EEVblog #1292 - JVA Electric Fence Controller Teardown

[EEVblog]

Follow up to the dumpster electric fence controller.
The designer and CEO of Pakton Technologies Paul Thompson sent in a new one for us to play with!
And yes, that of course means multimeter destruction and high speed camera fun!
Listen to the podcast: https://theamphour.com/481-an-interview-with-paul-thompson/

[radix]

Could the flat spot be due to exceeding the probe common mode range? Both inputs to the difference amplifier get clipped at the same voltage, which results in zero output. The first spike also just seems too fast.
If the output is floating, there could be various parasitic capacitances that influence the common mode voltage.

Otherwise i would be really interested about the reason for the weird pulse shape. My naïve interpreation of the transformer-capacitor-thyristor network doesn't provide an explanation.

[johnlsenchak]

Itt was  pretty  "shocking"  that the cheap  China made   test meter  didn't  survive   against   that fence  control  unit  LOL   "Shocking"  I'm here  all day   !

[twospoons]

That wave shape looks like a total menace for EMI generation. Imagine that on a couple of km of fence wire...

[Full disclosure: I worked for Stafix many years back, designing fence energisers]

[Razor512]

Why can't they do a more modest home security version where it can do an output that works okay for deterring human criminal behavior. For example, a modest 1500-2000 joules around common points of illegal entry, and an alarm system that will use the criminal as a siren. It would overall be more helpful since it will allow you to locate the criminal via sound, and then deal with them more easily.

[Brumby]

Why can't they do a more modest home security version where it can do an output that works okay for deterring human criminal behavior. For example, a modest 1500-2000 joules around common points of illegal entry, and an alarm system that will use the criminal as a siren. It would overall be more helpful since it will allow you to locate the criminal via sound, and then deal with them more easily.

Your criminal would probably put you up on charges for assault ... and likely win.

... and if they injured themself in their reaction, you can add a lawsuit for damages.

[EEVblog]

Could the flat spot be due to exceeding the probe common mode range?

Nope, nowhere near it.

[Psi]

I would have thought the capacitor rubber mounting was to prevent mechanical damage from the repeated high current pulses causing the caps to move back and forward as their magnetic field interacts with the earths magnetic field.
Like how railguns throw around their heavy 50mm copper cables as if they are made of paper.

The actual movement maybe super tiny in the JVA controller but over time might crack joints if they were hard mounted.

[tautech]

Nah, all the fence units I've looked at had solid mounts for their pulse grade caps and generally just a custom strap but mostly just cable ties. One I'm looking at now has a total of 4 double stacked and strapped together onto a lug in the case.

[twospoons]

The ones we built at Stafix had the caps soldered to the PCB.  I'd guess the standoffs are because they make one controller board for different size energisers, which would need varying amounts of cap storage. The standoff is just a simple way to mount the caps, and customise to the energisers requirements at the same time.

The only capacitor failure mechanism I saw was from too high peak current, which would slowly burn the metalisation off the film where it meets the end termination.

[Psi]

Yeah, that makes sense.

[joeqsmith]

A few things to mention.

From your video, it sounds like your 121GW breaks down.  Based on what I saw,  my bet is it arcs across the switch contacts for the two PTCs used for the low impedance function.  It would have been interesting to see what was going on, like the low cost meter.

The second half of the wave form has a similar FWHH as what I use.  I use a 1us rise time and a 2 ohm source but I doubt it would make much difference.    I suspect you could have ran this waveform across the BM235 with every function selected and not see a failure.   Count off 5 pulses, flip the leads and repeat for each function.     

You could try this with different versions of your 121 but don't expect them to survive.