Fuse requirements for DF5 Pro

[Jim_MI]

Short version: Fuse to FF is suddenly blowing and I don't know why?

Long version: I wired my SOT fishing kayak with a 5A inline fuse at the +terminal of the12V battery, then to a Blue Sea Systems marine grade 6-circuit fuseblock. I am only energizing 2 circuits, each through individual ATC blade fuses; one for a cigar-lighter style USB charger (to keep cellphone charged out on the water) and one for my DF5-Pro Fish Finder. I used 3A blade fuses for both the USB charging circuit and the FF circuit. The fuse block is in a guaranteed dry location. The battery and various power lines lay in the bottom of the kayak hull and may occasionally get damp but never submerged. The battery-to-fuseblock wire and the power line from fuseblock-to-DF5P use 2-pin Quick Disconnect fittings that are soldered and heat-shrinked for water protection and I only fish fresh water. The battery-to-fuseblock plug is disconnected between outings so I can charge my battery "offline" without affecting peripherals. Everything worked fine for the past 6 months until this morning. I unplugged the battery charger and plugged the battery power line into the fuse block but the DF5P did not fire up. The USB charger was getting power. I checked the fuse block and discovered that the 3A fuse in the DF5P circuit was blown. I replaced with another 3A fuse and that immediately blew. I visually examined all wiring connections and found no faults. Checking with a multimeter, I find proper voltage with no short between the fuseblock and the DF5P quick disconnect plug. When I check continuity across the terminals of the quick disconnect plug going to the DF5P however, there is a "short" detected. But, without knowing the wiring inside the DF5P, I suspect that this is normal. So 2 questions:

Q1: If one checks continuity between the + and - power lines of a DF5P MFD, would it normally show continuity (ring-out as "shorted") or has mine suddenly gone bad for some reason?

Q2: What are the proper fuse requirement for my wiring situation? Review of the manual shows that a 5A inline fuse should be used between the distribution panel and + power line to the DF5P (see pages 23 & 38) but elsewhere the specifications are for 2A slow blow or 3A thermal fuses (pages 39, 132).

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Jim,

Q1: If one checks continuity between the + and - power lines of a DF5P MFD, would it normally show continuity (ring-out as "shorted") or has mine suddenly gone bad for some reason?
A1: With the power/transducer cable disconnected from the display, the no continuity should be measured when tested from the cable's power leads. Should you instead find continuity, then the cable would appear to have a short and should be replaced. As the Power/Transducer Cable are produced as s single component, it must be replaced or a Dragonfly Power/Transducer Extension Cable may be added to the cable to essentially bypass the Power/Transducer Cable's power leads. The Power Cable / Transducer should be sent to Raymarine’s Product Repair Center to be bench checked / serviced.

If in a pinch for time, you may want to determine whether the short is within the block on the cable's power leg. If so, then the block may be cut from the cable's power leg and then the cable's power leg may be spliced back together (simply splice leads of the same color).

Q2: What are the proper fuse requirement for my wiring situation? Review of the manual shows that a 5A inline fuse should be used between the distribution panel and + power line to the DF5P (see pages 23 & 38) but elsewhere the specifications are for 2A slow blow or 3A thermal fuses (pages 39, 132).
A2: The correct fusing for Dragonfly 4/5 displays is a 2A slow blow fuse. A 3A thermal breaker would be used for circuit protection systems featuring thermal breakers rather than fuses and the circuit supplying power to the Dragonfly 4/5 display was powering another device as well as the Dragonfly 4/5 display.

[Jim_MI]

Thanks for the quick reply, Chuck. I have sent everything in for bench testing and repair. For future reference though, I am unclear about your suggested workaround. I assume that you are referring to the elongate rectanguloid plastic block near the plug end of the power cord. HOW would I determine whether the short is within the block? Is it a matter of checking continuity between certain pins on the plug end and certain wires on the power end? If so, which pins? Or is it a matter of just cutting it out, splicing wires back and seeing if that makes it work? If the latter, then what purpose does that block serve; why is it even there?

Jim

[Chuck - Raymarine - Moderator]

Jim,

Unless the cable was damaged, the rectangular black molded component on the Dragonfly display's power cable is the most common source of such failure. As specified within my initial response testing is performed by disconnecting the Power/Transducer cable from the display and additionally disconnecting the power leads from the circuit supplying the cable with power. Continuity testing is performed from the end of the cable which has been disconnected from the circuity supplying the cable with power. Should the temporary workaround to remove the rectangular black molded component be undertaken, testing would once again be performed from the end of the cable which has been disconnected from the circuity supplying the cable with power while the cable is disconnected from the display.