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Converter Fuse Protection

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There is a 60 amp Progressive Dynamics converter in my motorhome. About a year ago, I noticed that the converter was cycling on and off, for example it would come on for about 10 seconds and then shut down for around 15 seconds and then come back on for 10 seconds and so on. This only happens when the battery is low and needs a lot of charging. Thinking it was the converter, I put in a 30 amp Iota converter and had the same problem.


After a lot of research it appears that the culprit is a self resetting fuse, brand ShortStop, which is doing the cycling. Thinking that the fuse had weakened due to excessive cycling, I removed it with the intent of getting a replacement. I was very surprised to discover that it is a 50 amp fuse. All this is factory installed, by the way, on a 2002 Endeavor gasser. My concern is that considering a 60 amp converter is feeding a 50 amp fuse, then the fuse is probably undersized for the application.


The wiring is 6 ga. J1127 SGX which is rated well above the 60 amp load being put through it.


Has anyone out there ever run into this situation? I would like to increase the fuse capacity to 65 amps at least. The ShortStop line of fuses only goes up to 50 amps, so most likely I'll have to go to a manually resettable breaker, if they exist, or else a single use Maxi.


Any ideas will be greatly appreciated.







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If the Converter is actually capable of delivering 60 full charging amps??????? and such can be what the NEC would consider a continuous load (like 100% duty cycle rating), it seems to me if you limit that down to 50 amps, your batteries will never realize the chargers full potential. IE even if you had a 100 amp charger but limited with a 50 amp auto reset circuit breaker, what you end up with is 50 charging amp capacity




If the converter has the true capacity to deliver 60 amps continuous??? And the wires ampacity is how I would size it as 125% over that, THEN ITS MY OPINION IF YOU USE A 50 AMP AUTOMATIC RESET CIRCUIT BREAKER ITS UNDERSIZED.


AGAIN, if that's all a part of the factory plan (limit output to 50 amps) because of a duty cycle or other consideration or temperature or other design factors THEN DO AS THE FACTORY SAYS NOT ME because I didn't design the darn thing. The fact you state it only happens when the batteries are low and that's when the converter is supplying its max ability makes sense, but if its due to the TRUE ability of the converter orrrrrrrrrrrr was just the circuit breaker is incorrectly sized I CANT SAY.


PS That 60 amp rating may be subject to temperature so maybe at x temperature it can only deliver 50 amps and that's why there's a 50 amp circuit breaker????

Or maybe your converter is NOT the original so the wire and circuit breaker were sized for the original unit????


Sorry no answer just more questions, but I just cant say for sure what's going on, but I bet Progessive Dynamics can tell you!!!!!!!!!!!!!!!


QUESTION is that Short Stop 50 amp protection device part of Progressive Dynamics orrrrrrrrrrrr part of the coach system???????????????? If its part and parcel and integrated into or a part of the converters overall system design I WOULDNT LOWER ITS RATING,,,,,,,,If its strictly a part of the coach wiring and has nothing to do with Progressive Dynamics and they assure you it can deliver a full 60 amps at x temperature for 100% duty cycle, then id consider use of a 60 amp circuit breaker provided sufficient wire ampacity.


Best I have to offer sitting here, see what other gents have to suggest.


John T

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I assume that this is for protection of the 12vdc output of the converter. If I understand you correctly, a 30-amp converter/charger wasn't much better than the 60-amp PD unit. This makes me think that it's the Short-Stop device that is faulty. You could replace the 50-a Short-Stop device with another one but your thoughts regarding a 60-a current draw through a 50-a device seem reasonable to me. So the simplest solution is just to put an in-line fuse into the circuit.


I don't think the Short-Stop devices are that expensive and I might be tempted to simply buy another 50-a unit and put that in place of the old one just to see how it works. Someone, somewhere, must have thought that the current loads of that 60-a PD converter were short enough duration to not be an issue.


Of course they might have been wrong in their assumptions.


But you can always just get a 70-a fuse and put that into the circuit instead.



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PS 1, usually a fuse or circuit breaker is installed to protect the WIRING from overload and overheating, instead of an electrical device. I would think the Converter has its own built in thermal overload protection and such IS NOT something that would be done using an external fuse or circuit breaker in its feed wiring to a battery bank, but again check with PD on that not me. Of course, there's no harm in protecting the wires from the PD to your battery bank, ESPECIALLY IF THE PD HAS NO PROTECTION IN WHICH CASE ID USE IT, but match it with the PD's true capacity.


PS 2, If an overcurrent protection device is used to protect the feed wires, it needs to be done AT THE ENERGY SOURCE AND BEGINNING OF THE CIRCUIT, NOT SOMEWHERE DOWNSTREAM. If that's the case there are portions of the wire UNPROTECTED. That's NOT how its done which makes me think its a coach thing instead of a part of PD's thermal protection system.


If PD says its unit can deliver 60 amps continuous, Id try a 60 amp auto reset circuit breaker (and adequate wire ampacity) right at the PD output.


John T

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If you can not find an Auto Reset 60 Amp, I would try two 30 amp Auto Reset breakers wired in parallel. Should be ok if both are correctly calibrated from the factory.

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Most of the new smart converters are able to put out a lot more amps than the nameplate says. My 45 amp one would peg a 50 amp meter well past the 50 amp mark. I'd guess the amp rating on the data plate is for the minimum input voltage and when fed normal line voltage they go a lot higher.


My suggestion is to check your converter, it may already have a fuse built into it that will protect it from over-current or reversed leads. You would still want a fuse to protect the wire from the battery to the converter with the fuse near the battery. That fuse should be based on your wire size as suggested, if you need a bigger fuse you first need bigger wire.

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