Delayed soft start relay for PowerCon daisy chain - Page 1
Forum section: electronics / projects

author: axero
author_rank: Regular Contributor
timestamp: February 26, 2019, 09:28:43 am
content: So I have a chain of lamps that draw quite a bit of power when their power supplies power them up which causes a power surge when switching the power to them because all of them turns on exactly at the same time. This is a bit problematic and sparks tend to fly from the switch when it happens.So I wonder if there is a relay when you feed power into it, it takes maybe 0.5 seconds before it bypasses the power from the power in to the power out PowerCon port. That way, not all of the lamps turns on at the same time. Instead they will power on sequentially.I've tried to find such a device but I cannot find. Not even sure how to formulate search criteria.

author: ajb
author_rank: Super Contributor
timestamp: February 26, 2019, 06:50:10 pm
content: I assume you're talking aboutthis kind of PowerCON, which means an entertainment lighting setting? (For those who may not be familiar, it's common for stage lighting equipment these days to use PowerCON connectors, with in and out on each fixture, so that power can be daisy chained from one fixture to the next.)Time delay relays are a thing. To support the full 15-20A rating of the connectors/wiring, though, you may need to use a contactor and control it with a time delay relay. It wouldn't be asoftstart, just a delayed one, but that really amounts to the same thing if you can stagger the starting of enough pieces of the load. A true soft start usually involves either active control of the PFC stage of the power supply (IE, buying a PSU with this feature built in) or using a thermistor in series with the power supply input.But I would be most concerned with why there are sparks flying from your switches! Unless you're in some sort of campy frankenstein movie that shouldn't be happening!

author: axero
author_rank: Regular Contributor
timestamp: February 27, 2019, 11:06:59 am
content: Yes, your assumption about the type of PowerCON is correct.Maybe I'm exaggerating things a bit but it is obvious that the main switch has problems handling the inrush current from the capacitors of the power supplies of these lamps, all at once. One by one, they are not a problem for the main switch.Contactors don't seem to be hard to find. Those I can find are designed for HVAC systems. There are single phase models available. Not sure why I should use a contactor, a simple relay should do as well. There are relays rated for 100A even. Perhaps a soft start after it will prevent it from welding.But time delay relays are a much trickier thing for me to find. Don't know what to search for here. Perhaps I have to build some kind of a transistor/FET circuit coupled with an RC circuit and a diode. Not sure how to calculate correct currents through the FET and how to get proper resistance and capacitance....

author: dmills
author_rank: Super Contributor
timestamp: February 27, 2019, 11:16:07 am
content: Search term: "On Delay relay".Something like a Finder 80.21.0.240.0000 would seem suitable?I would suggest that a real automation vendor will likely be much cheaper then Farnell or the like for these.You might find that there is a power rail inside the lamp that comes up a second or so after mains is applied, in which case just use a standard relay and use that rail to switch it?Regards, Dan.

author: ajb
author_rank: Super Contributor
timestamp: February 27, 2019, 04:31:43 pm
content: Quote from: axero on February 27, 2019, 11:06:59 amIt really depends on what your "main switch" is, but inrush current is a well-known phenomenon and applies to all sorts of appliances. How have you established that the inrush is sufficient to cause an actual problem?QuoteI wasn't sure if you'd be able to find a time delay relay rated for 20A (since your relay will need to be rated to match the PowerCON through). Maybe you can, in which case, sure, you only need the one thing.