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PCB mount AC/DC converters in the UK

I'm looking for a very low power AC/DC converter (240VAC to 12VDC or

24VDC). It only needs to switch a relay, so it seems silly to use a transformer+regulator and I would prefer a small PCB mount component. After fairly extensive web searching I've found two candidates: Recom RAC05-12SB/24SB and Aimtec AME05-12SZ/24SZ. But I cannot find any supplier in the UK for either of these devices.

Does anyone know where in the UK I might get either of these, or alternatively are there any other devices of a similar type I can consider?

Reply to
Clive Backham
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Sorry, please ignore. I have found the Recom device at RS. (Searching for RAC05 didn't work; searching for RAC5 did).

Reply to
Clive Backham

Make sure you label it carefully. Wouldn't want someone thinking that 12V was safe.

Why not use a mains relay?

Reply to
CWatters

It's a bit complicated. The application is to switch on power amplifiers when a source component (Slim Devices Transporter) is turned on. I can arrange to get a 3.3V DC signal out of the Transporter when it's on, but cannot find any relay capable of switching 10A mains AC with a coil that triggers at such a low voltage. So first I have to step it up with a transistor, which in turn needs a power supply. I happen to already have a relay that triggers on 24VDC, so I thought that the neatest solution is to use the mains that's going to be switched by the relay as the initial power source. Hence the requirement for a 24VDC PSU. And I didn't want to be bothered with transformers and regulators.

Reply to
Clive Backham

Makes sense just don't forget that transformers provide safety isolation. Some AC/DC converter modules will as well but perhaps best check. Perhaps use an opto isolator in there somewhere.

Reply to
CWatters

When all you want to do is to turn on 24V relay, you don't need any regualtors. A simple unregulated 24V power supply will do as well on your applications. 24V relays can nicly take slightly higher or lower voltage than their nominal voltage without problems.

Another approach: Take a small SSR that you can drive from 3.3V power source and can control mains AC at low current. Make that SSR to control the coil current to 10A capable relay or contactor (mains voltage coil).

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Tomi Engdahl (http://www.iki.fi/then/)
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Reply to
Tomi Holger Engdahl

Agreed - the D2W202F will work down to 3v at 3mA and switch 240v 2A

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Order Code: 1200279 at £5.58

so connect that to a decent relay e.g. Order Code: 1169288 DIN rail mounting at £9.95

Geo

Reply to
Geo

=20

Interesting option - at first sight it's certainly much simpler and cheaper than using a PSU. I happen to have a power relay with 240VAC coil, but I'm not sure it will work as-is....

The DC resistance of the coil in the relay is 8800 ohms. So naively, I guess it will pull about 27mA. However, the spec says the coil reistance is 9000 ohms (seems fine within sample tolerance) but also says it pulls 9mA. So I conclude that calculating current from voltage and resistance is rather more complicated for AC than DC.

Anyhow, given that the SSR you mention states a minimum load of 60mA, am I correct in believing that the relay won't pull enough current to cause the SSR to operate? (I note that even the DIN-rail relay you suggested states it only pulls 25mA, so perhaps I've just completely misunderstood the meaning of the "minimum load" spec for the SSR).

Reply to
Clive Backham

No - I did not match them properly - sorry my fault for a quick scan through their relays. Farnell do have some power SSRs which /might/ do the job directly. e.g Opto22 240D25 (240v 25A) but some heatsinking would be required to dissipate the 13 watts. One caution - can the 3.3 volt output, that you have available, supply enough current to drive anything useful?

Geo

Reply to
Geo

directly.

dissipate

The only one I could find was the Crydom PF240D25. It has an integral heatsink and supports passively-cooled loads up to 10A (which is plenty enough).

Good point. The PF240D25 pulls 15mA. The 3.3V output that's available is primarily designed for use with an IR Blaster (as a way of controlling external devices using IR remote codes). I presume this means it is expected to drive an IR LED, which I'd have guessed requires something of the order of 20mA (but not sustained, of course). I've posted a question on the Slim Devices forum to ask whether it can deliver this much current.

Thanks for your very useful comments.

Reply to
Clive Backham

After some experimentation, I concluded that the SSR approach wouldn't work. The PF240D25 has an input impedance of 300 ohms. So I tried loading the 3.3V IR Blaster feed with 300 ohms and the voltage dropped to 2.5V, which is probably too low to trigger the SSR.

I ended up going back to my original plan, using a transistor to step up the voltage. Found a suitable PSU at Farnell (Traco Power TML05124). It wasn't cheap, but it does the job.

My thanks to everyone who helped.

Reply to
Clive Backham

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