It's their smallest and cheapest contactor - about $A30 so not all that cheap, but capable of switching at lot of current at mains voltage.
I had to put one into Cambridge Instruments cheapest electron microscope sometime around 1985.
-- Bill Sloman, Sydney
We did that once, and the wirewould resistor died of fatigue. The replacement was porcelain-on-steel, which held up fine.
But that was a much bigger load.
An NTC inrush limiter could be shunted by a relay when the DC comes up. That sort of self-times.
The problem with NTCs is that there's no guarantee that multiple power interruptions can't occur within their thermal TC. The relay + power resistor approach is a lot easier to specify AFAICT. (Full disclosure: I've never designed an AC-powered box that didn't have a separate power supply--they've been so cheap and so good for so long that it never came up.)
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I don't know if this will work for your particular situation but very interesting:
EEVblog at 14 minutes...
Also at 24 minutes.
There's a guarantee that they can occur. It's not a problem.
Either works. Thermistors are just a partial solution to the issues fixed resistors create.
NT
You can get relays with tungsten pre-make contacts:
Almost big enough for your load.
It is interesting to test a few relays to destruction by inrush current. Under some conditions it does not take very long at all, with slightly different conditions they keep going with no problems.
Regardless of how robust a switch or relay you can find, a better solution might be to reduce the inrush current.
Especially if you manage to sell multiple instances of your product to the same customer and they want to put them all on the same circuit, and if they will sometimes switch on the power remotely to the whole rack/installation, the total inrush current for the external contactor can become unreasonable quite easily.
At least having a relay inside your product could stagger the inrush current pulses, but reducing the magnitude of the inrush current might be worthwhile too. It might also improve reliability - sometimes the mechanism of failure during a mains surge is not excessive voltage, but rather excessive current in the rectifier at the input of a SMPS, due to the surge attempting to produce a very large dv/dt on the reservoir capacitor.
Looks like I'll have a giant AC inlet module on the back (IEC connector, fuses, EMI filter, and switch) that turns on the three power supplies. At DC levels, I'll have a mosfet-based switch board between the supplies and the loads, with a tiny switch on the front panel for that. That's a non-trivial design.
I need a Spice model for a MAX809. If I can't find one, I'll have to hack an equivalent.
My customer doesn't like accessing things from the back of their jammed racks, but they don't mind a soft switch on the front. But one specific requirement is that it must not be switchable by a technician's butt. They did not specify the size or gender of that butt. Another research project, I guess.
And they want an air filter that is easily replaced from the front.
Never consult a customer before you design something.
AC relay wiring would be a nuisance. The soft-switch thing can have some big fastons for the DC connections, and a little ribbon cable to the switch and a few LEDs on the front panel.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
I designed a mosfet-based DC switch, but it's complex.
A big triac is a possibility. I could drive that with just a switch and maybe a fusable resistor from anode to gate. That would put AC line voltage on the little switch up front.
Maybe tiny power supply, DC switch, opto SSR, triac.
There would still be a giant, in practice inaccessable, switch on the power inlet on the back.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
On a sunny day (Sat, 05 Sep 2020 10:52:02 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in :
Triac gives you the option of a slow start and reduced inrush current, either by starting on a zero crossing of the mains or simply slowly increase firing angle. Does not have to be a very complex driver circuit.
I do have several Meanwell in series, have 5 of those. Mains fuse never blew, but at 230 V current is half of what you have over there. Also one on all day at 7 V. These things are reliable so far.
If in series backward diodes?
--- + --------------- 0 / 12 or 24 V (depending how many on) | ___
12V / \ --- Schottky |--- - ---- |
--- + ---- | ___
12V / \ --- |--- - ----
Dunno how accurate it needs to be..
Perhaps a single AC-365vdc PFC front end, feeding your many supplies.
The PFC section will allow for a normal line switch, emi and inrush spec. Some may have an isolated enable line for soft I/O control.
A universal input power supply may react unexpectedly with the DC input - you'd have to check it out. As long as some protective circuit isn't activated, any input pfc section should just feed-through.
Downstream inverters and housekeepers will be expecting the voltage supplied. As you're not synchronizing your units, I don't imagine the noise from the separate conversion stage will make much difference to the flora and fauna.
Something like a Cosel DPG750 or on ebay
Or an AC-48V converter to run different DC-DC converters with 48V input.
RL
PS about switches that are immune to bumping into google 'locking toggle switch'. Something like this
EATON makes a line of high inrush power switches rated for up to 100A and g ood for 20,000 actuations, tested against switch bounce during the inrush, guaranteed to avoid arc welding or otherwise damaging the contacts. They la st forever and don't cost that much. Form factor is panel mount, an automat ion industry gizmo. You have to register with EATON to see the details so t hat's where I stop.
A 50 amp relay costs $3. Maybe I'll just switch the AC into the supplies. All I need is coil voltage.
Pity; I design a elegant mosfet-based output switch.
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SYMBOL cap 208 336 R0 WINDOW 0 -67 14 Left 2 WINDOW 3 -67 55 Left 2 SYMATTR InstName C2 SYMATTR Value 1m SYMBOL res 352 320 R0 WINDOW 0 62 44 Left 2 WINDOW 3 60 77 Left 2 SYMATTR InstName R2 SYMATTR Value 0.2 SYMBOL diode 544 320 R0 WINDOW 0 65 -8 Left 2 WINDOW 3 70 24 Left 2 SYMATTR InstName D1 SYMBOL res 544 432 R0 WINDOW 0 -69 77 Left 2 WINDOW 3 -67 108 Left 2 SYMATTR InstName R3 SYMATTR Value 1K SYMBOL nmos 176 816 R0 WINDOW 0 137 41 Left 2 WINDOW 3 74 71 Left 2 SYMATTR InstName M2 SYMATTR Value FDB045AN08A0 SYMBOL res 32 960 R0 WINDOW 0 63 45 Left 2 WINDOW 3 48 76 Left 2 SYMATTR InstName R4 SYMATTR Value 250K SYMBOL cap 208 1216 R0 WINDOW 0 -63 32 Left 2 WINDOW 3 -63 67 Left 2 SYMATTR InstName C4 SYMATTR Value 1m SYMBOL res 352 1200 R0 WINDOW 0 65 38 Left 2 WINDOW 3 69 67 Left 2 SYMATTR InstName R5 SYMATTR Value 2 SYMBOL zener -176 1056 R180 WINDOW 0 -77 48 Left 2 WINDOW 3 -168 10 Left 2 SYMATTR InstName D2 SYMATTR Value BZX84B8V2L SYMATTR Description Diode SYMATTR Type diode SYMBOL g -336 960 R0 WINDOW 0 55 33 Left 2 WINDOW 3 51 68 Left 2 SYMATTR InstName G1
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SYMBOL res 1568 32 R0 WINDOW 0 65 38 Left 2 WINDOW 3 69 67 Left 2 SYMATTR InstName R7 SYMATTR Value 2 SYMBOL cap 1392 48 R0 WINDOW 0 -63 32 Left 2 WINDOW 3 -63 67 Left 2 SYMATTR InstName C6 SYMATTR Value 1m SYMBOL pnp 1200 560 M270 WINDOW 0 145 61 VLeft 2 WINDOW 3 102 87 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N4403 SYMBOL res 1040 480 R90 WINDOW 0 82 56 VBottom 2 WINDOW 3 99 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 1K SYMBOL Digital\\schmitt -560 416 R0 WINDOW 0 56 120 Left 2 SYMATTR InstName A1 SYMATTR SpiceLine VHIGH=5 VLOW=0 SYMATTR SpiceLine2 VT=4 VH=0.2 SYMBOL npn -752 336 R0 WINDOW 0 105 22 Left 2 WINDOW 3 78 62 Left 2 SYMATTR InstName Q2 SYMATTR Value 2N4401 SYMBOL res -704 528 R0 WINDOW 0 61 44 Left 2 WINDOW 3 60 74 Left 2 SYMATTR InstName R9 SYMATTR Value 10K SYMBOL res -896 464 R0 WINDOW 0 61 32 Left 2 WINDOW 3 62 67 Left 2 SYMATTR InstName R10 SYMATTR Value 10K SYMBOL res -896 208 R0 WINDOW 0 -96 40 Left 2 WINDOW 3 -97 76 Left 2 SYMATTR InstName R11 SYMATTR Value 10K SYMBOL cap -1056 480 R0 WINDOW 0 61 18 Left 2 WINDOW 3 63 54 Left 2 SYMATTR InstName C7
SYMBOL sw -1232 496 R0 WINDOW 0 54 43 Left 2 WINDOW 3 54 78 Left 2 SYMATTR InstName S2 SYMATTR Value SP SYMBOL voltage -1440 496 R0 WINDOW 0 44 169 Left 2 WINDOW 3 -23 215 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V5 SYMATTR Value PULSE(-1 1 10m 0 0 250m) SYMBOL res 112 -64 R90 WINDOW 0 77 54 VBottom 2 WINDOW 3 88 55 VTop 2 SYMATTR InstName R12 SYMATTR Value 1m SYMBOL res 480 688 R90 WINDOW 0 77 54 VBottom 2 WINDOW 3 88 55 VTop 2 SYMATTR InstName R13 SYMATTR Value 1m SYMBOL res 1312 768 R90 WINDOW 0 77 54 VBottom 2 WINDOW 3 88 55 VTop 2 SYMATTR InstName R14 SYMATTR Value 1m SYMBOL res -304 480 R90 WINDOW 0 72 54 VBottom 2 WINDOW 3 85 55 VTop 2 SYMATTR InstName R15 SYMATTR Value 10K SYMBOL npn -256 448 R0 WINDOW 0 105 22 Left 2 WINDOW 3 78 62 Left 2 SYMATTR InstName Q3 SYMATTR Value 2N4401 TEXT 280 168 Left 2 ;FDD86367 TEXT 816 1184 Left 2 !.tran 500m TEXT 816 1232 Left 2 !.model SP SW(Ron=.1 Roff=1Meg Vt=0 ) TEXT 480 88 Left 2 ;5V SWITCH TEXT 400 432 Left 2 ;Load TEXT 600 456 Left 2 ;PV Opto TEXT 280 920 Left 2 ;FDD86367 TEXT 440 992 Left 2 ;12V SWITCH TEXT 400 1296 Left 2 ;Load TEXT -128 944 Left 2 ;PV Opto TEXT 904 1000 Left 3 ;Crate Power Switch TEXT 952 1064 Left 2 ;JL Sep 5 2020 TEXT 1624 136 Left 2 ;Load TEXT -1192 608 Left 2 ;POWER TEXT -1192 640 Left 2 ;SWITCH TEXT -528 568 Left 2 ;STM810 TEXT 1640 624 Left 2 ;FDD86367 TEXT 1112 328 Left 2 ;-12 SWITCH
-- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
You can get zero-voltage switching SSRs as well, e.g.
AQJ116V Panasonic SSR RELAY SPST-NO 10A 75-264V $18.08000 @ qty 100
That'll prevent the Romex in the walls going thump when you turn on the box, too. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I'd be concerned about the 180 amp inrush melting a 10-amp SSR. The first quarter cycle might be bad.
I'd have thought that people would make SSRs with a contact closure input, but I haven't found any. They all need "coil" voltage.
We used to make CAMAC crates that had a giant transformer, and if you got unlucky with the power switch, you could literally hear the romex thump in the wall. An NTC thermistor fixed that. I expected cool-down time constant problems but never saw any.
I guess I could switch the DC outputs with three relays.
-- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
There wouldn't be that big an inrush, surely? If it's 200A at the sine wave peak, it would be considerably less near zero. The hold-up time of the supply is only one cycle of 60 Hz at full load, so the zero-volt-switched inrush would be about 2x the average current. The one-cycle nonrepetitive surge current rating for that one is 100A, which I'd think would be lots.
(They make 250A surge-rated SSRs in the same series.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I've found specified inrush currents to be worst case and wildly over the top in general.
The only way to specify is to measure it on a scope + percentage, otherwise you'll over engineer the solution.
One relay driven by three diodes in an and config so that all psus must be pok to enable the outputs ?...
Chris
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