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John, if the existing one has been declared “grabage” you might assume that the failure is very near the coil end[s] and see if you can find the break and measure the ohms. And maybe be lucky and

A little more detain on this transformer. I found the code A-4931* on its side. I found some Standcor catalogs online with A-47xx numbers, but not A-49xx. * corrected. original post erroneously stated

I have not posted for a little while for various reasons but have returned to the SX17 project in the last few days and followed up on the previous suggestions. I am reasonably certain that the mains

As far as I know, the inrush current problem was due to the limitations of vacuum tube rectifiers then in use.? Filter capacitors just do not care about the initial charging current.? At the instant

Halden?I can't answer your question.? I don't know all of the pitfalls of using an SSR in place of a mechanical switch.? I don't know if there are any unintended consequences.? The SSR will turn

I usually work on tube audio, so we as a group have been installing movs to lessen the shock to transformers and filaments for a while, and filter caps when converted to s/s rectifiers

Maybe a spark gap, or a s/s equivalent...would fix it. ________________________________ Sent: Thursday, July 4, 2024 4:41 PM To: [email protected] <[email protected]> Subject:

Halden, that is common and in many forms you always see the reference It is easy here if you use email and indent [what I normally do] , I used to be able to do it on line, but my secret does not work

Halden, very interesting and thoughtful comments getting into the nitty-gritty. Re the turning off part: The switch needs to break any current and open the conduction path enough to withstand the

Rick , so have you or anyone looked at switch-off transients of the original switches? And also contact bounce on closing for other reasons? Re some SSRs see

FYI, in case my posts don't seem to be in logical order, it's because they aren't.? My messages appear on the forum in a sequence different from that in which I submitted them for posting.? Maybe

Hi Jim, Thanks!? So, would an SSR that turns on at zero voltage and turns off at zero current put the core back to zero every time and prevent current surges at turn-on? Halden

Hi Don, Thanks for bringing us back to the original question and for mentioning one of the options I hadn't listed!? Turning the transformer OFF at a particular time relative to the AC voltage cycle

Scott, I worked on three phase power supplies that had some premature transformer failures. The engineers had us install MOVs across the primary windings for all three phases. Never seen another

It appears that some experimentation could? in order. If you have a dual trace scope, you can easily measure the input voltage & current on the transformer primary and observe the phase difference

I wonder if a MOV could be somehow used to soften the inrush, if not one perhaps 2 in some kind of toggle arrangement. ________________________________ Sent: Thursday, July 4, 2024 2:56 PM To:

Halden, your investigation is interesting and detailed. IMO, the DC [resistance only case, ignoring all inductances] is the extreme limit which won’t be reached. Inductance does not go away,

I suppose one could use a zero-crossing SSR in series with a TRIAC.? TRIACs turn off when the current is at zero.? One would have to turn the TRIAC on before or at the same time as turning on the

HaldenTo answer your last question first, hysteresis causes the core to be magnetized.? The strength of the magnet in the core is dependent on where in the AC cycle the lagging magnetic field stopped

Thanks, all, for the comments and lessons! It seems we're converging on using zero-crossing transformers that are capable of switching whatever current the transformer would draw if only the winding's