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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Solid-State Relay instead of a contactor?
I am building a new compressor from a salvaged C-H tank and other parts, the
99.99 5 hp pump from HF, and a new 5 hp, 1 ph motor. The new motor is too much of a load for the pressure switch. I can get a contactor from Ebay, but I can also get some 25-amp solid-state relays a lot cheaper. Anyone have any thoughts on this option? The motor has built-in overload protection, so that's not a strong consideration. -- Bob (Chief Pilot, White Knuckle Airways) |
#2
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Solid-State Relay instead of a contactor?
On Fri, 30 Dec 2005 12:26:21 -0500, the renowned "Bob Chilcoat"
wrote: I am building a new compressor from a salvaged C-H tank and other parts, the 99.99 5 hp pump from HF, and a new 5 hp, 1 ph motor. The new motor is too much of a load for the pressure switch. I can get a contactor from Ebay, but I can also get some 25-amp solid-state relays a lot cheaper. Anyone have any thoughts on this option? The motor has built-in overload protection, so that's not a strong consideration. SSRs need a decent heatsink for that current (16A or so @240VAC). If the SSR fails on (which they are wont to do) you'll be testing the safety relief valve. I don't see a lot of advantage to using an SSR in this application- the compressor is noisy anyhow and the life probably won't be an issue. Sometimes they have trouble turning off with motor loads- try to get the kind that is "back to back SCRs" rather than the triac kind. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
#3
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Solid-State Relay instead of a contactor?
Bob Chilcoat wrote: I am building a new compressor from a salvaged C-H tank and other parts, the 99.99 5 hp pump from HF, and a new 5 hp, 1 ph motor. The new motor is too much of a load for the pressure switch. I can get a contactor from Ebay, but I can also get some 25-amp solid-state relays a lot cheaper. Anyone have any thoughts on this option? The motor has built-in overload protection, so that's not a strong consideration. I have an SSR on my 2 Hp compressor. I had the first one blow (shorted) so I used a much higher rating and have had no further problems. The motor has an 11 A @ 240 V rating, and I'm using a 600 V 50 A SSR. Jon |
#4
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Solid-State Relay instead of a contactor?
Ignoramus24987 writes:
I do not think that you can get solid state relays much cheaper than contactors. They are available cheap on eBay, but mostly these are used units swapped out from planned maintenance. |
#5
Posted to rec.crafts.metalworking
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Solid-State Relay instead of a contactor?
On Fri, 30 Dec 2005 12:26:21 -0500, "Bob Chilcoat"
wrote: I am building a new compressor from a salvaged C-H tank and other parts, the 99.99 5 hp pump from HF, and a new 5 hp, 1 ph motor. The new motor is too much of a load for the pressure switch. I can get a contactor from Ebay, but I can also get some 25-amp solid-state relays a lot cheaper. Anyone have any thoughts on this option? The motor has built-in overload protection, so that's not a strong consideration. Not a good application for 25-amp SSRs. Start current on an induction motor, particularly one with a compressor load, can exceed 10X rated load current. SCR's and triacs can take that for a cycle ( 1/60 sec) or so, but a compressor motor can take a significant fraction of a second to get started. |
#6
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Solid-State Relay instead of a contactor?
Don't understand why you want a SSR.The only advantage of SSR is they
are quiet.Try a mercury relay |
#7
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Solid-State Relay instead of a contactor?
On Fri, 30 Dec 2005 19:07:09 -0500, the renowned
(tony stramella) wrote: Don't understand why you want a SSR.The only advantage of SSR is they are quiet.Try a mercury relay On an inductive load? Good way to get a mercury-laden explosion unless they are specifically rated for that load (few are). Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |
#8
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Solid-State Relay instead of a contactor?
Richard J Kinch wrote:
Ignoramus24987 writes: I do not think that you can get solid state relays much cheaper than contactors. They are available cheap on eBay, but mostly these are used units swapped out from planned maintenance. I have a small supply of new in the box Crydom 2425s. $10 each, that includes shipping in the continental US. They were for a project that never happened. |
#9
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Solid-State Relay instead of a contactor?
tony stramella wrote:
Don't understand why you want a SSR.The only advantage of SSR is they are quiet.Try a mercury relay Yes, indeed! The contactor that was in my compressor was actually louder than the compressor, and every time the motor started, I'd jump a foot! Now, there's no huge clang when it starts. Jon |
#10
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Solid-State Relay instead of a contactor?
Thanks for the offer. I've put a bid in for a contactor, which I might get,
but I'm still interested in trying some SS relays. OTOH, as someone said, I probably should go with something in the 40-50 amp range. My motor is a 20-amp 230 V motor and, assuming that a 2425 is a 240 V 25 amp relay, it might be marginal in this application. -- Bob (Chief Pilot, White Knuckle Airways) "Cydrome Leader" wrote in message ... Richard J Kinch wrote: Ignoramus24987 writes: I do not think that you can get solid state relays much cheaper than contactors. They are available cheap on eBay, but mostly these are used units swapped out from planned maintenance. I have a small supply of new in the box Crydom 2425s. $10 each, that includes shipping in the continental US. They were for a project that never happened. |
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