Internal fuse for the WFCO 55 Amp Converter?

I remember a jerk owner of a dragger a net fishing boat who fumed because I was forced to reach a long distance to disconnect a negative battery cable on an eight battery 32 volt system.

"Here, gimme that" he snatched the two 1/2" wrenches out of my hands then went to a positive terminal, broke the bolt and nut loose then managed to jam one of the wrenches against the hull.

Yep. The wrench turned red - orange then white.

It burned a hole the size of a silver dollar through a 5/16" steel hull.

It ruined the lug on the end of the cable and blew the post off of the 8-volt batteries.

"I'm not paying you for that damned (Snap-On) wrench!"

Later when he reversed the polarity on the alternator, he came to me with the blown 8SC4006-U Motorola 100 amp alternator, he snarled "How much are you going to charge me to fix it? He also had to buy a another new 8-volt battery -- $250.00"

"Why, nothing John. They have lots of them in San Francisco" The hole in the new construction freshly painted boat became a minor joke of the harbor.

My payment was the school of hard knocks. The action of what that wrench did shook me up. Another time, in a rush a cable accidentally brushed an alternator output stud. I spent the next four hours mumbling-stupid-stupid-stupid as I changed four of the 12 rectifiers of my freshly rebuilt alternator.

I am very picky now how I treat exposed battery contacts.

Simple multi meter check of RP fuses... if b,own, replace.. if converter Donets work then g9 buy a new converter.

And many RVs don’t follow RED BLACK standard.... often RED WHITE or WHITE BLACK...

Hope OP gets new converter installed. Fan coming on for 10 seconds and dropping off most likely indicates failure of power supply circuit on the converter...

As reported, the fuses saved the converter ok without much fuss, but at the battery post there was quite the spark and fizzing. I see that the fat lead post the clamp was on has a big messy scar into it where a clamp tooth melted in.

I have also done the "drop the wrench" trick across battery posts and saw the sparks and how the wrench gets welded to the posts.

I wonder if there is a safer way at the battery in case you screw up and do an RP by putting a connecting post in the mix with a fuse between that and the real battery post.

years ago on a popup forum I suggested folks pick over/under on the number of reverse WFCO hookups the coming spring!

The older PUs without battery charging capability isolated the battery from the power converter, reverse hookup caused the lights to operate and the furnace fan to run backward - they could not get the furnace to light!

BFL13 wrote:


Voltage at the clamps now 13.75 Everything is good with the converter. Put it back in the attic. 27s back on their Float.

You are welcome. :)

And a belated "thank you"!

Errors are cruel down here Mr. fj12ryder. Example making a right turn when your tires are against the curb and forgetting the sidewalk is used by more than a few idiots. Making the same right and having someone to your left make the parallel turn then squeeze into your lane.

Few people have insurance.

Like last night. The light changed to green off to my left I see a speeding Nissan, 50 feet from the intersection the light turned red for him. People behind me honked to get a move on. He roared through as I laid on the horn. Of all things a FEDERAL highway patrolman was across the street in his car at an Oxxo store. Red lights and siren. He roared down Calle Delante. I have no proof but I'd like to think my horn altered the federal. They do not take bribes. And the infraccion will cost the dumb**** around 200 dollars.

Head's up means walking down a sidewalk not trusting what's in front of your feet. Not trusting the grand sale in the store will show up in the cash register receipt. Waiting an hour at Costco for an electric cart only see to a twenty-something girl driving around in another cart holding a 4 year old in her lap and having absolutely nothing in the basket. For more than a hour?

I am going to drop by the commandancia next week and recommend the cops pay a visit to large store disabled parking zones. When they find no placard, they take the license plates. If the owner plays cute and uses special hardware, the cop calls for a tow truck.


This is utter head's up living. So when it comes to connecting wires and designing a circuit I play no games. The charger I am building came with an ammeter shunt so WRONG I burst out laughing I had to order another. It was checked right out of the box fresh from Guangdong Province.

The biggest help I have is my high definition camera. Lots and lots of erasable photos. Some I print like the convoluted routing of the Spirit serpentine belt.

It's mot that I am better than other people on the contrary I do not trust myself.

Automotive fuses may or may not operate fast enough to protect the converter. The converter diodes may also not operate fast enough.
It is possible for some to fail and as many not to fail.
To make a blanket statement, they always fail is wrong!

I happen to have a converter I got in 2011 that I do not expect to use again, so I tried it. It says it has RP protection and it has four 40 amp fuses for that.

https://www.boatandrvaccessories.com/products/powermax-pm3-100-100-amp-converter-charger

(the photo in that is not a 100 amper--ignore that bit)

I used a set of cut-off jumper cables for the connection. Voltage at the clamps 13.75. I have a pair of 27s in the garage on a Float charger from back when I used these batteries with the RV.

So--being real brave (or stupid) I clamped the converter backwards to the battery bank. Neg post first if that matters. Very Big sparks at the pos battery post and nasty popping at the converter, plus burning smells. Yipes! Removed clamps from battery bank, voltage at the clamps now zero, zip, nada.

Unplugged converter 120v, took out the four blown 40 amp fuses, replaced with four good ones, plugged the converter 120v back in.

Voltage at the clamps now 13.75 Everything is good with the converter. Put it back in the attic. 27s back on their Float.

You are welcome. :)

Nope. Not after I take the time to reduce error. Without the speed bumps, lots of red faced errors.

Power fuses are there to prevent a toasted device from turning into mount Vesuvius.

road-runner wrote:
I'm also interested in further info about the converter being bad if the fuses are blown.

I have 39 years as a RV tech and still working. When I have the fuses blown on a Converter, I have never had a converter work after replacing them. Maybe there is the exception, but I have never found it. Doug