I was asked by a friend to look at a portable dehumidifier that had stopped working. The small roll-around unit had been working fine in the basement but had suddenly stopped running and wouldn't respond when you pushed the membrane keyboard buttons.
When I disassembled the unit on the test bench and plugged it into a power source, the microprocessor signaled a beep that it had reached the post and was running properly. The display LEDs that indicate the set point for humidity control still remained black, as well as all the indicator LEDs.
When I checked the hex buffer inverting chips, it was noted that the digital inputs to the buffer were not shifting to a good zero or one level. When I looked at the input circuit, I could see that the input buttons were not pulling the input levels to a true zero. They actually voltage divided the 5V DC through the pull up resistors, but it was not low enough through the hex inverter buffer to tell the micro to run the dehumidifier.
In reality, there was nothing wrong with the unit, it just wasn't being told to turn on. The pushbuttons were the small, silver-plated versions used in a typical computer mouse. Silver, when exposed to a damp basement, will tarnish and become a poor contact. I replaced all of the buttons with good contact types, and the dehumidifier hasn't failed since.
I wonder how many dehumidifiers have been thrown out simply because the manufacturer used the wrong kind of pushbutton for a damp environment.
This entry was submitted by Jim Ellsworth and edited by Rob Spiegel.
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Jim, I wonder if the company is aware of this problem. Did you or your friend contact the company about this problem and solution? If they don't know then this may give them a reason to issue some kind of repair or recall options for owners.
It's scary how many manufacturers don't pay enough attention to all of the design considerations that go along with optimizing a product for its environment. This was a nice find, as noted, but a real bogus oversight on the part of the manufacturer. That kind of testing, especially given what the dehumidifier is supposed to do, isn't rocket science--just common design sense. A simple, cost-effective choice of another type of material for the push buttons would have been all that was necessary to avoid any issues.
It is interesting how many companies make mistakes like this. It reminds me of the old 1960s British sports cars I had. They were really fun, but terriably unreliable. The engines were relatively heavy and overdesigned. They would last forever. It was always some switch or small part that would break. We joked that these were designed by their new engineers.
Good question, Nadine. Even so, I would think manufacturers should test their products in consumer applications before sending then off into the consumer world. The last place they want to find out about problems is from their customers.
Nadine, in most of the cases the best part is it may be only a minor or silly faults. But in a fast life mode, nobody has the time to just check atleast the basic things before calling a service person.
@Mydesign: That's my point. For the most part, we don't investigate or repair things. It's not only that no one has tme to check. No one checks it out at all in small appliances.
@Mrmikel: I think good designers and engineers take all consumers into consideration. Designing for our own interests would put us out of business quickly. Today, overseas does not equal cheap design, the way it did in the past. Design schools throughout Asia are full of bright, creative people who are creating unique products for their local markets.
When I was early in my career one of the best pieces of advice I was ever given is, "If you can't find the time to do it right, you will have to find the time to do it over." That is still a fact of manufacturing. You may get away with poor slipshod design for a while, but probably sooner rather than later it will bite you.
As an exercise in "discovery" & satisfaction for the more experienced among us, it would be interesting to find out WHO the manufacturer of this dehumidifier was, and get more info on the design team. IF the "chief engineer" of this company has an advanced degree from one of our prestigious business schools (think M.B.A. here!!), then it's no wonder that the switch design was marginal from the outset. Experienced engineers would have nixed using a pad switch w/ silver contacts, instead opting for a tad more expensive gold contact, which exhibits no oxidation properties. And, IF the engineers were recent grads, with little real world experience, the silver oxidation & migration phenomenon would have been alien to them.
I worked for a company that made agricultural electronics. We quickly found that it's very difficult to manufacture a membrane switch that's reliable in an outdoor environment. We went through several vendors before finding one that could manufacture a robust switch. Most of the problems were from silver migration, where the silver trace in the switch panel migrates to an adjacent trace. Not surprisingly, a more robust switch also cost a little more money.
Since the problem with the humidifier was caused by a switch making marginal contact I wonder if the pull-up resistor was too stiff to work properly as the product aged?
When I went shopping for a dehumidifier several years ago, I of course looked at the cheaper ones first, which are aimed at consumers. Although they're a lot prettier than the industrial versions, they just didn't look serious: I live in a rainforest and I wanted to buy something that really works here. So I passed those by. The only electronics in my $900 portable, rollaround, commercial-grade industrial-strength, ugly gray metal Ebac dehumidifier are probably a few sensors and the LED "full" light on the front panel. More germane to this story, the only front-panel control is a mechanical rotary dial to indicate what percentage humidity I want it to keep. Although we've had to open it up and clean out the air filter every couple of years, it's been a workhorse and well worth the investment.
Anne, we had one of those non-electronic dehumidifiers and ours put in 10 years in one basement and another 20 in our Massachusetts house. It had one dial that went from OFF through LOW (humidity) to HIGH. The coils filled up with dust and required a thorough yearly cleaning with an outdoor hose, but otherwise the dehumidifier kept running and running and running. We left it for the buyer when we moved to Utah where we have no humidity problems.
Now that people note problems with small disc switches on front panels, I wonder how long our washing machine and dishwasher will last. I can't think of more humid operating environments. Perhaps the manufacturers used gold contacts.
It may have just been designed cheap overseas, but it could have been designed in the desert Southwest, where humidity (and its problems) doesn't occur to people. In western Oregon, we think about humidity all the time.
It causes problems when designers/installers from dry climates work here in the summer, and don't have a clue about driving rain and 70% humidity for 6 months of the year.
On the other hand, static damage occurs to those folks often, but is not so much of a problem here.
mrmikel, that's an interesting point. But--designing dehumidifiers in a desert state?! That doesn't make much sense. Or at least, it doesn't make sense to not do your homework about the environment the product will be used in.
Jon that sounds a lot like mine. I think we've had it about 5 years, maybe more. The dial goes from Off to High, but with numbers representing relative humidity percentages. Cleaning it every 2 years seems to be enough (no animals and we keep dust down due to allergies).
We've also had a problem with a soft disc switch on the washer. I bought it before meeting my husband and as soon as he saw it he said "That won't last much longer!" He's already replaced the mechanism underneath at least once. The ones I really dislike are the touchpads on the kitchen stove: I have to push them harder and harder to make the timer work.
I looked around our house and found the same type of "switches" on our dishwasher, stove, microwave oven, washer, and dryer. All the large appliances seem to have them. I suppose the alternative comes down to LCDs with touch screens, but I wonder how easy it is to clean off dirty-finger marks and smudges without activating something. Perhaps some smart designer would include a "clean-up mode" that deactivates the touch-LCD panel for a few minutes so someone can wipe it clean.
Jon, those touch screens worry me, too. Just like the ones at grocery store checkout stands that can't handle thousand of pushes by impatient people, the ones on my stove can't handle years of pushing by only one cook several times a week. They are cleanable with a light touch, but you often have to reset them afterward. I just wish they were more durable. Actually, I prefer knobs and dials.
Good point, Ann. As well as the durability, I also wonder about the cleanliness of the keypads in stores. Every time you use one of those, you're effectively shaking hands with the last few dozen people who have used it.
I bought a fairly cheap unit from Sears about 27 years ago. This has a Neon indicator to tell you when it's full. ( What's an LED?? ;-) It runs about 5-6 months every season.
As noted in some of the other posts, I've had to clean it out pretty much yearly. I've also had to pull it apart and oil the fan motor bearings a few times because the fan stopped spinning once when it was about 3 years old.
I don't think the Humidistat uses silver or gold contacts but I'd bet the electrical current is sufficient to keep them clear. No standby current either. How can you get Greener than that?
My guess is that the button switches did not use silver, since that material is "expensive", but rather some much cheaper substitute. Many times, after a product is designed it gets it's bom cost reduced, often by people with only an accounting degree, and having all the engineering skills that an accounting major study provides. So the expensive switch gets replaced by one using electroless tin, which is cheaper. Of course the pull up (or pull down) resistors may not be in spec either, ading to the complication.
Actually, I am now having push button panel problems on my relatively new dishwasher, which the membrane assembly does not want to continue to sick to the control panel, My guess is that the really good adhesive would have added a cent to the cost of the dishwasher.
That slogan goes " Never Time to DO IT RIGHT, Always time to do it over". I once worked for a company that was often in a rush to do things before they knew what to do. The result was often a lot of expensive scrap. That organization is no longer in business, by the way.
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