On 07/29/2015 11:40 AM, Pat wrote:
On Wed, 29 Jul 2015 19:32:06 +0100, MJC
wrote:
In article ,
says...
On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams
wrote:
You have an interesting problem. I hope you figure it out. I have
never used SS relays, but I can't image they cause spikes and other
anomolies that would kill a simple AC motor. Is the relay rated for
inductive loads?
I can't be bothered to study SSRs so I just speculate... Could it be
that the ones you use just deliver one polarity of AC instead of both,
like a rectifier? Resulting in a DC component which the fans do not
like...
Mike.
That's an interesting thought. Even if most SSRs handle full AC,
maybe this particular one is faulty and only passes one polarity. That
would certainly make the fan motor unhappy.
Pat
The motor would run at half speed at best.
The motor won't overheat though unless it stalls/is jammed and can't
self cool.
It is more likely that the motors are just of a cheap quality
construction (for example are the UL or CSA rated?) and fail far too
easily. A SS AC modular relay is simply a high current TRIAC and these
are used on many fans around the world - what do you think a motor speed
control is?
A moments research pulled up this PDF:
http://www.omron.com/ecb/products/pd...utions_ssr.pdf
(quote)
The following will demonstrate the process to determine the effective
ratings of non-motor control rated Solid State Relays for use in motor
control applications:
Example question: “Can I use a standard Solid State Relay (which is not
included in the Crydom Motion Control Brochure and therefore without HP
or KW Motor rating) to control the start/stop of a motor?” The answer:
Yes, you need only to consider the motor nominal current value (FLA),
inrush current value (LRA), motor power factor (typically 0.1 to 0.9) to
select the appropriate turn-on switching type (zero-crossing or random)
and possible need for SSR transient protection to select an appropriate
Solid State Relay.
(end quote)
John :-#(#
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