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Old 23rd December 2016, 06:40 PM   #1
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Join Date: Dec 2010
Default Transformer Taking a Fall

Hello all,

It's been sometime since I posted anything.
Anyway, I Dropped a large 1930's transformer that is 1050VCT, so 525V with full wave rectification. It is an open laminatation with two end bells...about 4" log

The laminations one one side shifted about down 1/16" - 1/8".
Would this still be safe to use? Or is it risky due to the epoxy/ tar moving inside?

Any comments are appreciated.

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Old 23rd December 2016, 06:57 PM   #2
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Join Date: May 2005
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Maybe yes; maybe no.

First, see if there is any continuity between the coils and core. If there is, it's no good. Test it by connecting a light bulb (one of the old fashioned kinds, not a CFL!) in series with the primary and power up with the secondar(ies)y open.If it hums, pulls excessive current, smokes, goes up in flames, then it's no longer any good. Strip it down, save the lamms and rewind.

If the current draw is light, just the inductive load current + core losses, then it should be OK. Next, try it with the full primary voltage applied and see if it still draws just small currents, and doesn't hum, smoke, explode, or get excessively hot. If it does any of those things, see above.

Side note: There may be some slight hum from loose lamms, but that's just annoying. Tightening the screws should stop lamm vibration.
There are no foxes in atheistholes
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Old 26th December 2016, 10:07 PM   #3
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Join Date: Dec 2010
Thank you Miles.

I did everything you said.

Everything checks out... though I measured almost 300Ma draw on the primary with no load. This is a large transformer with 1050VCT with a 300Ma draw along with 5V and 6V taps. So the losses may be normal for a 1030's transformer.

Thanky= you for all your help and contributions to this site.

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Old 28th December 2016, 12:22 AM   #4
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TonyTecson's Avatar
Join Date: May 2003
Location: Palatiw, Pasig City
power soak that with no load for about 20 minutes and see how warm the cores get...

if that were mine, i will dunk it in a vat of air drying electrical varnish. i will loosen the
bolts and nuts, remove the end covers...
planet10 needs your help: Let's help Ruth and Dave...[B
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Old 16th January 2017, 01:02 AM   #5
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Join Date: Dec 2010
Originally Posted by AJT View Post
power soak that with no load for about 20 minutes and see how warm the cores get...
Will do.

I just realized I said "normal for a 1030's transformer"... I meant a "1930's" transformer... over 76 years old.

Maybe my concern is unfounded... but a 76yr. old transformer seems like it could damage easily with older materials being used vs. modern epoxies.

On the other hand... much of the old stuff has passed the tests of time.
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Old 16th January 2017, 03:20 AM   #6
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Location: Palatiw, Pasig City
just be careful when handling, it sure can use a varnish bath....

you can use wooden or rubber mallets to align the core....
planet10 needs your help: Let's help Ruth and Dave...[B
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Old 16th January 2017, 05:46 AM   #7
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Location: Melbourne, Oz
You may be able to borrow an insulation resistance megohm meter. I got a digital one pretty cheap off ebay, and use it to test all restored amp transformer/choke insulation (1kV is available for mains testing), and also coupling cap and old switch leakage, and even if MOV's are still functioning.

Electricians pretty much have to check all AC mains wiring with that device when installing new circuits.

The outcome is similar to the lightbulb test using AC mains input, and earthing core and secondary, but it is also gauges how leakage current is flowing. Old vintage transformers will typically show more leakage than a modern transformer, due to the type of insulation material, and moisture and pollution ingress over decades.

Last edited by trobbins; 16th January 2017 at 05:49 AM.
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