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Converter fuse size

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  I am curious as to why a 55 amp converter only has 30 amp fuses.

 

  I think a 65 amp Progressive Dynamics only has 40 amp fuses.

 

 Safe Travels,.   Vern

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I notice in the manual for the Progressive Dynamics converter I had on my previous trailer the external fuses were listed as "Reverse Battery Fuses" and apparently blow if polarity is reversed.  Perhaps they are not intended to fuse the normal output of the converter?

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The converter, being a battery charger, has fuses on both ends. There are 120 volt ac fuses for the line side. There are 12 volt dc fuses on the battery, (load), side, that should be close to the battery. The amp rating of the converter is the charging amperes to the battery, and of course any load applied to the converter. I use a marine three stage charger. 50 amp, 12 volt battery. It has a 15 amp fuse on the 120 volt  side. It is recommended a 10 ampere over the charger output. With a 50 amp charger at least a 60 amp fuse. 

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Of course, as I'm sure you already understand, It depends on if you are protecting the 120 VAC "INPUT" or the 13/14+ VDC "OUTPUT". The 120 VAC feed "wires" themselves are protected by a breaker in the panel while the charger itself can well have its own internal input overload protection

If the chargers OUTPUT is full true 50 "continuous" amps rated, its likely protected by a proper 50+ amp overcurrent protection device or circuitry sized so as to allow the full 50 amps of "continuous" charging current to flow into the batteries and not trip, yet if that's exceeded by X amps over X time it will trip. The ""Time Current Curves" describe such parameters.

As far as the 120 VAC INPUT, the way I was taught in NEC seminars was to compute the MAXIMUM "CONTINUOUS" CURRENT,,,,,,,,,,Then size the wiring to have a minimum ampacity of 125% of those amps,,,,,,,,,,,,,,,,,,,,,,,,,Then size the overcurrent protection device to match and protect the wire.

 If a charger is designed and rated to pass full "continuous" 50 amps of DC charging current into your battery, I don't see how such could have a standard (NOT dual element or time delay etc) fuse or breaker that would trip at say 30 to 40 amps ??????????????  UNLESS   the 50 amp "rating" has an asterisk etc  whereby 50 amps was ONLY a short term or surge type of rating. If that were the case its possible to use dual element or time delay type of fuses that might be labeled 40 amps, yet they may allow 50 amps for x time.  

Sorry, absent the diagram and specs I cant say from here how the charger is designed and protected against overload. Maybe the fuses in question are only a part of a more complicated overcurrent protection circuit and not merely straight standard IN and OUT devices.

 Darn if I know

John T  Too old n rusty to answer this very well grrrrrrrrrrrrrrrrrrr 

 

 

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