Comments by "SeanBZA" (@SeanBZA) on "Contactors: how we power the big stuff" video.

  1. To keep the ants out you just shake borax all over the base of the AC outdoor unit, and on the base of the electrical connections. Redo every year, and you will never have ants again. Same for electric gate motors, I keep a bag with borax, another with blue death and a can of spray for the quick removal.
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  2.  @danl6634  I installed an inrush limiter on a 7.5kW motor, because the original installer connected the DOL starter incorrectly, and it was starting in delta, then switching to star. Then dropped a phase in the one contactor due to arcing or dust. I replaced the lot, plus put it all, along with the 7.5kW soft start unit, into a dust proof cabinet, and set run up time to 30 seconds. Solved the issue of the unit tearing itself out of the floor bolts. Of course the biggest issue was to remove that 130kg cast steel frame motor from the gearbox, where the shaft was kind of not willing to separate, even hanging the entire motor mass off it. Had to use a BFH and crowbars, and the trolley I had under it suffered badly. New one was light, only 78kg, so easy to lift up with the chain block, and that shaft was well greased.
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  3. Common in smaller units, it is around a third of the price cheaper, though I change them to double pole ones when replacing them, even though I live in a country with 230VAC mains, as the double pole unit as a spare part means you only need to keep one to cover both use cases, and then a second 3 phase unit for bigger units that run on 3 phase, where you have a 4 pole unit typically, with 1 pole also used to power the single phase cooling fan separately. Double pole means less issues with tripping when the wiring outside gets wet, as you typically will have the unit hard wired, and thus simply turning it off will allow you to fault find and isolate the unit. Plus compressors often fail as a short to ground, with split phase the unit might keep on running at part power, till the motor itself burns out the wiring.
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  4.  @sprockkets  Lucky for me compressors pretty never need a heater, too hot to ever get them freezing.
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  5.  @postersm7141  Or the ones that arc across when open, so the motor sort of runs on. At least till the contactor catches fire.
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  6. You are wrong with the internal pressure switch in the condenser, it is normally run on the low pressure side, and is set to provide protection in the case of low refrigerant, switching off the compressor when the suction side pressure drops too low, from a loss of refrigerant. Then you do have a thermal cutout inside the compressor, that does break the full current, though better units also include an external overtemperature switch, turning off the compressor when it exceeds 120C case temperature, with the internal one operating around 140C. Better ones also include another switch in the high pressure side, turning off the compressor, typically with a non resettable trip, when pressure is too high, normally caused by the fan not running to move air over the fins, or the fins are clogged solid, and the high pressure side rises up in pressure to a very high pressure from the hot gas being in there.
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  7. Yes, but the cheap AC ones typically do not provide that option, you need to move to the industrial ranges to get those, along with interlocks and time delay units that either clip on or screw on top. you also run into issues with the lower power coils not having enough ability to drive add on blocks, the only thing you can do on those is to have interlocks to keep them from physically closing if the other is closed.
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  8.  @sprockkets  Only ever had one unit that actually came with a heater for the compressor, and that was because it was run really hard, with inlet suction at 0C, for a split AC. It killed compressors, and eventually just charged it to around 5C at suction, and it ran a lot better. After all discharge temperature was around 70C on the high side, dropping to 40C when the hot liquid left it, so it was definitely running flat out. Put a large liquid line drier on it to give more liquid volume and a little more restriction as well, fixed cap tubes and not wanting to do the manufacturers designing for them. Left the heater off then, it was a lot happier, just pulling a nice puddle of water from the air instead of the ice block.
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  9.  @leeroth5604  Part of the cost cutting, saving 20c on the contactor makes a big profit over 100k units.
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  10.  @Stego27  Yes, though most commercial ones will have power factor correction, so the initial current will be a large single cycle pulse to charge all the PFC capacitors, then the lights will turn on in under a half second. Incandescent lights have a much worse surge, I built a soft starter for a light box, that used 40 40W golf ball lamps, because the switch on surge was large enough to trip the breaker it was on. Soft starter made the surge low enough that it would not trip, and they came to full brightness over 2 seconds. easy to compensate with exposure time anyway, as you had a latitude of 5 seconds for the photographic plate exposure, and more variability due to temperature. Original artwork was done with Letraset and large format photo negatives, and then later on a Apple Mac and a Imagewriter dot matrix printer onto transparency, followed by a Laserwriter when they came out, doing laser tranparencies.
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  11. Lots of controls, and also large distances internally, and keeping them clean. Normally the control is done using light fed via optical fibres, so as to keep insulation distances high, and keeping tracking to a minimum.
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