Using old large transformers for something useful

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RogueRose

Joined Oct 10, 2014
376
I have access to a lot (100's) of old power transformers probably 1000va - 2000va and I think almost all of them come from old APC UPS's. Many of these use a primary winding of 2" wide x 20 - 24g copper roll instead of wire, which is actually pretty useful in itself as there are some with about 30-50ft of the copper sheet/roll (what's the right name?). I've tested many of these and they have a split secondary of 12/24v and they are made to charge the 12v batteries in the UPS.

I think these would obviously be ideal for a battery charger as high amperage chargers of good quality are pretty expensive. I can also set it up as a 12/24v charger which is somewhat uncommon in chargers. IDK how useful the 6v chargers are as they seem to have been more common in older battery chargers when there were a lot of vehicles that still ran from 6v - so alot of chargers pre ~1990 seemed to often have the 6v option.

Another idea was to make a "magnetic chuck" or "magnetic vice" to hold parts when doing work on it. I'd probably cut the top of the laminations off and either remove one winding or leave it alone, and then run DC voltage through the primary to make an electromagnet. These are very nice size of the steel body being 3.5" wide x 4"-6.5" long x 3.75" high so these are pretty large and weigh 18-36lbs

I also find transformers like this one, which has a total of 4 windings, 2 on each side with both sides having identical windings. This thing weighs about 50-55lbs and IDK the VA rating, I suspect it is 3300VA. I was wondering if this transformer could be used as an isolation transformer by inputting the 120/240 into the primary of side A - running the output of the secondary on side A into the secondary of side B, then have the primary of side B be the output (120/240v) of the isolation transformer. Would it work this way? Would there be a better way to do this?
 

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drc_567

Joined Dec 29, 2008
703
... There should be a market for isolation transformers ... used for oscilloscope isolation and similar applications ... always an advantageous workbench accessory. However, it will be necessary to verify that there is no continuity between the primary input and secondary output. A 1:1 winding ratio could be configured using primary to secondary and then secondary to primary, as long as prudent VA ratings are observed ... Enough useable power capacity to safely isolate an oscilloscope should be possible. ... Some diligence would be necessary to insure that there is no continuity whatsoever between any of the primary to secondary windings ... e.g. perform an actual continuity test ... using a meter ... Also insure that the transformer chassis is not connected to either winding.
... With the types of power transformers described in the original post, there may be a question of transformer polarity ... not a problem as long as the output voltage is actually verified prior to connecting any type of load.
 

sagor

Joined Mar 10, 2019
108
Most of the high VA transformers are actually the inverter transformers. They ran 12V/24V into the windings to produce 120V outputs. Many UPS at high wattage ran on 24V or even 48V battery banks, and often split those in two to feed one, two, or more transformers to produce the 120/240V (depending on make/model).
So, the 12/24V is actually the "primary", the 120V is the secondary. You can run them backwards, keeping in mind the loads (VA ratings).
To charge batteries, they would not use a 2000VA transformer. A regulated charging circuit of 5 to 20A would suffice, which would be in the 200-400VA range.
 

nsaspook

Joined Aug 27, 2009
6,255
Probably get more for the transformers, intact.

Or, maybe wire them end to end, in reverse, and bring on the apocalypse.
My usual evaluation of something like this is if it actually had value beyond brute labor in the current product instead of gathering dust, some enterprising person would have taken it already.
 

Yaakov

Joined Jan 27, 2019
1,532
My usual evaluation of something like this is if it actually had value beyond brute labor in the current product instead of gathering dust, some enterprising person would have taken it already.
One case where this heuristic would fail is in forgotten warehoused items.
 

Tonyr1084

Joined Sep 24, 2015
3,556
Back when I was young my dad would tell me to never let a car battery sit on the concrete because doing so would drain the voltage from it. That may have been true back in his day but battery technology is pretty good at isolating battery drainage from sitting on concrete. I believe, not certain, it had something to do with the construction of the casing of the battery.

That being said, I have an older car battery sitting in my garage on a trickle charger I made from an old 12 volt 2 amp power supply. I had to modify the circuitry to give me a continuous 13.6 volt output, but it has been holding that battery charged at that level for a few years now. I use it to play an old car radio when I'm out there working on cars, woodworking or welding something. One thing for sure is you don't need a monster transformer for a battery charger. Small and light weight - as long as it can do the job it's designed for.

I have a commercial battery charger (6V 20A / 12V 40A capable) that can be used as a jump starter for cars with weak batteries. My neighbor has borrowed it on many occasions. He's notorious for not fixing something until it's thoroughly broken. Hoses, belts and weak batteries - he keeps on going until total failure. Even then he still finds a way to get a few more miles out of it.

I like the KISS principal. Though some have a different take on the acronym I like mine. Keep It Stupidly Simple. (as opposed to Keep It Simple Stupid as many seem to prefer)
 

ian field

Joined Oct 27, 2012
6,543
I have access to a lot (100's) of old power transformers probably 1000va - 2000va and I think almost all of them come from old APC UPS's. Many of these use a primary winding of 2" wide x 20 - 24g copper roll instead of wire, which is actually pretty useful in itself as there are some with about 30-50ft of the copper sheet/roll (what's the right name?). I've tested many of these and they have a split secondary of 12/24v and they are made to charge the 12v batteries in the UPS.

I think these would obviously be ideal for a battery charger as high amperage chargers of good quality are pretty expensive. I can also set it up as a 12/24v charger which is somewhat uncommon in chargers. IDK how useful the 6v chargers are as they seem to have been more common in older battery chargers when there were a lot of vehicles that still ran from 6v - so alot of chargers pre ~1990 seemed to often have the 6v option.

Another idea was to make a "magnetic chuck" or "magnetic vice" to hold parts when doing work on it. I'd probably cut the top of the laminations off and either remove one winding or leave it alone, and then run DC voltage through the primary to make an electromagnet. These are very nice size of the steel body being 3.5" wide x 4"-6.5" long x 3.75" high so these are pretty large and weigh 18-36lbs

I also find transformers like this one, which has a total of 4 windings, 2 on each side with both sides having identical windings. This thing weighs about 50-55lbs and IDK the VA rating, I suspect it is 3300VA. I was wondering if this transformer could be used as an isolation transformer by inputting the 120/240 into the primary of side A - running the output of the secondary on side A into the secondary of side B, then have the primary of side B be the output (120/240v) of the isolation transformer. Would it work this way? Would there be a better way to do this?
A certain proportion of the current draw will be "magnetising current" that exists whether the secondary is loaded or not. big transformers consume big magnetising current - so efficiency could be an issue. If I had loads of them - I'd pay the scrap dealer a visit.
 
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