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How test chest magnets with no console??

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  • How test chest magnets with no console??

    I’m assisting in restoring an 1875 Henry Erben organ, electrified c. 1923. (I’ll post an update later.) Blower, 3-phase motor starter, reservoirs and DC rectifier all are in great shape, because organ’s restoration was on-going until pastor in 1990s decided they no longer could afford it, so he bought a cheap electronic and sold the 3-manual console. (Parish was about to close, but now is run by a ‘traditionalist’ Catholic religious order, using ancient Latin Mass exclusively, etc., so membership has quadrupled over past 12 months--despite COVID!)
    So now we are ready to test the chest magnets using a wire with alligator clips, with rectifier turned on, but no console.
    ***What 2 wires do I need to connect to energize each magnet?***
    I know I first have to ID polarity of 12v DC coming from rectifier to spreader board. Then what??

    I plan to start with the Swell, since the chest-to-spreader board wiring was replaced with modern color-coded telecommunications wire shortly before the organ was shut down. (See top row of spreader board photo. Wires to Swell go off to the left, red wires that went to console go off to the right. When we finally locate an inexpensive, used 3-manual console, I plan to abandon the red spreader board-to-console wires and replace them with color-coded tele wire: less frustrating than trying to ID each one of those red wires!) Thanks in advance for your help!

  • #2
    Because you have so many cut wires, I would not energize the rectifier, and turning on the blower will probably cause a bellows to activate an air switch which would energize the rectifier. If you want to test the magnets for function, all you will need is a small DC wall-wort type power supply or a battery. the current draw of a 90 ohm magnet will be about .13 amps, (12 volts / 90 ohms = .13 amp ), not very much at all. clip one end of the supply to a ground wire wherever it is still connected to your spreader board and then try each magnet individually with the probe end of your power supply. DC magnets can push or pull. You will want them to PULL the armature (small leather or paper covered steel disc ), up. Change the direction of the supply wires if you find that you are not pulling the armature up. Wires coming from the magnets may be coated with shellac as an insulator, touching coated wires will not complete a circuit. You can probably do all your work at the spreader board. To remove insulation from the phone cable , believe it or not. I pinch it between my finger nails and pull. Any nick from a stripper may cause a break later.
    Here is a nice picture of some magnets. https://www.mmdhigest.com/Tech/mValves.html
    Regards Pat


    • #3
      I agree that testing should be done without turning on the power supply or blower. If you just wish to check for continuity, this can be done by connecting an ohmmeter between the return line from the chests and the pin on the spreader board. The reading should be around 90 ohms either way. BTW, a typical primary chest magnet is not polarized and will work equally well wired either way. After all, it is just a U shaped electromagnet attracting a small steel disc which doesn't care which end of the magnet is North or South.
      Larger chest magnets, e.g. direct electric, may be polarized for two different reasons:
      1. They may be magnetically polarized if the manufacturer has glued a small magnet on the armature to assist the magnetic attraction. Such magnets will work promptly when wired one way but will be sluggish, or fail to operate at all, when the electrical polarity is wrong.
      2. If the the magnets have a spark suppressing diode wired across them, then they must be connected to the correct electrical polarity or the diodes will blow.
      Neither 1. nor 2. is likely to apply to a 1923 electrification.
      If you wish to test the magnets for operation, somebody inside the organ will have to listen for, or visually check for operation of the small disk inside the electromagnet. Not easy to do!
      For testing purposes, I usually use a test wire connected in series to a 10 ohm. wire wound resistor. At 15 volts, the test current can then never exceed 1.5 amperes even under a direct short, while 10 ohms is not enough to impede the operation of a 90 ohm chest magnet. Especially when using the main organ rectifier for testing, the short circuit current can easily exceed 50 amperes which puts you in welding territory and wires that will heat red hot instantly.
      BTW, you will probably want to replace the existing rectifier with a modern switching power supply of the type typically used to charge batteries on motor-homes or boats. They are available locally and relatively inexpensive. The power supplies offered by organ supply houses are usually just rebranded versions of these same supplies.


      • #4
        Thanks for catching the error of the U shaped magnet statement, wasn't thinking. Simple magnetic circuit.


        • Coenraads
          Coenraads commented
          Editing a comment
          Like science, the Forum is peer reviewed and self correcting: one of the features I appreciate most whenever I post something on the Forum.

      • #5
        BTW the outlet controlled by air switch into which rectifier is plugged was disconnected when organ was shut down 25-30 years ago, so the only way to turn it on is with a heavy-duty extension cord. I was concerned about shorts, so thanks for the recommendation to use a “wall wort” Instead of rectifier. I have a number of those from various old DC items that were discarded when no longer functional, but I kept the power supplies. I have a 12v one from an old alarm system which is no longer in use, but the wall wort still works. ***So just to clarify, I connect the negative of the wall wort to the ground on the spreader board, and the positive to the wire going to the chest magnet: is that correct?***
        Also if you look at the photo of our spreader board, you’ll notice that there are no pins: just a slot into which you slip the 2 wires to be connected then twist them together (= 1920s technology; the last organ tech to work on the organ used a low-voltage ‘wire glue’ to secure the connections).
        Also re rectifier: my understanding is that this ‘evens out’ the voltage in response to varying demand. Do I have that correct? Does a “switching power supply of the type typically used to charge batteries on motor-homes or boats” do the same thing? Is that what organ builders are using today? (The chassis of the 1923 Westinghouse blower motor, rebuilt in 1980s, still has the no-longer-wired DC generator attached that was used to drive the chest magnets before the rectifier was installed c. 1990.) Thanks for your help!


        • #6
          To answer your *** Question ***, Yes!
          But not all wall warts are equal. If it is older or rather hefty for the current it supplies, it could very well be a linear supply consisting of nothing but a transformer and some diodes. Nothing wrong with that, but it is unlikely to have circuity that would detect a short circuit and shut itself down. You'll know it's not happy when the case begins to melt.
          More modern wall warts are likely to be of the switching type that packs a lot of current capability into a compact package. They often do have protective circuitry. But I would still recommend that 10 ohm resistor in series. Then you can probe to your heart's content and nothing bad can happen.

          If you look at the old, linear rectifier, it will likely have a massive transformer with a lot of expensive copper wire in it feeding some rectifiers. It is likely this supply is not regulated meaning the voltage drops as more current is drawn. An older, electromagnetic switching system won't care, but a newer solid state system will be unhappy with such a power supply.
          Power supply manufacturers have discovered that they can dispense with the cost and weight of a traditional transformer, by throwing in a pile of electronics that operate at higher voltages and higher frequencies (hence switching) meaning that a small, inexpensive toroidal transformer will do.
          Unless you know what you are doing, do not attempt to repair a switching power supply. First of all, the voltages used inside are potentially lethal and even if the supply is turned off, the capacitors inside can still retain a wicked punch. Secondly, if you take one apart, you'll see that it is clearly built in such a way that it cannot be repaired even if you could troubleshoot the complex circuitry. I haven't a clue.

          The local cathedral has a large four manual tracker organ but the stop action is all electrical. Each of the divisions has a 50 amp switching power supply to run the massive slider solenoids. These were provided by a high end organ supplier (along with the combination action) and yet two of them failed in recent years. I replaced them with Go Power! GPC-55-MAX 55-Amp 4-Stage Converter/Battery Chargers fromAmazon and they work just fine.

          I was in the middle of doing a conversion from electro-pneumatic to solid state on a large four manual Casavant. I've built the circuitry but installing it has been put on hold due to Covid. Answering questions helps pass the time. You talk about acquiring a 3-manual console but make sure you know what you are getting into with regards to the switching system you may wish to use. I'd be happy to share what I've learned over the years installing systems from various manufacturers.