Inverter loose connection advisory

[RVDude]

Just thought I'd pass on a discovery I made today.

I was charging the batteries under genset at max bulk mode charge when I smelled "that unmistakable smell" of burning insulation. Fortunately I was in the coach and immediately powered everything down and mounted a frantic search. I discovered the problem inside the inverter 110v feed access panel. Photos follow. Under full bulk charge there is 20amps (120VAC) going through that wire. My guess is that the set screws were not properly tightened resulting in high resistance and the resultant overheating. Obviously the temporary fix is simple as you can see from the wire nut photo.

My point is that it might be prudent to put on your TO-DO lists to cinch down the set screws inside that panel and maybe even have a go around in all the service panels and circuit breaker boxes. BUT: DO NOT do this unless you have some electrical experience!

The ISSUE:


The temporary fix using a wire nut to bypass the wire block:

[RVDude]

Just thought I'd pass on a discovery I made today.

I was charging the batteries under genset at max bulk mode charge when I smelled "that unmistakable smell" of burning insulation. Fortunately I was in the coach and immediately powered everything down and mounted a frantic search. I discovered the problem inside the inverter 110v feed access panel. Photos follow. Under full bulk charge there is 20amps (120VAC) going through that wire. My guess is that the set screws were not properly tightened resulting in high resistance and the resultant overheating. Obviously the temporary fix is simple as you can see from the wire nut photo.

My point is that it might be prudent to put on your TO-DO lists to cinch down the set screws inside that panel and maybe even have a go around in all the service panels and circuit breaker boxes. BUT: DO NOT do this unless you have some electrical experience!

The ISSUE:


The temporary fix using a wire nut to bypass the wire block:

[Jetsmania]

Hi! WOW It's a good thing you were in the coach. Like you said, make sure you have electrical experience before you poke a screwdriver in there! That's all hair curling voltage there! Are you sure thats from a loose connection, and not from the strip not being able to handle the 20 Amps?? Paul

[RVDude]

jets: That is a superb point about the block itself being able to handle the load. I suspect that it is Newmar that adds the block and not Magnum. I have reported this incident back to Newmar and will report anything that I hear from them. I also noted the grounding lug for the 12ga wire is attached using only a small #8 screw through a painted surface... Hmmm?

WARNING: Scientific mumbo jumbo follows...
I measured the loads on the wires after I fixed them and was a little surprised at just a fraction short of 20ampsAC on that wire when under full 123ampDC charge and negligible interior AC loading. It is a 12ga wire feeding into 2*12ga into the inverter so that is not a problem. My math tells me that 123ampDC should only need about 11ampAC so I don't know where the rest of the 20ampAC feed is going. The output wires were measured at about 1ampAC. Hence, my total input should only have been 12ampAC (11+1). These inverters are better than 90% efficient so add another generous 1ampAC for efficiency making a total of 13ampAC input. So, I am at a loss to explain the difference between the calculated 13ampAC and the measured 20ampAC!

[jjbsmith]

We had the same juction block melt down on the inverter side of a Xantrex Prosine inverter. This was not in a Newmar product.
It's a good idea to check those screws thanks for the heads up.

[Jetsmania]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the measured 20ampAC </div></BLOCKQUOTE>
Hi! Where did you measure 20 Amp Ac at?? Paul

[Chickadee]

G'morning RVDude: Thanks for the heads up regarding this potential problem. We travel in an 08 4502 Essex and still learning about all these things, so bear with me. QUESTION: Is this 110v access panel located ON the inverter and do you happen to know WHERE my inverter is located?? I assume it's attached to the overhead inside an after basement bay inboard and behind the Oasis as was the case in our former 06 Mtn. Aire. Also, since I do NOT have electrical experience to any degree, I suppose it'd be better to have a Newmar Svc. facility check this out....huh?....or what do I have to watch out for if trying to tighten these connections? Thanks. Steve & Lynette

[Jetsmania]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">WHERE my inverter is located?? </div></BLOCKQUOTE>
Hi! It is located in the bay that is in front of the outside entertainment center bay. It is white and hanging from the chassis rail. There is an access panel that comes off that allows you to get to the wiring. I would not be trying to tighten anything without first making sure all power is dead in the invertor!! If you touch a screwdriver to the side of the invertor while tightening the screws, and you have voltage present, you will have curly hair!! Time will tell if this was just a loose screw or a design flaw. Paul

[phototex]

Your measurements make me wonder about the published efficiency of the charger. Typical overall charger efficiencies I have seen for laptop computer batteries are in the range of 50 to 70%, and the efficiency is affected by how "smart" the battery is. Perhaps they are publishing the efficiency of charging into a resistive load and not a real-world battery? My guess would be that charger efficiency would also vary depending on the type of battery you are charging (gel, AGM, flooded, etc.).

[Chickadee]

Paul: Thank you. Steve & Lynette