Repair or replace this transformer - Page 1
Forum section: electronics / beginners

author: humpty
author_rank: Newbie
timestamp: March 18, 2024, 11:02:27 am
content: Hi, we have a transformer that controls some window blinds. I am told that it no longer works. I'm trying to replace it or get it repaired. I've contacted a few companies that supply transformers with no luck. I'm not sure whether the company Ulmer still exists, emails bounce back. And I don't know what most of the numbers on the cover mean! Here's a photo, is there enough info here? Any suggestions re replacement or repair appreciated!

author: CountChocula
author_rank: Unknown
timestamp: March 18, 2024, 01:24:51 pm
content: You should be able to replace this with any transformer that has similar characteristics. This one takes mains power (230V) in input, outputs a voltage of 24V and is capable of supplying up to 2.5A of current.Unless you're familiar with electrical work, dealing with mains power is potentially fatal, so I wouldn't advise doing the work yourself, but any certified electrician should be able to find a suitable replacement for this unit; it won't be the exact same model, but it doesn't need to be.—CC

author: shapirus
author_rank: Super Contributor
timestamp: March 18, 2024, 01:55:34 pm
content: Note that output is marked as 24 VDC, so there must be a rectifier and filter inside, apart from the actual transformer. And this doesn't sound like a usual combo to me.If the case isn't glued/sealed, it may be fairly easy to repair it, as it's unlikely that it's the transformer itself that failed, and, since it seems to have a good old 50/60 Hz mains transformer inside, followed by a diode bridge and a filter capacitor, the failed part must be one of the latter two, each being trivial to replace.There may also be a fuse inside that blew, in that case replacing it may get the transformer working again, but it'll require to figure out why it blew in the first place, or the problem may happen again.If a full replacement is necessary, it can, most likely, be replaced with a switch mode PSU (much more common today than linear types) with the appropriately rated output, but it's desirable to confirm that the intended load's input doesn't require anything specific and is indeed designed for a 24 V DC supply.p.s. it seems to be designed for outdoors use, so any replacement or repair has to keep a reasonable level of moisture protection, if that's so.

author: humpty
author_rank: Newbie
timestamp: March 18, 2024, 02:58:08 pm
content: Thanks!It runs seven interior window blinds (all in sync, not separately). My guess is that the blinds got stuck and that someone was impatient and did a lot of forwards/backwards with the rocker switch!! Might that cause it to break?Can I just tell my electrician to find a "switch mode power supply unit mains input with 24V DC up to 2.4A output" (with full acknowledgment to EEVBlog!)? He hasn't been able to find a replacement himself, hence me coming here. Googling this myself throws up lots of these things, it doesn't seem to be exactly the hardest thing that you've been asked!...unless I'm missing something!

author: shapirus
author_rank: Super Contributor
timestamp: March 18, 2024, 03:11:03 pm
content: Quote from: humpty on March 18, 2024, 02:58:08 pmWell, maybe you need to find a better electrician... This is something that anyone remotely familiar with electricity would've been able to figure out.Knowing what the window blinds expect on their power input would help to give a more definitive answer. Is it possible to trace where the power lines from the transformer's output go to? I mean they should come to the motor, some control block before the motor, or whatever is driving those window blinds. It has to have some markings on it that will likely state the input voltage and current among other stuff. Maybe also the model/part number that can be googled....and yes, trying to power a stuck motor for a sufficiently long time can potentially blow the fuse or, if the fuse fails to do its job, the diode bridge.

author: wasedadoc
author_rank: Super Contributor
timestamp: March 18, 2024, 03:44:14 pm
content: The symbol beside the 110 degrees C text on the 60 VA line is a thermal fuse. That is the most likely part to have failed if the unit has been subject to prolonged overload. Not difficult to replace if you can get to it.Most of the electricians who install wiring, power outlets, lights and switches don't have a clue about transformers, power supplies and the internals of sealed boxes. They don't need to.

author: themadhippy
author_rank: Super Contributor
timestamp: March 18, 2024, 03:55:01 pm
content: Quotenot any more,the days of a sparks being able to deal with industrial, commercial and domestic electrickery are long goneQuotebuy it yerself,https://cpc.farnell.com/mean-well/lrs-75-24/power-supply-ac-dc-24v-3-2a/dp/PW04809chuck it a suitable box,job done

author: humpty
author_rank: Newbie
timestamp: March 18, 2024, 09:53:10 pm
content: DIY? I’ve tended to avoid things that might kill me. But it is tempting!

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: March 26, 2024, 03:29:22 pm
content: It looks like it's not just a transformer inside but a power supply. The letters DC indicate that. You need to buy a suitable unit like this:https://meanwell-ps.com/products/hsg-70-24.Do not mix up the "+" and "-" when connecting it