Sunday, July 15, 2012

Houston, we've had a problem

We are at the North Carolina State Fairgrounds in Raleigh (map). We've stayed at the fairgrounds before, but in the intervening two years they've built a new campground here near the equestrian complex. This one is outside the main fence, making coming and going easier when the fairgrounds gates are closed, and is also more level. Full hookups with 50 amps are $25. The old RV spaces are also still available and we saw a half dozen rigs there. There is some sort of horse event this weekend, and several rigs here are the combination RV/horse trailer type. There are perhaps 45 spaces in this new campground already, and they look to be in the process of expanding it by again as much.

You may have gathered from today's post title that not all was rosy here aboard Odyssey. Just like her namesake from Apollo 13, the crew heard a loud bang and then watched in horror as the main power voltage plummeted to zero. In our case it happened as we were getting ready to leave Birchwood. I had unplugged the power cord and finished my walk-around. I sat in the driver seat and switched off the high idle control, and in that instant I heard a pop and we lost the inverter, which was running two air conditioners at the time.

Usually when the inverter cuts out like this, it's an overload condition and the unit shows a red error light. This time, the inverter was off altogether, with no lights at all, and we realized we had lost all 24-volt power to the house systems. Louise detected the smell of burnt electrical components in the battery/inverter tunnel, and we immediately shut down the main cutouts for both the 24-volt and 12-volt systems. This latter item then took out our GPS and backup cameras.

So there we were, still in the camp site, engine running, but with no power to the house systems, including the refrigerator and the driver air conditioning. We had two choices: renew for another night in Durham and stay there to work the problem, missing our visit here in Raleigh, or continue here instead, knowing we'd have power here as well and that it was less than half an hour's drive. We decided to press on.

After we made a quick inspection of everything we could see without removing dress panels, and the burnt smell had dissipated, we elected to turn the 12-volt systems back on for the drive. That would let us use the GPS and backup camera as well as the FanTastic fans upstairs. We drove with several windows open, which made it at least tolerable. As we were driving we discussed the probable causes for these symptoms, and my best guess was that some failure inside the inverter had overloaded the 24-volt input, blowing the 400-amp class-T fuse from the batteries.

Once we arrived here and got settled in, I had to "hot wire" the air conditioners, bypassing the 24-volt control system to get two of the three units running. One unit always runs through the inverter, which was now offline, but we can select which of the three that is, and we selected the bedroom where we did not need the cooling during the project. I also switched the refrigerator supply from the now-dead 24-volt bus to the still-working 12-volt bus (the fridge works on either voltage), and hooked our water manifold up to the campground spigot since our pumps were also dead. With all the major systems thus bypassed, we could work the problem in a somewhat more leisurely manner.

That said, we could not simply run over to visit the cousins as planned, because the fridge and other 12 accessories were now running strictly from batteries, and we were uncomfortable leaving the bus unattended without knowing the root cause of the burning smell and electrical failure. While I was jury-rigging the power, Louise called her cousin to say we'd be late, and started emptying the battery tunnel of the items we store there.

Once I got the dress panel over the port side batteries off, the problem was immediately apparent. The built-in battery stud to which the main power take-off cable was attached had pulled right out of the lead. A small "puddle" of previously molten lead had oozed from the main terminal onto the battery casing. The terminal stud and retaining nut was black with char. The class-T fuse, by the way, was fine.

It took me a few seconds to realize what had happened. In hindsight, it was entirely preventable and entirely my fault, thus proving that even electrical system experts make mistakes. Basically, having the main power cable on that terminal by itself meant that all the current into and out of the entire bank, which can be well in excess of 150 amps when the inverter is running a pair of air conditioners, was running through the little pot of lead in which the stud, really nothing more than an 8mm hex bolt, was embedded. There is even a sticker on the battery warning against using the stud terminal for high-current applications.

Regular readers may recall the saga of installing these batteries almost exactly one year ago. As I wrote back then, after getting the batteries in place, we realized that the stud terminals were just a hair shorter than the ones on the batteries they replaced, older items of the same make and model. When I put all three cables onto the stud terminal on this battery, there was not enough stud length to get the nut on properly, and I even had to jury-rig the nut, upside-down, for a day until I could get a post adapter.

Now, had all three cables stayed together on this stud, as they were for four years with the last set of batteries, all would have been well. That's because three quarters of the total current would have been coming in from the three adjacent batteries via the connector cable, which would then be in direct contact with the main power cable. The amount of current coming through the lead holding the stud to the battery would have been just one quarter of the total.

By moving just two cables to the new post adapter, rather than all three (the stud on that adapter was not really long enough, either), the other three quarters of the current now came in through the post adapter before going out through the built-in stud terminal. With 12 straight days of 100+ temperatures in the last couple of weeks, and non-stop running of two air conditioners through the inverter whenever we we not plugged in, the lead began to soften and ultimately melted, allowing the stud terminal to pop right out. I'm sure it arced while separating, leading to the scorch marks and burning smell.

All's well that ends well, and I was able to secure all three cables to the post adapter and get the battery system back on line. I also tightened up all the other terminals in the battery bay. No harm done to anything but my pride, and a couple of muscles in my back (it's a tight squeeze in the battery bay). We made it over to the cousins' house shortly after 5 and had a nice evening together over a light dinner. This morning, I am mostly recovered even from the muscle soreness.

After we get everything loaded back into the tunnel and the battery monitor re-programmed, we will get under way to New Bern. I am hoping the Elks Lodge there will again let us use their power outlet, as I expect we will need air conditioning for the two days we will be there. Our broker comes in tomorrow around 10:30 to help us look at boats.


  1. Do you need to watch that battery post connection since part of the original post to plate lead is melted away....? But it wouldn't be good to change out only one battery leaving the others a year older either.... Never good answers in these kinds of problems.....

    1. We'll keep an eye on it as a matter of course, but no, I don't think this will be an issue. The lead that has melted away was really only in the path from the plates to the now-missing stud terminal, and not between the plates and the automotive terminal.

  2. And I was just telling myself sitting here in the M/H washing the dog after reading that great reply on Bus-nuts that Sean really knows his stuff and like you stated in that post you don't always take your own advice. No mater job well done. Even though I don't boat anymore can't wait till you start living aboard and began writing about the problem's that come with water. Tight lines my friend.....

  3. Thanks - once again - for an excellent overview of a problem, and its solution.

    Yes, your story is a message to myself: Every time I think I really understand something, and couldn't possibly missed something important, real life returns to remind me that I always need to be a student.

  4. I am always amazed at how resourceful you and Louise can be when these issues arise! I had exactly the same problem when I installed our 6 AGM's this spring. I used an insulated stud mounted above the battery bank for the 3 cables so I only had one 4/0 cable on the battery itself. I'm hoping that will prevent meltdowns. I had a meltdown on a terminal last year, but that was caused by a loose connection.


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