DIY weed zapper - Page 1
Forum section: electronics / projects

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 12:29:00 am
content: I'm trying to build a weed zapper. My first attempt with a flyback transformer (driven from a modified ATX PSU, can draw pretty good 1" arcs from it) took too long (a few minutes) to kill the weed, so I'm assuming it needs more current and less voltage. (It does burn the weed if I just let it arc, but then it doesn't have much effect on the root.)What voltage and current should I go for if I wanted to zap a weed in seconds?

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 11, 2014, 12:53:05 am
content: This sounds similar to the termite zappers. I don't know the answer to your question but I'm interested to know how you made your weed zapper.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 01:29:19 am
content: Just an ATX PSU modified to output about 24V high frequency AC, then put through a flyback transformer to boost it to 15kV or so. The return of the flyback connects to mains ground and the high voltage output to a piece of scrap steel, the entire assembly mounted on a plastic broomstick. In its current state, it's not a particularly useful device as it's faster to remove weeds by hand. Flyback transformers aren't built to put out much current (a few mA at most). I think it just needs more current but I'm not sure how much more.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 11, 2014, 02:09:07 am
content: Interesting, I have a flyback and I think I have an ATX PS. How high is AC freq? The weed becomes the source to ground and burns? Or some other cellular phenomena? Boiled? Steamed?

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 04:00:06 am
content: ATX PSUs run on the order of 30kHz or more. I assume resistive heating is the main mechanism that kills the weed but there might also be some electrolysis effects with DC.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 11, 2014, 04:28:20 am
content: Quote from: NiHaoMike on March 11, 2014, 04:00:06 amThis might work for gophers too!! And/or their evil minion brethren voles and moles!!Can you try it on a t-bone steak?

author: Tinkerer
author_rank: Frequent Contributor
timestamp: March 11, 2014, 04:35:15 am
content: So were you planning on sweeping an area with it? or did you have anything specific in mind?If you had invidual hard to remove weeds in mind, I would suggest charging up a cap and letting a jolt fly on discharge into the plant. Although you could do a quickly charging cap for quicker strikes.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 11, 2014, 08:03:46 am
content: The highly creative Matjaz Vidmar from Slovenia has you covered, just get some scrap Microwave ovens:http://www.rfdh.com/ez/system/db/lib_jnl/upload/3553/1132374365/%5BMWJ0510%5D_An_Improved_Microwave_Weed_Killer.pdfSpoiler alert: You might turn on flourescent bulbs in the proximity of the running device !

author: ConKbot
author_rank: Super Contributor
timestamp: March 11, 2014, 10:58:41 am
content: Thats a serious array of magnetronsBut since the TS is talking about more current, at a high voltage, I'd say a Microwave oven transformer is probably in order. I'm sure some people will throw fits, but I think explaining the risk would be better then just throwing out mindless warnings.While the MOT will fry up a weed real good, and it will fry a person up real good too. They output ~2KV AC at a few hundred mA. A few hundred mA is well into the range capable of causing cardiac arrest, and 2KV is more than enough to push that few hundred mA though a person. And in this application, one output of the MOT will be grounded, so the other output will be potentially lethal if touched, only one point of contact instead of needing two.Personally, I'd use something likehttp://www.powerwerx.com/wire-cable/test-lead-wire.htmlthis 5kV test lead wire on a chicken stick for frying up the weeds. As for the practicality of this? If you want to mess around with a MOT and burn a few weeds, have at it, but I'd suggest that it is too dangerous for casual use walking around the yard frying weeds.

author: pinkysbrein
author_rank: Contributor
timestamp: March 11, 2014, 12:24:31 pm
content: This is such an incredibly bad idea ... but I do agree with using MOTs, flybacks just won't be able to sustain the necessary power.Why not get one of those big propane weed burners, still a hint of danger but far more forgiving...

author: bookaboo
author_rank: Frequent Contributor
timestamp: March 11, 2014, 12:30:19 pm
content: Surely the EMF of such a zapper would annoy the neighbours, though if you didn't like them.....

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 03:16:19 pm
content: I want it to be based on a switching supply (inverter) so it would be light enough to easily carry and use. And I read that at a sufficiently high frequency, it would be (slightly) safer as it would be more likely to just cause a bad burn instead of a shock. The transformer is going to be mounted on the end of a plastic rod with the pushbutton and inverter on the other end.So it looks like I'll aim for 2-3kV at a few hundred mA, on the order of a few tens of kHz.

author: bookaboo
author_rank: Frequent Contributor
timestamp: March 11, 2014, 03:23:38 pm
content: Quote from: NiHaoMike on March 11, 2014, 03:16:19 pmTempted to make a smart arse comment but I'll politely point out this isn't a good idea.Was worth investigating but now the project isn't viable, on to the next one I think.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 05:46:54 pm
content: That amount of power is tiny compared to what Photonicinduction works with. But his rig isn't exactly portable...As far as marketing such a device, it's obviously going to be problematic just from a legal perspective. But I'm not planning to do that. I just want something that can save a lot of time taking care of my yard. (And I don't think I'll actually need the full voltage and the full current at the same time.)

author: SeanB
author_rank: Super Contributor
timestamp: March 11, 2014, 06:05:51 pm
content: Buy a BBQ starter stick and a portable tank of LPG and carry it around to cook them? Cheap, quick and very fast to cook the weeds.

author: Macbeth
author_rank: Super Contributor
timestamp: March 11, 2014, 06:17:00 pm
content: Quote from: babysitter on March 11, 2014, 08:03:46 amHoly FSM! I think I'll just stick to my bottle of Rosate 36, thanks!

author: chinglish
author_rank: Contributor
timestamp: March 11, 2014, 07:17:43 pm
content: "It does burn the weed!" - "Doesn't have much effect on the root!" - "Cheap, quick and very fast!""What Photonicinduction works with!" - "Holy FSM!"Starting at only129.99!Now with 99% more Ozone!0800-MIKESELECTRICBUFF

author: Marco
author_rank: Super Contributor
timestamp: March 11, 2014, 07:55:28 pm
content: Quote from: NiHaoMike on March 11, 2014, 03:16:19 pmIt can burn a weed ... it can literally burn holes in your skin.

author: Zepnat
author_rank: Regular Contributor
timestamp: March 11, 2014, 08:35:02 pm
content: Could you not repurpose this with some sort of after burner ?Jet powered snow blowerEdit: sorry now I realise you want to kill just the weeds and not the whole garden

author: Nerull
author_rank: Frequent Contributor
timestamp: March 11, 2014, 09:48:18 pm
content: Quote from: NiHaoMike on March 11, 2014, 03:16:19 pmHigh voltage and "I read that..." are usually a bad combination. You really need to know your stuff before playing with it. Half remembered things you read somewhere once are not a great foundation for safety.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 10:54:35 pm
content: Main safety is to simply keep clear of the end whenever it's plugged in. The control would be momentary so it only operates if I hold down the button. High frequency AC output so no output capacitance to hold an unexpected charge. The mains rectifier would have minimal capacitance so it won't hold much energy when unplugged.

author: wemme
author_rank: Regular Contributor
timestamp: March 12, 2014, 12:12:30 am
content: Automated weed sprayers have been around for a wee while.Navman use IR cameras to determine the difference of weed vs crop.Then use a solenoid weed sprayer to kill the weed.RegardsBart

author: NeilP
author_rank: Contributor
timestamp: November 03, 2017, 08:17:36 am
content: I’d like to revive this old thread and see how you got on with this.With the slow turn against herbicides and the huge fuel expense for flame or steam weeding, electro weeding is still out there and being developed into commercial field sized units.I have added links here below from my mate Merf form Uni Days.I came across this thread in my search for a home build design.Any of you still playing with this ?http://ubiqutek.com/http://rootwave.co/http://www.bhu.org.nz/future-farming-centre/information/bulletin/2016-v1/back-to-the-future-electrothermal-systemic-weedkiller

author: Marco
author_rank: Super Contributor
timestamp: November 03, 2017, 02:20:19 pm
content: Not me. I do admit your links make a good case for it. Weeds have been getting kinda rampant in my neighbourhood since the local government is no longer allowed to use glyphosate. I doubt it would ever fly as a consumer product though.I think I'd put the electrode in a transparent cup which you have to press down around the weed, with pressure on the rim being necessary for activation. Just to get some kind of safety. I'd not use a ZVS, they blow up too much. Just use a chunky ignition coil as an actual flyback, easier to control the power.PS. ahh, looking at the pictures from ubiqutek I missed the obvious safety ... thick boots and a grounding strap, any energy through the strap means you cut the power. Still a lethal weapon for everyone near though.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 04, 2017, 05:25:31 am
content: Didn't go much further because I found a free low tech yet safe and effective solution to killing weeds. I'll just say that urea "corrodes" plant leaves if applied in high concentration (most effective on a sunny day), but dilute it with water and it becomes a fertilizer. Hence it's possible to kill the weeds and actually help nearby plants you want to keep. (Hint: use a spray bottle to accurately apply it!)