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)

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

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

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.

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.

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

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

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.

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

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.