Defective fuse

[Target9000]

So we installed a Victron battery monitor and in the saga of putting the shunt in backwards had some drama with having to reverse the PCB board and losing one of the screws! But that isn't what this is about. After getting that all sorted out we connected it up and the monitor wouldn't turn on.

Well I suspected immediately that the pos+ lead wire was the problem. It should work if it has power right?

I went through measure voltage with my multimeter and between the end of the lead and the pos bus I found it was showing 4v. Odd. The batteries were at 12.9v.

I checked from the pos bus to the first part of the post lead where the fuse holder is and it read the correct 12.9v. Then I checked the other side. 4v.

So I took the fuse out and just pushed the two ends of the cheap little fuse hold together and the thing came on. Turned out the fuse itself was the issue.

The fuse is a little 1amp glass fuse. It doesn't look burned and it does conduct some current but it drops voltage from 12.9v to 4v.

Has anyone ever heard of this? I thought when a fuse blew it just wouldn't conduct at all. Do I have some sort of mutant defective fuse? Ah well, I'm putting a better fuse holder in and replacing it. Just thought I'd share a rather frustrating discovery.

[cal40john]

Had an old Subaru car years ago. It was the first one I had ever seen with the fuse box under the hood. It used the AGC glass cylinder fuses. First 2 times was a troubleshooting nightmare, I'm slow it took 2 separate failures to get used to the problem. The fuse box wasn't adequately weather proofed. Damp/water would get into the fuse and the cap would corrode off of the link. Fuse looked like there was nothing wrong with it, but it would have a high or infinite resistance. The end cap of these fuses would easily pull off the glass and at that point you could see the corrosion.

John

[Stu Jackson]

Yes.

Try this: Victron Battery Monitor Troubleshooting - SailboatOwners.com

scroll to the top for the start of the topic.

I find it very handy to peruse more than one message board, never know what you'll pick up.

[Target9000]

Spot on good advice Stu.

[mbianka]

Originally Posted by Target9000

So we installed a Victron battery monitor and in the saga of putting the shunt in backwards had some drama with having to reverse the PCB board and losing one of the screws! But that isn't what this is about. After getting that all sorted out we connected it up and the monitor wouldn't turn on.

Well I suspected immediately that the pos+ lead wire was the problem. It should work if it has power right?

I went through measure voltage with my multimeter and between the end of the lead and the pos bus I found it was showing 4v. Odd. The batteries were at 12.9v.

I checked from the pos bus to the first part of the post lead where the fuse holder is and it read the correct 12.9v. Then I checked the other side. 4v.

So I took the fuse out and just pushed the two ends of the cheap little fuse hold together and the thing came on. Turned out the fuse itself was the issue.

The fuse is a little 1amp glass fuse. It doesn't look burned and it does conduct some current but it drops voltage from 12.9v to 4v.

Has anyone ever heard of this? I thought when a fuse blew it just wouldn't conduct at all. Do I have some sort of mutant defective fuse? Ah well, I'm putting a better fuse holder in and replacing it. Just thought I'd share a rather frustrating discovery.

It certainly can happen. In my decades of trouble shooting electronics I've come across a few fuses that looked good but, were faulty. That's why I always do a continuity check with a meter on fuses that still look good on faulty equiptment. Sometimes it might just be a small mechanical break in the fuse link that opens up just enough to prevent current flow.