Relays and Power Supplies  

Re: Relays and Power Supplies

So I am building an enclosure for my printer and adding a temp sensor to my Pi. Additionally, I want to have a set of lights and a few fans hooked up (2 fans blowing in and 2 blowing out)

I got a relay like this https://www.amazon.com/JBtek-Channel-Module-Arduino-Raspberry/dp/B00KTEN3TM/ref=sr_1_4?s=electronics&ie=UTF8&qid=1497745667&sr=1-4&keywords=5v+relay

I am trying to figure out how to provide the power needed to each terminal. I am somewhat electrical savvy but this is a bit more complicated.

My biggest concern is the 12v power supply for the fans https://www.amazon.com/dp/B06WP7ZMGS?th=1

Should I just get a standard 12 power back and supply power to each of the terminals? Or should I get a power bank like this and provide each terminal its own connection? https://www.amazon.com/eTopxizu-Universal-Regulated-Switching-Computer/dp/B00D7CWSCG/ref=sr_1_7?s=electronics&ie=UTF8&qid=1497745544&sr=1-7&keywords=12v+power+supply

My biggest concern is if I wanted to use one terminal to power a set of lights as well. I have a regular wall plugin cord use for lamps but I know this is way too much power for the fans. So these terminals would theoretically allow me to supply the higher voltage to one terminal, and then find whatever 12v power supply is necesseary to the other terminals for the fans?

Hi,

I am not sure if the you should use the Prusa PSU to feed your raspberry Pi (2,5A at 5V =12,5W ???) but should be not a problem to run the relays (up to 60mA per port = 4x0,3W at 5 V) and the two fans (4x 3,3W at 12V). That is not much current you pull. So in theorie the total Watts you would draw (Pi,Relays,Fans) ~12,5W+1,2W+13,2W = 26,9W max. Check:
http://shop.prusa3d.com/forum/improvements-f14/has-anyone-grabbed-the-12v-rail-and-powered-a-rasp-t4099.html#p30623
http://shop.prusa3d.com/forum/improvements-f14/steal-some-power-from-the-psu-t2884.html

For the fan control you should google a bit 'raspberry pi 12V fan PWM'.
This https://hackernoon.com/how-to-control-a-fan-to-cool-the-cpu-of-your-raspberrypi-3313b6e7f92c
should be better than the fan controlled by the relays. With the relays you will have 100% fan on or off, with pwm you can control the fan speed. Controlling fan speed could prevent too much air movement in the enclosure. ABS is sensitive to air movements.

Each of the 4 relays switches their power. So if you connect 110v/220v AC to the 1st relay and 12V DC to the second they will work independent. Be careful with AC and high current DC !!!
http://www.instructables.com/id/Raspberry-Pi-With-4-Relay-Module-for-Home-Automati/

Maybe you should go for LED strips controlled by the RPi instead using AC lights in the case.

Hope could help a bit.

Re: Relays and Power Supplies

I dont need to power the Pi itself, its the devices hooked up to it via the relay. I think I got most things figured out except for the power supply for each terminal. I understand the difference between 12v and 5v but its the watts and amps I'm not sure about.

If I used the 12v terminal from the psu for example, can I power any 12v device via the relay? If something required alot less amps or wattage, how do you diminish the power?

I found this cooling fan that uses regular AC power that I was gonna hook up to the relay and control via octoprint. https://www.amazon.com/gp/product/B01LVW4SLP/ref=s9_acsd_al_bw_c_x_1_w

I found some LED light strips to use as well that use 12v DC. Does it matter what normal input they use or can I just use the 12v relay from the PSU then? https://www.amazon.com/Eclipse-LED-Light-Strip-Accent/dp/B006U5SE7U/ref=sr_1_14?ie=UTF8&qid=1497819402&sr=8-14&keywords=led+light+strip

Re: Relays and Power Supplies

Rather than use relays, you may consider using a darlington pair IC such as this one: http://www.picaxestore.com/index.php/en_gb/electronic-components/ics/ico050.html

Basically, you power the item direct from a +5V or +12V rail and switch the negative with the Pi via the darlington pair.

You can derive almost any power rail you need from the printer PSU by using a boost or buck converter such as this (buck): https://www.banggood.com/XL4015-5A-DC-DC-Step-Down-Adjustable-Power-Supply-Module-p-945599.html?rmmds=search

You must common the negative rails for this to work.

Peter