Maintenance & Restoration

Bob Miller · 03-20-2012, 12:21 PM

Sudden thought....
Be certain that NONE of your 120VAC ground or Neutral wires are also connected to that buss bar. The 120VAC lines should see the entire trailer like a giant extension cord and there should be no connections to the same ground that the battery is connected to. With the shore line unplugged, and all breakers ON, check for continuity between all pins in a 120 Outlet and chassis (DC) ground.
If you are talking about a Buss Bar inside the converter it MAY be connected to AC ground and you don't want to also use that for your battery. In the OLD daze, when there were just lights and fans to deal with, than might have been OK, but microprocessors do not like seeing any part of the ac signal on the dc inputs.
Bottom Line: The Battery ground/chassis ground must not be connected to any of the A/C wires....

Bob Miller · 03-20-2012, 12:47 PM

A Quick Thought
The 120VAC system in the trailer must be completely seperate from the DC side, this includes grounds. If the Green 120 VAC ground wire is connected to the same buss as the battery ground it can give microporcessor electronic stuff lots of problems. The battery (-) must be connected to the frame, the 120 VAC ground MUST NOT be connected to the same ground or the frame. If the Buss you are talking about is inside the converter it is usually the AC ground and must be floating apart from the frame etc.
With the shore power cord unplugged and the breakers all on, check for any continuity between the 120VAC outlet pins (all three pins) and battery ground. If there is a connection, it something that will have to be fixed. Microprocessors DO NOT like any a/c component on the DC lines and the green ground is a good place to find that. In some trailers I have even seen the neutral wire connected to the green ground. Back when all we worried about were lights and fans that was OK, no more. The A/c system should look like a giant exrension cord to the shore line.

**rabbit** · 03-20-2012, 01:18 PM

AC is all on breakers. DC fuse block and buss bar in separate cmpt. I did try jumping the socket shell terminal to the DC buss bar with an alligator clip lead. Result continues the same at inverter. Can I check for an "AC component" to DC current with multimeter?

jack

Bob Miller · 03-20-2012, 02:21 PM

No, a multimeter can't see the a/c leakage. But you can test for continuity between the a/c wires and the frame of the trailer with one. Those should all be open circuits. Also check between the green a/c ground wire and the DC ground buss, there should no continuity between those either. Many a trailer has had the a/c ground connected to the frame, along with the ground side of the battery, it shouldn't be that way any more.

**rabbit** · 03-20-2012, 04:57 PM

Thanks Bob, I'll do as much of that as I can understand how to do. I can see that there's a mess created by theory (changing over time) and no theory (the way your brother-in-law does it). Also thinking about cutting my education short and dropping out of school to run a chunk of #14 straight to the battery on the advice of another poster. Any harm in that? I noticed the Rat Shack lighter socket pigtail had an inline fuse; guess I should do also, huh?

jack

Bob Miller · 03-20-2012, 07:47 PM

If your shore cord is plugged in you will still have the same problem if it is being caused by cross tied grounds.
As mentioned, if you get a lot of voltage drop or have a low battery, the inverter will complain loud and clear.

floyd · 03-20-2012, 08:46 PM

It may not be this obvious, but look at the cord end. They often have a metal nut on the end next to the spring loaded button. This can work loose and short out the outlet. Sometimes even leaving the nut inside to wreak further havoc!

**rabbit** · 03-21-2012, 04:14 PM

Problem solved! To all who responded with advice and experience, thank you and my abject apology for being such a dunce! This evening I had an inspiration. I have four duplex receptacles in the trailer: 1 in front dinette, two in the galley, one in the aft "master suite". On shore power, I can plug 'n play with the laptop to my heart's content. So when do I really need the 12vdc socket for the inverter? Yeeeesss, when I'm off the grid!!!! So I shut off the AC breakers and guess what? The inverter works just fine plugged into the "devious current" socket despite the "muscular" wattage claim on the back. I guess there's no AC component when there's no AC. Something for all of us to ponder. I'm going to add label to the effect: "USE ONLY OFF GRID" in case what's left of my mind should somehow forget this little episode.

jack

Bob Miller · 03-21-2012, 04:33 PM

Problem Solved
Yaa... But...
You still have a cross connected ground somewhere and at some point you may either plug a DC accessory into your 12 volt socket and get a smoke greeting or, worse yet, you may get a short in something on AC and, if you also don't have a good ground to the power source to trip the breaker, you can wind up with 120VAC on the frame of your trailer. Best bet, find the cross tie and emiminate that problem before you become french toast.

**rabbit** · 03-21-2012, 05:01 PM

Can't find anything like a strap to frame; "anything like" being a wire in a round lug on a sheet metal screw. Not too worried I'll wind up with 120 to the frame but the "cross-connected" ground does worry me.

jack

Jon Vermilye · 03-21-2012, 07:24 PM

Quote:

Originally Posted by Bob Miller

No, a multimeter can't see the a/c leakage. But you can test for continuity between the a/c wires and the frame of the trailer with one. Those should all be open circuits. Also check between the green a/c ground wire and the DC ground buss, there should no continuity between those either. Many a trailer has had the a/c ground connected to the frame, along with the ground side of the battery, it shouldn't be that way any more.

You might want to take a look at NEC Article 551.55 Interior Equipment Grounding & 551.56 Bonding of Non Current Carrying Metal Parts.

While there should never be a bond (connection) between the neutral & ground (or frame) it is required that the AC ground be connected to the frame of the trailer. If this isn't done, a fault from either the hot or neutral will make the trailer chassis (and all metal attached to it) hot, resulting in a shock hazard to the earth.

If your trailer is wired to code you will find a wire between the ground buss in your distribution panel & the chassis.

**rabbit** · 03-21-2012, 08:28 PM

I'll take the service/converter box out again and look. Thanks.

jack

**rabbit** · 03-24-2012, 07:10 PM

Looks like what was required was less theory and a bit more praxis. I ran a #14 white from the DC buss to the lug on the socket shell tonite and (with the AC main breaker off) was able to power the inverter and my laptop AND 2 DC LEDs, 1 incandescent in the range hood, the range hood fan and the FantasticFan on high spd without an apparent brownout, red light on the inverter, or loud beep. I removed the tap to a side marker lamp lead in the frig comptmt (attached by wire nut) and spliced the sidemarker lead with a butt connector. This is considerable improvement on the experiment hooking the buss to the shell with an alligator clip lead. I had used the allligator jumper to ground a 12 ga. shotshell reloader in my basement so the gator clips were probably not clean metal. I did have the converter box as far into the aisle as it will come to open the clamp on a box connector to get the lead thru but didn't have enuf slack to examine the problem of tied grounds or frame ground on the AC. If the retrojockeys at Camping World et al weren't so damn stingy with wire (some of this stuff looks like it was installed with a barbed wire stretcher and cranked up to high C) maybe a bit of troubleshooting could be done by simple physical examination but I found it impossible to do so--probably also partially due to my own lack of sophistication about matters electrical. Again thanks to both Bill and Jon for the patient advice.

jack