About replacing SMPS or Battery Backup UPS transformers - Page 1
Forum section: electronics / repair

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 14, 2021, 05:11:38 pm
content: Hello,Today I have a dilemma.I'm repairing an APC XS1500 Battery Backup.The problem is that a capacitor leaked electrolyte and did some board damage but worst of all, it shorted an EE19 Class 130B transformer which has been rendered garbage because it shorted and burned inside.The Transformer I need is an EE19 Class 130(B), 430-0601-Z, BCK-EE19-4699A. Maybe you can shed light on obtaining one of these?This is the exact specs of the bobbin. I contacted CoilTech and they replied immediately. The minimum purchase is 5000 units.And that is assuming I could successfully rewind the bobbin to OEM specs. Ideally I could get 10 of them to experiment with rewinding.I'm wondering if you've run into a situation like this with a transformer? what did you do?How UNlikely is it to ever find a perfect match for an SMPS push pull or even flyback transformer that has burned out on a given board?I mean, all it takes is a small change in wire diameter, number of turns etc to have a totally different transformer, even with the exact same bobbin, right?I looked through Mouser and DigiKey but neither had anything close to a substitute / replacement.What to do?Thanks

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 15, 2021, 05:52:19 pm
content: Well ok then.What do you guys do when you need a transformer that isn't readily available?Any sources?

author: Alex Wolf
author_rank: Regular Contributor
timestamp: October 15, 2021, 11:00:00 pm
content: Quote from: ThermallyFrigid on October 15, 2021, 05:52:19 pmI know only 3 sources:1) "recycling" (scavenging) from e-junk;2) doing it by yourself from e-junk;3) placing a small custom order in China.For all of the above, you need to unwind the original transformer, count the number of turns in the windings, measure the diameter of their wires and calculate their cross-section, draw a diagram with respect to its terminals and winding layers, and write off the parameters of its core (although in this case there is a marking). However, it is possible to calculate a new design, there are not so strict requirements for work.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 16, 2021, 01:24:55 am
content: Thank you.This is what I suspected but was wanting affirmation.Much appreciated Alex.Does this forum do group buys where a number of people might go in on things like this?

author: Alex Wolf
author_rank: Regular Contributor
timestamp: October 16, 2021, 03:22:36 am
content: Quote from: ThermallyFrigid on October 16, 2021, 01:24:55 amI'm glad to help.And yeah, that's why they are so invaluable. Usually they don't fail, but when it does happen, the repair is not economically feasible as a rule with the very few exceptions. 😔 It's a small backup, just 1.5 kVA: so if you don't have 100 of them, I don't think it would be advisable to place a custom order for the transformer. It’s just cheaper to buy a new UPS. But maybe, just maybe, you can find a manufacturer on Alibaba/AliExpress and such, which will agree to accept your the very small order (usually from 10 pcs).

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 16, 2021, 12:48:45 pm
content: I had a thought. For anyone wanting to experiment a bit and still make use of a UPS with a problem like this.All UPS Battery Backups have two primary functions.....1). Provide inverted Power from batteries during a mains power supply failure2).Recharge the depleted batteries.Power Inverting for AC supply is handled by the large (actually huge) transformer in the UPS.So, if the small transformer mentioned is bad, why not disable the charging circuit and only use the Inverter AC supply side circuit?There are many ways of recharging the batteries externally, including inexpensive 12 and 24 volt battery maintainers.Circuitwise, I'm not sure if this can actually be done....it's just a thought.It could be the board will not function without it at all.As mentioned, buying a new UPS is sometimes the only total solution because of transformer issues.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 16, 2021, 03:43:07 pm
content: UPSes with failed batteries can be found cheaply pretty much anywhere.Unless there's something really special about this one, I'd source a used replacement and consign it to the parts bin. Should cost significantly less than a custom transformer order.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 16, 2021, 04:39:41 pm
content: Quote from: PaulAm on October 16, 2021, 03:43:07 pmI've found that people generally overprice these used units without battery.Few really good deals.For a 1300watt unit for example $70 +$30 shipping on ebay is about average.Where are all these cheap ones you mentioned?

author: andy3055
author_rank: Super Contributor
timestamp: October 16, 2021, 05:26:04 pm
content: The best bet is to source a parts unit from eBay like others have suggested. Since it is a very small transformer, would it be possible to wind it by hand yourself? You can buy the magnet wire quite easily.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 17, 2021, 03:09:38 am
content: Quote from: andy3055 on October 16, 2021, 05:26:04 pmHello Andy.I ran into a few issues attempting that route. Repairing the transformer. But I really wanted to give it a go.The first issue was that the phenolic bobbin was broken so that the pins were essentially floating free on one side. I'm quite sure this happened before I ever got the unit and it had been working.But I'd bet it caused some noise or ripple or some fluctuations in the output.The second issue was that the ferrite core was extensively epoxied to the phenolic bobbin. This, of course, to ensure that the ferrite core does not move around and thus cause fluctuations in the voltage.The tiny ferrite core wasveryfragile and cracked super easily while attempting to deal with the epoxy. So reusing the old phenolic bobbin and ferrite core quickly became a no go.On a brighter note, I found some transformers in Poland that might be suitable substitutes and they are on the way.I'm enjoying the journey and the repair of the UPS is not my primary objective....it's just a vehicle.Finding out what I can actually repair and learning about transformers, inductance and so much more is worth the trouble to me.I hope others enjoy electronics as a hobby as much as I do.

author: TheMG
author_rank: Frequent Contributor
timestamp: October 17, 2021, 04:32:15 pm
content: SMPS transformers are kind of tricky, since the great majority of them are design-specific. Everything from the ferrite core, bobbin, winding configuration, number of turns, etc, is all chosen to fit the application. Even if two transformers from different products look the same they could be different enough to not work properly. Thus the suggestion to find a parts unit to pull a transformer from.

author: andy3055
author_rank: Super Contributor
timestamp: October 17, 2021, 04:40:47 pm
content: Quote from: ThermallyFrigid on October 17, 2021, 03:09:38 amBelieve me, I know the feeling. These things with epoxy are a no win situation.If a similar core is available off the shelf, creating a bobbin is not that difficult. But then again, the core material may have different characteristics and that may not work also. Either way, it is not a sure shot to say the least.

author: james_s
author_rank: Super Contributor
timestamp: October 17, 2021, 06:29:39 pm
content: Quote from: ThermallyFrigid on October 16, 2021, 04:39:41 pmThat is cheap.Having a replacement custom transformer made is going to cost you more than $100, and so will doing it yourself if you value your time even at minimum wage. Once you replace the transformer you still have all the other work it needs and how do you know it won't just blow up some parts again when you plug it in? Are you sure the transformer is even bad? There is nothing in the picture to suggest this, maybe the bottom looks much worse? I have never even once encountered a faulty SMPS transformer. The windings are often just a handful of turns so they will appear as a short if you try to measure them with a DMM.

author: Alex Wolf
author_rank: Regular Contributor
timestamp: October 19, 2021, 10:29:05 am
content: Quote from: ThermallyFrigid on October 17, 2021, 03:09:38 amNext time boil it for approximately 15 minutes, and it will disassemble easily without significant force. Just remove tape before.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: October 23, 2021, 03:11:46 am
content: Great idea.Will the heat change the magnetic characteristics of the ferrite core?

author: james_s
author_rank: Super Contributor
timestamp: October 23, 2021, 06:45:53 pm
content: No, you'd have to go a lot hotter than boiling water to do that.