Ok, so you are correct.

Why would four 12V bulbs blow if they were wired in series?

How many bulbs blew?

Are the four bulbs identical?

 

Ok, so you are correct.

Why would four 12V bulbs blow if they were wired in series?

How many bulbs blew?

Are the four bulbs identical?

4 bulbs blew.. not the same, 2 were 100/90w high and low bean, and the other 2 were just 55w single filament.. Ive got another smaller transformer, when I put in on the 45v winding, I get 42.5vac 8.2a.. I let it run for 5 minutes and both transformers got slightly warm, Im thinking about running this but keeping a close eye on it.. the impedance on the winding is 2.5ohms I think,, im not in front of my notes right now

 

ok,, I think ive got all the info I was asked for...the resistance on the winding cold is 2.1 ohm,,hot is .8 ohm ,, the voltage dropped to 34.5vac 9,8a... the test duration was 2 hours.. I don't have a temp probe, but the transformer was warm but I could still touch it without being burned...

 

ok,, I think ive got all the info I was asked for...the resistance on the winding cold is 2.1 ohm,,hot is .8 ohm ,, the voltage dropped to 34.5vac 9,8a... the test duration was 2 hours.. I don't have a temp probe, but the transformer was warm but I could still touch it without being burned...

The resistance can't be less when it's cold. Did you mean 2.8 ohms? If not, then you're having a problem with thermoelectric voltages interfering with your resistance measurement, and you will have to make the measurement another way.

If you could still touch the core, then you were well within the class A temperature range.

If the winding voltage was 34.5 VAC with a current of 9.8 amps, that's 338 VA, well beyond what a 5 pound transformer should be able to output. I wonder what's going on here? This measurement was made with light bulb loads, and no rectifiers involved, right?

 

cold= 2.1ohms hot= .8 1.3 ohms lower when hot. 4 new bulbs is series.. 34.5vac 9.8a no rectifier, warn to touch

 

Do you have another bench power supply?

The way to measure the hot resistance is to pass a known current, such as 1 amp DC, through the winding when it's hot and measure the DC voltage across it. If you do use 1 amp, then the voltage across the winding when the 1 amp is passing through it, is equal to the resistance in ohms.

 

cold= 2.1ohms hot= .8 1.3 ohms lower when hot. 4 new bulbs is series.. 34.5vac 9.8a no rectifier, warn to touch

How are you measuring these amps?

34v with 4 bulbs in series is 8.5v AC per bulb.

8.5v and 9.8A per bulb doesn't sound right to me. I use 100W headlights for dummy loads and 12v 7A or so is pretty typical. Many are less than the rated wattage at 12v as the rating was done at 14v. And at 8.5v they might be only drawing a few amps.

And 2 hours of that transformer at 338W output power should have made it very "ouchy" hot indeed, that is way above its continuous output power rating.

I have a feeling something is wrong with your measurement procedure or equipment.