Mosquito Magnet Repair Info

A few days ago I was checking the MQTT feed from the instrumented Defender, and found it in an error state. The MQTT logs showed the unit rebooting and restarting several times during the day. Then it stopped restarting. Attempts to remotely restart the unit failed. The unit was dead, again.

I had been noticing increasingly frequent reboots over the last month, with the system lasting for a couple of hours, then rebooting. I chalked it up to possibly poor WiFi reception or MQTT server outage somehow causing some issue. I spent a while looking over the code to see if anything like connection problems could cause a reboot, but was not able to find any such mechanism. Only the trap’s web page has that option, and it was not the source. My most recent issue dealt with combustion temperature dropping too low during operation, but this was different: unable to run after a cold start, when high case temperature was not a factor.

Perhaps the controller intermittency was causing the problem. I was afraid of burning out or degrading my igniter by constantly cycling it from cold to hot, which had happened last year when I had intermittent on/off switch problems.

I took the second master NodeMCU module and replaced the existing unit, which had become stuck in the connector. Prying the unit off, I noticed some corrosion on the module pins. This could be the problem. The temp/humidity sensor pins had been quite corroded at the start of the season, and would not work at all. I also noticed that the module was covered with mosquito parts, dust, and other awful looking stuff. Perhaps this could be another problem causing the intermittent reboots. I hadn’t bothered to insulate and protect (e.g., conformal coat) the controller or the connector, and instead placed it in the far forward of the case, away from the exhaust port, as a way to keep it out of the elements, and rely on the positive air pressure to keep outside moisture in check. This was not good enough. Also, there is no protection from condensation when the trap is not running. I don’t do this, or other niceties like screwing the case top the the bottom, to facilitate modifications, plus I just want to see what happens (not recommended).

Replacing the controller fixed the intermittent controller problem, but the trap still did not start. Perhaps the obstruction at high temperature had also increased at low temperatures. I examined another used valve assembly I had purchased. Using fine drill bits, I measured the valve intake and exhaust holes. For the record, the hole from the valve to the nozzle is a #56 drill size (1.16 mm). The gas line to valve hole is #73 (0.6 mm). I could clean the hole using the #73 drill bit straight down, and a section of solid copper wire bent to just fit into the hole to the nozzle. I opened the valve on the Defender, and cleaned the holes. There might have been a bit of a deposit on the gas line side, but the other hole to the nozzle was clear. I reassembled and restarted, but no temperature rise at all! This is unusual because the igniter on itself should cause a few degree temperature rise, but there was nothing. Was the NodeMCU module not driving the igniter?

I found the IOT controller schematic, traced the wiring, and, sure enough, the red wire from the module to a via on the IGN net had come off, the result of me stressing the wires more than usual because the connector had stuck to the corroded module pins (no, I didn’t strain relieve the wires onto the PCB…). Also, the solder joint to the via looked deteriorated as well. I cleaned and resoldered the connection, and inspected the other connections, and tried again. I removed the igniter, and it worked, able to burn the wooden part of a match stick with no issue. Good. Not thinking, I restarted the trap with the case off, but the trap still did not start.

I was starting to wonder what was happening here. What could be left? Earlier, blowing out the nozzle with a tire pump had worked. I tried that again, including higher pressure of 100 psi using higher voltage to the pump with the car running, but still no luck. I decided to replace the nozzle.

I disassembled the unit completely, cracked the combustion chamber, and removed the nozzle and valve assembly. I took all my old nozzles and attached them in turn to the spare defender valve, and ran the tire pump pressure test. Open (no nozzle) resulted in 25 psi. The installed nozzle was 77 psi. Other units ran from 86 to 103 psi.

Unscrewing the test nozzles, I noticed moisture on the filters. Several of them, one after the other. Where was this coming from? It must have been the very humid air being compressed by the tire pump. I was alarmed because I can’t imagine that forcing water into the nozzle is a good idea. I realized I shouldn’t have been using a tire pump, but rather a source of dry compressed gas, for example, a CO2 cartridge, just like the manufacturer initially recommended…. It looks like the tire pump is not a good choice. I need another source of compressed gas, at least on very humid days.

I finally tested a brand new nozzle, it read 66 psi, much lower, wow! I decided to install the nozzle. I washed the plastic parts, drove around the area hardware stores looking for a #8-32 x 1/2 nylon bolt to hold the thermistor (these never last and have to be replaced every time), replaced the broken nylon standoffs (they last longer, but ditto), then reassembled the trap. With the case off, I started the trap, but it still did not start!

I then removed the igniter which was apparently working, and replaced it with a brand new one. With all parts replaced, I thought it had to start. I washed the top cover, put it on, and started the trap. Success! The trap was running!

These multiple efforts took most of a day. Time to reflect.

I first remembered that the trap does not start with the cover off, so the trial with the new nozzle was flawed, and I don’t know if it was the nozzle or the igniter. I am saving the igniter and will replace it after a few days to see if that was the problem, but I suspect that it was the nozzle.

Next, pondering why the trap start doesn’t with the case off, I finally realized something. It’s all about carburetion, or the process of mixing fuel and air. The fuel flow is fixed by the nozzle and its restriction. The air flow is supplied by the fan, which blows into one or two holes in the side of the combustion chamber into a large channel that directs the air to the vicinity of the nozzle. If the air flow is too high, the mixture will be too lean, the igniter will not light the fuel, and the air will not even warm up sufficiently to register on the thermistor. To start the combustion, the air flow must be restricted to make a richer mixture, much like with a choke on a gas engine. After the combustion is established, the mixture can be leaned to yield complete combustion (unburned propane is a mosquito repellent).

The case and catch basket constrict the air flow. You can hear it when you open the catch basket. With the catch basket hatch open, and especially with the case off, the air flow is greatly increased, making the mixture too lean to start. A few years ago, I had realized this, and used a piece of paper over the fan to restrict the air flow so the trap would start with the case off for testing. But I had forgotten all of that on this day.

I believe a rich mixture is what the lower initial fan speed is all about. I had never understood this simple point, and thought perhaps it was lower to allow the igniter to reach a higher temperature for better ignition. It takes about 10 seconds for the igniter to get visibly hot. Accordingly, the Defender software now reduces the motor speed during initial igniter activation. However, the software sets the fan speed to 100% at the same time as the gas is turned on. I now believe this is a mistake. Looking back at the wiki, which measures the thermistor ramp pulse width as a function of elapsed time:

0	Turn switch on	13.5 ms (room temperature)
2:57	Solenoid on, Fan low speed
3:10	First pulse width change	13 ms
4:02		8.0 ms

The chart plainly shows that the solenoid and low fan speed onset are simultaneous in the original Defender. The fan goes back to high speed after perhaps a minute, when combustion is established. I will modify the software to accomplish this for more reliable starting.

A lightly plugged nozzle restricts the gas flow somewhat, which might be Ok. The trap would just produce less CO2, but would still work as the vacuum is still working full force. The range would be reduced. But it all relates to the need to keep the nozzle filter clean. Perhaps “cleaner” propane?  CO2 quick clear cartridges? Both?

Time for a software update? No, time to catch mosquitos! Not a safety issue, so the software can wait.

Happy trapping!

P.S. A horrible violent rainstorm with momentary power loss yesterday caused the trap to restart, and the secondary NodeMCU unit was programmed for a lower temp of 70°C instead of 40°, so it tried to restart at the higher temperature, and that didn’t work. Later, I noticed it off, and rhe temp and humidity were 25°C and 84% respectively! It took 4 attempts to restart the unit. I guess I have to update the software sooner rather than later.

Coming off two bumper (full basket) catches, I was sanguine regarding the power cable intermittent that would reset the trap unless it was hanging from the trap just so. The cord to the trap runs across a patio, so passer’s by may kick or step on the cord from time to time. And, the wind also blows occasionally. I was recording the trap (this is the IOT instrumented Defender) and noticed occasional losses of network connectivity and reboots. I didn’t want to touch anything as long as the mosquitos were being caught in such numbers. I believe catching is more important than fixing.

Yesterday, the trap was in a fault that is the same as “no gas,” which is caused by low combustion chamber temperature. Upon startup, the trap reached only 42°C after about 3 minutes instead of between 110°C and ~125°C. The gas was only weakly igniting, a problem with the propane flow.

The tank was replaced only a couple of days ago. I purchased this propane at a store that sells propane by the gallon for $2.16. They typically put in 4.2 gallons to fill an empty 20# tank, and the cost is about $9, much less than the $20 my neighborhood hardware store charges. But the hardware store uses the side release screwdriver valve to release air, while this store uses some hose that supposedly sucks the air out of the tank. I was wondering if perhaps their method was not working correctly and I was getting some air in the tank interfering with combustion. Before delving into that and fiddling with the side valve, I decided to try what had worked a month before, but this time each step done independently and in order.

This time I tried five interventions followed by resetting the trap. Fortunately, I have to wait only about 3 minutes for a result because of the WiFi instrumentation and the smartphone MQTT client.

1. I connected another power supply I was using with the backup Liberty trap, and it showed no sign of intermittency (hooray, an issue addressed),  but after resetting the trap, there was no improvement.
2. I banged on the regulator to unstick any parts that might be impeding the flow of gas. No effect.
3. I used the Gas Reset tool. No effect.
4. I then used a bicycle pump and pumped away in the hot sun. No effect.
5. I then disconnected the trap and carted it around the house to the garage where my 12 volt electric automobile tire pump could have a go. I connected and ran the pump for about 5 minutes. The pump gauge read initially about 77 psi, falling to about 73-74 psi. Not a large change to indicate blowing away an obstruction. I then reinstalled the trap and it started perfectly!

I don’t know how or why this worked. There may be an obstruction between the valve and the nozzle, or the nozzle is getting a bit clogged. After the catch drops off, I want to disassemble the nozzle – valve assembly and inspect the valve output to nozzle pipe. Perhaps there is some gunk in there that expands with temperature, choking off the propane. I can’t imagine what that might be, though. Another mystery that will have to wait for mosquito downtime, which doesn’t show any signs of happening soon.

Happy as can be after nearly 2 hours directly under the hot sun with combustion chamber temperature of 127.4°C and an inside case temperature of 58.3°C.

Temp=127.4C (0) at 5:6354 F=1 I=0 G=1 S=1 E=0 T=58.3C H=4.7% M=11096 (209/1014:4887) R=45~140 B=0.0 V=3.1

And I have no evidence of air or contaminants in the propane from the new supplier. Although i cannot “exonerate” them, there is insufficient evidence of anything other than good propane in the tank.

A reader used the site contact form to ask for suggestions. There is no general email sending capability from this site, so, in order to answer his query, and generally to facilitate discussions on MM matters, I created a new Forum on this site and posted his request there so that I could reply.

Anyone can read the forum topics. To post a topic or reply requires a user account on the forum, which is available upon request. This is a very low volume hobby topic, with responses only as time permits. Using the forum for other MM related discussions probably will be ok as long as it doesn’t get out of hand.

P.S. Defender All Time Catch

I moved the Defender mentioned in the previous New Oddity post out of the path of a particularly aggressive lawn mowing crew to a side of the house onto a paved stone patio where we have noticed too many mosquitos. After about 2 weeks, the Defender’s catch basket was completely full. It was just shocking and appalling. It was the largest catch for this machine, ever. I am contemplating how to count or estimate the mosquitos in that basket. I had better do this quickly, because the replacement basket is already 40% full. As a plus, now when we go to the pool in the evening, we are no longer devoured by these tiny beasts.

Having just accomplished a record catch, I have to pronounce the trap working, and the comparatively low catch mentioned in the previous post a consequence of its placement then in a location where it caught the now second largest number of mosquitos mentioned last season.

On my previous post “It was the Valve” below, I reported that changing the valve stem, and cleaning and manipulating the coil contacts fixed the problem of the trap failing at high case temperatures. I am grateful for that.

This season starting early June, the trap exhibited a new anomaly. After warming up to about 120°C and running for a period of time, the trap combustion temperature declined to about 75°C and stayed there. This happened when the case temperature rose to about 43°C. (This trap has the wireless controller installed, and I record and display the data continuously, so have a complete record of the operating conditions, including the external case temperature and humidity sensor.) The trap was catching very few mosquitos, and none were observed alive after the trap was running at 75°C for a few hours. Accordingly, I have to conclude that the trap was “not working.”

I fiddled with the contacts, removing and cleaning them (there was a small deposit of some dark material on the female contacts visible under the microscope), and reassembled. This did not fix the problem. Then I substituted sealing tape for the valve mechanism to bypass the valve, and that did not make any difference either! A new issue!

Fortunately, the wireless controller has remote control troubleshooting commands. One turns on the ignition, and another turns off the gas, each for a specified number of seconds. Turning the ignition on when the temperature was 75°C had no effect. Turning the gas off for about 20 seconds initially resulted in a combustion temperature rise, which seems backwards. It is as if there is something blocking the gas flow that relaxes as the gas pressure is reduced, letting more gas into the combustion chamber.

I restarted the trap by turning the gas off for about 50 seconds plus ignition on for about 90 seconds. The temperature rose to over 110°C, but the result was short-lived. It fell down back to 75°C. No mosquitos were caught during this period. My raw notes:

Reinstalled the valve core, then attached auto tire pump, and pump delivered 80 psi, falling to 75 psi or so. This is not necessarily low enough, the nozzle might be clogged. Re-attached the tank, used the orange reset tool on regulator, and restarted. Experiment of ignition on 120 seconds with gas off 20 seconds near end restarts combustion from 77° to 115°C. Temp first started to go up when gas was turned off … !!!  During this time Temp/Hum declined from 45° to 44°.  Might be a clogged nozzle or gas passage causing burn problems. Or the regulator??? But how could the regulator be affected by case temperature?

The regulator cannot be affected by case temperature. However, the gas reset tool could affect the old style regulator, which might be flaky, delivering the wrong pressure. I don’t know what the right pressure is supposed to be. The old style is adjustable, and the end cap fell off and was lost a few years ago. Perhaps I should replace it, but the new regulators have fixed pressure of 11 column inches of water, which would not work if the Defender needs a different pressure.

So what could the case temperature have to do with the gas flow? It could be the nozzle or some obstruction in the passage between the valve and the nozzle. I suppose I will have to tear it apart, again. But for now, the trap is on and working perfectly. Not too many mosquitos, though, but there are always a few live ones whenever I check. I suppose I mostly decimated the population with last year’s incredible bumper harvest. At least I am not getting bitten. The next time I notice a fall, I will try the gas reset tool alone without the tire pump, and see if that helps. Another year, another mystery. Such fun!

I said I would report back after a few weeks, but that didn’t happen. It is now the middle of the winter, and the snow is falling all around. No mosquitos. But the earlier log post speaking of action in the next few weeks still remained, like an itch that needs scratching. So here it is.

The valve core, solenoid, and connector change definitely fixed the problem. The trap continued to work flawlessly for the remainder of the season, and the trap is still in use to measure the outside temperature, although it is in the “off” state and the propane disconnected. The controller module continues to run and upload the temperatures inside the case.

I did not experiment further to determine whether it was the valve contacts or the electromagnet that was failing at high temperatures because I convinced myself that the most likely problem was the contacts, that is, the connection between the controller board and the solenoid connector. Without thorough cleaning and some anti-oxidation treatment, it is only too tempting to believe that this connection could become intermittent at elevated temperatures.

To some extent, I regret not having resolved this issue during the season as I said I would, but, really, there were and are more pressing concerns in life than theoretical anti-mosquito research. Nonetheless, I plan to replace the original magnet and valve mechanism after a thorough cleaning and inspection, and see what happens this coming June, when the mosquitos will start to stir. We will just have to wait to see what happens to either the trap or these plans in the next three months.

 

It has been several weeks since my last post. Since that time, I adapted a real time signal viewer to display the messages transmitted by the wireless controller I programmed and installed to replace the existing PIC controller, which I carelessly blew up. The viewer displays 19 of the parameters transmitted by the controller. This real time or recorded view was helpful to figuring out what was going on, much better than examining huge message log files.

As shown on earlier entries on the wiki, the combustion chamber temperature rises upon ignition and gas, then reaches a steady state where it remains for a few minutes. The interior case temperature continues to rise during this time. When the interior temperature reaches about 40°C, the combustion temperature starts a sudden rise toward about 165°C, much hotter. However, before it gets there, combustion ceases for no apparent reason. As the temperature falls, it is still not possible to restart combustion using a combination of gas and igniter commands until the case temperature declines to about 30°C.

The programmed algorithm uses only the combustion temperature probe value. The case temperature and humidity is transmitted but not used for control. The controller is programmed with two combustion temperatures, a low and a high. The high temperature is intended as a safety feature, temporarily shutting the gas flow and cooling the chamber. However, I set the temperature to the highest value that would stop combustion before it failed. That value was 140°C. I introduced a new algorithm that, at that temperature, enters the startup state. The startup state turns off the gas and waits for the trap to cool down to the startup maximum temperature, now 40°C, then starts the trap.

This works during the hot summer days, but the unit oscillates on and off constantly until the outside temperature drops and the unit stays on for the evening and night until it gets hot the next day. The downside is that the trap is operating only about 50% of the time during the day, which is not very effective in catching the fewer mosquitos flying around in the heat. It also repeatedly cycles the igniter, consuming its useful life more rapidly.

Under the theory that the combustion stops because the gas flow is interrupted at high temperature, I installed a 40mm miniature 40mm 12 volt fan to blow fresh air from the switch opening onto the valve assembly. This fan has an output of 4.1 cfm, which seems laughable compared to the existing fan. Using sealing tape to create an air intake duct from the switch opening in the case, the fan was directed on the valve. There was no effect.

But it still had to be the gas valve. What else would stop combustion? I disassembled the valve, and cleaned the orifice and interior, which was not obviously clogged, and reassembled. No difference.

Today, I used a T9 bit to unscrew then remove the active part of the valve, and taped over the port with sealing tape to bypass it, using the tank valve instead (dangerous), and restarted. The trap worked perfectly! The combustion temperature rose to 130°C, and the interior temperature to 50°C, and stayed in a perfect steady state! This is definitive proof that the valve was causing both the temperature rise (runaway) and the stoppage, because neither occurred after bypassing the valve.

So either the coil was opening up, or the magnetic plunger was losing its magnetism at high temperature. I removed the coil, removed the contacts from the connector, inspected, cleaned, and measured the coil to be 200.4Ω, regardless of any vibration or wiggling. Both connectors had gold plated contacts in good condition. I sprayed DeOxit contact cleaner anyway. I took the plunger assembly from another valve, installed it into the Defender, and plugged the coil back into the controller, moving the connected in and out to dislodge any possible contamination on the male connector.

After one hour, the combustion probe temperature is a very steady 130°C, and the case temperature is a pretty hot 55°C. That is 15°C hotter than the previous failure point. Its working!

Changing two variables leaves the question: is it the coil / connector, or is it the valve mechanism that made the difference? After a day or so, I will restore the original mechanism and see if that works, and will know for sure.

The end is in sight. I hope I can find the screws to the case. Stay tuned.

The Defender stops combusting, cools down, and eventually stops with an error when running at a high temperature for a period of time. I have so far no explanation for this failure. Apparently, combustion just stops, even though the propane solenoid and air flow fan is still on. Should be impossible. A voltmeter on the valve solenoid indicated that the solenoid was continuously powered even when the temperature hit extremes, which refuted an earlier theory. Also, once it stops, it will  not restart until the trap completely cools down, regardless of the commands sent to the unit. The ambient case temperature at 40C is not that high to cause problems for the controller. It is possible that the conducted heat might mess up the solenoid.

We know that combustion requires fuel, oxygen, and, to start, ignition. Something must be interfering with the fuel or the air. Perhaps the gas valve is shutting down when its temperature (via heat conducted through the brass fittings) gets too high. Perhaps the air flow is closing down because of something swelling up and restricting the two passageways from the fan to the combustion chamber. I will have to disassemble to investigate (but not now). Fortunately, this problem occurs only during the heat of the day, when the sun is shining on the trap, and then it is too hot to catch mosquitos anyway. In the evening, when things have cooled down a bit, I can restart the trap. Actually, this failure saves propane and energy, but I would like the trap to run per spec.

Perhaps it would be wise to limit the temperature to, say 140C. But how to do this? The chamber temperature is a function of the gas, the air flow, and the ambient temperature.

We could reduce the gas flow by modulating the solenoid signal, e.g., one second off every X seconds. After the valve is shut, there is still sufficient gas to continue combustion for some period of time. Some experiments to see how long it takes closing to cause combustion to stop indicate it can tolerate several seconds of the propane solenoid off and still recover.

The air flow is a function of the restrictions from the net and ‘trumpet’ air intake. The installing the net box certainly reduces the air flow dramatically. Replacing the net box with a new one had no effect. We do not have the capability to increase the air flow, since the fan is on full blast, and we don’t want to fool with the vacuum apparatus.

Perhaps switching the gas off periodically would result in a lower operating temperature by causing a net pressure reduction and lower gas flow. But do we want to reduce the net gas flow? After all, we want the carbon dioxide to be emitted. … More later. For more information, see the wiki

If anyone can think of an explanation, please let us know.

When trying to troubleshoot the new wireless controller for my old Defender, I decided to leave no stone unturned and order a new catch basket (the gadget that works like a net to catch and hold the mosquitos) because the old one might be restricting the air flow too much because of accumulated mosquito awfulness on the screen material. At the last minute, I decided to throw in some Quick Clear cartridges so that I wouldn’t have to set up my electric air pump to blow into the unit every second tank. Well, lo and behold, the Mosquito Magnet brand cartridge is no longer available on the Mosquito Magnet web site (although other brands are still being sold). What was going on?

I called the Mosquito Magnet support line, waited a few minutes, and asked about the cartridges. The operator said there was a recall of units made between 2014 and 2016. She said that if the cartridge was used improperly, it would damage the regulator on those units, so the ‘product manager’ decided to withdraw the product. I asked whether it was necessary to periodically clean the trap to blow out the contaminants in the propane. She said this was no longer necessary.

She said the improper use was use while the trap was running,  which back-fed the high pressure gas into the exit port of the regulator, damaging it. Of course, using the air pump, I have done this several times. Fortunately, the regulator on my old units was not in the 2014-6 range, so presumably no damage was done.

Or was it? The pressure on the pump with the valve closed went up to 120 psi and stayed there. If it were blowing out contaminants, I would expect the pressure to drop as time went on, but no. Some times, the pressure would indicate around 40-50 psi, which I considered more reasonable. However, I now realize that this occurred when the solenoid was open, and I was back-feeding the regulator at that time. Anyway, the pump or cartridges never made much or any difference. And the directions were faulty: the cartridge would not run for 30 seconds — it was gone in one big whoosh. If partly unscrewed, a weak flow ran for about 30 seconds, but did that make any difference?

So, no more cartridges. I will keep it up with the pump, with the solenoid off (trap unplugged). Out of superstition or habit, I suppose. And I will change the nozzles or at least clean them from time to time.

This is not really a blog about repair, but rather the “Do It Yourself” method of keeping old Mosquito Magnets alive and catching Mosquitoes. By “yourself” I mean someone with a technical or engineering background. This does not contain the standard consumer oriented information, but rather information gained from sometimes hot and sweaty reverse engineering in the field, while constantly on guard for or attacked by uncaught mosquitoes.

By the way, we are spelling the plural of mosquito interchangeably as mosquitoes and mosquitos (which I prefer, but others do not). Reminds me of George Bush’s Sr’s  VP and the “potato” incident.

Since 2016, I have been maintaining a wiki on the MM Defender and Liberty. This wiki has contained dated sections that should have been in a blog. But it would have been too much work for a hobby project.

In July, 2018, a new project has started emerged to replace the existing controller in the Defender and Liberty with an inexpensive wireless development board. This has resulted in lots of entries into the project wiki that should be blog entries. This blog is created to hold these entries as separate posts.

There may seem like a lot of moaning and groaning in this blog. Sorry, but that is just the way it is. I really cannot afford to spend the time I do on this project, it is a bit of an embarrassment, given that I could buy a new trap for $300 or so. But it irks me to throw these machines away. I need about 3 of them, even though each one is supposed to cover about an acre more or less. I hate those mosquitos.