help with relays

[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]

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

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:

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.

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.

[Franco B]

Thanks BobA 

[shfifty]

thanks for the info Bkahuna, it was very helpful

why don't you use USB powered speakers?

because i already have a set of logitech x230's which are mains powered. And usb speakers just wont have the power output i'm looking for, i want my windows to rattle whenever i hadouken

[Marsupial]

you'd be surprised at how much USB powered speakers can blast. I got a set from a local surplus (they were on liquidation) and I was thinking of using them on the go, but powerfull as it is, I will keep them as a main source of speakrs for the PC.

On my cab, I go a totally opposite route as you. I want the PC in the cab to remain powered. But I modified a power bar to run from the switch on the top of the cab. This powers the marquee, monitor and speakers. So I can leave the cab "off" and still have computer activity.
One could power the whole PC this way too.

[JustMichael]

thanks for the info Bkahuna, it was very helpful

why don't you use USB powered speakers?

because i already have a set of logitech x230's which are mains powered. And usb speakers just wont have the power output i'm looking for, i want my windows to rattle whenever i hadouken

It sounds like a smart strip would work perfectly.  Plug the pc into the control outlet on the smart strip and then plug your other devices into the other outlets.  When you turn your pc on, the other outlets will power up in effect turning on those devices.

[Blanka]

It sounds like a smart strip would work perfectly. 

+1
Only wondering how much a smart strip uses......

[shfifty]

It sounds like a smart strip would work perfectly.  Plug the pc into the control outlet on the smart strip and then plug your other devices into the other outlets.  When you turn your pc on, the other outlets will power up in effect turning on those devices.

I considered this originally, but the speakers are the only accessory that i need this for, so i cant really justify the added expense. Plus i already have a bunch of relays so i might as well build it myself, for free.

Also the speakers are already being hacked/de-cased with a new potentiometer and some 4" auto speakers so it doesnt bother me to add another modification while i'm at it 

[JustMichael]

Do you turn on the pc and monitor separately then?

[Blanka]

How are the speakers powered?
If it is having some simple 12V rail powered digital amplifier chip inside, you can feed that from the PC powersupply instead from the built in AC converter.

[shfifty]

Do you turn on the pc and monitor separately then?

I just leave the monitor on all the time, i'm aware that it still draws current when in standby but this doesnt really bother me.

How are the speakers powered?
If it is having some simple 12V rail powered digital amplifier chip inside, you can feed that from the PC powersupply instead from the built in AC converter.

This is another option i suppose, except the amp is inside the sub enclosure, which i don't intend on modifying.


Anyway ive been looking up on the smart strips, i didnt realize how cheap they are. So maybe i will just get one. However i cant seem to find a 240V version with australian sockets. Does anyone know where to find one?

[wweumina]

Bunnings and Officeworks both have powerboards with master and slave sockets.  Usually go for about $55 aus.