Hi,
I'm using a 12V DC /240V AC relay to power on my audio amplifier when the main Processor comes out of standby (it has a 12V trigger out that goes high).

Amplifier is a Crown XLS 2502 XLS 2502 | Crown Audio - Professional Power Amplifiers
Crown XLS2502 Stereo Amplifier Review | Audio Science Review (ASR) Forum
Notably the Crown XLS series have a "sleep" mode where the amp can be triggered off but it flashes a bunch of bright obnoxious LEDs furiously when used and this is non defeatable... so I am looking at using an external relay. (Design doesn't allow covering them effectively and I don't want to snip them off).

My relay is an electromechanical one that triggers at 12V/70mA DC, closing contacts for the 240V AC powering the amplifier.

I'm trying to work out what additions are optimal to prevent any power spikes or damage to the relay... and crucially my audio gear.

It's been years since I have worked with this sort of electrical componentry and I'd appreciate some up to date guidance.

1. Do I need to de-energise the relay coil to protect the coil and trigger circuitry?

2. Is a soft-start setup a meaningful addition for Class-D amplification which doesn't use large toroidal components?

The relay module is this one: 12VDC DPDT Relay - 10A 240VAC/24VDC Contacts | Jaycar Electronics

I'm also soon to have this Dual Pole solid state relay: https://www.amazon.com.au/gp/product/B09P8JV1MW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 and interested in how it may be employed.

Are there risks that are likely or of extreme consequence using the relay on its own?

Thanks for any advice on offer .

 

If it is capable of 2400W output, and about 90% efficient, then the power consumption will exceed 2600W or 11.5A @ 230V AC - a 10A relay isn't going to last, especially considering inrush current. A 16A relay might just be good enough, but a 25A or a contactor would be better.
The power supply will have its own soft-start from the 325V bus to the amplifier DC power rails, but there may still be a large inrush as the 325V DC capacitor charges. The manual doesn't say how big the inrush is - you might just have to measure it.
It's debatable whether a solid-state relay or a mechanical relay will cope best with the inrush. With the solid state relay, it will start at mains zero-crossing which is an advantage. The disadvantage is that the SSR will dissipate 1W for every amp of supply current.
I think that the main objective would be not to switch it too often. Startup is the point that it will be under the most stress.

 

Can’t find any details regarding the 12v trigger that you want to use for driving the remote relay.
Would be helpful to know drive capability and any protection that is built in.

 

Hello, Protecting the relay coil and trigger circuitry: To protect the relay coil and trigger circuitry, it's advisable to include a diode across the coil. This is known as a flyback diode or snubber diode. The diode helps suppress voltage spikes that occur when the relay coil is de-energized, preventing potential damage to the circuitry. Soft-start setup: A soft-start circuit can be beneficial for audio amplifiers, even for Class-D amplification. While Class-D amplifiers may not have large toroidal components, a soft-start circuit can help prevent inrush current and voltage spikes that could stress the amplifier components or power supply. It gradually ramps up the power to the amplifier, reducing stress on the circuitry.Solid-state relay (SSR): The dual-pole solid-state relay you mentioned can also be used for powering on the audio amplifier. SSRs are generally faster and more reliable than electromechanical relays because they have no moving parts. They provide a solid-state switching solution and can be suitable for audio applications. When using an SSR, ensure it is compatible with the power requirements of your amplifier. upsers

 

A dual pole SSR would seem superfluous. All it would achieve is dissipating twice as much power and making twice as much heat. Single pole would suffice.

 

Where I live code requires both poles of the 240 volt supply be switched.

I would go with a relay that has a higher current rating, even if I had to stage the output from the processor. (lack of current available)

And this may only be me...but I would never buy that kind of high power relay from Amazon.

 

Are you sure the 12V on signal can supply 70mA?

 

Are you sure the 12V on signal can supply 70mA?

That's a good question.

Both of the trigger outputs on my DENON can output 150mA.

 

Thanks for all of the replies so far.

Answers to questions and advice offered

Unfortunately Anthem do not disclose the current capability of the 12V trigger on my processor. I know it manages 75mA because I tested it at that. What strain it places on it? Unknown. My preference is to aim at about 20mA if possible.
I *could* purchase an Emotiva 12V trigger unit which is designed to run multiple triggers and that would offload the risk if damage did occur (also I'd have the specs).

I'm not going to buy from Amazon - it was just an example. The risk of relays with underpowered and underspec internals is too high in that market space and no validation of components is possible. Foteh clones specced at 25A and using a 16A chip have been shown as present on there.

I like the idea of a SS relay however the heat output I do not like. Even acknowledging that a 10A max, 90% efficient Class D Power Amp will spend little time at anywhere near threshold current... it will still run hotter than any comparable electromech model I think. I'm not comfortable putting one in an enclosure with no vents or ancillary cooling/sinking. To place one in with the appropriate sink I could redesign and print a new enclosure... and it will be much larger than the existing one which is the same size as a dual gang GPO and maybe 50mm deep.

I ended up using a small solid state DC relay (20mA trigger current; 2A max current @ 240V AC) to switch a larger AC electromechanical relay (240V AC, trigger current 16.7mA, max 40A connection)... and I've yet to get it functioning (I need to test the 12v relay having confirmed the AC relay functions). I'll rewire it today just to confirm continuity on the 12V relay as I'm unsure if I killed it when soldering (or if the AC relay did on powering off and sending a V spike).

I'll attach my schematic and perhaps advice can be offered on that . I'd like advice on whether the AC relay is at risk of spiking voltage into the DC relay on powering-off as one specific point.

Excuse the very basic drawing - for simplicity I've not included the second Neutral switching element on the FRABPC-s2. I want to get it functioning before I add that in as a first step.


By convention, would it be better to connect the reverse the 'live' Active to NO not Common? This way the relay can never have a live NC contact...

 

If the LEDs are simply too bright, it should be easy to reduce that with just a bit of paint very carefully applied to the visible portion of the LED.
Switching on and off rapidly of a high power amplifier is generally a bad plan.

 

UPDATE: All working now... the solid state relay was broken. I replaced it and my little circuit now functions.

As a question, I was unable to verify the Solid state relay working by a continuity test. Is this due to the nature of a solid state relay (vs a coil one with dry contacts), or an element of a design created for AC current?

I suspect it's the former but can't work through why in my head .

 

If the LEDs are simply too bright, it should be easy to reduce that with just a bit of paint very carefully applied to the visible portion of the LED.
Switching on and off rapidly of a high power amplifier is generally a bad plan.

Possibly that would be fine but doesn't overcome the high power draw.

I'm not switching it off rapidly... the LED's flash rapidly. Why on earth would I be switching it on/off rapidly?

 

Not all signal triggered circuits work the same, and as I am not at all familiar with the system mentioned I made that remark.