Treat the variable frequency drive with kindness

Variable frequency AC drive controllers are all sorts of amazing. They rectify AC power to DC then give you 3 phase AC at the desired frequency to let you run the motor at the desired speed, anywhere from just a few RPM up to full tilt. They can also, if misconfigured, drive you up the wall at 60 cycles per second.

I’ll save you the pain of having to watch me scream about Johnson Controls Metasys, here’s the data showing that this one air handler is not happy. This graph is showing its air output temperature. This morning I came in to find half the facility nearing meltdown and decided to see if I could do anything about it.

There’s the drive for that unit’s blower. I found it shut off on a DC bus overvolt fault. The automatic fault restart was not enabled, so it just sat there.

I restarted it and watched it ramp up to full speed…. fearsomely. After it’d let the place cool down a while I revisited the settings. This Yaskawa controller actually has pretty good documentation and a setup routine designed to aid in quick deployment (I CANNOT say that for all the controllers I’ve come across in the wild). Right away I noticed the amperage and wattage limits set in the controller did not match the motor, which did not appear to be original to the unit.

Yeah uh I’m gonna have to recommend you not do that. I filled out the proper values in there, turned on fault restart, and ran the auto tune, which sounds like angry crickets on this unit.

Aside from the drain pan looking suitably foul, I’d say it’s happy again.

I dunno, I realize that variable frequency drives are probably a bit of crazy black magic to a lot of HVAC people, but pleeeeeeeeeaasseeeee make sure you have the thing configured right for whatever motor you’ve wired to it! It does make a lot of difference!

Oh, and the Johnson Controls corporation is a bellended bagbiting cockwomble. There i said it ok

Shift Register Drivers

I’ve been using the Texas Instruments TPIC6595 and TPIC6B595 shift register with high current low-side driver ICs for a while for various tasks, usually driving LED lights and displays.

Someone posted a picture of an old gridless Tung-Sol VFD tube on Facebook and I thought to myself, well…. these are neat, but if you wanted to connect them up to a modern microcontroller, you’d need tons of pins unless you can easily multiplex it. TPIC6B595 wouldn’t really help you here as you’d need to drive +30V or so to the anodes.

I remember trying to figure out if there was a nice convenient high-side equivalent to the TPIC6595 series when playing with flip-dot display panels, and came up with nothing. Well, now I searched it again and came up with the MIC5891 which is exactly that, and it’s good to 35 volts! It’d be perfect for driving the VFD anodes.

The Important Fun Note: Driving a display this way with latched drivers will allow you to achieve a completely flicker-free readout, which is VERY important if you want to have your display appear on screen in film/TV applications! ESE clock displays operate like this (though I seem to vaguely recall they use something like 7490’s behind a set of D latches).

Alexander Graham Bell’s Evil Quantum Entangled Cock Cage

Please forgive my unusual reaction, the stress of current events and a grueling work schedule have affected my state of mind a bit.

If I told you too much about this system it’d make your mind snap like an overstretched rubber band

Nobody who works here now was responsible for this all getting so fucked up, they just inherited its load-bearing zombie corpse.

who took my nice fluke anyway

Exsqueeze me? Baking powder?

Another day, another case of being thoroughly perplexed by RF Central gear—
When the mast goes up but the signal doesn’t go out, it’s time to investigate.

schwiiiiiiinnnngggg

The forward/reflect/12vdc return meter always seemed to show 00.0 if the PA was off… -1 if the PA was on, in any field.

TWO different bad amplifier units…. one was waiting on the shelf as a spare, one just came off the truck.

 

So what’s inside? I forgot to take a photo but if you remove the hex screws on the back it reveals a Stealth Microwave SM2025-44L, 25 watt linear amplifier for 2000-2500 megacycle DVB applications. Sadly. Stealth Microwave is long gone.

Interestingly the amp bricks are specified as having an internal output isolator. Nifty.

The other major part inside the amp brick is a bias tee that splits 12vdc power sent up the coax out to run the fan and the amplifier.

And now, it gets… horrifying.

I found a datasheet on the SM2025-44L and it’s specified as taking a mighty 8.5 amperes. I mean, at least it isn’t gonna arc furnace anything, but the voltage drop CANNOT be nontrivial anymore.

This has to get to it on the coax. The coax from the indoor unit in the truck to the outdoor amplifier unit is not a short sweet little run. See the big black coil up the mast in the first pic? There’s probably at least 45 feet of coax in there, plus another dozen at least to land it from the feedthrough in the roof to the IDU in the rack.

WHY DID THIS EVER WORK AT ALL? Or does it? I don’t….. I can’t even——- No——— I need to go home and collapse in bed and place the kitteh on top of me and stop trying to think for this week. DONE. I’m so done. What the hell.

I’m in the wrong business

A certain vendor that will remain nameless charges $4600 for one of these, or a minimum of $550 to repair one. Also I accidentally turned on the WordPress block editor and how the hell does this work it’s like someone tried to use vim on an acid trip what the fuck

Storm Stopper

Seen after I emptied out its jackpot…Cyclone is a really kinda old game now, I remember first seeing them in the early 1990s. It’s still fun as heck and I can usually get the jackpot on it unless it’s been set to evil mode.There’s a hidden adjustment as to how easy it is to get that jackpot. The clock that advances the light that’s on runs at least 32 times as fast as the lights stepping around the table. The “winnability” adjustment can be set so anything from all 32 clocks all the way down to one will actually win. If it’s set particularly hard you’ll often see the game do evil things like reverse from the jackpot light you stopped it on to the one before it. It’s not subtle about the fact it’s dicking you over.When it’s not set to evil though it’s just pretty and fun to play.Speaking of games of skill… I spotted impending Rifa Madness in some video distribution amps at work.I’m using them as an excuse to get the 25 year old nightmare fuel out of there so I don’t have to fear the black burst signal being pulled out from under us. I was trying to upload an image of the waveform but the photo just won’t pass through Comcrap, so here’s an unrelated thing

Well, somewhere, engineering was attempted

Here’s a supermicro that pissed us off this week. It’s from 2015 and clearly got dumped on us as the result of a certain “text-that-gets-scrolled-on-the-bottom-of-the-news” vendor cleaning out back stock when my workplace ordered a new system.

Blaarffff. It literally seems like the bios doesn’t like certain monitors, and you have to fight it for hours to get video. You’d think with a vendor like Supermicro you’d get a board built with better parts but this thing looks like a damn Soyo. Remember Soyo? They drove themselves out of business by delivering dumpshit. This Supermicro sure looks like overpriced dumpshit complete with “hey look it’s 2001 again” capacitors.

More folderol to follow

Read more “Well, somewhere, engineering was attempted”

Snap, Crackle, Pop! Triax Crispies.

I’ve always found the old school triax connections used for some studio cameras….. charming. Triaxial cable looks mostly like a RG-6-ish coax with another dielectric layer and another braid over it, with the end result looking a bit more like RG-11… until you see the freaking WEIRD connector it terminates into. It’s like a ginormous shell around a BNC. Trust me when I say you do not want to be coiling this cable up and have the connector fly over and smack you in the— uhhh— output spigot and terminating resistor. OW. But anyway—

Cameras hooked up by triax can be powered over the triax. To do so, the Camera Control Unit (CCU) sends a high voltage – 120-170 vdc I think, down the cable, between the outer and inner braids. A DC/DC converter inside the camera powers it and any ancillary equipment like lights hooked up to the 12v output it provides. It works great, but you MUST ensure that the voltage has been removed from the cable before unplugging it. On some systems, it seems like powering down the camera tells the CCU to stop sending that voltage (or it drops to just a few volts – just enough for it to power whatever onboard the camera tells the CCU that the cam is connected and requesting to be powered up?). Anyway— at my old station I had a few instances where someone would unplug the cable hot and it would make the camera mad or even carbon-track the plastic inside the connector.

Today I found out what happens if the cable ITSELF gets angry:

tri-axial foaming cable

From top to bottom: The outer jacket with subtle black mark from the fault within, the middle dielectric and inner braid, and the outer braid, which frayed then burned in half at the fault location.

The ridges are from the connector’s strain relief. This fault occurred right behind the connector, where the cable was getting flexed a lot.

The CCU reported the cable was shorted out, and this was confirmed by a resistance reading of about .15 ohm at the connector on that end as measured by the onboard multimeter on a Tektronix 2236

All three elements of the cable – the center conductor, inner braid, and outer braid were shorted together.

I was able to lop off the end of the cable and remake the connector. The connectors we had in stock were circa 1996 and were made by Kings about, oh, two corporate umbrellas ago. Currently they’re under Winchester Interconnect and Winchester has no documentation on the connector including what the strip lengths are for the layers of the underlying cable. Canare and Cinch have different takes on the same thing. I managed to get it back together with new parts for the center.


The center is pretty much a crimp type BNC. Not shown, the….. ridiculous oldschool clamp thing used to hold the outer braid to the connector body, nor the giant ball-bonker connector body itself.


Not sure if it’s the world’s most perfect installation, but hey, it passed the Smoke Test and the camera’s back up on it and in service.