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Can a relay use AC or DC?

  1. Oct 25, 2012 #1

    I found a cool site to buy odds and ends electronics. It sells RF wireless remote systems equipped with relays. With halloween coming up this will be really fun to play with }:) .

    My question is, the description states the relay output is 125V VAC but if can't I run VDC through it too?

    I want to use it to power DC electric motors. Can this kind of relay handle AC/DC interchangably?

    Also, the input does not state amps. I'm assuming I can just wire up a 12V battery and not fry it. How can I measure the proper amps needed? Lastly, do I need 12V or is that a max? Using a 9V would be convenient.


  2. jcsd
  3. Oct 26, 2012 #2


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    I'm not able to open the link from work (it's blocked for some reason). The output can handle either AC or DC. The input current at 12V should be specified, or they should give you a coil resistance that you can use to calculate the input current that you need to supply. Generally you need to drive the input coil at the rated voltage -- the relay may not actuate if you use a lower voltage (or your 12V source cannot source the required current at 12V). Have fun!
  4. Oct 26, 2012 #3
    Perhaps your popup blocker?

    I hope the supplier is better at electronics than it is at writing websites. I would be reluctant to buy from one that is so busy showing off that it ends up being rude and inconsiderate to potential customers, though I have seen worse.

    Berkeman has said all you need to know about the relay.
  5. Oct 26, 2012 #4


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    Blocked by my work's IT department for some reason. It says the domain is blocked, which could be for various reasons, I suppose. I'm able to get to shopping sites like Amazon (and actually use them to buy stuff for work sometimes), so I'm not sure why IT doesn't like this one. Whatever.

  6. Oct 26, 2012 #5
    I am fairly certain the site content is made by the manufacturer, who are most likely Chinese.

    The product does not have specs on input amperage. Only voltage. I'd need 8 AA in series to get 12V. I don't know why they just didn't go with 9V. Can I use a resistor or some capacitors or something? The only 12V battery I can find is expensive.

    Per the relay output, do I only have to keep it below max watts (V*A) or keep below both max V and max A?

    Thanks for your help guys.
  7. Oct 26, 2012 #6


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    FWIW I tried your link and got a pop up window that was forcing me to sign up for something or other before I could get any further, so I gave up.
  8. Oct 26, 2012 #7


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    How much current do the motors take, and what voltage do they run off of?

    If it's not too much current, and a voltage less than about 60Vdc, you might be able to just use 5V reed relays.

    Relays that are rated for 125Vrms at the output are meant to be used with AC mains circuits usually. They have enough galvanic isolation (creepage and clearance distances and insulation) to isolate the AC Mains circuit on the output from the input coil circuit. That way it is safe for you to touch your drive circuit without worrying about getting shocked by the AC mains high voltage.

    What are your motor specs? And are you sure you want to order from that company? Why not just order from Digikey or Mouser? They generally have pretty good prices, IMO.
  9. Oct 26, 2012 #8
    Regarding the site, what does typing in dinodirect.com do? The link works fine for me.

    I haven't chosen a motor yet. I have an old paper shredder AC motor, some dc hobby motors.

    The purpose is that this is a wireless system. So when people are walking up I can hit a button and something scary pops up. It's fun when you can control it you know?

    I have never seen a unit like this. Most products like these are atleast $40. The listed product is $6 with free shipping. It is also very small. I like those features.
  10. Oct 26, 2012 #9
    Regarding the site, it may be Chinese, I don't know.

    But it certainly is a prime example of the American way.

    I think it is presumed you only visit the site to buy something.

    So there is a popup which asks you to fill in what currency you wish to pay with and where you want delivery.
    You cannot proceed until this is completed, but you do not have to buy anything.

    This is logical if you accept my basic premise but some obviously find that offensive.

    The site itself is rather brash to my taste.

    So all in all I felt less inclined to buy rather than more so.
  11. Oct 26, 2012 #10


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    Hmm, a Chinese website with prices too low to be true, and all you have to do is buy some stuff (with free shipping!) using your credit card...

    Sounds just fine to me.... :wink:
  12. Oct 26, 2012 #11
    Well to be fair, the prices aren't too good to be true. I am getting less. The problem I find with most online shopping is that although there are a sea of stores, there are not many options.

    I just want the most basic parts. I press a button (wireles) and a relay switch flips.

    I could gut a toy rc car for $20 but i'm left with all this waste. Their site offers a barebones item. So in theory, the price should be fitting to the product.

    After reading online reviews it seems they are a legit company but their supply chain is junk and they short orders.

    Back to the quest!
  13. Oct 26, 2012 #12
    Last edited by a moderator: May 6, 2017
  14. Oct 26, 2012 #13


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    Very cool that you found it on Amazon!
  15. Nov 6, 2012 #14
    The relay is rated at 10 amps. But the radio circuitry does not include specs. Got it today!
  16. Nov 7, 2012 #15
    I can't upload a picture, but the seller contacted me and gave me the chinese directions lol.

    Operating voltage DC +6--24V
    static state working current < 6MA
    working temperature --40C-+80C
    receiving sensitivity 105DBA
    working band 315----433MHZ
    output voltage : intercourse direct current
    output current <10A

    it uses this chip http://www.alldatasheet.com/datasheet-pdf/pdf/35134/PTC/PT2272-L4.html

    The 6MA throws me off though. There aren't any batteries with that small an amperage. But batteries are rate in mAh not mA. What kind of battery should I use?
  17. Nov 7, 2012 #16
    OK, after some research hear is my conclussion.

    If I hooked up a million 12V batteries in parrallel it would not fry my device because the current is only related to the voltage and resistance. The circuit was designed for 12V so they knew the current draw at 12V.

    I can hook up ANY <=12V battery and not damage the device.

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