Power supply to Arduino

Good afternoon

1. I would like to buy an external power supply to my Arduino. Should I buy one with 5V or 6V?

2. It's better to buy some 5V relays to protect my Inputs?

Thanks on advance Best regards Pedro Ferrer

If you intend to connect to the DC jack on the board you want a power supply of ideally 7V - 9V. 12V is OK if you're just running the Arduino from it.

Not quite sure of what you intend to do with the relays......

It's better to buy some 5V relays to protect my Inputs?

No. In order for a relay to protect your input you will have to amplify your input to make it drive a relay. That is just plane daft. Normally the inputs don't need protecting but if you really must then use opto isolators.

Good evening

Thanks for the replies.

12V is OK if you're just running the Arduino from it.

12V!? Are you sure? Since it seems that I don't need relays for Inputs, but I'll need to use relay for Outputs because I need to activate 220V sockets. This relays has to be 12V? Right?

I'll appreciate your help once again Thanks on advance Best regards Pedro Ferrer

When you feed 12V into the power jack of an arduino the on board regulator cuts it down to 5V.

This relays has to be 12V?

The relay has to be what ever voltage rail you want to drive it from. This could be 5V or could be 12v. Either way you will need to drive the relay with a transistor, like it shows here:- http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

Good morning

Thanks Grumpy, but my doubts remains...

When you feed 12V into the power jack of an arduino the on board regulator cuts it down to 5V.

So, feeding Arduino with 12V power unit, my Outputs will be 5V or 12V? The relays has to be like transistors? Can't be like this one http://www.google.pt/imgres?imgurl=http://www.allspectrum.com/store/images/G5V1f.jpg&imgrefurl=http://www.allspectrum.com/store/product_info.php%3Fproducts_id%3D512&h=300&w=300&sz=38&tbnid=ggPnBVKpYGJWzM:&tbnh=116&tbnw=116&prev=/images%3Fq%3Drelay%2B5V&zoom=1&q=relay+5V&hl=pt-PT&usg=__64gVRWMnhbIglDmNoP3JdV_b7RQ=&sa=X&ei=rtqqTPO4M5Hm4AbH9N3BCA&ved=0CCsQ9QEwAw?

Thanks on advance Best regards Pedro Ferrer

If you're wanting to switch mains, personally I'd go for solid state relays over mechanical relays, much easier to interface and can be driven directly from an arduino digital pin, no transistors, no inductive kickbacks so no inherent snubbing circuitry. One slight gripe, they have a small leakage current when turned off which is enough to give you a jolt when the mains side is open circuit.

Good morning

Thank you Pluggy. But the 5V solid state relays can actuate 220V or they are weak for that?

Thanks on advance Best regards Pedro Ferrer

So, feeding Arduino with 12V power unit, my Outputs will be 5V or 12V?

The output from an arduino is always the power supply voltage. This is a maximum of 5.5V anything over that will fry the arduino. So you can never get more than 5V from an arduino output.

In order to drive a 12v relay you have to use a transistor to get the voltage up. An arduino output has limited current capability so you can't drive a 5v relay direct from the output, if you try you will fry the arduino.

5v solid state relays can drive mains. However at the level you are asking questions I would strongly advise you that you are not experienced enough to play with mains yet.

it doesn't matter what you feed the Arduino the output will be 5v as it is after the on-board regulator

depending on how often you are going to be switching the loads i would either recommend using relays (if not that often) or solid state as pluggy said (if you are going to be switching them a lot or want to be able to dim the loads)

there are some nice Sensitive (30mA coil) 5v low current relays (only rated at 1.25A) http://www.mouser.com/ProductDetail/Tyco-Electronics-Axicom/C93401/?qs=sGAEpiMZZMs3UE%252bXNiFaVPLyw4rx8UbUWgnqNM2Qg0g%3d i have used them for several projects and they are nice as i don't have to worry about any leakage current or overheating

or if you need more current you could use a Darlington Transistor Array (ULN2803A) to up it to 12v 500mA /ch for 12v wiring diagram checkout http://fritzing.org/projects/arduino-knight-rider-with-8-blue-12v-led-modules/ just replace the LEDs with 12v relays

or just use the solid state transistors

Good morning

I've already saw the Relay. I also have it here http://pt.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=C93401&x=0&y=0 The pins are too short to apply on a breadboard or I can apply on it without any problems?

Thanks on advance Best regards Pedro Ferrer

Grumpy is right, this guys going to kill himself. I have far too much respect for mains at 220+ volts to even think about routing it through a breadboad.

Good morning

this guys going to kill himself

No way! That's why I am asking your help...

Usually mechanical relays has bases to apply on DIN rail. The solid state relays also have it?

Thanks on advance Best regards Pedro Ferrer

SSRs are available to mount on DIN rails which is probably the favoured method of switching mains - google is your friend. A whole different league to mounting a tiny PCB relay on a breadboard. They are much simpler to inteface than mechanical relays, you need nothing more than 2 pieces of wire to connect it to an arduino. You need to takes measures to stop a mechanical relay destroying the arduino with inductive kickback and anything with more than trivial power demands will need a larger relay and transistors and stuff to drive it. I have a 40A SSR I bought to switch an electric shower, it only needs a few mA at 3 - 30 volts to switch it. Pretty cheap on Ebay too.

Good afternoon

I intend to buy the following:



But still don't find any support to apply it on DIN rail... Can somebody help me?

Thanks on advance Best regards Pedro Ferrer

Good evening

Meanwhile I've found this... http://www.winfordeng.com/products/brk2x5.php

I'm asking them if is possible to found this product at Europe.

I'll let know as soon as I have an answer.

Best regards Pedro Ferrer

Good afternoon

I would like to receive some more help. Which kind of solid static relay 5V do you recommend to work with powers bigger than 250W/220V. To know Ampers I'll do I=P/V... but the voltage will be 220V or 5V

Thanks on advance Best regards Pedro Ferrer

Look at this selection for Solid State Relays:-

I read this and I too am thinking... "This guy is going to kill himself".

The nature of the questions you ask, clearly show that you do not have a clear understanding of which voltages show up "where" and why.

You need to understand your AC MAINS LOAD. There is no issue with the CONTROL part of the SSR. It just needs a TTL logic signal from your Arduino. If you have a 15AMP SSR, that's 15A at 220VAC on the CONTROLLED AC MAINS pins.

It is my opinion, you should never start any AC MAINS project until you don't have to ask any more questions about it because you have "studied" enough to know the facts. Charging ahead without knowing how to respect your logic pins and your AC Mains is a sure way to end up with trouble... or to be electrocuted.

Thank you. I'll explain my question.

The following SSR have 2A and supports 60W. (Potencia nominal máx.) http://pt.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=C93401&x=0&y=0

I=P/V Following the formula, I don't get 2A...

That's why my question.

Please let me know Thanks on advance Best regards Pedro Ferrer