can't make this fan operate smoothly and problem free, I will unbolt the whole darn thing and throw it out, then replace it with an aftermarket fan. I don't believe in the philosophy of throwing things away and replacing them untill I have exhausted all my other options. I am still waiting for my second gas tank to show up here, as the first one was damaged in shipping by UPS.---consequently I have a little "screw around time" before the roadster sees any real road miles. I know that slow-blow fuses are made exactly for this application, where there is a spike in start-up current demand, then a much lower amperage draw for normal running. I really think I have to "try this and see" before I do anything drastic. Thank you for your help and interest Denny. I haven't ran the car since I rewired the fan, so will know more (I hope) when I get a chance to do so.

brianrupnow you're not suppose to have a 60 amp. spike at the fuse, the relay should take care of that. sounds like the relay is not doing what its suppose to. would you mind telling us where you have the relays wires going. the bat should be taking that spike.

It1s10---I used a Ron Francis basic wiring panel that has a built-in relay for the electric fan. The wiring in this panel is all "internal", but it has one teminal clearly marked "cool fan" and the instructions show a wire leading from that terminal to the cooling fan, and then from the cooling fan to ground. There is one fuse clearly marked Cool Fan (and the Francis instructions say "For Cool Fan use 30 Amp fuse"), and the Francis instructions say "Cool Fan (12 ga.) connects to the positive terminal of the electric cooling fan. The fan also requires a good ground. Note: if a cooling fan is not being installed, ground the relay ground terminal and this circuit can be used for another ignition controlled accessory" In my case, I have ran a wire from the "relay ground" terminal thru a thermostatically controlled switch, then to ground. When it gets up to temperature, it grounds out the "relay ground", causing the relay to activate and operate the fan circuit. After I blew the 30 Amp fuse twice, I wired two spade terminals onto wires, attached them to an aftermarket ammeter, and plugged the "spades" into where the 30 Amp fuse normally goes. I then grounded the "relay ground" wire, and observed what the ammeter did. It spiked to 60Amps, then dropped back to 28 Amps after the fan came up to speed. I didn't like that very much, so I wired the hot lead to the fan to the low speed fan input wire (this fan has a hi-speed wire and a lo-speed wire). I then observed that the fan spiked to 60Amps on initial start-up, then dropped back and ran at 15 to 17 Amps.

i dont know, but it sounds like to me the relay ant doing what it suppose to. do you have a 12v hot all the time wire going to the panel or to the fan relay?

Today I went for a 50 mile cruise with the roadster pickup. This thing is amazing, in that the temp stayed at a constant 150 degrees, and the fan never tried to kick on at all. I had to set in my driveway for 5 minutes with the engine idling before the temp went high enough for my fan to come on. It came on, ran till the engine temp fell back to about 175, then shut off. I waited till the temp came back up and the fan came on again. I let it cycle on and off about 5 times, and there is no fuse blowing, so maybe hooking up the low speed wire on the fan has fixed my problem. The v-belt drive to the alternator squeals a tiny bit when the fan starts, but my fan belt is fairly loose, and I'm out of adjustment, so will have to buy a shorter v-belt. Touch wood---maybe the problem is solved.

Originally posted by brianrupnow
Today I went for a 50 mile cruise with the roadster pickup. This thing is amazing, in that the temp stayed at a constant 150 degrees, and the fan never tried to kick on at all. I had to set in my driveway for 5 minutes with the engine idling before the temp went high enough for my fan to come on. It came on, ran till the engine temp fell back to about 175, then shut off. I waited till the temp came back up and the fan came on again. I let it cycle on and off about 5 times, and there is no fuse blowing, so maybe hooking up the low speed wire on the fan has fixed my problem. The v-belt drive to the alternator squeals a tiny bit when the fan starts, but my fan belt is fairly loose, and I'm out of adjustment, so will have to buy a shorter v-belt. Touch wood---maybe the problem is solved.

thats great low side is all i ever run on mine with ac.