Anyone had issues with blown mega fuses on 3G conversion?

[Danny128]

I took the Bronco to vacuum it out today, but it wouldn't crank when I tried to start it up. The battery was almost completely dead, but I was able to get someone to jump me off.

On my way home, the Bronco cut off while I was stopped, so I got another jump and went to O'Reilly's to get the alternator/battery tested. I noticed that the 175A mega fuse had some black gunk on the sides and got it tested. It was blown, so I got the 150A in-line breaker they had to get me home.

Now, it cranks right back up after I shut it off, but I'm wondering if anyone else had had issues with the fuses blowing. I want to make sure something bigger isn't wrong (wiring and such), as it seems like it would take a lot to blow those fuses, especially when I don't have a big radio, wench, or other loads on the fuse.

Thanks,
Danny

 

[Jdgephar]

I would hope your wiring is okay and not causing current spikes that blew the fuse.

Could be a loose connection that is getting hot and then a smaller surge of power melted the fuse.

I didn't have any issues on my plow truck with a mega fuse and a 3G upgrade. I had a fuse holder with bolted down terminals for the wiring though.

Maybe someone else can answer if 175 amp is high enough for the 3G alternator. I thought I had a larger one, but it's been awhile since I had that truck.

 

[DirtDonk]

Should be more than enough for normal use. Don't think I've ever heard of anyone blowing even one of the smaller ones either.
Not sure if it's possible for there to be a defective fuse, but I suppose in these days of defective everything, anything is possible.

I would definitely check all the connections. Make sure you're getting full battery voltage on the Yellow wire too, as a lower reading would not only indicate a voltage loss somewhere in that circuit, but would (I believe) cause the alternator to overcharge.
Not sure it could overcharge enough to blow that big of a fuse, but some of these 3G's are putting out 150 amps just in their basic form.

Good luck. After checking all the connections, I'd replace the fuse and drive it to see if it was just a 1-time deal. Make sure you have a volt-meter in the system somewhere too, so you can monitor things as they happen. And not when the battery is dead.

Is it one of ours Danny? If so, and you determine that the fuse was the problem, let me know and I'll send you a replacement you can use as a spare.
In fact, even with a stone-reliable circuit like this, a spare fuse is never a bad thing to have handy. As you found out...

Paul

 

[Danny128]

Thanks for the help, guys. I'm always impressed at how quick people are to respond and give up some of their time to help others on here.

Paul, it wasn't your fuse, but I'll check over the connections and the voltage on the yellow wire.

Would you recommend just monitoring the battery voltage on the load side of the fuse?

I'm going to get my gauge cluster refurbished relatively soon and will swap out the ammeter for a volt-meter when I do.

Thanks again.

Danny

 

[DirtDonk]

Yep, that's the way to do it. You can easily test it at the battery posts even, because you should have the same reading.
With the engine running, you should be seeing roughly 14.5 volts on a healthy charging system.
When engine is off, the battery voltage should start at a little under 13 right after, then slowly go down to approx. 12.5 volts for awhile.

A new volt-meter is the way to go once you are at the point of working on your gauges. In the meantime, if you'd rather know immediately of a problem without opening the hood (and like cool stuff). These are very cool: http://www.wildhorses4x4.com/product/16781
I was actually looking for the one we have (or had?) that simply plugs into the cigarette lighter as a temporarily permanent easy to read digital voltmeter. I don't see it on the site right now however, so we may be out of them. Hope it's just temporary. They were sweet!
The one in the pic is for a hole that you'd make somewhere, so not considered quite as "temporary" as the plug-in model.

Paul

 

[Rustytruck]

Make sure your starter isn't wired to go through the mega fuse. The 3 G alternator wouldn't blow the Mega fuse in normal operation as it would have to put out that amperage at full speed. There would also have to be a draw on the other side pulling the amperage. A 175 amp draw would smoke all of your wiring sizes except for maybe a battery cable. I would be looking for a short by the alternator and I would be checking the voltage in the battery looking for a shorted cell. If you have a mini starter instead of the stock Ford I would look at those power lines. To blow a properly wired Mega fuse you would have a serious issue.

 

[ransil]

My guess the fuse blew on the first jump, a dead battery will cause the alternator to go full output.