# The Board

A kind of geeky post follows. I am an engineer, so please forgive me while I spin the propeller on my hat! 🙂

Just in case you’re unfamiliar with the propeller hat, Wikipedia has a quick article on them at https://en.wikipedia.org/wiki/Beanie_(seamed_cap)

Awhile back, in my Minimal Engineering post, I was talking about the poor design of the circuit board that controls my camper’s refrigerator and how I had to order a new one. The place I ordered it from said it would be 5-7 weeks for to arrive, so I was pleasantly surprised when it arrived today. I wasn’t expecting it for another month.

This was good news.

Even better, I examined the circuit board and I did not see anything “fancy” being done within it to monitor how much current the 12 volt section of the refrigerator is consuming. So, it doesn’t look like I will need to make changes to the circuit board, and I should be able to have it control a relay and have the relay control the 12 volt power going to the refrigerator.

A relay is essentially an electromagnet that controls a switch. The nice thing is that the electromagnet needs only a small amount of current, in this case around 1/10 of an amp, to control the flow of a much larger current, like the 17 amps needed by the 12 volt section of the refrigerator. The old control board, even in its current “fixed, but fragile” state, will be able to handle the current needed to operate the relay, so I won’t bother to replace the old board. This will save some time and also allow me to keep the new board as a spare.

The only thing I’ll have to consider is if the relay on the control board will be okay to handle an electromagnet type load instead of a “regular” load. If the relay on the board is not rated for an electromagnet type of load, I’ll add two 25 cent components to my external relay to compensate for this. Either way, when I’m done, the refrigerator control system will be (re)designed to operate for the long term and not just long enough to exceed the warranty period.

The best news will be when I get the relay system wired in place and it actually works. All the thinking, considering and calculating is fine, and it gives me confidence that it will work, but until it’s actually going, there is always some amount of doubt.

But first, I need to continue to pack for our impending house sale, change the oil filter, air filter and oil in my vehicles and cook some dinner to take to a potluck dinner at a friend’s house.

It’s always something….

# Minimal Engineering

Today, while on the way home from a weekend at a music festival (my wife as in one of the instrument competitions) , I noticed the camper refrigerator wasn’t working properly.

The refrigerator operates on 12 volts DC, 120 volts AC or propane, and the DC part wasn’t working.

There was an error code being shown on the display, so I looked it up in the manual. The text for that error code was, “Unit not operating correctly”. Wow. That was not terribly helpful.

After checking the two fuses protecting the wiring going to the refrigerator and finding them okay, I searched around on the internet and found some wiring diagrams that included enough information for me to start figuring out the problem.

After about 20 minutes of checking, I decided it was a problem on the control circuit board (the ‘brains’). To access the control board, one must remove the refrigerator from the camper. That took about 90 minutes. It took another 30 minutes to remove the control board.

What did I find?

Well, it was quite annoying. There is a fuse on the control board that is inaccessible until one removes the circuit board. Worse yet, this fuse is smaller than the fuse in the easily accessible fuse panel. So, the hidden fuse will likely “blow” before the easily accessible fuse. This fuse had “blown”. But it was not due to a short circuit or an “overload”.

It was caused by a poor design.

The refrigerator’s 12 volt system uses 15 amps. The pieces that connect to the fuse on the control board have an absolute maximum rating of 15 amps. In the electronics world “absolute maximum rating” is something that must never be exceeded for any length of time, and it is best to operate things at less than “absolute maximum”.

It’s sort of like a car engine with “red line” on the tachometer. The “red line” is the absolute maximum rating and, obviously, one never keeps the engine at that speed for any length of time.

So, what happened. The connection, which was being used at “absolute maximum “, started to get hot. This caused the connection to become worse, which made the connection get even hotter…which caused the connection to get worse….and so on.

The fuse was charred and eventually got hot enough to melt inside of the fuse and the solder holding the fuse connections in place. The control board was also charred.

I reworked the fuse connections and replaced the fuse, so the refrigerator is working again on 12 volts, but I don’t think it will last very long.

I called a camper service/parts place to get the needed part ($250) and found out the manufacturer had extended the refrigerator warranty from the listed 1 year to 2 years. This camper is 20 months old. So, I put everything back together, kept the charred fuse and called to make a service appointment. Had I known it was still under warranty, I would have just called for the service appointment. I also found out the part is currently on backorder and is likely unavailable for the next 2-3 months. So, after they examine the unit and decide it really is bad, I’m making some modifications to the system so that the control board, even with the charring, will likely last for many years. The control board will control a relay that I’m adding to the system. A relay is essentially a remote controlled switch that uses a small current to power an electromagnet in the relay and the electromagnet operates a switch capable of handling 30-40 amps of current. This relay needs about 0.1 amp from the control board, so the control board won’t be stressed. The relay will then do the “hard work” of switching the 15 amp current needed by the refrigerator, and since the relay is being used far below its ratings, it should last a very long time. I paid$12 for the components.

The second problem is the comfort heater (furnace) only works when the camper is connected to commercial power or the truck engine is running and charging the battery system. I did do some checking on the furnace and came to the conclusion that the logic circuit board/safety system of the heater is at fault. This circuit board costs around $250, so I decided to wait and get this fixed under warranty. The third problem is the microwave oven. Yes, I know, a microwave oven. I’ll just say that using it makes our wilderness experience complete. Anyway, the door doesn’t pop open like it should when I press the “door open” button. Instead I also have to pull the door open while pressing the button. Since I was waiting to get the furnace fixed under warranty, I just added the “microwave oven door won’t pop open” to the list for the warranty repair work. # Shakedown Cruise Well, it looks like I have “found” a suitable shakedown cruise for the new truck and camper. I received an email asking if I were available early next week to do some more work within the Grand Canyon and I said “yes”. Tomorrow or Friday they will let me know if I will be working at Phantom Ranch or Indian Gardens. A space for the camper will be available at the South Rim and “eat and sleep space” will be available at whichever place I will be working. I called a friend who can check the weather station at Phantom Ranch and at 10pm Arizona time, it was 96F/36C degrees and they said it will likely be even hotter next week….sigh…. It’s a dry heat…just like in an oven. 🙂 # Saving Money Today I was able to not spend about US$30.

In September 1986 I bought a work table for the new computer that I was using to complete the thesis for my master’s degree. Along with the table, I bought a nice lamp to go with everything else–an example of “one new thing requires several other new things.

The lamp recently started to intermittently go dark as well as not lighting up when the switch was turned on. A gentle tap of the lamp would return the lamp to normal so I ignored it for awhile.

Yesterday it annoyed me enough that I decided to see what I needed to do to fix the problem. Fortunately the lamp was old enough that it was fixable. Instead of glue, it was held together with screws, albeit screws that needed a strange 5 sided drive with a hole in the middle so that a regular “strange 5 sided drive” would not work. I dug deep, very deep, into my tool collection and found the correct tool, a tamper proof pentalobe Torx bit. For what it’s worth, I didn’t know the name of the tool until I read the box containing the tool bits.

Anyway, when I took the lamp apart, I found the problem. A wire going to the lamp socket had overheated and burned apart. The two ends of the wire were sometimes touching and sometimes not touching, which is why a gentle tap would make the light work.

I was both surprised and annoyed at my discovery.

The lamp uses a halogen bulbs which must operate above 250C degrees in order to work properly. I measured the temperature of my lamp’s socket and found it reached 290C degrees in about 2 minutes. The manufacturer used wire with an insulation with a maximum temperature rating of 60C degrees!

As the lamp was used, the plastic insulation overheated and eventually fell off the wire. It looks like the lamp designers knew this would be a problem because small channels were made in the lamp fixture to hold the wires physically apart so that even if the wire insulation was gone, the wires would not touch together and cause a short circuit. Eventually the wire itself was damaged by the heat and broke.

I replaced the burned wires with wires designed to directly connect to things as hot as 400C degrees. If the incorrect wire lasted 34 years, I guess the correct wire should last until my daughter needs to figure out what to do with the lamp.

The wire is normally very expensive but because I needed only two short pieces, I was able to buy some “scrap” wire too short for much else for US$5. And that’s what I did to not spend US$30.

# I’m Back Home

I’ve been working on the railroad….No, that’s not quite right. While there is a railroad going to the Grand Canyon, it stops at the canyon’s rim. Instead, for the past couple of weeks, I’ve been working at the water pumps at Indian Gardens, which is about 1/2 way down from the South Rim of the Grand Canyon. My specific part of the project involved the radio (wireless) portion of the system so the park staff can remotely monitor and control the the water pumps.

I have a bunch of pictures, but since they were taken while I was “on the job”, I don’t think it appropriate that I share them.

The work was hot, 107F/42C degrees in the shade. At one point the computer I was using shut itself off due to overheating and I was wishing that I could also shut off for awhile.

In Another Gem, 1994, I had posted about another job in the Grand Canyon where I got to ride in a helicopter. That didn’t happen this time. This time I was walking.

Please, if you go there, be careful. The idea that is phrased as, “I’ll hike until I’m tired and then turn around.” is a trap, and it’s not necessarily a live catch trap. That idea needs to be rephrased as, “I’ll hike down hill, in the cool temperatures, until I’m tired and then I’ll turn around. Oh Sh–! It’s all uphill and it’s hot as Hell. I am soooo screwed….”