Main > Main Forum

help with relays

(1/3) > >>

shfifty:
need some assistance. I want to use a relay to turn the speakers on and off, and was thinking of hooking it to either a spare molex connector in the psu or one of the 12v fan connectors on the MB. This is so the speakers are only switched on when the PC is running.

my questions are

1) Do i need some form of resistance other than the relay in the circuit? For example, i will also be powering 2 fans and some other accessories from the psu. Should i wire the relay in series with one of the accessories, or just connect it alone?

2) Should i wire it a spare molex connector or a fan connector on the MOBO?

thanks in advance   

Marsupial:
why don't you use USB powered speakers?

BKahuna:

--- Quote from: shfifty on August 15, 2010, 12:02:55 am ---1) Do i need some form of resistance other than the relay in the circuit? For example, i will also be powering 2 fans and some other accessories from the psu. Should i wire the relay in series with one of the accessories, or just connect it alone?

2) Should i wire it a spare molex connector or a fan connector on the MOBO

--- End quote ---

1: If it's a 12v relay, then no; it should hook straight to the 12v supply. Don't hook it in series with anything or it won't get the full 12 volts. It should be wired in parallel with everything else.

2: I would go with a spare molex and leave the motherboard out of it. It's also customary to wire a reverse biased diode (1N4001 or equiv) across the relay pins that accept the incoming 12 volts. This will lessen the inductive kickback when the relay turns on or off. What this means is the cathode of the diode (the end of the diode with the band) connects to the +12v line, and the anode (the end without the band) connects to the ground wire. Without this diode, the relay can create EMF and maybe even freak out your power supply.

Franco B:
Sorry to semi-hijack this, I thought it would be worth posting this here rather than starting a new thread.

I have just designed this circuit to switch power between two devices:




--- Quote from: BKahuna on August 15, 2010, 12:39:36 am ---It's also customary to wire a reverse biased diode (1N4001 or equiv) across the relay pins that accept the incoming 12 volts. This will lessen the inductive kickback when the relay turns on or off. What this means is the cathode of the diode (the end of the diode with the band) connects to the +12v line, and the anode (the end without the band) connects to the ground wire. Without this diode, the relay can create EMF and maybe even freak out your power supply.

--- End quote ---

This is the part I was interested in. I presume I would need a diode for each relay? Does the amperage of the PSU effect the diode choice? For reference the PSU outputs:

3.3v DC - 12A
5v DC - 15A (20A Peak)
12v DC - 4A (5.5A Peak)

If 1N4001 diodes would be suitable, could I use [1N4001S] diodes?

BobA:
The amperage of the relay does not affect diode choice as the load does not pass thru the diode it is only there across the coil to protect from the inductive spike when the coil switches off.   You can use and 1n400x where x is 1 to 4.  The last number only increases the voltage handling of the diode.   Could not find any difference with the 1n4001s spec so it should be fine. One diode at each relay is probably the safest way to go as they may not all release at the same time.

Navigation

[0] Message Index

[#] Next page

Go to full version