using an adjustible buck-boost for 12VDC-> 20VDC for defender?

Good morning

TL;DR in order to make the defender portable without having cords strung across the lot, can I use one of the cheap 12VDC -> 20VDC buck-boost voltage converters to power the defender?

First, thank you for the guides and all the info.

I have an old defender I bought like 20 years ago and it's been showing it's age the last few years.
Using info on the web and mostly from the writeups here I took it apart and cleaned it all up. Split the combustion chamber and cleaned that up and put a new nozzle in it. After a couple of days of fits and starts it has so far been running continuously for almost 3 weeks. Woot!

I have not been able to move it around as recommended because I buried the power cable. I could get another power unit, but I don't want cables running along the top of the ground. Normally I'd just look at a 12VDC source, big battery or solar unit or some other portable thing, but the power unit is 12VAC, and looking at the schematic it looks like (the igniter I think?) a massive capacitor turns the rectified but still ripply 12VDC into 19-20VDC. Of course a battery doesn't have that kind of ripple.

another alternative is a 12VDC -120VAC converter, but that's expensive and usually causes more problems than it solves for electronics.

So, in order to get the 12VDC -and- 20VDC, can I just use a 12VDC gel cell or other deep cycle battery and run it into one of the cheap 12VDC->20VDC buck-boost voltage converters, and from that converter 20VDC into the defender? That will take care of the 20VDC requirement, and it looks like there is an 'incoming' voltage regulator that can take the 20VDC back down to 12VDC for the defender parts that require 12VDC.

Does this seem reasonable?

Thanks!

ltgcc wrote:

I have not been able to move it around as recommended because I buried the power cable. I could get another power unit, but I don't want cables running along the top of the ground.

If you really want to move it around, you might want to consider getting a used Independence, or Liberty Plus model. Those have thermo eletric generator devices that allow it to start on batteries and then run on the TEGS indefinitely. I'm not sure how long a defender can run on batteries alone. The fan draws about 600-700ma continuously, so even a 17ah Gel cell would only run about 24 hours.

Also, it appears that the power transformer for the defender is designed to drop some voltage when the ignitor is lit. The ignitor can draw over 2a when lit, and the voltage of the power transformer drops a bit. If you have a voltage converter, it would have to maintain 20v at 2a, and that may be more than the ignitor is designed to handle, and will probably result in shortened life.



Edited 1 time(s). Last edit at 07/18/2022 10:00AM by Independence.

... The fan draws about 600-700ma continuously, so even a 17ah Gel cell would only run about 24 hours...

That, plus the demands of the igniter, would rule out a battery without an additional (solar?) source of power. The trap should continue to run especially on overcast or rainy days.

The power transformer sag, plus the low voltage zip cord resistance limit the inrush current to the igniter, which would require current limiting in the boost converter, but not too much, otherwise the regulated 5 volt supply will drop out, or the 12 volts to the propane valve will be insufficient. The original design is kind of a marvel in how it manages to balance what might be considered deficiencies into a "tuned" system. Batteries are very "stiff" (able to supply rated voltage at high currents). Other users who have used stiff power supplies found their igniters failing after a few startups. (Their solution was a gradual ramp up of power to the igniter, which, if optimally implemented, could be superior to the original "saggy" power transformer and long zip cord length design.)

BTW, burying an old zip cord not designed for direct burial doesn't seem like a long-term solution.

... (the igniter I think?) a massive capacitor turns the rectified but still ripply 12VDC into 19-20VDC...

The capacitor is not on the igniter circuit. It is on the 12 volt DC side (see the wiki and the blog). The full wave rectified voltage has a RMS value of say 19 * 0.707 or about 12 Vrms. Accordingly the Defender should not get 20 volts DC (ouch). 12 volts alone (with appropriate current limiting) should do it. Besides, 12 volt batteries are higher voltage anyway when charged.

... I don't want cables running along the top of the ground ...

Do you have grass? If so, you can use "the clips" to hold the cord against the ground so you don't see the cord, cut it with the lawn mower, or trip on it. For me, it is a hassle to move the trap other than a few feet (to not permanently kill the grass) side to side. I have a lot of slack in the cord where it crosses a walkway. Disconnecting the trap means you have to restart it, wearing out the igniter...

If you need to have a trap in a completely new location to intercept mosquitos, consider getting another trap. It is far easier, and, when the first one breaks, the second one keeps going until you can fix the first one!

The thermal power cordless models can be a solution, although they are generally less reliable, as the thermo electric voltage source eventually fails, and inexpensive replacements are generally not as effective.