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Up until now, this MarkVIII has performed flawlessly and actually, it may not be the fans' problem at all - but I need some help on this one. PLEASE bear with me fella's because I'm not strong in the electrical lingo department...so here goes:

The main power supply from the battery to the fan goes to a square shaped fuse box. It was part of the Black Magic kit I used before and I just kept it in place. This little silver box has two posts on top, one goes to the battery for power supply and the other goes on toward the 75amp Bosch relay which eventually feeds power on to the fan.

With the key turned forward, the fan runs for about 20 seconds, stutters and then shuts off. Wait about 15 seconds and it fires back up again and will repeat the process until it doesn't run at all.


One of the terminal posts' (on the square fuse box I mentioned above) gets very hot to the touch just before it (fuse box) 'clicks' and the fan shuts off. It's the post that feeds the power supply to the 75a Bosch relay. The other post doesn't heat up like that at all. Also noticed that the main power supply going over to the battery is very hot where I've spliced two sections together with a crimp connector. Very weird.

I've tried connecting the two power wires together, bypassing the little silver fuse box altogether, and when I did the entire power supply line got hot to the touch.

Thinking it was the 75a Bosch Relay, I've tried swapping in the smaller 30amp relay but I'm getting the same results.


I've also noticed a 'click' noise (coming from inside both the 75a and the 30a relays) everytime I disconnect/reconnect the battery. I use a battery quick disconnect switch. I've never noticed that click sound before and I always kill the battery after cruising around.

Could it be the fan itself fella's? Any idea what I'm overlooking here? This problem started completely out of the blue with no electrical wiring changes done whatsoever. Thanks in advance.

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502 Rat Infested 1970 Malibu - Gold Member #39
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[This message has been edited by Wes Colby (edited 08-25-2001).]
 

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If you have a fat wire going straight to the fan, from the battery, and it's getting hot, not a good sign.
The fan sounds like it wants more power than it did before. Another not so good sign.
If the wires were not getting hot before and now are, the fan motor wants more power. Maybe the motor is binding up causing drag. That would cause it to want more power to spin. My guess is a motor problem. The rest makes sense.
 

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Wes what are ya doin' putting that Black Magic crap on a Mark VIII fan. That's like tits on a bull. Always wanted to say that


What size fuse do you have on it? I use a 40 Amp piece that has a square box with two flat copper pieces that accept screw in terminals. Best to make those high current connections the best, and surface area contact is KEY.

If your heating up wires, but not blowing a 40 amp fuse, then I suspect a bad connection. Most liekly int he heated wire.

IF you suspect the fan is dragging, spin it and see, it should go round-n-round quite easily like mine.

Also, be sure you running at least 10 gauge wire. 12 maybe for a short distanc. Adnt he only two female plugs should be at the fan terminals themselves.

The relay control should not be a problem, but check to make sure that when the fan does "cut off" for the first time the relay has 12 volts across it's two 'male' control terminals to activate it. then proceed to check your fans supply in pieces for + voltage with a common chassis ground: battery, before fuse, after fuse, FAN.

I have my relay after the fan between it and ground. -good luck cheif, and if things go bad we'll compare motor empedances. just Ohms that is.

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Discussion Starter #4
Thanks guys for the feedback. John, the fan spins just fine and I couldn't detect any unusual drag. I think you're right in that the fan was wanting more power but it couldn't get it bc it looks like that ole' 40a fuse WAS the culprit. It's identical to what you are using Mike. I completely removed the fuse and just held the two wires together with my fingers. Alas, no intense heat build-up and she stayed on with no hick-ups. I don't understand how a bad fuse can cause heating within the wiring.


The fuse would simply shut off the circuit before and then try to start up again but would finally just quite. Guess it was causing some sort of restriction inside.

I'm using 8 guage wiring throughout and I did replace the section that was heating up near the old crimp splice. No more heat coming from that end of the wiring either. I'm on the hunt tomorrow for a new 40a fuse.

Mine rattles a tad on the inside. Ya' think they're supposed to rattle like that?


Thanks for the help fella's.


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502 Rat Infested 1970 Malibu - Gold Member #39
Keep America Beautiful - Drive A Brute Force Chevelle!
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Wes
Not so much the fuse but perhaps the poor crimp joints. Electricity is not that hard to understand. Just remember, you always want a good tight fit to get the juice flowing.
 

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Discussion Starter #6
Thanks John...unfortunately for me, I never took a strong interest in electronics and now the simple stuff still gets me stumped.
I can always count on TC though for help.

Besides, what fun would it be if I knew everything about anything?!


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502 Rat Infested 1970 Malibu - Gold Member #39
Keep America Beautiful - Drive A Brute Force Chevelle!
http://homepages.about.com/wescolby/1970bruteforcechevelle
 

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knowing everything about everything.
hehehe

Your fuse rattles 'ey? Must be one of those new NASA approved units.


I'm pretty sure that is the problem. What happened "inside" your fuse's enclosure is analogous to a problem that came up a short while ago with another Mark VIII user. Tried to use the bladed fuse holder with the rubber boot. just a bad connection before or after teh fuse. enough to cause heat and soon enough a capacitance like open. Only when yours cooled the circuit was completed again.

[This message has been edited by BB_Mike (edited 08-26-2001).]
 

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Discussion Starter #8
YOU are correctomundo Mike.
What you've said validates my assumption about what was going on inside that little silver fuse box. It would cool for several seconds and try to reconnect the circuit again.

I'm off to NAPA for the new, improved, rattle-free fuse. Thanks again bro.

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502 Rat Infested 1970 Malibu - Gold Member #39
Keep America Beautiful - Drive A Brute Force Chevelle!
http://homepages.about.com/wescolby/1970bruteforcechevelle
 

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I have seen fuses here at work that after some use would open but if you did a check on them with a meter they would show continuity but have a little (5-10 ohms) resistance. You could put it back in the prober and it would turn back on for 5 minutes then open back up. It could be that bad fuse but likely it's the conections for it.

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If you are talking about a little silver box with a plastic side that has two terminals sticking out of it then you're talking about an automotive circuit breaker. It's not a fuse.

These things have a bimetallic strip inside them that heats up with current. At a certain current they will "click" open a set of contacts. Once the piece cools it will "click" back and re-make the contact. They aren't real accurate and aren't great protection because they just keep re-making until they either self destruct or someone disconnects the power.

I thought that fan drew around 38A. I'd want a 50A breaker on it myself or a real 50A time delay fuse.

Peter
 
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