Looking for a particular power supply - Page 1
Forum section: electronics / projects

author: paul23
author_rank: Regular Contributor
timestamp: August 21, 2013, 08:19:48 pm
content: This has nothing to do with my other thread regarding power supply circuit. This is for a control board for a Spa. The board is dead and nothing happens at all. There is a plug in type SMPS board which has nothing coming from it at all so I am pretty sure that the power board is dead. The dealers for the spa´s don´t sell just the power board, you have to buy the full PCB at around 500€ so I figured it would be easier to just change the power board, the thing is it´s funny voltages and I can't find one similar.It´s a 4ch supply with +5V/0.2A, 20V/0.6A, +12V/0.15A, +9V/0.05A. It has a mains input (230VAC). I've looked on Mouser, Digikey, RS and Farnell and none of them have anything close. I could get away with two separate supplies if needed, say one doing the 5V and 12V and the other doing the 9V and 20V. The 20V I think just powers the coils on some relays which are rated at 18V and the silkscreen for the plug that power board plugs in to also says 18V, so 18V might do instead of 20V if absolutely necessary.Does anybody have any idea where I might be able to get one? I don't have time to troubleshoot this one, I am too busy with work, but I will have a go when things quiet down a bit.Thanks

author: mariush
author_rank: Super Contributor
timestamp: August 21, 2013, 08:33:04 pm
content: You can get a 19v laptop adapter from Amazon and you have your 20v power supply sorted. 19v is close enough that I doubt it would matter.Alternatively, you can get a 24v power supply and adjust the output down to the minimum, let's say about 21-22v. For example a meanwell 24v psu is about 17$ on ebay :http://www.ebay.com/itm/Mean-Well-MW-AC-DC24V-50-100-350-400-600-1000W-1500W-Switching-Power-Supply-PSU-/111115520782?pt=LH_DefaultDomain_0&var=&hash=item19df004b0eand allows you to set 24v +/- 10%From there, you can get 12v and 9v using simple linear regulators... the currents are low enough to not be an issue with heating. just get a 7812 and a 7809 linear regulators and you have 12v and 9v.5v you can get from 19v using a dc-dc converter ready made from digikey etc. , for examplethis gives you 5v 0.5A from up to 28v :http://www.digikey.com/product-detail/en/R-78E5.0-0.5/945-1648-5-ND/2834904this gives you 5v 1.5a from up to 36v :http://www.digikey.com/product-detail/en/OKI-78SR-5%2F1.5-W36-C/811-2196-5-ND/2259781

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 21, 2013, 09:00:54 pm
content: Like mariush, I think that, at the low currents involved, using a linear regulator to make 12 and 9 volts from 20V would be what I'd do. A laptop power supply is a cheap source of 19 or 20V. To lower the voltages to 12 and 9 V, I might use a couple of LM317 regulators, since I've got a pile of them around, but the 7809 and 7812 are perfectly suited to the task, too.I'd probably generate the 5V directly from the mains using a separate plug pack, rather than going through the 20V intermediate and getting a DC-DC converter. The "best" solution would depend on how much space is available and what power supplies/plug packs I can find in my junk box or the local thrift store. If you google "5V 3A power supply" you'll find a bunch for sale for less than $10. (I know the requirement was only 2A, but 3A gives a little extra margin, and they're not expensive). But my local thrift store has a box of used power adapters for very little money, and by sorting through them and reading the nameplates, I'd probably find one that would work.One caution: I'd want to check and make doubly sure any power supply used around a spa has an output that is completely isolated from the mains input.

author: paul23
author_rank: Regular Contributor
timestamp: August 22, 2013, 07:37:27 am
content: Quote from: AG6QR on August 21, 2013, 09:00:54 pmThe 5V rail is only 0.2A (200mA) i missed the decimal point off on my original post, edited now.If possible I wanted to just replace the power supply if I could, I don't really have the time at the minute to make anything. I could I suppose fit a couple regulators on some perf board if really necessary, and use laptop supply as suggested, but really it would be better if I could find a supply ready made to do the job.