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Description: Your 5 volt system can wield great power with this big beefy relay board. How does 20 amps at 220VAC sound? The Beefcake Relay Control Kit contains all the parts you need to get your high-power load under control.

The heart of the board is a sealed, SPST-NO 20A Relay. The relay is controlled by 5V logic through a transistor and an LED tells you when the relay is closed. This is a kit, so it comes as through-hole parts with assembly required which makes for some nice soldering practice. Screw terminal connectors on either side of the board make it easy to incorporate into your project.

Note: There are some pretty beefy traces connecting the relay to the load pins, but the 2-pin terminals are only rated for 8A max! If you plan on connecting a larger load you'll need to solder directly to the board. As always with high current and voltage, play it safe and use you judgment when deciding how much of a load you want to put on a board.

Note: Although we have revised this PCB to provide better isolation for the high voltage traces, this board is really meant for someone with some experience. If you're uncomfortable soldering or dealing with high voltage, please checkout the PowerSwitch Tail II. The PowerSwitch Tail II is fully enclosed making it a lot safer.


Replaces: KIT-10733

Comments 77 comments

  • Sparkfun and crew - please get an engineer on staff that has done line voltage designs. It seems obvious that there is a disconnect somewhere. As other have pointed out, your second try still doesn’t make sense. When people use these things in projects, they want to know you have sweated the safety details.

    Sorry, I like what you guys do in general.

    • Can you elaborate the danger here? Is this product completely unsafe? Or just in some cases?

      I see a lot of concerning comments here, so I’d like to understand exactly what the risks are.

      • The design of this board is not perfect, which we are aware of, and it is in the system getting revised. As with any AC circuit, safety precautions do need to be taken to prevent injury, especially in a kit such as this where you could potentially have exposed wires. However, we do also sell several hundred kits each month and have only had a couple returns in the last year on them due to malfunctions. If you don’t feel comfortable with the high voltage circuit, we definitely do recommend the Powerswitch Tail II as recommended above in the product description.

  • That relay should be rotated 180 degrees.

    • Sparkfun just released a new revision on 2/10/11 - has the relay problem been corrected in this new version?

    • This will remove a few centimeters of copper. Joel saw this shortly after he sent v1.6 to production. v1.7 is already in the works.

    • Yes, and although it’s a lot better than the previous design, it really should have more clearance between the mounting holes and the live area, it’s still way too close for mains voltages (especially for using it for 220V-250V mains).

    • could not agree more

      • For those wondering why the relay should be rotated 180 degrees, I’m assuming it’s because it provides further isolation between the LV and HV sides with little rework. The HV terminals would be closer to HV traces and the LV terminals closer to LV traces.

        • Yes, that’s why, this should be better isolated. Funny, the Eagle files show the relay rotated around!

    • I agree. It’s the first thing I noticed.

  • Seriously this company rocks for all that you guys do, and develop, to make things easier for the newbs.

  • An important point for power relay drive. Supressing the coil flyback with a freewheeling diode D1, is a poor practice. This prevents the relay from being able to open as entusiastically as it should. Ideally the circuit would use a zener in series with D1 (to limit the flyback to maybe 2x the rail voltage) and appropriate protection for the LED. Along the lines of

  • Watch out for the error in the description and datasheet attached. They changed the relay from a SPST-NO to a SPDT switch. The datasheet attached on this page is for the old product. Check out the actual part under the parts wishlist or this: . I wasn’t paying attention when i ordered replacement relays from another site since i was looking at the parts on this page.

  • Quick question, What board revision is currently shipping? Thanks

  • Could you guys please put Version numbers on the boards so we can tell what board is showing?

  • for NC hack, drill out the NO terminal using a 3/16" bit. Solder relay. Lastly run short insulated wire of proper size from NC terminal on relay to the large output terminal hole.

  • Can someone let me know how many volts / amps the wall wart power supply should have that I plan on connecting to this device? Want to make sure I have enough power for the circuit and relay.


  • Ok, someone make sense of all this for me. I just want to switch small loads on regular 110V household electric. I’m thinking stuff like a lamp, ceiling light, small electrics, etc. I don’t have experience with mains stuff yet, but I have to start somewhere. I’ve seen the PSTII but frankly it’s too much $$ to drop on a single relay. Can someone tell me if this is ok to plug and play? I really want to use these with my arduino, but the comments always scare me away.

  • Can I run a 24v DC system through this and step down to 5v through my controller to switch it on and off?

  • There are a few issues with this board that we can see - the terminal blocks are really the weakest link that we can see. Sure it won’t meet creepage and clearance, but the little terminal blocks are just scary! We’ve seen this sort of block loosen over time, and I wouldn’t trust it not to heat up if you were passing any current through it. PLEASE PLEASE PLEASE use the power switch tail, which should protect against a lot of these issues!

  • Having an issue where the LED lights, but the relay does not switch. Ideas?

    • Might have burnt the relay. I had an issue when i was hot-switching the relay and then heard it sizzle and it started smoking. Do you still hear it click? If it doesn’t then there might be something wrong with it.

      • Still operates fine when I have it rigged to be controlled by an arduino pin. The problem occurs when I set it up with an analog circuit I have set up. Perhaps it is an issue of insufficient current?

        • Updated: I see what is going on here. The relay is drawing the current directly from the 5v bus. You still need the amp to close the relay, but it’s not coming through the arduino, it’s right off the 5v. You’re never going to get more than 5 amps from USB. You need a bigger power supply, like a beefy transformer.

          This begs a bigger question, though – what are you doing with these 14 mains level relays? If you are trying to run 14 things off of one household circuit, the “you’re gonna have a bad time” times are just starting. Don’t burn your house down.

  • I was wondering if someone could help me out with a problem I’m having. I have the relay controlled by a pin of my uC. I was positioning my circuit components (I wasn’t working on a live circuit, just moving it) when I heard a big zap. I think the 120VAC pins bridged. My uC was connected to my computer with an FTDI cable and after the big zap, the computer turned off and now won’t start. Is this because something crazy got sent up to the computer over the cable (I don’t think so) or because the bridged relay drew a ton of current from the power strip and triggered something that immediately cut power to the computer?

  • Hello, I got 14 of these, and they are great. Recommend them 100%.

    I want to put something on the rear to protect from any sort of shock. Would something like a glue gun over specific pins on the rear do the job? If so, which pins are needed?

    • Whether there’s a shock hazard or not totally depends on the voltage you’re switching with the relay. But in any case, your hot glue solution is a great one; some blobs over the pins with super-fat copper traces (between the relay and the “load” connector, see the bare-board pictures above) should do the trick (but be careful anyway!)

  • Hello, if I got 14 of these and a Arduino Mega, does anyone see any issues with this? I will also have other items attached to the mega, but from what I understand these Beefcakes do not draw much power from the Ardunio itself.

    Would it then use 14 analogue pins on the mega?

    • That’s correct, they will not draw much power from the pin you’re using to control them. You use digital outputs (not analog) to control the relays.

      • Hi Mike, I have finally connected this all up nice and happy. The only problem is they are not happy.

        When I start turning them on, after 5, the LED turns on, but you do not hear the click of the Relay, then if I turn the first one off, the 6th relay then clicks on. Its like the Mega can only power 5 at a time.

        WHen there are none on, I check the 5v, and its reading 4.98v. When I have 5 on, its reading 3.8v, with it going down a little with each one. I have the Mega powered by USB and a 5v 2amp plug.

        Can you think of what I am doing wrong?


        • I think I have worked out each relay takes the 5v @ 1amp. That seems huge. To power 14 of them, I dont know how I will do it.

          Does anyone have any ideas?

          • Are you sure your transistor is oriented right? It should only require a few mA to open the transistor on this board. It sounds like there is an assembly problem.

  • Can anyone suggest a microcontroller for this? I was looking but most of the ones i see (Arduino) can only output 40 mA and the relay requires 180 mA

    • That’s what the transistor is there for. It turns on with a weak signal from a microcontroller pin (a few mA), and does the hard work of switching the higher current that the relay requires. You can connect this to your Arduino (or pretty much anything else) without issues.

      • Ok. Im a little new to this and just wanted to make sure. Thanks!

        • No problem at all, please feel free to ask ANY questions and we’ll do our best to help you out. Have fun!

  • Is there any reason this won’t work? To use the double-throw capability of the relay, I soldered tabs to the three high-current pins of the relay, sandwiched between the PC board and the relay body, and hanging out over the sides of the PC board. I will solder or screw 14ga. stranded wires to the tabs. I want to control a 220v, low current load. It is the control circuit for a gas-fired spa heater.

  • hi i would like to use this relay to control some load on my rc car…my question is what must i do to use a 3rd channel signal from my receiver to control the really….i tried just hooking it up but the relay just stays closed…can’t seem to control it…would it be that my receiver puts out a digital signal like that to a servo?

    any help that would steer me in the right direction….thanx

  • It would also be nice if there was an NC option (normally closed, apply control voltage to interrupt power). It would require the high-voltage side to have a three-terminal block, and one extra trace.

    • I would be worried about the safety issues with that. It’s very counter-intuitive when someone inexperienced has a board that “work” (meaning the relay isn’t interrupting the circuit) when the power to it is OFF, and I could see people getting hurt with that.

  • Has this been updated to revision 1.7 yet?

  • For those wishing to use a lower voltage signal to energize the coil (e.g. 3.3v as per a few comments) change the resistor network feeding the transistor base so that it provides more current - though be sure to limit the current to something your signal can source. There is a good writeup of the calculations here: If you are switching this thing with something sensitive you might think about swapping out the transistor with an optoisolator e.g.

  • How much current is required to run those ? I have a project with a power supply providing only 1000mA and im using a LCD screen with some LED and 4 of thoses relays. One of them doesnt seem to work when assembled on my project but work fine alone. I tried to switch relay connection and what ever position this relay is, its always the same one that doesnt work. The red LED is on but no contact. I think theirs not enough of 1000mA for everything.

    so, how much current will it draw ?

    Thank !

    • According to the Tyco data sheet, depending on the particular relay model used it’s either 185mA or 200mA, so assume 200mA and you’re safe. The relay in the picture doesn’t look like the quality Tyco brand one, it appears to be a cheaper Chinese knock-off, so the actual coil current may be different. 4 of these on at once is going to be dragging around 800mA. If you move the relay around and it’s always that same one that doesn’t work, then there must be something wrong with that unit - suggest you contact SF customer service. If you’re using these near a micro, you should really decouple the supply by (as a bare minimum) having a decent electrolytic cap (at least a few hundred uF) near the relay’s supply lines and at least one small cap around 0.1uF too. Isolating the micro power supply further would be advised if you want to avoid noise problems.

  • Can I switch this with 12V instead of 5V? The relay’s datasheet looks like it can handle it, but can the pcb?

    • You can switch 12V on the output, but you wouldn’t want to put 12V on the coil side (shown on the circuit diagram above as ‘RAW’). The relay they are using has a 5V coil and 12V will not do it any good, it will get very hot and likely fail at some point. You could buy another relay in the same brand and configuration, but with a 12V coil and fit it to this board, that should work fine(see the data sheet for 12V coil version), but you would want to increase the resistor in the Base circuit (R2) to about 2k2 (2200 Ohms). The LED resistor should be OK as is, but you could also increase that to 1k8 or 2k2 if you like.

  • I am a total newbie here, so please forgive my simple questions. I am looking to build a relay switch that will turn off the main load when the 5V power is supplied.

    The application is I am looking to cut A/C line power to a trickle charger for a generator battery when the generator is running.

             House A/C ----> Relay  ----> Trickle Charger

    Generator –> DC Transformer –|

    The instructions for the trickle charger indicate that the charger should be removed when the generator is running. So currently, I have to unplug the charger before starting the generator, and I want to remove that step to simplify startup for my family.

    My question is, can this project be retrofitted to allow the 5V current to turn off the main load, rather than turn it on? If not, is there a similar project (or finished product) that I should consider?


    • This PCB can’t do that directly, but the relay itself can. (There are three pins that the relay can connect together, but only ever two at a time. Hence one is normally not connected (open, NO) and one is normally connected (closed, NC). When you apply power to the coil side of things the paddle will switch spots.) This PCB ignores the NC pin in favor of switching the NO pin. Normal behavior for what it’s designed to do.

      Anyways: To accomplish what you are going for you would have to use the pin not currently in use with this board. I’d heartily recommend getting somebody who has experience with and understands the dangers of 120 AC on a PCB to whip up the design for you. Should only take a few minutes, and then you can get the board fabbed by BatchPCB.

      And on that note: You might want to consider the PowerSwitch Tail II and call it good: It’s a safer product already in a nice enclosure that’ll eliminate having to deal with mains power in the open air. Trouble is you’d still be dealing with the whole 3-to-12-volts-activates-my-output bit. Could always crack it open and see what can be done about it. :-)

  • OK. So I got this relay a few months ago for a project I was planning but didn’t read through the comments. I am wanting it to run a 115v, 1.5amp compressor. I know the compressor spikes but thought this relay would be plenty.

    Is this relay safe for my application?

    Also, is it only a problem if I use screws in the mounting holes? I am planning on housing the relay in a plastic box (an old laptop power supply box). Would this help with safety?

    Any help would be appreciated. I want to leave this circuit on for long lengths of time and don’t want it to have a good chance of burning my apartment down!

    • It will work, but you’d be better off using a proper contactor if it’s a long-term thing and you want to be extra sure. You can think of a contactor as a big industrial relay, designed for proper big industrial loads. You can get them in various ratings and coil voltages, but I’d suggest going for a 20A one if you go that way. They are also significantly more expensive than this, but you sound like you want peace of mind. The problem would be finding one with a 5V coil, as the lowest you are likely to find is a 24V, but you can use a smaller relay (or this one) as a pilot relay to switch 110V to the contactor coil and use a 110V coil (which are readily available) on the contactor. They are also a fair bit bigger, however there are good compact ones, but they are a bit harder to find. If you want to go that way let me know and I can point you in the right direction.

      One important thing is whether it will be switching on and off frequently, like when it reaches pressure and later bleeds down below the air pressure setting. If it’s on and off all the time, you would be better off with a real contactor. But if it’s just ‘on’ and the compressor pressure switch does all the switching on and off, then it should be OK.

      DON’T use metal screws to mount this board if you are fitting it to a plastic case. Either use a properly Earthed metal case or use Nylon standoffs or similar. I’ve complained and complained to SF that the creepage distances are too small and they still are in this revised model. Stick with Nylon supports and you should be fine.

      You would also be well advised to add an appropriately rated fuse or circuit breaker in series the incoming live wire before this relay, that will give you a bit of extra protection. Leave a note if you want more details and I’ll try to check in every now and then.

  • Any hints on connecting a bank of 16 of these to a RasberryPi?

    • Top of my head… You’d want something to isolate the RPi from any potentially catastrophic voltages (via an optoisolator or similar) and you’d need to either level-shift things up or get a relay that will trigger at 3V3. (Personally I’d go with the former.) I know SparkFun carries some larger relay boards but they have their own restrictions.

      An external supply to actuate the relays would be good as well, since the on-board regulator will go nuts if you try pushing a bunch of relays with it. Wouldn’t want to subject your USB brick to that kind of load or the RPi to that much noise either. (Remember: The Raspberry Pi has NO 5V REGULATOR, so anything you put back on that line will cause issues back on the Pi.)

      If you are switching a lot of 120 then I’d recommend going with the spade-type connectors for the relays - That way you don’t have to worry about getting the PCB right, plus it’ll cut out the cost of any terminal connectors you’d need. Still have to be careful about the control side of the relay though.

  • Do you sell an enclosure this will fit in? I like to be able to enclose any high voltage connections.

  • Will this work with the following fan:

    Or motors in general?

    • This board will handle AC or DC resistive (“lamp”) or inductive (“motor”) loads up to the weakest link in the circuit (the relay can handle 20A, but the screw terminals can only handle 8A). Because your motor is less than 2A (starting current might be a bit more), you should be fine. Be careful when working with 120VAC, and good luck!

      • Though you are talking about the limit being the screw terminals, some might incorrectly gather from this that the inductive rating of the relay is 20A and the only limiting factor is the screw terminals and may be inclined to solder wires on thinking (incorrectly) it would then handle 20A with an inductive load. Like any switching device, including big industrial contactors, the rating for inductive loads is much lower than the resistive or ‘general purpose’ ratings, it has to be or else the inductive spike will cause (more) arcing and can easily weld the contacts together if over the ratings. Also, many parts of the world are running 230-250V, so this has to be taken into account and suitably derate the contacts.

        For those that don’t understand, this means if you increase the voltage you are switching, you need to drop your expectations of the safe switching capacity of these (or any other) relay accordingly. Likewise if you are switching inductive loads (eg. motors, ballasts, anything with a coil), like others have advised here, you need to drop the rating considerably (see the data sheet to get some idea). Likewise when switching DC, as it’s harder on the contacts when switching DC (especially opening the contacts with an inductive load). As I’ve said in other postings (and others have said too), the way the relay is orientated on the board is very poor, mixes the high and low voltage areas and the clearances are still too close for comfort, especially when it’s going out to a hobby market where probably the majority of the users really have very little (if any) knowledge of working with high voltages and loads.

  • Hey Sparkfun, is the bundled relay included with this kit SPST or SPDT? I ordered this kit and a separate COM-10924, which is listed as SPDT. The two relays look identical, and the parts list for this beefcake kit points to the COM-10924.

    Can I use this kit for a SPDT application?

  • Anyone know what is currently being sold, is it v1.6 or v1.7? If it is still v1.6 is there an ETA on v1.7? Thanks.

    • I ordered one a couple weeks ago and the one I received appears to be v1.6, since the relay hasn’t been rotated back to the preferred position yet.

  • Can this PCB handle the same current and voltage as the Relay? Can it really handle 240VAC at 20A?

    I still recommend using Quick Connect Automotive Relays. They can handle the current, they’re easy to connect to and you dont have to worry about your PCB frying under the AC load.

  • You’ve made a mistake its 240VAC not 220VAC. Well That’s what it says on the relay.

  • I’m not a total electrical newbie, but I wanted a little feedback, this guy should be able to handle either of these, right? (as long as it’s on 110?)

  • What are the dimensions of this assembled kit?

  • Just getting into Relays and I am looking to control a 12V DC pump that is rated up 7.5A. I thought that a kit would be much easier / better than buying things piecemeal. Yay Sparkfun (again).

    However, being a Relay newbie, I am still parsing through whether this “20 amp at 220VAC claim” means this is a dead end for me. I need 12V DC up to 7.5A. Seems that 8A is more common, but I really wanted a kit to help me get started.

    Any ideas?

    • Shouldn’t be a problem, you’re not exceeding either the Amps or Volts ratings, and it doesn’t care if it’s AC or DC on the load side. Mostly you need to make sure you’re not pulling more Amps than rated, and not exceeding the voltage either of course.


      As AtWrk has now informed me, the above statement is wrong. I didn’t think about the arcing issues that you don’t have so much of with AC, given that it zero-crosses at 60hz. Doh. After looking around it looks like the derating is significant, up to a factor of 8. However, at 12V I’m not sure how bad an arc would be. Unfortunately I can’t think of a safe way to use the encapsulated relay to find out, as it’s not really possible to see the contacts.

      • Whether it’s an AC or DC load makes a BIG difference in choosing a relay–particularly when it’s an inductive DC load (e.g. a motor). DC loads are harder on the contacts so relays are typically rated much lower for DC than for AC, if at all.

  • Just a heads up for everyone. I know it says 5v but for kicks I tried to run the relay off 3.3v and it won’t trigger. Not really a surprise but I wanted to give it a shot anyways.

    • Tried the same thing. Should have read here first… At least it didn’t fry anything.

  • What is the ETA on the updated board? I have one of the previous generation (v1.5?) that I’d like to replace with something safer. I also have an unused v1.5 board, can I return that? I didn’t realize how unsafe that version was.

    • I’d like to say that after emailing them, sparkfun has offered to replace my old version and components, and send me the new version kit! Very good service on this one! Thanks!

  • An important point for power relay drive. Supressing the coil flyback with a freewheeling diode D1, is a poor practice. This prevents the relay from being able to open as entusiastically as it should. Ideally the circuit would use a zener in series with D1 (to limit the flyback to maybe 2x the rail voltage) and appropriate protection for the LED. Along the lines of

  • Way better than the previous version but it could have been better if relay are rotated 180 degree, bigger terminal block (use barrier type) as the 5mm terminal is rated 8A only, 2Oz copper PCB, and some vias connecting the top & bottom copper pour.

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