I'm working on a project to control an existing light fixture (with two lights) with an Arduino. I want to use a 5v relay module. On the top it has this:
10 A 120 VAC
7 A 240 VAC
5 A 240 VAC
I know some about watts, amps, and volts to some degree, but I'm confused about how they relate to each other.
I'm worried about causing damage, considering I'm working with higher power/voltage electricity.
The outlet I'm working with is 120 volt, and the lightbulbs say they are 10.5 watts each, with each pulling 98 mA.
It is safe to set up the relay at the light switch to control the lights with an Arduino?
Thanks!
I hate having to say this but the questions you ask demonstrate that you do not have enough knowledge to work safely with mains electricity. Please find a project that won't kill you or burn the house down if you make a mistake.
These relays are widely used with AC loads. The relay usually already has galvanic insulation between the contacts and the coil, but to improve noise insulation it is also common to use optocouplers. For this reason, some modules are already manufactured with optocouplers.
Is the lamp incandescent?
Assuming it is incandescent, and that is 98mA for each lamp, then it would be possible to use a relay for up to 100 lamps. But incandescent lamps also have a low resistance when it is cold, so it would be interesting to consider this, to avoid premature wear of the relay contacts.
On security, it needs to be clearer in what aspect you refer. Because in AC and Arduino loads, one usually wants to know about the safety of insulation, so as not to be affected by an electric shock. But there are also other concerns, such as lightning strikes, which cause the electrical network to have a very high over voltage, so the relay can have a low insulation and let this discharge pass from the contact side to the coil side.
In the case of lightning protection, it is most appropriate to use some additional devices to prevent the discharge from reaching the devices connected to the electrical network.
You have no way of knowing what relays the op is talking about. Sure, s/he mentioned the ratings, and we're probably all picturing a blue cube Songle style of relay but there's no way we can talk with confidence about one of "these relays" unless the op gives a part number.
If there is no deterring you from pursuing this course of action then you need to define the total load per relay in amps and specify load configuration in terms of SERIES or SERIES-PARALLEL etc (ie, how many bulbs per relay and
how are they wired ?)
Once you do that it is possible to calculate the
the energy in J in order to design a snubber to
reduce contact arcing on opening (arcing typically
is on opening rather than closing because the current is already flowing) If this is for holiday
lighting and only turned on once a day and off once a night then you can forego the snubber.
I know some about watts, amps, and volts to some degree, but I'm confused about how they relate to each other.
Power (Watts) = Voltage x Current
So for 10.5W I get 0.087 Amps = 87mA.
You didn't say how many bulbs you have but your relay should be able handle it.
It is safe to set up the relay at the light switch to control the lights with an Arduino?
Relays are isolated so if you wire it correctly, and if the lethal voltages are insulated/protected and if don't touch the AC circuit when it's live, you are safe and the Arduino is safely isolated from the AC.
The Arduino cannot directly power a relay coil so you need a relay driver circuit or you can get a relay board with a built-in driver. (If you're using a relay board, there's AC on the board and it's not easy to insulate.)
fionning_macara:
You have no way of knowing what relays the op is talking about. Sure, s/he mentioned the ratings, and we're probably all picturing a blue cube Songle style of relay but there's no way we can talk with confidence about one of "these relays" unless the op gives a part number.
Part number isn't great(*), please always provide a link to a datasheet or product page for every piece
of hardware you mention in a question so we know what it actually is - there are literally 10's of thousands
of relays out there, perhaps 100's of thousands...
(*) Our job is to figure out the problem, the poster's job is to find/google the datasheets once so we don't all have to do it individually (finding ambiguous multiple results often!).
Thanks for your input!
I will be asking for help from someone with more experience than myself to wire it up, so thanks for being honest about the potential danger.
I have two bulbs, as I mentioned already. Here's the datasheet for the relay. However, the relay I'm using is on a board, so it's easier to hook up to. Here's the picture, thanks for the help on resizing it. I have it wired so the relay is controlling a separate 5v led circuit, and that works well.
