Hi,
I've taken an E-I transformer from an old organ, but there are only voltages written on it. Is there an (easy) test to determine the max output current? (one that will keep it in tact 😉 )
I've taken an E-I transformer from an old organ, but there are only voltages written on it. Is there an (easy) test to determine the max output current? (one that will keep it in tact 😉 )
There's no precise way, but you can get a ballpark figure by measuring the secondary resistance. Then estimate the current that would cause the voltage to drop by 5%.
If you knew the cross-sectional area, that would tell you the VA capabilities. A check of the gauge that the wires in the windings are will tell you how much current to expect. Generally, 700 circular mils per amp is what most transformers are designed for.
Jocko
Jocko
load test
I have found that you can get a 16-ohm load out of an old toaster. (sadly, this is a US 110V standard). This works pretty well to stress a solid state Xformer (Volts 70-110)
Did you say this was a tube Power supply?
I have found that you can get a 16-ohm load out of an old toaster. (sadly, this is a US 110V standard). This works pretty well to stress a solid state Xformer (Volts 70-110)
Did you say this was a tube Power supply?
I want to use it to power my gainclone.
I do not understand what you mean with the using of the 16 ohm load from the toaster.
The transformer delivers 2*18.5V = 37V
37V / 16 Ohm = 2,31 amp
I need at least 180VA so Iout must be a 4.9Amp minimum.
Is what are saying the following?
Hang a load to it to see if the outputvoltage will be the nominal at a specific expected current. Lower the resistance in steps to see where the outputpower no longer increases? Use loads that can dissipate a lot of power.
If I find the current-limit that way, what would be the nominal outputpower?
I do not understand what you mean with the using of the 16 ohm load from the toaster.
The transformer delivers 2*18.5V = 37V
37V / 16 Ohm = 2,31 amp
I need at least 180VA so Iout must be a 4.9Amp minimum.
Is what are saying the following?
Hang a load to it to see if the outputvoltage will be the nominal at a specific expected current. Lower the resistance in steps to see where the outputpower no longer increases? Use loads that can dissipate a lot of power.
If I find the current-limit that way, what would be the nominal outputpower?
transformer testing
There are a couple of issues here. First, if it has multiple secondary windings, you have to use the circular mils calc and secondary voltage measurements to figure out the current of the winding you're interested in. You'll likely overload that winding before you overload the primary or core.
If it has only one winding then the entire transformer (primary, secondary and core) will likely contribute to the overload condition. When that happens, the efficiency of the transformer drops dramatically and it will overheat if run that way for very long (the secondary voltage is also well out of regulation by that point). The best way to figure out how heavily you can load the entire transformer is to monitor the input versus output power and plot the efficiency (and power loss) as you load it. But that's kind of a pain to do.
In the Amplifier thread someone posted a VA per KG estimate which is a decent way to get a ball park idea to see if further testing is warranted. The secondary DC resistance SY pointed out is another rough guide. Yet another somewhat more accurate test is to load it until the secondary voltage drops to 90% of the no-load value and use that current value.
You can BRIEFLY overload wirewound ceramic (or metal encased) power resistors by a factor of 2X - 5X if you keep the time to a few seconds (just long enough to make a reading). Although you might want to wear safety glasses🙂 So you can use relatively inexpensive 50 watt resistors, for example, for your test loads. You can also try various heating appliances you might have around the house (clothes irons, etc.).
Audio amps are somewhat forgiving transformer loads unless you plan on doing sustained sine wave testing or driving really low impedance loads. The nature of music is such the average energy is relatively low compared to the peak power needed. So a final technique might be to just try it and see how warm it gets after working the amp hard for a few hours (monitoring it along the way).
There are a couple of issues here. First, if it has multiple secondary windings, you have to use the circular mils calc and secondary voltage measurements to figure out the current of the winding you're interested in. You'll likely overload that winding before you overload the primary or core.
If it has only one winding then the entire transformer (primary, secondary and core) will likely contribute to the overload condition. When that happens, the efficiency of the transformer drops dramatically and it will overheat if run that way for very long (the secondary voltage is also well out of regulation by that point). The best way to figure out how heavily you can load the entire transformer is to monitor the input versus output power and plot the efficiency (and power loss) as you load it. But that's kind of a pain to do.
In the Amplifier thread someone posted a VA per KG estimate which is a decent way to get a ball park idea to see if further testing is warranted. The secondary DC resistance SY pointed out is another rough guide. Yet another somewhat more accurate test is to load it until the secondary voltage drops to 90% of the no-load value and use that current value.
You can BRIEFLY overload wirewound ceramic (or metal encased) power resistors by a factor of 2X - 5X if you keep the time to a few seconds (just long enough to make a reading). Although you might want to wear safety glasses🙂 So you can use relatively inexpensive 50 watt resistors, for example, for your test loads. You can also try various heating appliances you might have around the house (clothes irons, etc.).
Audio amps are somewhat forgiving transformer loads unless you plan on doing sustained sine wave testing or driving really low impedance loads. The nature of music is such the average energy is relatively low compared to the peak power needed. So a final technique might be to just try it and see how warm it gets after working the amp hard for a few hours (monitoring it along the way).
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