hephaestoskin
Posts: 9
Joined: Fri Jul 26, 2013 4:18 am

PiFace: High Voltage/Amperage Relay Board?

Wed Jan 08, 2014 4:25 am

I am looking for a reliable relay board for use with PiFace Control & Display for use in switching on and off 450w/3.5A high power LED lighting systems for professional aquariums. Ideally a compact design that has 4 individually controllable relays. Does anyone know of a reliable manufacturer/source for such a board?

User avatar
Richard-TX
Posts: 1549
Joined: Tue May 28, 2013 3:24 pm
Location: North Texas

Re: PiFace: High Voltage/Amperage Relay Board?

Wed Jan 08, 2014 4:34 am

Why do relays when you can use a transistor?

I see no reason why you could not use a Adafruit Led driver board and a few P or N type MOSFETs Mosfets can handle at least 60 amps of current.

http://www.adafruit.com/products/355
http://www.adafruit.com/products/815

Now if you want to toggle line voltages, then a solid state relay is painless and easy. The nice part about a SSR is that they are opto-isolated, usually zero crossing which keeps surges to a minimum and cost about $6 on ebay.
Richard
Doing Unix since 1985.
The 9-25-2013 image of Wheezy can be found at:
http://downloads.raspberrypi.org/raspbian/images/raspbian-2013-09-27/2013-09-25-wheezy-raspbian.zip

hephaestoskin
Posts: 9
Joined: Fri Jul 26, 2013 4:18 am

Re: PiFace: High Voltage/Amperage Relay Board?

Wed Jan 08, 2014 4:42 am

I had originally gone with the idea of a solid state relay for ease of wiring. I'm new to DIY electronics so I thought it best to keep it simple. I will be switching line voltages, in fact I will be wiring up a 110v outlet box to control sockets individually but still allow me to keep my warranty on my lights in tact... considering they are $1250 each, that is important.

hephaestoskin
Posts: 9
Joined: Fri Jul 26, 2013 4:18 am

Re: PiFace: High Voltage/Amperage Relay Board?

Wed Jan 08, 2014 4:10 pm

Ok so it seems after some late night digging I found these, thoughts?

https://www.sparkfun.com/products/10636

Paul Moir
Posts: 46
Joined: Wed Dec 04, 2013 7:25 pm
Location: Nova Scotia, Canada

Re: PiFace: High Voltage/Amperage Relay Board?

Thu Jan 09, 2014 4:32 am

Look nice and compatible. Pretty much guaranteed on after 6ma makes them directly compatible with the Pi's GPIO using only a current limiting transistor.

Only real issue worth considering with SSRs is that they almost always fail on. That can be a problem in some applications, but it hasn't stopped some manufacturers of residential ovens!

Also, you don't say but if you try to use these with DC current, they will never turn off. They use phototriacs which will not turn off as long as current is conducted through them. In AC the 0 point turns them off. If your LEDs are setup with a DC power supply, you'll need to use a DC SSR, which will be mosfet based and likely more expensive.
http://www.digikey.ca/product-search/en ... ageSize=25

hephaestoskin
Posts: 9
Joined: Fri Jul 26, 2013 4:18 am

Re: PiFace: High Voltage/Amperage Relay Board?

Thu Jan 09, 2014 4:57 am

My LED lights are in fact AC driven, one reason I want to control a set of 110v outlets is that all my equipment is. So these should work just fine. I found a nice assembled board I can purchase and use as a model to create a relay 4 or 6 relay hub. Learn by example. As for failing in the ON position, I will program in an alarm to alert me if the system fails to respond. Very helpful to know. Now I just need to brush up on my Serial communications, Python, pySerial and PiFace, locate some very high quality humidity, temperature, light, CO2 sensors and magnetic door switch and I should be good to go :)

Thanks!

Paul Moir
Posts: 46
Joined: Wed Dec 04, 2013 7:25 pm
Location: Nova Scotia, Canada

Re: PiFace: High Voltage/Amperage Relay Board?

Fri Jan 10, 2014 5:22 am

If you have enough GPIOs, you might consider skipping the piface entirely. You can directly drive those SSRs with the GPIO pins.

I did a project using a piFace about a month ago. I'm still not entirely sure it was worth using. It did save some time, but the implementation isn't fantastic in either design or execution - particularly the terminal strips on the board are horrendous, but the lack of securing method is hard to forgive. But it is supported by the wiringPi library (I was only willing to use C or C++ for the project as it had to be done quickly and I have no python), and it is ready-made. 4 relay outs, few real switches in (one hanging on an interrupt), and a serial comm to a sensor.

Tarcas
Posts: 740
Joined: Thu Jan 09, 2014 5:38 am
Location: USA

Re: PiFace: High Voltage/Amperage Relay Board?

Fri Jan 24, 2014 9:15 pm

In the name of keeping things simple and, as you put it "ease of wiring," avoid the DIY Relay circuit and go for a pre-manufactured relay board such as this one:
http://www.ebay.com/itm/New-Style-5V-4- ... 53fc7871f3

Cheaper than you can get all the parts for, and it's already designed and built for you. If you're driving it from the Pi, make sure the one you get has separate VCC and JD-VCC. Normally they're jumpered together, which works fine for the Arduino but since you're using a Pi, the VCC needs to be 3.3v to match your GPIO, and the JD-VCC needs to be 5v to drive the relays.

They'll handle 10 amps at up to 220V AC so your 3.5A 110V lights will be a walk in the park. I built a box with 4 separately switched outlets like the one that you're talking about, and it took longer to strip all the wires than it did to connect them to the screw terminals. Super quick and easy!

As for easy wiring, it's as simple as connecting ground, 3.3v and 5v from the pi, and one signal pin for each relay straight to a GPIO on the pi. Total of 7 control wires for 4 relays, all from the pi. Couldn't get much simpler. I had mine up and running in about 5 minutes, and running scripts that I had written for LEDs in another few minutes. Note that most of these relay boards are active low, so 0 is on and 1 is off. Easy to account for in your scripts, as long as you're aware of the issue.

I'm fairly new to this too, but as far as I know, the only drawbacks of these vs. solid state is the audible click and the inability to do PWM. If you're leaving them on all day, the click shouldn't bother anyone, and if you're using these with $1250 lights, you probably don't want to PWM them anyway, for the sake of longevity. (I'm just assuming that PWM will wear out an LED and/or its power supply faster than leaving it on, but I'm new to this too so I could be mistaken.)

User avatar
Tage
Posts: 287
Joined: Fri May 24, 2013 2:29 am
Location: St Thomas, Ontario Canada

Re: PiFace: High Voltage/Amperage Relay Board?

Sat Jan 25, 2014 2:19 am

Tarcas wrote:In the name of keeping things simple and, as you put it "ease of wiring," avoid the DIY Relay circuit and go for a pre-manufactured relay board such as this one:
http://www.ebay.com/itm/New-Style-5V-4- ... 53fc7871f3
there are simpler ways of killing yourself and creating a fire ,why bother buying crap like this on the internet?
my advice is: don't buy stuff like this without having a guarantee that the design meets necessary electrical safety requirements.

Return to “Automation, sensing and robotics”