I noticed I had a huge voltage drop from my charger to my battery bank. As explored I found I had a 1.1 V drop across my blue sea ANL 400A fuse. With the current off, there’s almost no resistance across the fuse. I’m guessing it’s still a bad fuse and it’s inducing significant resistance when there’s any flow across it, but these are expensive fuses so I wanted to see whether or not there was something I was missing before I replaced it. Thanks.
Voltage drop across blue sea fuse
- Thread starter Djk
- Start date
sunshine_eggo
Happy Breffast!
Are you saying that you measured 1.1V with your voltmeter leads on opposite sides of the fuse?
Confirm that your connections are good. Loose bolts/nuts or something interfering with the connection will cause voltage drop.
Confirm that your connections are good. Loose bolts/nuts or something interfering with the connection will cause voltage drop.
It was actually measuring directly touching the arms of the fuse
sunshine_eggo
Happy Breffast!
It was bulk charging, so probably around 120A. Fuse was slightly warm. Thanks for taking time to help with this by the way.
OzSolar
Whatever you did, that's what you planned.
What's the voltage drop across your entire system?
120A x 1.1v = ~130 watts of heat being generated across that connection. After a few minutes I think that would be dangerously hot as in melting stuff, not just slightly warm. I'm missing something. Can you repeat the voltage drop reading with a different meter?
sunshine_eggo
Happy Breffast!
This is my thinking as well. Have you confirmed the voltage drop with another meter?
OK, it was a bad lead on the multimeter. It was positional, so I wasn’t seeing it a lot of the time, but I had to bend the lead in a certain way to get it to contact the fuse, and that was what was causing the problem. Replace leads and everything is normal now. Thanks for all the very smart folks that pointed out that what I was saying was probably not real because of basic laws of thermodynamics.
sunshine_eggo
Happy Breffast!
whew!
OzSolar
Whatever you did, that's what you planned.
Glad you found it!! I'm not ashamed to share that I've been stumped like this several (ok many) times so now when I'm getting readings that don't make sense I take a step back and often find that either my testing methods or my testing gear are the issue. EG: I've seen a multimeter do wierd things with a low battery long before the "low battery" icon appears.
edit to fix typo
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I have went down many rabbit holes to find my batteries were a tat bit off. First thing I do if getting weird readings is change to fresh batterys.. it always seems to solve it….those meters can send you all over the place… it’s not like a flashlight…gotta have strong battery’s.
Lt.Dan
Solar Wizard
I noticed this too with my clamp meter. When I start to notice current bounce around, it's time to change the batteries. Funny how that works.
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