Yeah, usually they are called AC 3 and AC 4, IIRC. What's right for your
case, is AC 3, for induction (squirrel cage) motors. Although the spec for
your timer says 16 A, it would be a good idea to use your timer to operate a
relay (magnetic contactor) and choose a single phase, two contact relay.
This will move the (electrical)stress of opening and closing the contacts
from the timer to the relay . I usually use those transparent single phase
relays, which here are called valve type, because they are trasparent and
look like old fashioned valves. They come with a base, that can be installed
on a rail (panel) or with screws, and when the relay is toast, you just plug
in a new one, instead of trashing the whole timer. BTW, the specs for AC 3
are: printed on any relay, and you can ask the vendor (where you buy it)
If a switch is motor rated it will generally have an HP rating on it.
You can usually get away with using small fractional HP motors on a
switch rated at 16a resistive but I would not use more than 1/3 to
1/2HP on one.
I believe what T.D is talking about is a "solid state relay" in the US
and that will handle whatever the relay is rated for on a very small
operating contact. They will even run directly off a CMOS device since
it is just a LED doing the signaling an opto-isolator on the low
current side and a big triac switching the load.
I wouldn't advise using an SSR to switch motors.
They are good for resistive loads and some inductive loads, but not
motors due to the way they fail. If the DIAC develps a fault the relay
can go "half closed" and burn out the windings in your motor.
I guess you never saw an IBM check sorter. They had about 50 SSRs
The only real problem was that these were 3 phase and since there is
never a true "zero crossing" they switched under power so they
generally used something with a rating 5x-10x the expected load.
They usually failed "full on". The single phase motors just ran all
the time and the 3 p motors tripped the over current device.
email@example.com formulated on Sunday :
No, I can't say that I have, I have seen SSRs fail full on & open
ciruit. That wouldn't hurt your motors, but I have replaced several
that would allow "half"voltage when they were supposed to be
Thermal protection should protect the motor, but if the motor doesn't
have proper protection or is running a refrigeration compressor.
There is a company in Australia (who I won't name) that used ssrs to
start refrigeration compressors. They went back to a coil relay after
they noticed the number of compressor failures increased.
Some failures were due to burnt windings and some were caused by
damaged valves from liquid floodback (caused by the compressor never
turning off and icing up the evaporator coil)
When I wrote I wouldn't advise using an SSR to start a motor I didn't
mean that you shouldn't ever use one.
I can understand the logic of using SSRs in that sort of applicaton
though, They have a higher switchlife, & no noise :)
The biggest problem I have seen was when you had ripple on the DC
supply (in a DC gate SSR) and it had a screwy wave form on the output
What brand were you using? I have had pretty good luck with Crydom but
I think the Opto22s are better. I have a bunch of them around the
house doing different things.
I've used several brands, Golink Crydom, Eurotherm, Omron...
The Eurotherms are very good, our company buys 40Amp SSRs mounted on
heatsinks W/DIN rail mounts. They are rated for a higher output voltage
too (660VAC) and work at higher temperatures.
The only ones that have ever really been a problem (we only use them
for resistive loads ie. Heaters) were Golinks.
We had heaps of them fail because of faulty resistors in the
optocoupler. Golink corrected the problem but we were out for alot of
warranty replacements and were not game to try them again...
We use Crydom in most products, they seem to be very reliable.
No, it's a normal electromagnetic relay, but I know how its called only in
greek. (Rele lychnias). See here, for example:
They just have a transparent cover, and usually are single-phase, rated
contacts for 16 A.
major in electrical engineering
Tzortzakakis Dimitrios laid this down on his screen :
In english, those are called plug-in relays.
The 10 amp units are easy to find and cheap, however the bigger units
do start to get expensive.
If the OP is looking for just a single pole then I would advise him to
look at this:
I have used hundreds of these and found them to be very reliable.
Actually, it is what I visualised when you described it, though I was a
little confused by your description of a "valve relay".
I would probably just describe it as a an "octal base relay" (though
sometimes they may have more than 8 pins). They usually plug into a
standard octal valve base which is presumably why you refer to them in the
way you do.
Can't say as I remember that particular problem. The biggest problem I
recall, was trying to get my head round the idea that the "HT" line was
negative WRT earth, especially with the early Germanium stuff.
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