First Serious High Power Audio Supply Questions

[tporter]

I am an audio newbie (ARM developer) building a test supply based on Randy Sloan's current-limited supply (Figure 7.4 in his APS book). Now the questions:

1. I have two transformers laying around - 1 from ??? that's labeled 430-7105 (which google has an answer or two about from a HAM group). The second was ripped from a Nakamichi Receiver 2 & has the number: 33J166HN & even the Nak manual has no info on this. Ever heard of either one of these? Is there a good source online (other than google) for identifying non-common electronic parts? What is the best way to test a transformer for key params? OK, that was three questions.

2. In Sloan's schematic, he has 2 pairs of 1.5 A rails. I would like to be able to regulate one of each pair, but don't quite understand what he's doing w/ the current limiting circuit. If I should post the relevant circuit, please let me know.

Last, I'm used to sourcing parts at Mouser & Digikey. I'm sure this has been answered in these forums many times, but I can't find an answer this morning: Where are the best places to source these monstrous reservoir caps?

Thanks for any help.

[mastodon]

1. I have two transformers laying around - 1 from ??? that's labeled 430-7105 (which google has an answer or two about from a HAM group). The second was ripped from a Nakamichi Receiver 2 & has the number: 33J166HN & even the Nak manual has no info on this. Ever heard of either one of these? Is there a good source online (other than google) for identifying non-common electronic parts? What is the best way to test a transformer for key params? OK, that was three questions.

Do you know what voltages they put out? Is there any indication of the power rating on those transformers (VA)? If not, some measurements and guesstimates will be necessary. Start by working out which leads are associated with which windings by measuring DC resistance between them using a multimeter. This way, it's possible to map the architecture and usually it enables you to figure out which winding(s) is/are the primary and which ones are secondary, especially if you take the wire gauge into account.
Measuring voltages is pretty straightforward; just hook up the primary to a known voltage and measure voltages across the secondaries. Voltage ratios are equal to turns ratios, so if you put 100V AC on the primary and measure 10V on a secondary, the turns ratio is 10:1, and (assuming you have 115V out there) the secondary voltage will be 11.5V, which probably comes down to something like 10.5 or 10V under full load, depending on the size of the transformer.

Estimating the power ratio of an unknown transformer is much more difficult. If you know what equipment the xformer was taken from and you know what the power requirements of that equipment are (approximately), then you can work out a rough estimate of your transformer's power rating. Lacking that information, you can try to work out something by putting a variable load on the transformer and measure the voltage on the secondary, and see when it starts to sag noticeably or the transformer heats up/starts humming. Visual inspection, taking into account wire gauges and core size can be used to calculate a theoretical power rating, but I'm no expert on that.

2. In Sloan's schematic, he has 2 pairs of 1.5 A rails. I would like to be able to regulate one of each pair, but don't quite understand what he's doing w/ the current limiting circuit. If I should post the relevant circuit, please let me know.

Post a schematic please, that'll certainly help.

Last, I'm used to sourcing parts at Mouser & Digikey. I'm sure this has been answered in these forums many times, but I can't find an answer this morning: Where are the best places to source these monstrous reservoir caps?

I'm in Europe, so I can't really help you there, but I tend to keep an eye on dump/army outlets around here to see if anything interesting comes by. In the US, depending where you are exactly, yard sales can be a good alternative. Otherwise, you're stuck with the outlets you mentioned, I guess.

[robertguerrieri]

i have a few 1000mfd caps 400vdc if you can use them (there larger than soda cans )

[AndrewT]

go and read MJL's thread on his build of a lab supply.
Lab Power Supply Design / Build

[Binary1]

I found a transformer made by Midwestco that has part number 430-7105. It was located inside of a UPS that I was assigned to repair. As a matter of fact, I have an extra one sitting on the floor at work.

It was used to charge a 12 Volt battery bank, so it must be rated at 12 Volts. If you're still interested, let me know and I'll look up the UPS ratings and project an estemated Output amperage for you.

[Binary1]

My mistake, the battery bank is 24 Volts and 18 Amp/Hours and it charges fully in 3 hours.

[hesener]

If you try the testing with AC voltages, please use a lowish voltage (e.g. 6V) and hook it up to the highest resistance winding you can find, if by chance you happen to step up this can be lethal...... you might also want to put a resistor e.g 1k in series with the AC source, to protect against overcurrents....

maybe I am being too cautious here, but better safe than sorry.....

[Binary1]

Hesener,

I thank you for your input. I can easily identify the Primary Winding and I do have experience with using a 6 or 12 Volt AC source to power the primary winding to discover the output voltages.

I do not know how to determine the output current. The secondary windings appear to be 12 AWG solid wire.

I expect the transformer output is 24 Volts at 30-40 Amps or greater. There is also a 2nd secondary winding that powers the control circuit. I expect that to also be in the 24 Volt range.

I will be careful as 1000 Watts of power can do a lot of damage in a short period of time.

[DJDestiny]

Originally Posted by Binary1

Hesener,

I thank you for your input. I can easily identify the Primary Winding and I do have experience with using a 6 or 12 Volt AC source to power the primary winding to discover the output voltages.

I do not know how to determine the output current. The secondary windings appear to be 12 AWG solid wire.

I expect the transformer output is 24 Volts at 30-40 Amps or greater. There is also a 2nd secondary winding that powers the control circuit. I expect that to also be in the 24 Volt range.

I will be careful as 1000 Watts of power can do a lot of damage in a short period of time.

Thought of a load bank yet ? Like multiple 24v bulbs in parallel .