![]() It was like a 0 to 18 volt Variac that was isolated from the line. They're normally built into equipment, and frequently look like toggle switches.I remember testing transformers salvaged from discarded TV's, radios and HiFi sets as a kid with my trusty Lionel train transformer. But these aren't found in service boxes for electrical distribution. Older motors didn't require that much starting current Magnetic breakers have somewhat different characteristics, and have a narrower acceptance range for overloads. The 20-amp Square-D breaker that I mentioned will carry 160 amps for 1 second.It's all because of motor starting current, and the fact that modern motors are much less efficient than their older cousins. They're thermal, and have a built-in time delay. Everybody expects a breaker to act like a fuse, but they don't. Quote:Originally posted by easyrider8:Thats a long time for a breaker to trip, I always thought they were a bit quicker than that.Hi Dave,I know. Ever give any thought to the circumstances surrounding your finding it? Maybe it was pulled out of a piece of equipment due to its being shot and wound up in your junk box?Curt-Curt, N7AH(Connoisseur of the cold 807)QCWA# 25085 AMI# 242CW forever Just a winding that is not used, if shorted will burn the transformer up.You mentioned that you found the transformer. There is no way to use it, regardless of rectifier configuration. If turns are shorted, the transformer is junk. Let it cook with no load, but full applied voltage to the primary for a while and see if it overheats or stinks up the house. Filtering this large amount of unbalance would be very difficult, at the least.I suspect that the transformer has shorted turns in one side of the secondary winding. Every other hump would be higher than the intervening humps. You may see a difference of one or two volts, but any more than that will be impossible to filter out the hum.Draw out a diagram showing full wave rectification. The high voltage secondary must put out equal voltages each side of center-tap. I have many of them in service here.As you and Huggy said, the dim bulb tester is certainly good security.-73 de Leigh W3NLB | | | | You can get fried to a golden brown in 20 seconds Product performance curves are available here This breaker is typical of those used in residential and commercial service. The Square-D type QO 20-amp breaker will clear in 5 to 20 seconds under this overload. AC mains breakers are designed to accommodate inrush currents of motors and similar inductive loads.The 50-amp load represents a 250% overload for a 20-amp breaker. Quote:Originally posted by easyrider8:Its awful hard to keep the circuit breaker from tripping when applying 50 amps to the 2.5 volt winding.The circuit breaker will certainly clear. If you connect 115 volts to that winding, your 700-volt secondary will be putting out 32,200 volts (that's 32 THOUSAND volts) before it expires.-73 de Leigh W3NLB | | | | ![]() Multiply those readings to find the actual values under normal line input voltage.An example of the problem: Some power transformers in early AC sets used black for the 2.5-volt filament winding. Connect that output to the lines you think are the primary of the unknown transformer, then measure the voltages on the other windings. Adjust the Variac so you get ONE (1) volt AC out of the filament transformer. Wire colors may change over time.To check it out, connect a 6-volt filament transformer to the output of a Variac. And even then check it out carefully before you apply line voltage to it. Hi Rod,NEVER believe a transformer color code unless there's a label glued to the transformer that gives the colors.
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