Custom Built 12v Trigger

Forums › Home Theatre (including HTPC and EPG Collector) › Custom Built 12v Trigger - HT Amplifiers

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gregmcc

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#1747360 25-Mar-2017 05:17

solutionz:

You should still assume this thing will spontaneously combust at some point and/or spew AC240V across your 12v leads.

Take some precautions:

Only ever connect to a RCDBO protected outlet.
Add a fused power inlet to the box: https://www.pbtech.co.nz/product/ADPGEN4004/Generic-PP4004-IEC-Male-Chassis-Power-Plug-with-Fu
Use approved fuses (1+1 spare): https://www.pbtech.co.nz/product/CARLTF7785/Littelfuse-00012512-Cartridge-Fuse-T-63A-5-x-20mm
Add a 3-pin wall outlet or C13 outlet: https://www.jaycar.co.nz/single-240v-gpo/p/PS4040
Ground the inlet directly to the chassis & outlet (or a proper busbar): https://www.pbtech.co.nz/product/CHSGEN9014665/Brass-Bus-Bar-Terminal-Block-24-Way
Keep the SSR centred in the enclosure clear of cabling and apply thermal compound between the SSR and chassis.
Might as well add a DC or stereo jack for the trigger input: https://www.jaycar.co.nz/3-5mm-enclosed-socket/p/PS0122

*Adding the inlet / outlets gives you additional accessible means of safe disconnection; avoids the need for grommets etc and reduces the amount of combustible material (double insulated cable) inside your enclosure.

Only problem with SSR's is they are never really off, there is always leakage current.

Only missing thing I can't see is cable restraint, a clamp to hold the cable

solutionz

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#1747597 25-Mar-2017 15:12

Aredwood:

Jaycar SY4040 relay. Rated at 30A 240V so no need to bother with fuses as you will only be using it with a 10A supply. You would still need to earth the metal box. But if building again from scratch, you could then use a plastic box. So no need to earth anything, as no exposed metal.

Consumer unit breakers are designed to protect the building wiring, not the appliance. Adding appropriate over-current protection to the appliance itself is "best practice" (i.e. 2-6A fuse).

Double insulation requires special considerations and testing to ensure no fixture, screw etc can become livened, there is proper separation between components and every outlet etc is in fact double insulated. It would be difficult to do properly with this setup hence IMO a grounded box would be safer (provided it is properly and securely grounded).

gregmcc:

Only problem with SSR's is they are never really off, there is always leakage current.

Correct a SSR will leak current on the switched side (which wont affect an RCD) however an RCD / RCDBO will protect the user from this unintended current (touching something left partially livened) as well as from a fault of the SSR sending AC across the 12v trigger to earth.

Maxcat

273 posts

Ultimate Geek

#1747869 26-Mar-2017 08:04

Guys thanks for the info.

Progress will continue with the safety additions over time.

But I have parked it for now.

I was scared by the prospect of current going back to the amp and having read elsewhere of this happening with a different 12v switching device, I thought I really need to remove the amp 12v link from the equation and use a 12v power pack.

So if you see the pic this is what I found. The Master plug is on when the amp is on, when in standby the master plug switches off the slave plugs, doing exactly what I need.

I am going to continue with my 12v project (including buying the Jaycar relay) but for now I await delivery of one of these power boards and I'll post an update later this week once it's in the system.

solutionz

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#1747911 26-Mar-2017 10:51

That board is a good idea and should help with avoiding ground loops by having all of your devices plugged into the same strip (at the same earth potential).

Maxcat

273 posts

Ultimate Geek

#1747985 26-Mar-2017 12:08

Yes I like it too. If not for the earlier warning post advice, I might not have found it!

They are designed primarily as power savers. So plug your PC and other peripheral devices (printers) turn off (theoretically) reducing stand-by power consumption.

For my use, hopefully, it will turn on/off my electronic crossovers.

As an aside, one step I thought on my box might be interesting, is I have cor-flute lying around and I have made a base and back for the box enclosure with a cut out for the relay.

In effect it creates a plastic barrier to bare metal, as none is exposed.

I will still earth and do the other steps, but as another step to safety, I thought it may provide additional safety by eliminating contact surfaces for bare wires.

solutionz

589 posts

Ultimate Geek
Inactive user

#1748052 26-Mar-2017 13:29

You can either ground every exposed metal part (class I) or double insulate everything (class II) - there's not really any "in between".

With the former (class I) you want faults to find a low resistance path to earth (via the chassis) in order to trigger protective devices (fuses etc) so adding unnecessary internal insulation like corflute would be an impedance, not to mention additional fire hazard and potential to breakdown electrically in unexpected ways. As mentioned the latter (class II) is harder to achieve properly and requires proper test equipment i.e. a Megger Tester.

Take a look at these threads:

An RCD (either on your outlet or RCDBO at your switchboard) will protect you against most shock hazards however a minimally rated fuse will increase protection against fire hazards arising from over current situations or certain arc faults.

Remember the 10A circuit breaker protecting your outlet is only its "operating current"; it can take up to 10-20x that current to trip possibly far exceeding the current carrying capacity of the conductors in your appliance.

Aredwood

3885 posts

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#1748409 27-Mar-2017 01:28

Maxcat:

Yes I like it too. If not for the earlier warning post advice, I might not have found it!

They are designed primarily as power savers. So plug your PC and other peripheral devices (printers) turn off (theoretically) reducing stand-by power consumption.

For my use, hopefully, it will turn on/off my electronic crossovers.

As an aside, one step I thought on my box might be interesting, is I have cor-flute lying around and I have made a base and back for the box enclosure with a cut out for the relay.

In effect it creates a plastic barrier to bare metal, as none is exposed.

I will still earth and do the other steps, but as another step to safety, I thought it may provide additional safety by eliminating contact surfaces for bare wires.

Other things you can do to improve it. Re route the wires and shorten them. So if a mains wire comes off it's terminal, it can't touch one of the 12V relay terminals. And same thing with the 12V wiring. So a loose 12V wire won't be long enough to touch a mains terminal. But do leave some slack on the earth wires. So if wires start getting pulled out of terminals, The earth ones will be the last to break. And Insulate the 12V wiring the same as if it were actually carrying mains. (only needed inside the metal box).

And wire a couple of diodes to the relay to stop it from producing any spikes when it switches off. like in this circuit.

Ignore the components marked M1 to 4.

As for fuses Im in 2 minds about using them in this application. Mainly because alot of switch mode power supplies draw a big switch on surge when you plug them in. So if you have a few plugged into a power strip together, sometimes the combined switch on surge can be enough to trip a circuit breaker on the switchboard. So it can very easily blow a low current fuse. Even though the normal power consumption is low. It then it becomes a nightmare to choose a fuse that will ignore the switch on surges, but will actually blow if there is a fault.

So a thermal type circuit breaker might be a better option. Such as Jaycar Sf2254 it is designed to mainly protect against overload, with the intention that the fuse / circuit breaker on your switchboard protects against a direct short circuit.

The other option is to simply build it so it could withstand an overload current of say 15A without any problems. Any properly designed appliance should be designed so that it won't produce a continuous overload under fault conditions, that would exceed the current rating of it's plug / power cord. This is often done by using over temp fuses inside the appliance.

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Maxcat

273 posts

Ultimate Geek

#1749166 28-Mar-2017 08:37

Aredwood thanks for the information.

The great thing in sharing my problem (and potential solution!) is the **LEARNING** that you and other posters here have provided.

Grateful thanks for the effort taken to help!

Progress has continued on my box (now earthed)and by chance I found another locally available Master/Slave power board.

Maxcat

273 posts

Ultimate Geek

#1750758 30-Mar-2017 15:46

The smart switching board arrived today and works exactly as I hoped.

The SLAVE switches are powered ON immediately the power amp/receiver is turned ON when connected to the MASTER input.

The SLAVE switches OFF (after two/three seconds) after the receiver switches OFF.

Perfect for what I need and will now allow for the safe switch off of four other devices in my HT rack.

My unit was delivered free at $21.00

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