Determining the amperage of an unknown transformer

I would try to get a measurement of the wire diameter. Use 600-700 circular mills to figure out the current capability. If it?s a small transformer then you can assume single insulation and get the wire size off the standard charts. Then you can load it and check for temp rise. Less guess work with the load selection.

Cheers

r a

ated

nt?

You jacking off at the mouth with this non-term is a saled from your ass, boy.

That is what I said. That is despite you trying to make the "data" you think you gathered mean something.

Two right in one day!

Yes... data. Meaningless.

It does not become information until is is processed correctly. Your version of "correctly" matches your method of using a machine in a completely different way than what it was designed for.

Information is disseminated data. Placing raw data on a chart isn't information if it isn't useful.

So, if someone bought one of those twenty from over ten years ago, they MIGHT see something there they could use.

OK.

When I refuted your bullshit about Signal, it was useful. Mainly to folks that wonder whether or not anything you say is worth placing any credence in.

Show me where I did that.

Show me where I did that.

Show anyone where that stupid crack has any meaning to anyone but you, ditz.

I think your observations were skewed by the same things that have skewed you in this group lately. Falwed logic and flawed engineering, and severely flawed vision of the bigger picture.

Sorry, but you making useless statements about how you THINK a company that has been making transformers for years does their task is a sad resume, for you Johnny.

More like an accurate indictment.

JF and JF :-)

You're now troll-feeding.

Leave JL with only BS to "debate". ...Jim Thompson

In a thread about transformers, nobody would expect you to talk about transformers. We expect you to whine and cluck.

I was talking

Confirmed!

Uh, what do you call the blue label ---> POWER VA ???

What did you think the overall title VA RATINGS --- WEIGHT GRAPH might mean?

Idiot.

John

Thanks for that. Quite useful, though our 50Hz xfmrs would be a little heavier, I think.

I been wondering lately how to tell the power split between two windings on a nice looking transformer in the 'junk box'.

Xfmr looks around 120VA with 9V and 33V secondaries.

I was thinking measure no load, then load to 5% or 10% voltage drop? Work from those results.

Tim's resistance measure would shed some light too.

Good double check of the other methods. Bit slow?

This xfmr is a good quality E+I one with earth screen, got the outside shorted copper turn and iron turn to reduce external field, switch and fuse in a partial enclosure. Destined for a bench power supply, I think. Once I have an idea where to set the power limits.

Using SLA batteries for testing stuff has produced some fun moments, watching the magic smoke escape ;)

That was an odd situation where a line of five 'HCMOS chips started emitting smoke from their middle pins, until the one in the centre one popped its top. Didn't blow the 35A battery fuse.

Grant.

vvvvvvvvvvvvvvvvv

^^^^^^^^^^^^^^^^^

Ruler and pens.

John

I think all these were 50/60 Hz transformers. All the ones we buy are.

You could measure the resistance and the open-circuit voltages. You could assume that each winding could be loaded to, say, 90% or 95% of its open-circuit voltage.

Oops, yes.

I don't suppose it still works.

Wirebonds make nice detonators, but don't pass a lot of I^2*T. The first atom bombs used exploding wires. Later ones used gold thinfilms.

I spent the weekend blowing up DC/DC converters, not too bad at only $4 each.

I unpotted one, but lost the transformer in the process.

ftp://jjlarkin.lmi.net/VASD1_top.JPG

Next project is to breadboard a current limiter circuit, and blow them up together.

John

for a

-48v.

I'm

s,

rated

rent?

Oddly parallel, or... impossibly parallel? Nicely? I suppose it is possible. Sounds like the typical statistical error issue though. Silly putty and play dough comes to mind.

I would load it up UNTIL it reaches max op temp AFTER all settling time. Then, all you need do is take note of those set-up parameters, and place your operating window inside of that at whatever cmfort level you want.

The op temp which YOU desire to run under with the fringe ranges you want will determine how hard you decide to push it, so one would think it best to simply "run it up" under observation, and slowly get to where you want the TEMP to be, then OBSERVE the set-up, then operate BELOW that plateau.

Did you see the Siemens/Orange County Chopper E-bike episode? There was a guy there "touching" wires together after it failed to spool up on initial trial. It was funny, he jumped off several feet away, and when the camera went back on him, he had a huge burn on his fingers.

And those dopes get over $10k an episode! (the mechanics, not the family)

You're a dangerous individual.

Wild circuit connections then.

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 vvvvvvvvvvvvvvvvv

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ^^^^^^^^^^^^^^^^^

You even define the word 'generate' differently.

I didn't define "generate" recently. I did a manual 1st order curve fit, like they taught us in all our high school and college physics and chemistry and engineering labs.

Don't you remember?

John

rated

Note that the lines are parallel but the slopes are *not* unity, namely weight does not scale directly with power. Do you know why?

(Hey, hold off and let him answer!)

John

It's just about as accurate as an estimate based on length and/or weight measurements can be.

The power handling capability of a transformer is directly proportional to the WaAc product; see page 4.3 of:

Since the WaAc product has dimensionality (length)^4, and weight has dimensionality (length)^3, the power handling capability of a transformer should be proportional to (weight)^(4/3).

If weight vs. power handling is plotted on loglog paper, you will get a scatter plot along a straight line with a different slope than if you had plotted WaAc vs power handling.

A plot of weight vs power handling is not quite as good as a plot of WaAc vs power handling for a number of reasons.

The ratio of WaAc to core volume is the same for all transformers with the same aspect ratio; that is, for all EI core transformers with a "square stack", that ratio will be the same no matter how big or small the transformer. If the core weight vs power handling for a bunch of transformers having the same aspect ratio is plotted, the plot should look the same as a plot of WaAc vs power handling, just with a different slope.

But, transformers having an "oversquare" or "undersquare" stack will have a different ratio of WaAc to volume, and the plot of WaAc vs power handling will not map to a plot of weight vs power handling in the same way as for a "square" stack.

Another source of error with a weight vs power handling plot is that the measured weight of a finished transformer isn't just the weight of the core; the weight of the copper, insulation, and mounting hardware, is also included.

Nevertheless, a plot of transformer weight vs power handling is a good start for determining the power rating of a transformer. To refine the result, a temperature rise test should be performed.

A fairly extensive discussion of this problem, with plots of a large number of commercial transformers is found at:

A well designed transformer should have the same current density in all the windings. It's not too hard to show that given a couple (or three) windings, with one winding carrying a current I1 and with an output voltage V1, and a DC resistance R1, and similarly, a second winding with I2, R2 and V2, the current density in winding 1 is proportional to (I1*R1)/V1, and in winding 2, it's proportional to (I2*R2)/V2.

Then the currents in the two windings (for equal current densities) are related like this:

I1/I2 = (R2*V1)/(R1*V2)

As in any "unknown" transformer, start by determining the approximate power rating from the cross-section; all else then falls in place.

Not a very good indicator..wire could be undersized for the MFG rating, or oversized, like i do: circular mils is current rating in milliamps.

Nah, everything connected to 5V blew up, except a TL431 'cos it had a current drop resistor ;)

Better you blowing them up than your customers :) Enjoy!

Grant.

Problem is discovering the difference between 9V and 33V windings' current capacity, can't see the 9V winding clearly to get an idea how thick it is.

Nah, electric 1/4 mile?

Boom! (Ouch)

When I was 13 I bared mains plug wires and touched them together to see how big a spark it would make. Blew the house cartridge fuse (the one they pull to cut the power from street, not the fuse box) up where the power comes in. So I stuck a nail in the fuse holder, so I didn't get found out.

Yeah, I think 24V hit 5V line via a bit of wire, like this one:

Got soft mains here, or it was very fine wire, hardly any noise, no blown fuse. Just the flash and muted whoomph from under the plug.

Grant.