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Posted By: togol plug-in relay - 06/15/07 10:32 PM
my buddy "Biodiesel Man" had curbs put in at his home and somebody other than me talked him into installing ropelight in the curbs... about 400' worth of the stuff.

so I made him a little panel with the usual timer / PE and a little 8 pin relay.
the problem ???
the two ropelight circuits are a bit high.... 9A and 11A on a relay rated 10A.
I was thiking of adding a second relay and running each circuit through BOTH of the NO poles on a relay

sound stupid?

I could get a definite purpose contactor and jam it in the box ( there is a pond pump control in there too )

but I thnk the ice cubes would handle it by paralleling the feed through them.

a bit unorthodox, but it could work , right ?

Posted By: NJwirenut Re: plug-in relay - 06/16/07 12:04 AM
Not a good plan.

Inevitably, one set of contacts will close or open a millisecond or 2 before the other, and will erode at a much faster rate.

The best solution is a relay with properly rated contacts.
Posted By: togol Re: plug-in relay - 06/16/07 12:31 AM
NJ, your taking all the fun out of this..;
Posted By: JoeTestingEngr Re: plug-in relay - 06/16/07 02:00 AM
What about just driving the coil of an A/C control relay like this one.
http://www.grainger.com/Grainger/items/6X567
You won't come close to overloading those contacts.
Joe
Posted By: gfretwell Re: plug-in relay - 06/16/07 02:32 AM
Why not a solid state relay?
Posted By: JoeTestingEngr Re: plug-in relay - 06/16/07 05:41 AM
I thought about suggesting an SSR but a majority are 3-32 VDC control input and he doesn't need a DC supply for anything else. The AC control ones tend to be more expensive than the A/C relay that will carry more current and make sense to more people. Lastly, he can feed each string through it's own set of contacts and perhaps, separate fusing.

Greg, I knew that you would think of using an SSR just like I did. What I didn't know is if you are always reminded of SSRs in the bottom of Cartridge Module Drives, used to control spindle motors. That was the first place I encountered one back when each MB weighed more than a pound.
Joe
Posted By: walrus Re: plug-in relay - 06/16/07 10:45 AM
You can get ice cubes with 20 amp rated contacts, maybe even 30 amp
Posted By: gibbonsseabee80 Re: plug-in relay - 06/16/07 11:37 AM
I would go with gfretwell's idea. At work we have systems with relays controlling small magnetic contactors. This might prevent re-work or premature failor later on. Just a suggestion. I like square d because the coil is enclosed/hidden and quiet.
http://www.grainger.com/Grainger/items/2CF80
Posted By: gibbonsseabee80 Re: plug-in relay - 06/16/07 11:49 AM
Sorry I meant go with JoeTestingEngr's idea. Sorry about that Joe
Posted By: Mountain Electrician Re: plug-in relay - 06/16/07 01:51 PM
A SSR would be a good choice for this application since space is an issue. Crydom is good, AC/DC control with high amp output available. A Crydom A1225 has AC control, 25 Amp output, and costs between 30 and 40 bucks. When you install it, put heatsink compound between the relay and the metal backplate or box or it may not last long. Properly installed, a SSR is a great spacesaver.
Posted By: JValdes Re: plug-in relay - 06/16/07 04:11 PM
Be careful with SSR's. If there is not a sufficient load/current draw it will not switch.
I have noticed over the years that when SSR's fail they usually fail in the closed position. SSR's are great in the right application.

I think you can find a cube that has a higher rating than 10 amps. But I have not seen or used one.
You can use a miniture (IEC) traditional relay, Then you can choose the one with the correct current requirement.
Posted By: JoeTestingEngr Re: plug-in relay - 06/16/07 06:09 PM
I like SSRs but I've never strung 400' of antenna on one and stuck it outside. Please remember that you have to worry as much about potential voltages across them when they're off, as load currents through them when they're on.
Joe
Posted By: togol Re: plug-in relay - 06/16/07 11:15 PM
Thanks everyone, I do have a 30A Definite purpose contactor for the pump ( there's a thermal at the pump)
and I have replaced Crydom SSRs when they have gone bad, just never thought of it for these little loads. but I will remember these ideas next time

I did find a 12A octal and a 15A cube but that would need a different base.both have an LED and push-to-test button and they are about $ 5 from http://web4.automationdirect.com/ad...imers/15A_Electro-Mechanical_Cube_Relays
Posted By: JoeTestingEngr Re: plug-in relay - 06/17/07 02:34 AM
http://www.allelectronics.com/cgi-bin/item/RLY-482/500/120_VAC,_40_AMP_RELAY_.html

How about this one Tom? You can't beat it for $2.50 .
Joe
Posted By: togol Re: plug-in relay - 06/17/07 03:15 PM
Holy Cow Joe, You just saved him a ton of $ I think the A-B that I used was around $12

what's next ?

Free ? smile
Posted By: togol Re: plug-in relay - 06/17/07 03:30 PM
...that's a cool link I like the $.65 screwdriver testers, gonna order some
Posted By: gfretwell Re: plug-in relay - 06/17/07 07:16 PM
I like the Crydom or Opto22 that operate up t0 40a with the 3-32v input.
We used about 50 of them in a check sorter. I ended up with a big box of them.
Bear in mind this is just a triac with a LED optoisolator driving it so you can think of the input as nothing but a LED behind about 500 ohms of resistance. (they draw 5ma@5vdc measured and I am assuming 2.5vd on the LED, maybe not exactly true but a starting place)
You can drive 40a 240VAC directly from a 4000 CMOS gate, pretty cool. I always slip a 2n2222 or similar in there but that is just me.
I have also driven the pick of an SSR directly from 120v using the two capacitor and two diode trick. It worked fine for many years. That is something an old IBM engineer came up with to drive low voltage indicators with from line voltage, Basically you have a capacitor in series with the load and another one across the load for a voltage divider and filter. I added 2 diodes to protect the LED.
Posted By: togol Re: plug-in relay - 06/17/07 07:25 PM
Greg I think I understand your circuit, just can't picture it..if you have the time, could you scribble the schematic and e-mail it to me ? and since I'm using the photoeye to turn the lights on I would need the cap diode trick as well since I have no idea what that is
Posted By: JoeTestingEngr Re: plug-in relay - 06/17/07 08:57 PM
http://www.opto22.com/documents/0859_Solid_State_Relays_data_sheet.pdf

OK, Here is the link for OPTO22's SSR datasheet. If you would choose to go the SSR route, I would urge you to carefully read pages 17 & 18. You will learn alot from those two pages. There is also some wisdom to be gained from getting burned by using the right part in the wrong application. I would guess a shorted output as your most likely failure mode.

If you ever have an application where it is essential to control AC within about an 8 mS window, look to SSRs first. Also, you have no contact bounce issues with SSRs. These SSRs have built-in snubbers which should help protect the output devices. But snubbers can fail too and can't be replaced if they're internal. External MOVs are a good idea.
Joe
Posted By: gfretwell Re: plug-in relay - 06/18/07 01:39 AM
If you are selling this you should just buy the 85-280VAC model.
Posted By: gfretwell Re: plug-in relay - 06/18/07 01:48 AM
IBM got in trouble with these SSRs on the 3890s because they are designed to switch on a zero crossing but 3p L/L is never zero.
They settled on the Optos at about 10x the required rating (3/4hp motor on a 45a, little shaded pole motors on 10s)
They did OK. The Crydoms seemed to fail more
Posted By: togol Re: plug-in relay - 08/08/07 12:32 AM
Joe ,or Greg, I finally picked up two Crouzet #GN 84134011 relays/like this one,
http://www.galco.com/scripts/cgiip.exe/wa/wcat/itemdtl.r?listtype=Catalog&pnum=84134011-CROU


there is no schematic but it looks like the switched load connects to terminals 1/L1 and 2/T1 and the control to 3/A1 and 4/A2...
I did not see any heatsinks for this relay in the Newark catalog , but it seems I need them since one of these will be pulling 21 A...so I looked at Joes' link and think I can figure out which one to use, but I still can't find them anywhere
Posted By: gfretwell Re: plug-in relay - 08/08/07 02:52 AM
I am torture testing a Opto22 in my garage on my air compressor as we speak 15a @ 120v.
I just put it in a 4x4 deep box with heat sink goo under it. I used one of those where the KOs are flush so I get good contact. It gets the box warm but I can hold my hand on it. I did space the box 1/4" off the concrete wall so the air gets behind it.

You can cut a regular LV separator so it fits over the SSR between the 120v side and the LV if you want to use the class 2 rules
Posted By: togol Re: plug-in relay - 08/08/07 08:55 PM
OK, I have everything in an 10X12 NM Hoffman type enclosure on a backplane .

that might be enough metal but I still need to know if my guess at wiring the terminals is right


Tom
Posted By: JoeTestingEngr Re: plug-in relay - 08/08/07 10:25 PM
http://www.galco.com/techdoc/crou/gn/gnssr_spec.pdf
Tom,
This is on the link you sent. Click on the specifications link after you click on the first documentation link. Page 1-12 shows that you are correct on your terminal assignments and the derating curves are on the bottom right of the same page. Newark showed at least 3 Wakefield half brick heat sinks of varying fin depths that the SSR could bolt onto. Just remember that something as simple as keeping the fins vertical can improve convective cooling.
Good luck,
Joe
Posted By: togol Re: plug-in relay - 08/09/07 01:32 AM
EUREKA.. the thing worked. we will find out tomorrow if if held !
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