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Old 08-21-2018, 10:06 PM   #1
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Brawny's Avatar
2004 30' Classic
London , Ontario
Join Date: Nov 2014
Posts: 71
Question Blowing SLC 50A Inline fuses

I'm replacing the Parallax converter in our 2004 30' Classic with a Boondocker BD-1260-L from Bestconverter, but somewhere along the line, things went off the rails, and I'm having strange issues ever since.

I replaced the converter while camping. Its a bit of a p.i.t.a to remove the couch - its held down with 6 bolts, but they're difficult to get at, and its definitely unwieldy to move! The AS was connected to shore power, and Go Power solar was connected and working. I flipped off the master disconnect switch, and swapped out the converters. While removing the Parallax, I shorted the ground strap (its a bare copper small diameter tube connected from the frame of the converter to the trailer chassis) to one of the two AGU 40A fuses mounted inside the box, causing it to arc.

I installed the Boondocker converter, replaced the 40A AGU fuse, and turned on the master disconnect all while still connected to shore power. Voltage appeared normal on the Go Power display, but I don't recall what it was. It could have been anywhere between about 12.6v to 13.6v or so.

When I disconnected shore power, the fridge would normally flip over to gas automatically, but when I checked it a few minutes later, the voltage had dropped (6v or so on the Go Power display), and the fridge had faulted and wouldn't run. Not knowing what else to do, I connected the TV, 12v reappeared, and after power cycling the controls, the fridge started and ran on gas.

We stopped on the way home, and I disconnected the TV on the off chance that the electrical issue might drain my battery while parked. Again, within a few minutes, the battery voltage dropped, and the fridge faulted.

I should mention that I didn't watch closely to see how quickly the voltage drop happened, but did see that the fridge didn't fault immediately either time.

When I got home, I pulled the couch out again, to get better access to the fuse panel and box where the converter lives. I removed both batteries, and put them on a charger to see what sort of shape they were in. The charger showed both batteries as being at 90% of charge, so I ran them both through one charge cycle to make sure they were topped up. I also disconnected the solar charger positive connector from the master disconnect switch and taped it up with electrical tape to make sure it wouldn't short to anything. This was done to remove the solar charger from the equation.

With both batteries removed and solar disconnected, I tried to follow the circuit to understand where the issue is. In testing the inline fuses for both batteries, I found they were open. These are the large ceramic fuses (SLC 50A) mounted on two fuse blocks to the inside front wall.

I had to order these and wait a while to receive them, so a week later...

I replaced both batteries in their boxes, and connected the first back into its holder. I measured 12-13v using my analog multimeter from the fuse to the ground bar inside the converter box. I replaced the second fuse in its holder, and measured it. Zero volts. Back to the other fuse, its now 0v. It looks to me like something happened when connecting the second battery into the circuit.

Not sure where to start troubleshooting now, and its expensive to replace these fuses in Canada, so I'd like to sort this out without sacrificing any more.

I don't believe the new converter is at fault. I've bench tested it and its putting out something like 13-14v without any load. Also, it was unplugged and without shore power while since arriving home an pulling the batteries.

I don't believe the batteries are at fault and I'm sure that I have them in with the right polarity.

The solar charger is now out of the circuit, with the positive wire wrapped in electrical tape.

The only thing I can think of is that possibly the ground strap is shorting out something, causing the 50A inline fuses to go. Strange how it worked with one battery connected, but when the second fuse was installed, both fuses blew immediately.

Any suggestions are greatly appreciated.
2004 30' Classic
2013 Dodge Grand Caravan
WBCCI #1783, Region 2, Ontario Canada Unit
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