| ▲ | nik282000 a day ago |
| I get a disturbing amount of equipment that does not take into account the inrush current of starting many loads at the same time. While each individual device is protected by a breaker that can handle the inrush of it's load the main breaker for the equipment is not sized to handle every load starting at the same time. The fix is to include logic that starts things up one at a time but convincing engineers, project managers, and machine owners that they didn't think of everything is an uphill battle. |
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| ▲ | 3eb7988a1663 a day ago | parent | next [-] |
| We used to have a turbopump that would trip the breakers every time you turned it on from cold. The pump seemingly attempted to spin up to max RPM before settling down to a more sustainable load. The only way to get the thing to stay on was to turn it on once, let it warm itself up on the initial attempt, trip the breakers, and try it another cycle now that it had some momentum and would pull slightly fewer amps. Sometimes took a few attempts to get that rolling start working. |
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| ▲ | jacquesm a day ago | parent | next [-] | | That's a great way to lose the breaker though. If you're lucky the latch will fail. If you're unlucky it will weld shut. | | |
| ▲ | 3eb7988a1663 a day ago | parent [-] | | Not ideal, but it was the only thing that worked. This was attached to a million dollar piece of equipment, so any remedial electrical replacement work would have been slightly inconsequential. Thankfully, it was one of those machines that you turned off as infrequently as possible, so we did not have to do this procedure too many times. The vendor did get the hint, and the second iteration of the device did slowly warm up the pumps so this process would no longer be required. | | |
| ▲ | jacquesm a day ago | parent [-] | | Yes, soft start is the way to go. Also: proper industrial breakers allow for temporary overload. I have a couple of pieces of gear that have inrush currents well over the limit of a normal breaker so I put them on a slow one and now it is fine. https://onccy.com/how-to-choose-between-type-a-b-c-and-d-min... | | |
| ▲ | margalabargala 16 hours ago | parent | next [-] | | > Also: proper industrial breakers allow for temporary overload Notoriously a crescent wrench makes an excellent 1000A slow blow fuse | | |
| ▲ | pseudohadamard 15 hours ago | parent [-] | | A 5/32" flat-blade screwdriver makes an excellent fast-blow fuse when dropped across exposed bus bars. And you can re-use the remains of the handle to stir your coffee once you've retrieved it from across the room. |
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| ▲ | pseudohadamard 15 hours ago | parent | prev [-] | | Soft-start is in theory the way to go, but it's very dependent on the motor type, there's a whole pile of different methods required for induction motors depending on whether they're capacitor-start, permanent split capacitor, shaded-pole, etc, so you can do it in some cases by lowering the voltage, or with a VFD, or a VSD, or the old-fashioned way with a centrifugal switch but that requires very careful handling. If as the OP said it's running million-dollar equipment you probably don't want to monkey with it at that level. |
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| ▲ | podocarp 20 hours ago | parent | prev [-] | | Reminds me of computer fans, some bioses seem to do that ramp up for no reason thing as well. | | |
| ▲ | qlte 20 hours ago | parent | next [-] | | Fans have a minimum speed needed to spin up when cold starting from 0 RPM. So it's safer to start at near max RPM and spin down to the desired target RPM if the controller doesn't know the exact operating characteristics of each fan. You can observe this with a speed control knob/ESP32 where a running fan will happily run forever with the knob turned down to e.g. a 30% duty cycle. But after turning to 0% and waiting for the blades to fully stop, if set back to the same 30% they won't move at all or you'll maybe hear a sketchy clicking/whine sound with the blades intermittently twitching. | | |
| ▲ | pseudohadamard 15 hours ago | parent [-] | | I've always assumed it was to calibrate the PWM sensor for fan speed, so it starts with no sensing active, runs up to max, and then the sensor kicks in and settles it down. You don't need to run a fan at max speed to get it to start, most will start with very little power applied. |
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| ▲ | sznio 12 hours ago | parent | prev | next [-] | | not exactly relevant to computer fans, but in case of your usual standing fan you need a way larger kick to get it going. if it fails to start but stays powered it will stay stuck, heat up and fail. this is why fans usually have the highest option as the first one, so you have to start it at full speed at first, and only then reduce it. | | | |
| ▲ | rrobukef 11 hours ago | parent | prev [-] | | You also want to be sure that, in the absense of fan-control, the CPU won't overheat. Full-on is safer than nothing until a driver is loaded. |
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| ▲ | wowczarek a day ago | parent | prev | next [-] |
| I assume you are talking beyond what (in the DIN rail world) type B/C/D breakers are meant to handle? It's sort of a solved problem - the ones I'm aware of are things like LynTec sequenced panels built exactly for this, and Siemens' SENTRON semiconductor CBs where you can control then curve to your spec. Convincing stakeholders though, is almost a job of its own. |
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| ▲ | nik282000 a day ago | parent [-] | | These were all across-the-line, 3-phase 600v starters so there was no option to slowly start things up. Soft-starters would have been ideal but they are 5x the cost. |
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| ▲ | cowlevel a day ago | parent | prev | next [-] |
| what? Inrush current is well known in electronics engineering. |
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| ▲ | kazinator a day ago | parent [-] | | In other words, convincing ignorants is an uphill battle. Those who know what "inrush current" means don't require convincing about the value of rolling starts. |
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| ▲ | a day ago | parent | prev | next [-] |
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| ▲ | veunes 12 hours ago | parent | prev [-] |
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