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Furman Punch-10 transformer

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  • Furman Punch-10 transformer

    I recently acquired a Furman Punch-10 rackmount unit missing its transformer. I was able to get the schematic for the unit, it shows the windings of the transformer, but no further detail (see attached pic). My question is, is there anyway to determine what kind of transformer I need to use since I know what the output voltages are supposed to be (+ and - 15V) and I know all the values of components in the power supply? It's a relatively simple design with very few components..
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  • #2
    Hook it up to a bench power supply and measure the current demand for the +15 and - 15V rails. Next look as the physical size of the transformer. Go and search for transformers of that size with secondaries in the range 15-0-15 to 18-0-18 (guess for now) and note the the maximum secondary current, primary and secondary DC resistance ( or regulation if not available).

    Now download Duncan's PSU designer tool (search for it) and plug your transformer data in to see if will work. Your goal is to ensure that the input to the regulators is not less than 18V at full load and lowest expected line voltage. On the other hand you don't want the voltage too much higher else you might overheat the regulators.
    Last edited by nickb; 09-29-2019, 10:41 PM.
    Experience is something you get, just after you really needed it.

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    • #3
      Originally posted by StormLord11 View Post
      I recently acquired a Furman Punch-10 rackmount unit missing its transformer. I was able to get the schematic for the unit, it shows the windings of the transformer, but no further detail (see attached pic). My question is, is there anyway to determine what kind of transformer I need to use since I know what the output voltages are supposed to be (+ and - 15V) and I know all the values of components in the power supply? It's a relatively simple design with very few components..
      Agree and add: please post the FULL Punch 10 schematic, may help reasonably estimate current/power consumption demands.

      Yes, the supply is simple, but we know nothing about its load .

      Thanks.
      Juan Manuel Fahey

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      • #4
        Originally posted by nickb View Post
        Hook it up to a bench power supply and measure the current demand for the +15 and - 15V rails. Next look as the physical size of the transformer. Go and search for transformers of that size with secondaries in the range 15-0-15 to 18-0-18 (guess for now) and note the the maximum secondary current, primary and secondary DC resistance ( or regulation if not available).

        Now download Duncan's PSU designer tool (search for it) and plug your transformer data in to see if will work. Your goal is to ensure that the input to the regulators is not less than 18V at full load and lowest expected line voltage. On the other hand you don't want the voltage too much higher else you might overheat the regulators.

        Good idea, I'll try this. Probably going to need to get another bench power supply though because I don't think I can get + and - 15V out of one channel, right?

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        • #5
          Originally posted by J M Fahey View Post
          Agree and add: please post the FULL Punch 10 schematic, may help reasonably estimate current/power consumption demands.

          Yes, the supply is simple, but we know nothing about its load .

          Thanks.
          OK, here's the full schematic Furman PUNCH-10 - Schematic.pdf

          Thanks

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          • #6
            Originally posted by StormLord11 View Post
            Good idea, I'll try this. Probably going to need to get another bench power supply though because I don't think I can get + and - 15V out of one channel, right?
            You will need two ( or a dual output supply). As Juan said, it may be possible to get an estimate looking at the schematic, thanks for that. It can get a bit time consuming and is prone to error.

            PS: Just took a look at the schematic. It looks like there are 10 x TL084, 1 x CD4013 and U12. The tyoe if U12 is not specified so can you take a look at the board and tells us what it is. Provisionally, the current it going to be really low. if we allow a typical 1.5mA / opamp that's 60mA. If we said 100mA max I think that would be pretty safe. This implies a transformer of at least 250mA due to ineffeciency of the rectifers. So, go see what you can find that fits and post the candidate's data.
            Last edited by nickb; 10-02-2019, 09:20 AM.
            Experience is something you get, just after you really needed it.

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            • #7
              This is an old thread, but I finally got around to working on this project again (have a little more free time right now..) So I ended up getting this thing to power on by applying positive and negative DC voltage to the inputs of both the positive and negative voltage regulators. Low and behold, this thing actually works fine. Next step, going to apply AC voltage with a variac to the pins that would normally go from the missing transformer to the power supply board. I'll just slowly increase the voltage up until about 20V or so, which should power the 15V regulators. Then it's just a matter of getting the right transformer that fits. I'll post back soon.

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              • #8
                Got this thing figured out.. it was actually much simpler than I thought. If you look at the schematic, you have a transformer with a center tapped secondary, leading into a full wave rectifier, which then leads into +15V LM7815CT and -15V LM7915CT voltage regulators. Both of these voltage regulators have input voltage ranges of around 17-30V. So it was just a matter of getting a center tapped transformer with a secondary voltage of around 20-30V (accounting for the voltage drop across the diodes of the rectifier). So I got a 24V transformer installed and got this thing to power on fine, thanks everyone.

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