My thirty year old Kitchen Aid dishwasher had a good screen to keep stuff out of the pump, and the design was such that the heavier stuff would accumulate in a wide channel below the screen so that the filter did not get dirty very often. In addition, the design of the filter system was such that the return water would slow as it approached the filter, assisting the chunks to fall into the collection channel, which was quite easy to wipe clean. It seems that the engineers responsible for that design knew a bit about fluid dynamics and how to drop stff out of a stream before it even reached the filter. Very good engineering.
As for the problems with the transformers and the fire ants eating the insulation, my conclusion is that those monsters came stright up from hell a while back and are never content unless they are causing problems.
I never intentionally use or purchase any transformers that include an internal nonreplacable device as mentioned. I have bypassed those devices in several transformers and never had any ill effects because of it. My impression is that the thermal protectors are very cheap quality and so some of them open at a temperature below the specified heat, rendering the product failed. So if a transformer has an external fuse, or other protection, removing the thermal fuse is not a problem that would cause a hazard.
Ratsky, please tell me if I'm remembering this correctly: Wasn't the federal government supposed to build a big particle accelerator in Texas in the 1990s, which ultimately had to be delayed (or cancelled?) due to fire ants being attarcted to the accelerator's huge magnetic fields?
We had a dishwasher that seemed to chip plates and no one could figure out why. Turns out we found bits of broken galss lodged in the sprayer, and smaller bits were apparently circulating through the spray nozzles at high exit velocities. It took a careful cleanout to remedy the problem.
Ratsky-- good to see your tag again. Can't tell you how many times bug-eaten wire insulation has appeared in the Sherlock Ohms and Made by Monkeys blogs. Seems there should be some off-putting chemical in the insulation to prevent this common problem.
Ants seem especially attracted to electric fields. I lived in Plano, TX some years back, and my house there had a low-voltage outdoor lighting system. It was fairly extensive, with a several hundred VA transformer. I had a series of failures, including one that got me a new transformer (in warranty) because of an open winding. It had dual outputs (separate windings), and the other one still worked. It turned out that each winding had an internal overcurrent protection device (besides the primary-side circuit breaker, and non-repairable) that would blow only if there was a major overload that peaked too quickly for the breaker to trip. I had lots of "fun" excavating all of that LV wiring to isolate the wiring fault, that showed up as a 0.1 ohm or so short on one LONG run of 12 AWG LV "burial" cable. I finally got to the problem: a splice (thoroughly taped, and with "lock" type crimp connectors) at a break-out point to split in 2 directions. For some reason, it had attracted a whole mound of FIRE ANTS that chewed away enough insulation to cause the short. Of course, I had to first wipe out the nest, wait for all the ants to die or otherwise depart, then rewire and re-tape that part of the run. All was well for a few months. Then, the same run failed again. Same spot, same reason (only this time it didn't kill the transformer, as the breaker did its job that time). I fixed it again, and the problem recurred a couple more times (that I know of; sold the house and moved back to Atlanta!). I did some checking around, and found that indeed fire ants for no known reason WERE attracted to electric wiring! Apparently, normal line voltage lighting doesn't have the problem; maybe the fields are strong enough that the ants get zapped before they can do much damage!
Our $400 late-model Frigidaire dishwasher has a strainer in the bottom to capture larger debris, to prevent the larger debris from entering the pump. It's a regular maintenance item to clean-out the strainer (preventative maintenance if done on a regular basis, corrective maintenance if deferred until clogged). My wife cleans-out the strainer about once a year, easily accessible and easy to clean. The dishwasher user's manual explains and illustrates how to clean the strainer. We're also careful to rinse all excess food before loading items into the dishwasher.
That's right, Ann. It seems a simple matter. So I'm surprised there are designs that make it so difficult for users. The fascinating part of this story, though, really is the bug getting into the control panel. How do you design to avoid that?
Rob, that's what I figured: there must be a (very imperfect) balance in designing these between filter hole size small enough to prevent damaging particles from passing through and filter hole size large enough to keep water flowing at the right rate of speed. Tim's dimensions are a lot smaller than a sunflower seed and larger than a size that I'd guess could cause a clog.
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Design News and Digi-Key presents: Creating & Testing Your First RTOS Application Using MQX, a crash course that will look at defining a project, selecting a target processor, blocking code, defining tasks, completing code, and debugging.
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