Aaron's 87

Well, I finally got my wiring sorted and late starter in. I replaced the fusible link feeding the fans with blad fuse holders (the old one was eaten up by battery acid). I found an old post stating the main fan drew 20 amps. Plus, the fusible link was marked 20. So, I used a 20 amp fuse, which immediately blew when the fan kicked on. I then tried a 25 - it worked but I'm afraid of burning up the fine wire left over from the old wiring.

What should I do. Could the 20 amp fuse have blown at 18 or 19? Is the fan drawing too much?

Tom Piper

Most electric motors draw much more current for a moment when starting than when they are running (some motors draw 13 times the run current when starting).
Try a 20 amp "slow-blow" (I can hear the comments now) fuse -- this type of fuse doesn't blow on a temporary surge.

Tom Piper

Steel Breeze

When the fan motor get kicked on, and is free to run. I takes about 10-11 amps @ 13.5 volts...

jfb

My 87 fan motor draws 14 amps. Rule of thumb is 2.5 times the running current for the start up current.

Aaron's 87

So...

Stick with the 25 if it works or go down to a 20 slow blow fuse?

Tom Piper

My personal opinion is to go with a 20 amp slow-blow fuse or a 20 amp thermal circuit breaker.


Tom Piper

Steel Breeze

Yes you are right. But at what voltage. I measured at the standard 13.5... Take her up to 15 volts, and check the current then. I would guess 18-20 amperes...

Steel Breeze

Tom, This cooling fan unit I am building. If it were to start up on high speed. It would draw 130 amps for about 1 millisecond, then work it's way down quickly. However, it will not be starting on high. When it switches to high, it will be instantanious. Therefore the fan will be turning at an already high rate of speed. I anticipate the current bump to be around 70 amps, for less than 1 millisecond...

Tom Piper

The resistance of the wiring, and such, will limit the current to something lower than that during that short time duration.

Tom Piper

Steel Breeze

Yes that's true, the wiring is fairly large, and short in length. There isn't much resistance there, but 130A is not much less than a starter motor draws 180A+. That being said, the wiring to a starter motor is quite a bit larger than the wiring supplying the cooling fans. 4 vs 12 gauge. So the size of the wiring to the fan can be an effective current limiter. I'll check all this on my car. Thanks...

Aaron's 87

I know I'm a wiring dumba**, but can I get blade type slow blow fuses to fit in the holders I have?

Steel Breeze

I've never seen any, if so they are rare. However you can get them in an AGC fuse (standard glass fuse, the most popular). Then buy a different fuse holder. Hey these stereo shops have some great fuses, along with some decent circuit breakers. Tell ya what, experiment a little, and see what works. Nothing wrong with a 30 amp fuse. Something gets in your blade, or the motor start to short circuit ect... It will blow the fuse in a heart beat. That way you don't have to go to all the re-wiring trouble...