Transformer Identification and Schematic needed

[RCpilot]

Guys, I was digging in some junk I had and forgot I had this old transformer. It will actually fit into the 15 amp Battery Charger that I have. This charger has much bigger diodes in it than factory as I added them. They are the stud kind and are screwed into a large heatsink. I don't know what they are rated I would have to open it up and attempt to cross the part numbers on them. Anyway, to the question, here are a couple of pictures of the transformer. I know for a fact that it came from a large battery charger like the kind you would find at a gas station back when they had a shop. I was at my place when I bought it and the case was rusted beyond repair so I dug the transformer out of it and saved it back. What I need to know is how to figure out the taps on it and how much current do you think I might get out of it. I am pretty sure the two smaller wires are the primary and all the colored wires and two sleeved wires are the different current taps. The primary measures right at an ohm and the secondary no matter which pair you choose are less than an ohm. The primary wires measures: .066" diameter and the secondary wires measures: .094" diameter. Two of the primary wires has sleeving on them and the rest are taps that have been looped out of the winding and wires attached of different colors. The colors seems to follow standard color coding, Black Brown Red Orange Yellow Green. If anyone has any idea of a schematic for this I would greatly appreciate it. The secondary wires attached to the loops is #14 the best I can figure as it's printed on the wire with just: 14 Type TW 600 Volt. I would guess that all the taps went to some kind of switch that rotated to select various currents and maybe the sleeved secondaries are the end of the coil? I would love to make use of it and beef up my current battery charger.

Kelly

[finnsawyer]

Since you don't want to hurt the transformer the key is to start with a low ac voltage into the assumed primary winding and then monitor the assumed output voltages.  A Variac works well for that kind of experiment.  You might also get usable data using a model train transformer to provide the voltage to the input windings.  There is nothing inherently wrong with connecting transformers in series, but you don't want to inadvertently connect two so they both step up.  Going from 120 volts to 12,000 can get nasty.

[Flux]

I think you can reasonably assume that the 2 thin wires are the primary. If you know the original primary voltage then it is reasonably easy. Just connect the primary to its intended voltage and measure the secondary end to end and end to taps.

If you don't know the primary volts then you have a bigger issue. If you have a variable supply then you can feed it at variable volts with an ammeter in series with the primary and increase volts, watching the ammeter.

I assume you are in N.America so it is likely to have been 110v or 220v. You should get to 110v with only a modest primary current. If it was intended for 220v you will get to 220v with modest current. If it was intended for 110v, when you get to about 130v the primary current will shoot up and you will then know that it was 110v. If primary current goes beyond about 2A then you are saturating it.

If you don't have a variable supply then it is safest to assume that it is 110v. It may have been wound to charge several voltages as well as having taps for charge current.

Possibly it may have been intended to charge 6, 12 & 24v batteries. You may be able to make some sort of guess when you have secondary voltages. for 6v you will have something 7 & 9v. for 12 then perhaps 13 to 16, for 24 perhaps 25 to 30v. If the original rectifier was an old selenium or copper oxide device the volts may be a little higher.If your lowest voltage tap is well below 6v then it may be reasonable to suspect that the primary was 220v. Without a variable voltage supply the safest thing to do if it looks to be 220v is to feed the primary through a large 220v load and measure the primary volts. If it is 220v then the transformer will have near 220v across it and the load very little. If most of the volts are across the load and the transformer has only about 130 then it will be 110 primary.

This is a bit hit and miss, if you are sure what you are doing it will work, but if you are not really sure what I am on about then You had better assume it is 110 and hope you have suitable taps for your needs.

It looks as though it is old so it may be class A rated so don't run more amps than will bring its temperature beyond where you can stand your hand on it after a long run.

I suspect it will not give much over 20A long term rating but you will only find out when running it.

Flux

[RCpilot]

Flux, today I connected the Transformer to an autotransformer that I have and slowly brought it up. Got all the way to 120 volts without incident and no real current flow. I started measuring the taps and the two sleeved taps seem to be the highest voltage at around 85 volts. Then from one leg to each tap I progressively saw the voltage go down. I didn't write down the voltages and will tomorrow. So far it seems to be a good transformer. Now I need to figure out how to make good use of it as a large battery charger. And yes I'm in North America, Missouri to be exact. I guess I need some kind of large rotary switch to be able to change charge currents. I remember the box it was in and it was one of those Garage Style battery chargers with a single pole type handle and it had wheels on it so you could pull it behind you like a golf bag. The box was rusted beyond repair so I saved the transformer for some day. Seems like the rectifier that was in it was one of those big square plate looking things. That was 12 years ago.

Kelly

[Flux]

Good, you are on the way. It seems to have been designed for very high voltage and it you want to use it for 24v you may only have one suitable tap so you may need a resistor to control the current. You may find a couple of taps that work at 24v.

The original rectifier would have been very lossy and if you replace it with silicon you will need to add some ballast resistance.

As it was high voltage and is wound with the same section wire throughout the secondary you will only be able to use it at about 1/3 of its rated VA so your current out at 24v will be somewhat limited but even so it should work fine.

Flux