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

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.

Had the design used better parts to connect to the fuse (an extra 75 cents…I checked…..) or the $12 system I’m going to set up, this problem wouldn’t have happened. My guess is that the engineer knew this, but was told to minimize costs and build it “just good enough”…with just good enough being “lasts long enough to make it through the warranty before failing”.


Pressure Canner Gauge Check. Part 2. More Ideas.

This is an idea for checking pressure canner gauges at home. It seems to work for me and I give it the “if it breaks into pieces, you get to keep all of the pieces” guarantee. In other words, use this for ideas, use your best judgement and don’t blame me if it doesn’t work for you.

Normally I’d just take the canner to the local USDA Extension Service office to get the gauge checked, but the office is closed because of Covid…so no gauge checks.

The last time I did have the gauge officially checked, checks were done at 5, 10 and 15 psi and if those readings were correct, the intermediate values were presumed to be correct. The person doing the tests also told me that the gauge should be replaced if the readings were incorrect by by more than 1/2 psi.

If you can get the gauge checked officially do that. Or, better yet, convert the canner to a “jiggle weight” pressure regulating system The jiggle weight replaces the gauge and needs no yearly check.

Yet another advantage of the jiggle weight is that the temperature control is much less critical and instead of having to continually watch the gauge, you can listen to the hissing of the weight while doing other things nearby.

Anyway, in a prior post, Pressure Canner Gauge Check. Part 1. I talked about making a manometer and about different methods of reducing the height of the manometer so I wouldn’t need such a tall structure to make the 15psi measurement.

Well, a friend loaned me a 40 foot tall “push up mast” that (before satellite television) was used to hold up the large television antennas and this gave me an idea to just make a “well manometer”. This is one that just uses one piece tubing going straight up, instead of a U shape. This saves a lot of tubing as I only need 35 feet, instead of three times the 35 feet amount–35 foot on each side of the U, plus another 35 feet to get the top of the U back to the bottom.

If you have a tall enough tree, you could use the tree instead of a pole, but you will need to ensure the tube goes “straight up”. In any event, it’s the height that’s important, not how things are supported.

I dug around in my bucket of brass plumbing fittings and came up with enough stuff to “give it a try”. Basically it’s a T-fitting with one end connected to the water supply, another end connected to the vent pipe on the canner and the third side connected to the tubing that extends up the pole.

In the picture, the water hose is obvious. the tube going up the pole is on the right hand side of the T and the hose going to the canner vent pipe goes from the left side of the T. I used that small valve on the water hose side of the T to control the water flow from the water hose and it made things a lot easier for me.

I have a Presto canner and a 1/4 inch ID tube fits perfectly over the vent pipe, so I matched the tube fitting on the T to that size.

I currently didn’t have any way to secure a 40 foot pole so I tried this as a proof of concept by using a 15 foot tree trimming pole. I used electrical tape to secure the top of the tubing and the tape measure near at the top of the pole and also at intermediate points on the pole. It doesn’t look it in the picture, but the pole is vertical…I used a level to check. Later I’ll mention why it’s “moderately important” to have the pole (and tube and measuring tape) as close as possible to vertical.

So, once everything was hooked up, what I did was to start the water flow, very slowly, so that the pressure in the canner began to slowly rise. At the same time, water also was flowing into the elevated tube. When the pressure gauge began to register and water began to flow out of the top of the elevated tube, I slowed the flow of the water so only a slight trickle was flowing out of the top of the tube. The slower the water flow, the better and just a few drips per minute from the top of the tube is great. If you can turn off the water flow and the pressure settles to a constant value, that’s even better as the water flow won’t cause an error…and it is a good test of the canner gasket.

When the water was merely a trickle from the top of the tube, I measured the distance between the top of the canner and the top of the water tube…13 feet.

Note that this is a surveyor’s tape and instead of the feet being divided into inches, the divisions are tenths and hundredths of a foot.

Note how I said “top of the canner”. This is important.

It turns out that 1psi will push water up 2.31 feet. More formally this 2.31 figure is for distilled water at 39F degrees, but tap water at temperatures comfortable to humans wearing light clothes is so close to 2.31 feet per psi that it doesn’t change anything enough to matter.

So, to get the pressure. In this case, a 13 foot tall column of water, at 2.31 psi per foot, I divide 13 by 2.31, which is 5.6psi. It’s hard to tell because of the the camera was not directly in front of the gauge, but the gauge needle was slightly closer to the 6 mark than the 5 mark on the outer scale, which is right where it should be. So, the gauge is accurate at 5psi.

When I figure out how to get a taller system, I can check the gauge at 10 and 15 psi.

Now, I need to figure out how to get the tube 35 feet in the air. What I plan on doing is calculating the heights i need for 5, 10 and 15 psi and using a string and pulley to raise the tape measure and tube to the correct heights and then letting the water trickle out the top of the tube. I thought about putting the tube at full height and measuring how high the water is pushed up the tube, but it is hard to see clear water in a clear tube from that far away. So, instead I plan on the “trickle out the top” method. As long as I keep the water flow to the absolute bare minimum, it will be fine.

The heights are 11.55 feet (11 feet, 6 5/8 inches) for 5psi, 23.1 feet (23 feet, 1 1/4 inches) for 10 psi and 34.65 feet (34 feet, 7 3/4 inches) for 15 psi.

The amount of tubing on the ground doesn’t matter as the manometer only “cares” about water above the height of the canner. So, it’s OK to have a lot of tubing laying on the ground.

The diameter of the tubing doesn’t matter. A larger diameter tube has more water, which weighs more, but the water is spread out over more square inches. The math works out that no matter how large the tube diameter is, it is always the case where each psi of pressure will push the water up 2.31 feet. It also works out that the tube varying in size along it’s length will have no effect…the 2.31 foot value is the same. This 2.31 value for water is for earth, but I doubt that will be a limitation. 🙂

Since errors in pressure for a canner can have dire consequences, some thought as to the various errors is worth while. Also, keep in mind the gauge is considered “OK” if the gauge error is less than 0.5psi.

The 2.31 foot per psi value is for distilled water at 39F degrees. Changing temperature from just above freezing to around 100F degrees would cause a 0.1 psi error. In this case, the error at 100F would be “gauge reads lower than the calculated manometer pressure”, so if the manometer calculation says 15psi, a perfect gauge would show 14.9 psi.

Tap water is not distilled water and and this can mess with the accuracy of the measurements, but it turns out that if the water tastes OK, the worst the error would be is a few thousandths of a psi (0.001 psi), so tap versus distilled water errors are not worth worrying about.

Another potential error is gravity being different from “standard”, but you don’t have any control over that. On Earth, the lowest value for gravity is atop a mountain in Peru and the highest value for gravity is on the oceans around Antarctica. But even at those extremes the error for a 15psi reading is around 0.06psi, so again, this isn’t an issue..

Another source of error is if the “uphill” tube is not vertical, so use a level to ensure the support pole is vertical. You can see what happens if you were tip the pole sideways…you can see that the pole length not the same as the height of the tip of the pole. At it’s most extreme, the pole laying on the ground, the pole tip height is zero, but the pole is still its full length. If the tip of the pole is “off of straight up” by a few inches, the pressure error will be less than 0.1psi, so pretty close to straight up and down is OK.

Yet another error is making a mistake in the height measurement. Even a foot error will only cause a 0.5 psi error and I’m quite certain the measurement can be made within an inch or so with no issue. A one foot error is “worth” about 1/2 psi error and a inch is 1/12 of that, so one inch works out to be about 0.04psi of error. This error can creep in if the tape measure and tube are not kept together, but again, even a slight imperfection does not cause a huge error.

The final source of error is letting the water flow too quickly. This is the biggest source of error and is the one that is most easily controlled, so go slow and if possible, stop the flow of water and let things “settle” before deciding if the gauge is correct at the desired pressure. I had a tiny bit of leakage around the safety plug on the caner, so I could not completely stop the flow of water, but I was able to slow the water flow to where only a drop or two of water per minute was coming down the pole.

If you’re careful, you should be able to check a canner gauge to ensure safe canning. But again, I’m not “there”, so I can’t tell if you’re making mistakes…so be careful.

Micrometer, Chalk, Axe

If you haven’t figured it out yet, I like to know how to do things “the old way”.

A couple of posts ago, I talked about using a slide rule to complete some calculations involving an electrical circuit.

The slide rule allows one to (reasonably) quickly make a series of calculations, but it gives only a limited amount of precision—3, maybe 4 digits worth of precision.

What this means is that when using a slide rule, one won’t often get an exact answer because you can’t tell if the result of a calculation is 0.391, 0.3911, 0.39107 or 0.3907311284892737550620845888890942676180151675764320757471065494645546820718925532. All of these are the value of the sine of 23 degrees but have increasing degrees of precision.

Below, the slide rule is set to show the answer for the sine of 23 degrees and you can see the answer as 0.391.

The same problem exists with very large numbers. Forget the sine thing for a moment. 3,907,311 (3.907311\times10^6) can not be shown exactly on the slide rule. About the best you can do is 3.91\times10^6, which is 3,910,000.

Most of the time, this is not a problem because the values used in the calculations are themselves not exact, nor is the result needed to be exact.

Calculating the gas mileage of a car making a trip of 53 miles is a good example. The odometer on my car measures to the nearest 1/10 of a mile and the gas used, even if one fills the tank before and after the trip, might not be accurately measured because one pump might automatically shut off sooner than the other pump. So, there is no point in making a uselessly precise calculation–or wasting the time to do so.

Back to sines.

In the old days, if a better answer for the sine of 23 degrees was needed than the 0.391 provided by the slide rule, then one consulted some books, such as this one, published in 1942.

This book has 541 pages that all look similar to this, which is certainly not entertaining reading.

Going to the page 278, I find 23 degrees and see that the sine for 23 degrees, 0 minutes and 0 seconds is 0.39073113.

If that isn’t close enough, then I have another, much larger, book, published in 1964 that gives the sine of exactly 23 degrees as 0.390731128489274, which should be “good enough” for all but a few circumstances.

In 1942, getting an answer closer than provided by a slide rule was quite an ordeal.

Imagine a calculation requires you to find the answer to to
12254\times sin\left(23\textdegree\right).
First you look up the sine of 23 degrees in the book and then do the multiplication…hand held calculators do not yet exist, so it needs to be done by hand.

It took me about 5 seconds to do this on the slide rule, which gives 4,790 as the answer, but about 10 minutes to do the work to get 4788.01926702 (I had to do it twice to make sure I did it correctly).

For what it’s worth, back then, “Computer” was the title of a job held by a person and there were entire rooms of (human) computers doing high precision calculations. My quick example took only 10 minutes, but what happens with a huge formula? What might take one person with a slide rule 2-3 minutes to get a 3 digit answer, might take 10 or 12 people a week (or more) to get an 8 digit answer.

So, the engineer would likely use the slide rule and then stop and decide if the better answer was worth extra effort.

Now, electronic computers and hand held calculators have eliminated the need for the mathematical tables and the concept of “is this close enough” has been diluted because it’s no extra work to get answers with 10-15 digits, even when the answer is what I call “uselessly precise”.

My car’s gas mileage on that 53 mile trip was 25.23241184 miles per gallon. Or maybe it was 24.91346521 or 25.22838452 miles per gallon. Or, maybe it was about 25 miles per gallon.

If all you have is a piece of chalk to mark where to cut and an axe to make the cut, is it worth it to make measurements with a micrometer? 🙂

Super Uber-Nerd-Geek. I Guess

So tonight, with nothing better to do, I went back to the days of old when I was in engineering school

I took the following AC circuit

and analyzed it at 60Hz to come up with the equivalent series circuit.

I started engineering school in the late 1970s and by then, calculators were affordable (as long as one ‘ate cheap’ for several weeks).

This time I used a slide rule. It was because I had commented on Marcia’s blog post . I had used a slide rule in my high school physics class and I wanted to see if I could still “do it”.

I succeeded and it took only a few 30 minutes, but I had to make lots of notes to keep track of the various intermediate results.

Computer programs make solving this kind of problem so much easier, but it’s not as super uber-nerd-geek as using a slide rule and some paper.

This whole problem is adding and dividing of vectors. Any vector can be represented (mathematically) in two different ways. One way most easily allows addition and subtraction, while the other way most easily allows multiplication and division.

It involves some trigonometry and algebra to do the back and forth conversions, but the annoying thing is when one is doing lots of multiplications and additions, followed by more multiplications and more additions, because each pass through the process requires going through the conversion process. And this problem requires lots of conversions.

Doing this certainly increased my respect for the engineers that came before me. 🙂

We’re Home

As the title suggests, we are back home in the desert southwest after completing my engineering work in the Grand Canyon and then traveling through Arizona, Utah, Montana and Idaho.

During our travels in Northern Idaho, we got to meet the folks behind the site, and we had a great few hours talking with them.

Besides the work at the Grand Canyon, our trip had a purpose– to look for “nice” places to move. My wife hates the desert heat and I dislike living in a big city. “Not hot” and “not city” leaves a lot of places and our favorites are: Kanab, Utah; Bonners Ferry, Idaho; Troy Montana.

My wife grew up in a tiny town in the “snow belt” of Upstate New York, so she is used to both the cold and snow. I grew up in a tiny high desert town where it rarely snowed but was both hot and moderately cold (115F/45C in the summer and 10F/-12C in the winter). I also did a lot of work on mountaintop 2-way radio sites where daytime temperatures struggled to reach -20F/-30C…so I am at least aware that there is a condition called “cold”. Still, before we make the final move, we will try to rent a place for the winter months to ensure our memories of “cold” have not been overly dimmed by 40 years of time.

Our new slide-in truck camper’s shake down cruise had only three problems to report.

The first problem was the lavatory faucet leaking water to the compartment below it. I fixed this myself because a replacement faucet was only US$16 and it took me less than 5 minutes to change to the new faucet.

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….”