Fuse blow repeatedly between battery bank and Magnum MS2812 inverter/charger

[Dean n Mike]

About a year ago, after about 3 years of normal operation, the 300 amp fuse between the batteries and the inverter/charger blew while the coach was in storage. I replaced it and had no issues for another year. I wrote this off to mechanical stress, as the cables were on opposite sides of the fuse terminals (one on top, one underneath).

A couple of weeks ago the fuse blew again, and failed twice more within 8-24 hours after being replaced (once with a 175 amp fuse I could get locally, once with a 300 amp one from Amazon). I’m now convinced that there’s a real issue with the wiring, battery bank or inverter/charger.

The last replacement lasted for 8 hours or so.

I’ve got two questions:
First, need advice/experiences from anyone who has similar experiences, please.
Second, when this happens, why doesn’t the inverter pass shore power through to the coach?

Thanks in advance for everyone’s help.

Mike

[twinboat]

First check the positive cable for charging against steel.

Second, the internal pass thru relay may need 12 volts to close.

[twinboat]

Can't edit, to late. Chaffing not charging.

[Dean n Mike]

Thanks, will look for that.

[Mark_K5LXP]

It's tough to blow a fuse like that with anything other than a fault current. Something that's cut or worn through the cable insulation, or if the cable shifted and is now touching something hot and it melted are both contenders.

Mark B.
Albuquerque, NM

[Dean n Mike]

I spoke to Magnum customer support, who suggested that the fuse might be slightly undersized, but could not explain why it would be failing now.

They suggested that a thorough cleaning of the battery terminals and a check of the wiring was the first option, looking for chafing as suggested earlier.

I won't be able to get out to check that until Sunday, will keep everyone apprised next week after I have a couple of days of operation after I do the service.

Thanks,
Mike

[AlanTerry]

Please post what you found. I am thinking a short from chafed wire.

[Dean n Mike]

So I went out to the coach Sunday and cleaned the batteries, connections, trays, etc. and replaced the fuse.

So far so good. I found no chafing, but the batteries were quite a mess. Once reassembled, it has run without issues, plugged in in storage, for 48+ hours so far.

Will be much more diligent about applying terminal protection spray in the future.

I also changed the hold down rods and brackets out for straps; my rods seemed to get as much corrosion as the terminals.

I’ll report back if anything changes, but for now I am thinking that this is solved. Who “woulda thunk” dirty batteries would cause this?!?

Mike

[Dean n Mike]

Could not find any issue with the wiring, so I pulled the inverter and took it in for repair. The service guy suspects the “FET Board”. I will post again when repaired.

Mike

[Pillbox]

Following
Curiosity is my name...

Terry

[sibe]

The board is bad?????? IMO 300amps would toast inverter. Charger.....if fault. Or than yes that unit is bad..


Let us know.. I had a bad battery smoke fuse cable.. But that is a one done.

[WorldCat25]

Originally Posted by sibe

The board is bad?????? IMO 300amps would toast inverter. Charger.....if fault. Or than yes that unit is bad..


Let us know.. I had a bad battery smoke fuse cable.. But that is a one done.

300 amp is the recommended fuse for my Magnum 2000. The actual Magnum 300 amp fuse and holder are a lot beafer than the original one which came in the rig. After blowing several I had the Magnum fuse installed and have not had a problem in 2 years. But I am paranoid about overloading the circuit.

[twinboat]

The FET board is the high amp board that the big FETs, between the battery cables, are mounted.

If the FETs are shorting out, it will blow the big fuse.

I've blown 3 inverters over the years.

[sibe]

Originally Posted by twinboat

The FET board is the high amp board that the big FETs, between the battery cables, are mounted.

If the FETs are shorting out, it will blow the big fuse.

I've blown 3 inverters over the years.Attachment 293952

cool. learned me some info...