Reverse Polarity Fuses Circuit Question

Posted By: Dutch_12078 on 10/04/15 07:44pm

It would make no sense at all for a converter manufacturer to parallel two 30 amp fuses instead of using a single 60 amp since they both sell for the same price. If anyone looked at the schematic or opened up a converter with reverse polarity fusing, they would see that the two fuses are NOT paralleled. Each one is in series with an output, one for the positive side and one for the negative side. The purpose of having both sides fused is intended to prevent a reverse back feed from the battery positive to the converter negative when it's connected incorrectly. The fuse on the positive output also provides normal overload protection when wired correctly of course. As Doug said, the fuses don't always work as intended though.

This is NOT what I have seen in the over 200 converters I have opened up in the past few years. Paralleling a set of fuses has many negative drawbacks electrically but can reduce costs in many ways including wire size, wire routing, part size, parts availability, etc.....

BLF - It depends on the converter (Yes the PD's do exactly the same "reverse" polarity fuse configuration some even have as many as 4 fuses in parallel, none on the "-" side). You can see in the picture there are sense lines that are used by the brains of the converter.

Bottom line in your case I would put a single 50amp fuse close to the output of the converter and use the proper size wire to the load and not worry about "reverse" protection