question

I may be able to add a solution or at least something to check. My new SmartShunt 500A had a similar problem. What I found was a voltage difference on 0.1-0.2V between the +ve battery terminal which the SmartShunt fuse connects and the termination on the SmartShunt. Long story short I found two issues;

-my fuse measured 5 ohms! compared to a replacement at 0.2 ohms. (fixed the problem) The self-consumption current of a couple of mA was sufficient to cause a voltage measurement error with the high resistance fuse. I've never come across such an issue before..

- the suppled fuse holder is rather crude, relying on spring contacts with the fuse end and when measuring the resistance of the assembled inline fuse holder varies with any mechanical movement. As any change in resistance can affect the system voltage measurement any instability is not desirable for long-term reliability.

I dislike the use of an old-style cheap fuse and holder, while they work, is not in keeping with the quality and reliability needed for such a precise high tech device like the SmartShunt. My solution is to use a self-healing polyswitch to protect the cable, no spare fuse required. The manufacture Little Fuse RXEF series has suitable devices.