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Author Topic: Quick solid state relay question...  (Read 2720 times)
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Is this the right way to wire them up?

Thought Id double check before messing with AC


my Relays are OPTO 22 (SSR), 240 VAC, 25Amp - Control 3VDC -32VDC
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On the AC side - can you explain what your colors represent?

Also, have you reviewed the tutorials and other information on the Omron site? They make SSRs and other relays, etc - mostly for industrial control, but they have lots of great articles and information that is applicable in general.

You might also need to think about heatsinking, depending on the load you are controlling (read the datasheet for your SSR as well)...
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Blue= neutral
Brown=Live

Not sure if I will ned a heat sink, plan on powering 240V, but for very sort 6 second every 10mins or so. what do you think? 
« Last Edit: February 23, 2012, 11:56:46 am by n00b » Logged

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Blue= neutral
Brown=Live

Not sure if I will ned a heat sink, plan on powering 240V, but for very sort 6 second every 10mins or so. what do you think? 

I'm pretty certain you're supposed to switch hot by code, not neutral - that neutral should never be broken (it's a safety issue); the only time you can switch neutral is if you are switch both at the same time (like you used to see in old PC AT power supplies - the switch on the front was a DPST that switched both neutral and hot.

Regarding the heatsink - what are you planning on powering (what sort of load and its rating) and what is the SSR rated for (with and without a heatsink)? That information will determine if you need a heatsink.
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Quote
I'm pretty certain you're supposed to switch hot by code, not neutral - that neutral should never be broken (it's a safety issue);

Agreed. Imagine this connected to a simple lamp. Electricity will go up the hot wire, through the lamp, down the neutral wire, and waiting for the switch to close completing the path to ground. If you go to change the bulb, even though the lamp is off the "hot" is there waiting to make a path to ground through you. Painful shock or death is possible. Place the relay on the hot side and the electricity stops at the relay, keeping you and others safe.
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I'm pretty certain you're supposed to switch hot by code, not neutral - that neutral should never be broken (it's a safety issue); the only time you can switch neutral is if you are switch both at the same time...
I've seen many instances in appliances, specifically espresso makers, where neutral (only) is switched when controlling resistance heating elements.  I don't know why, or even if it is a good idea, but this seems to be the standard practice in that industry.

Jim
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well wired it up with the live being broken by the relay and it works.......though one strange thing, Will stop and start a AC motor and a lamp, but when I connect a lamp with CFL bulb and when its supposed to be off it just strobes till turned on?
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well wired it up with the live being broken by the relay and it works.......though one strange thing, Will stop and start a AC motor and a lamp, but when I connect a lamp with CFL bulb and when its supposed to be off it just strobes till turned on?

SSRs are not 'perfect' relays that always turn on or off when commanded. They are sensitive to the type of load being switched and if there is too much capacitance or inductive reactance when switching certain load, they can have problems. Search on 'snubber circuits' to find out more information on this problem using SSRs.

Lefty

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well wired it up with the live being broken by the relay and it works.......though one strange thing, Will stop and start a AC motor and a lamp, but when I connect a lamp with CFL bulb and when its supposed to be off it just strobes till turned on?

CFLs are sensitive. You may also find that, when turning on with a SSR, they actually buzz a little bit. I ended up ripping out an SSR and using a regular relay in some circuits because of this.
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Shouldn't there be a diode over the relay pins that connect to the Arduino ?
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Shouldn't there be a diode over the relay pins that connect to the Arduino ?


I dont know?  smiley-eek-blue
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try this explanation :
http://en.wikipedia.org/wiki/Flyback_diode

I'm certainly no expert, in fact I hardly even make the novice noob level, so I really don't know anything about SSR relays. But I do recall some of the "God" members of the forum discussing the diodes a while back to prevent damage to the IO pins on the Arduino.

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Read this (and, like I noted, the other Omron guides):

http://www.ia.omron.com/support/guide/31/overview.html

Notice the input side - essentially connected to an LED, which triggers a triac (called a "phototriac coupler" - works very similarly to an optocoupler, with the phototransistor replaced by a phototriac).

Thus - no "flyback diode" is necessary (that's only necessary with an electromechanical relay, where the relay's coil gives an "inductive kick" that is absorbed by the diode and released as heat).

Depending on your load, though, on the output side of the SSR - you might want to incorporate a MOV (metal-oxide varistor); this would basically perform the same thing as a diode for the inductive kickback of certain loads (like large AC motors), where you couldn't use a simple diode (because of the AC). Some SSRs have them built-in (or something similar). Once again, the Omron site can provide more details on this - here's also another source:

http://www.electronics-tutorials.ws/io/io_5.html
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Shouldn't there be a diode over the relay pins that connect to the Arduino ?


The "SS" in "SSR" means that there are no mechanical parts, and thus no inductor coil to generate kickback. The only thing that needs protecting is the diode in the SSR, against overvoltage if it's a 3V device. However, if your spec says 3-30V, there is no way the Arduino can harm it.

If you want to protect the switching side of the relay, get some high-wattage TVS-es or varistors or something.
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An often overlooked requirement for SSRs are the need for proper heat sink if operating the device at anywhere near it's full rated current. A SSR will drop around 2vac across it's output terminals so if your running a SSR at it's max rating of say 25 amps that's 50watts of heat and the device will self destruct without proper cooling. Those max current ratings only apply if you keep the device operating temperature below it's max rating. There is normally a 'derating' chart or graph in it's datasheet showing how much less current you should attempt to draw through the device depending on temperature. Ones I've used in industrial applications required finned heatsinks that were maybe 10" x 5" x 5".

Lefty
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