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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Bob Chilcoat
 
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Default 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)



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Spehro Pefhany
 
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Default 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
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Jon Elson
 
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Default 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

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Richard J Kinch
 
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Default 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.
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Don Foreman
 
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Default 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.



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tony stramella
 
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Default 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






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Cydrome Leader
 
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Default 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.
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Jon Elson
 
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Default 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

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Bob Chilcoat
 
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Default 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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