I'm trying to use a relay to turn on/off 16 lamps togheter (AR111 50W 12V each one) and also I'm using Groove System but the relay from Groove System supports only 5A (http://www.seeedstudio.com/wiki/File:Twig-Relay1.jpg). What can I do to turn this possible: manage with Groove System all these lamps togheter? Is it possible to use another stronger relay to be started from the smaller relay? Any ideas?
Thanks in advance!
A starter relay for a car engine might be a possibility.
Unless things have changed since I last took a car to pieces the starter relay is part of the starter motor.
It should be easy to get a 30 or 40 amp relay intended for cars (maybe there are even heavier duty ones). You could split the load over two or three relays and switch those relays with another relay controlled by the Arduino.
...R
zoomkat:
A starter relay for a car engine might be a possibility.
Really? Those are probably not rated for continuous duty, take vast energizing
currents, and are usually integral to the body of the starter motor itself!!! Or is
there some other kind of relay you are thinking of? 70A is a pretty massive
contact rating for a single relay / contactor.
Are these lamps 12V DC ? If so then some MOSFETs are a much better plan, easy to
parallel them up and no power wasted energizing them. Do a few lamps per MOSFET
to keep the current levels sane, and sequence them on start up (inrush current for
a filament bulb is about 10 times steady current, remember).
A powerful latching relay would be another alternative, but 70A is a very large load
to switch, especially considering inrush of 10 times that. There is possibly such a
device available already for automotive/lorry use.
Really? Those are probably not rated for continuous duty, take vast energizing
currents, and are usually integral to the body of the starter motor itself!!!
You ever work on cars? 8) Use a small pilot relay or transistor to operate the starter relay from the main 12v power supply. A local auto parts store probably has a generic Delco starter relay for ~$10.
Well, what I want to do is control my lamps in my house. In some parts are lamps 100W 110V, in other are togheter 16 lamps. Is there any relay or similar that works like my "wall switch", independent of the voltage? I just want control some switches that turn on/off a lot of lamps. These car relays could be the solution if I start them from my Grove Relay (5A), but they waste energy, is that?
Any other ideas are welcome! Thanks!!
Car relays won't be suitable for mains voltages but you should have no trouble sourcing mains relays that are controlled by low voltage DC.
All relays waste a small amount of energy when their coil is energized but it is normally trivial compared with the energy consumed by the load.
I can't recall if it was already mentioned but you will need a transistor between the Arduino and the relay as the Arduino can only supply about 20mA from its digital pins and that's not enough for the relay coil.
...R
Any other ideas are welcome! Thanks!!
Sure, you need to sort out why you said "AR111 50W 12V each one" in your first post and "lamps 100W 110V" in your second post. Are your lamps 12v or 110v? 
zoomkat:
Sure, you need to sort out why you said "AR111 50W 12V each one" in your first post and "lamps 100W 110V" in your second post. Are your lamps 12v or 110v?
Kkkk!! Sorry! I mean that I have a switch that controls 16 lamps AR 111 50W 12V in one situation, I have another switches in the house that controls other lamps 100W 110V that in some cases are alone, in other cases are groups of 5, groups of 10 of these. I'm looking for a way to solve my problem: convert my Grove Relay 5A in a solution to turn on/off these cases.
Just to check, because I'm new on the area: if I have 16 lamps of 50W 12V each one, I need a relay of 70A?
Amperage per lamp:
a = 50 / 12;
a = 4.16;
So, 16 lamps of 4.16 = 66.56A (rouding up to 70A). Is that correct? Thanks in advance!
I'd encourage you to read the Yourduino ArduinoPower tutorial for getting started with relays. The tutorial is so well done it tells you pretty much everything you need to know.
andremilani:
So, 16 lamps of 4.16 = 66.56A (rouding up to 70A). Is that correct? Thanks in advance!
Yeah. And I assume you appreciate that that is a lot of amperage needing at least 6 ga copper wire to carry 70A of current.
Relays capable of carrying that amount of current aren't uncommon but they'll cost around ~$10 and you'll get stuck with wiring up a transitor, flyback diode, etc. to energize the relay's coil. If you can break your lights down into groups of four (~16A each group) then you'll have an easy time finding a four relay board to switch them. When you look around for a relay board make sure that the relays are rated for at least 20A at greater than 12V DC; that rating will be printed right on top of the relay.
Robin2:
Unless things have changed since I last took a car to pieces the starter relay is part of the starter motor.
Small engines (used in generators, riding mowers, etc.) with a starter motor use a starter relay independent of the starter. It's only in newer cars where the relay is part of the starter.
Just sayin' so if you're ever looking for a big relay you'll know you can always find one in an auto parts store or anywhere where mower parts are sold. Nobody will look at you funny for asking for one, but they might not understand your request unless you call it a "solenoid".
Chagrin:
Robin2:
Unless things have changed since I last took a car to pieces the starter relay is part of the starter motor.Small engines (used in generators, riding mowers, etc.) with a starter motor use a starter relay independent of the starter. It's only in newer cars where the relay is part of the starter.
Not just small engines; I know for a fact that on my 79 Bronco (with a 6.6L V8) - the starter relay is separate from the starter (the starter has a Bendix gear instead of a solenoid to kick the pinion in place), mounted on the fender. It was also the same way on my old 1994 Ranger 4-banger. Basically the positive from the battery goes straight to the relay, then from the relay to the starter motor; thick cables all around - lots of current.
Such a relay is different from a "starter solenoid" - a solenoid is something used instead of a Bendix gear system to kick the pinion of the starter motor in and out from the flywheel ring gear (whereas the Bendix uses a spring and the under-run/over-run of the speed of the flywheel vs engine speed vs starter speed to kick in/out).
Anyhow - the starter relay looks something like this:
http://www.tractorpartsinc.com/images_products/ford_tractor_starter_relay_6_2676big.jpg
Ultimately, though, such a relay is intermittent duty only - if you try to keep that much current running through it constantly, it'll melt or catch on fire.
High-current relays for AC mains voltages are typically called "contactors", and are typically used in home air-conditioning systems. Most of the time, these contactors use 24 volts AC to operate the coil (in the air conditioner is a transformer that converts the 220vac to 24vac); even the few 120vac contactors I have seen use 24vac for the coil (but there do exist ones that use lower DC voltages as well).
Another good place to get high-current relays are from/for older electric golf carts (generally rated for 36vdc at a ton of amps - and continuous!).
Something else to keep in mind is that for the most part, the contacts are rated for current, not voltage; you'll often see relays with a contact rating of something like "250vac/20A and 12vdc/20A" - so mainly pay attention to the amp rating of the contacts, not the voltage (I once replaced a relay in a waffle maker with a 12vdc 40A Bosch automotive relay because I couldn't source the proper Osram in time for a restaurant to open - the relay controlled the voltage to the heating elements - it's worked fine for about a year now in daily, constant use - anecdotal, though).
Be aware that AC relays/contactors may rely on the 0 VAC crossing point to extinguish the arc, which does not exist with DC current.
And that AC relays are NOT suitable for use on DC since their coils rely upon inductive reactance (XL) to limit coil current. In other words their DC resistance is many times lower than their inductive reactance (XL) so if used on the equivalent DC voltage they WILL burn up.
cr0sh:
Such a relay is different from a "starter solenoid" - a solenoid is something used instead of a Bendix gear system....
They are referred to as "starter solenoids" quite regularly as a Google image search will show. I'll wholeheartedly agree that it's a bad name for it but ... y'know.
Ultimately, though, such a relay is intermittent duty only - if you try to keep that much current running through it constantly, it’ll melt or catch on fire.
I would suggest the OP spend $10 on a starter solenoid made for starting large engines like below and do some testing. The OP could energize the coil in the solenoid for 24 hours and see if it over heats. If that test ok, then he could power his 12v lamps thru the starter solenoid and monitor its temperature to see if overheating is an issue. If there is heating, then he could purchase one or more solenoids and divide the load between them. I doubt any cheaper solution is going to be available for DC loads.
Chagrin:
They are referred to as "starter solenoids" quite regularly as a Google image search will show. I'll wholeheartedly agree that it's a bad name for it but ... y'know.
I tend to chalk that up to mechanics not understanding the electrical components (it's crazy how many don't - and don't want to - and look on it as "voodoo" or something - despite the fact that the amount of electrical devices in a vehicle have only expanded over the decades).
Also - in my experience - mechanics tend to call it a "selenoid" (or some variation thereof)...lol 
zoomkat:
I would suggest the OP spend $10 on a starter solenoid made for starting large engines like below and do some testing. The OP could energize the coil in the solenoid for 24 hours and see if it over heats.
I tend to wonder if part of the reason these "relays" aren't continuous duty also has to do with the contact ratings; that the contacts can only handle high-amperage for so long.
Then again, for an automobile starter, you are talking hundreds of amps - so it might not matter for something half or more lower than that. I have seen old Popular Science articles that used such relays to control motors that had smaller current ratings in a continuous fashion (most of the time it was for some kid's homemade ride-on toy).
I agree that some testing with such components would be in order...
cr0sh:
I tend to wonder if part of the reason these "relays" aren't continuous duty also has to do with the contact ratings; that the contacts can only handle high-amperage for so long.
Here's a picture of the innards of that Ford relay you linked to earlier. The "washer" connected to the ...rod thing... is easily 1/8" thick and the copper bolts sticking out the sides are each all one piece -- each one is basically a 1/4"-28 bolt with a large, rectangular head. Picture is not mine but I have torn one apart in the past.
Lots of copper there. If it wears out I'd expect it to be from repeated energizing of the coil and arcing of the contacts, but in continuous use the contacts should be fine (?). Like zoomkat I would expect the coil to overheat first.
