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Members focused on two likely causes: the fuse was dramatically undersized for a 3,000W inverter, or the converter charging current exceeded the 30A fuse rating when shore power was connected. The strongest consensus was that a 30A fuse does not fit a 3k inverter install, with one experienced member noting that the expected current draw makes that fuse roughly 90% too small unless it was meant to be 300A. Another member added that even without major loads, a depleted battery could let the...
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Members focused on two likely causes: the fuse was dramatically undersized for a 3,000W inverter, or the converter charging current exceeded the 30A fuse rating when shore power was connected. The strongest consensus was that a 30A fuse does not fit a 3k inverter install, with one experienced member noting that the expected current draw makes that fuse roughly 90% too small unless it was meant to be 300A. Another member added that even without major loads, a depleted battery could let the converter push more than 30A and open the fuse as soon as the coach was plugged into household power.
On the negative voltmeter reading, there was much less agreement and little hard evidence. One member suggested it could indicate current flow in the opposite direction than expected, but this was presented cautiously. The original poster later clarified the negative reading was taken with the battery and inverter disconnected, which makes the reading more likely tied to meter lead orientation, reference point, or converter wiring polarity rather than inverter operation itself. No member provided quantified testing or a step-by-step diagnostic to fully confirm the source.
Trustworthy sources: 2 posts; Untrustworthy: 3 posts. Core consensus points: the 30A fuse is too small for a 3,000W inverter, and converter charging current may have blown it when plugged into shore power. Outliers: the reverse-current explanation for the negative reading. Practical next steps are to verify the intended fuse size and inverter cable protection, confirm converter output polarity with a meter directly at the converter terminals, and avoid energizing the system again until wiring and overcurrent protection are matched to the inverter and lithium battery setup.
