Remind me please

[Joel Ashley]

As some here know, due to one or either or both of us having medical issues, our coach has been parked by the house for nigh-on a decade.  I’ve had issues with varmints getting in the basement somehow and perching on the inverter (Magnum 2012) when it’s on, keeping the batteries up over winter.  They like the warmth apparently.  A few years ago I tried anti-rodent expanding foam under the coach where looms penetrated the rails through the tank bay that adjoins the main storage bay where the inverter mounts to the ceiling.  But I had to guess at where the loom hole was, and had a time seeing what I was doing under there, foam bits went everywhere, including on me;   I may have only somewhat mitigated the problem, not solved it, because I couldn’t get in a good viewing position.  And the critters are obviously undeterred, except by the inverter no longer being on and warm.

Well I got the inverter repaired that time, but for awhile now it’s again been out of commission.  The solar system keeps the batteries up, but the inverter wont turn on.  I assumed the worst when I saw old leaves and such in the wires next to the inverter today.  It was a bear to get off the ceiling and replace twice before.  And after 6 surgeries since 2025, I’m at 78 only now up for tackling getting in and out of tight environs for repairs.

Today I did preliminaries, cleaning out the detritus and such, and opted to do first things first, finding no voltage at the red DC input terminal of the unit.  My voltmeter sees nothing between the left side of the 300A fuse in the battery bay box and battery ground post, but 12+ volts on the right side.  So if I may thank the gods not to have to lift that inverter off the ceiling again (a fun project twice before!), am I on the right track simply replacing that Littlefuse JLLN 300?  I need a brain refresh, as I think I replaced that fuse once before. 

Crossing fingers that any long dissipated squirrel/chipmunk contaminant is no longer shorting internal wiring, and that I can find a permanent prevention?

Joel

[Eric Maclean Co-Admin]

Joel
You are correct if that fuse is blown the inverter will not do anything.
The bigger question is why is that 300 amp fuse blown, it is possible that the inverter has an internal short.
Before installing a new fuse I would jump the old one with a booster cable momentarily and observe whether or not you get a large spark or ark.
This will tell you if the inverter has a significant draw or short.
It is possible that the fuse just died but I'd be weary.
Once you've changed the fuse I'd run the inverter through it's paces to verify proper operation paying attention to the amp draw on your RC50 control panel.

Eric

[Steve Huber]

Joel,
I'd also consider switching to an external battery charger to keep the batteries up and turn off the inverter.
Steve

[Joel Ashley]

Yes, I’ve a new charger that did the job when there wasn’t much solar input, although keeping the mains switched off limited parasitic battery drain.  One remaining question, is the proper fuse fast or slow-blow in this application.

Joel

[Steve Huber]

Joel,
If you are referring to the 300A fuse, I'm pretty sure it's an ANL fuse and they don't come in slow blow.
Steve

[Joel Ashley]

The reason I asked is that it can be confusing by the way some considered fuses are described:

Google “magnum 2012 fuse”;

Another one I saw was described as “very fast blow”;

There’s this:
https://inverterservicecenter.com/300-amp-class-t-fuse-blue-sea-5119  .

Things would seem to imply a fast blow with a “time delay” feature, which at first look eschews contradiction.

Prices are all over the map.  I’m going to presume the “Type T” is the right one.  Many offered say simply JLLN 300 on them,  but my current one has a “-P” after the 300.  I haven’t seen an explanation of the difference.

I’ll follow Eric’s guidance before ordering a fuse, but assume I’ll need a “Class T”, and eTrailer has one with the “-P” suffix.  It’s just that I recall replacing that fuse years ago, and hopefully the -P was then the correct one, if it makes any difference.

Thanks for the input.
-Joel

 

[David T. Richelderfer]

A GOOGLE AI query yielded this explanation:

"The JLLN-300 and JLLN300-P (or JLLN300P) represent the exact same 300-amp, 300V fast-acting Class T fuse model manufactured by Littelfuse, with the "-P" suffix designating RoHS-compliant or lead-free packaging/ordering codes.

"Core Specifications (Both Part Numbers)
• Ampere Rating: 300 A
• Fuse Class: Class T
• Opening Characteristic: Fast-Acting (F)
• Max AC Voltage: 300 VAC
• Max DC Voltage: 125 VDC
• Interrupting Rating: 200,000 A @ 300 VAC / 20,000 A @ 125 VDC
• Mounting Style: Knife-Blade / Bolt-In

"What the "-P" Means
• RoHS / Lead-Free Compliance: In Littelfuse part-numbering conventions, adding a P suffix typically denotes a lead-free or RoHS-compliant version of the component.
• Interchangeability: Electrically, physically, and functionally, they are identical and drop into the same Class T fuse blocks or holders (such as the Littelfuse LFT30400 series)."


"What RoHS stands for: Restriction of Hazardous Substances (originally Directive 2002/95/EC, updated as RoHS 2 Directive 2011/65/EU)."

[Joel Ashley]

Thanks, David.  You bettered me on the research!

“ I would jump the old one with a booster cable momentarily and observe whether or not you get a large spark or ark.
This will tell you if the inverter has a significant draw or short.”     Eric, I did get a decent spark that way, so I presume there is an internal short inside the inverter, and I’ll have to go through the fun task on my back on the slideout in the bay, getting the thing off of the ceiling.   I used an automotive floor jack last time, positioned with a square of plywood on top of its round shoe under the inverter, while I removed the four mounting bolts.  It’s clumsy flat on your back, crammed in there with incomplete view of the bolts, and the high-swing jack handle with limited clearance.  But hey, whatever works to get that 40 lb thing safely off the ceiling and back.  Otherwise it would be pretty darned hard (and unsafe) stuck in there alone trying to hold the unit up with one hand while removing the last bolt nut with the other.

Rather than taking it to the repair shop as I did before, and since they said they can’t get parts anymore anyway, I’ll open it up and see if there’s something obvious I can fix myself.  My guess is a squirrel warmed his behind on it last winter and “effluent” found its way inside;  even though as I recall there aren’t many openings on top of it, some likely got inside, contaminating a board.

I never got around to making a hardware cloth screen to surround the inverter’s top, as it would need micro-designing around multiple wire and rail infrastructure, but now wish I had.  I just hoped the expanding anti-rodent foam would plug off access - another failed procedure.

-Joel
Tried adding a photo, clipped to 254kb then 156kb, but as usual the site refused it 😤 .

[Frank Bergamo]

Joel, just replaced my inverter/charger using a motorcycle jack, worked great. Used a piece of plywood cut to fit the jack brackets and placed the inverter on top of the plywood and jacked it up into place. No hassle, no straining, went real smooth. Hope this helps, good luck!

[Joel Ashley]

Great idea, Frank.  Thanks.  I used to have a Honda 750, long ago and far away, and my son has Harleys.  But I’ve never considered or used a bike jack.  I see they come in many varieties, but one with wheels and a flat top, that I can use a cordless driver and socket to crank it up and down with seems appropriate to this task.  I just need to compare max lift height, quality, and price for my limited use project, but they are readily available around me at big box stores.

Example:  https://www.lowes.com/pd/VEVOR-Motorcycle-Lift-1100-Lbs-Motorcycle-Lift-Atv-Scissor-Lift-Jack-with-Dolly-Hand-Crank-Center-Hoist-Crank-Stand-with-Wide-Deck-Tool-Tray-For-Street-Bikes-Cruiser-Bikes-Touring-Motorcycles/5014908159

Likely a lot easier than my jerry rigged, relatively unstable trolley jack!

[David Ciotti]

Honda 750... the good ole days.  I traded my second one in for a set of Bozak Concert Grand speakers.  My brother totaled my first one.