Power supply for stop action magnets

[viscount_hw]

Hi all,

I'm in the process of restoring an old console for a Hauptwerk project which will have 60 Kimber-Allen drawstops. The original power supply is old and will need replacing. It's very hard to find a way of estimating the power required! There is a 3 Amp breaker on the existing supply which seems to be of a slow-blow type, powering 50 stops on the current organ. This seems like a very small current for so many stops. A few of the stops have large capacitors strapped to them, presumably to reduce the peak current requirement? A rough guess of 0.5amp per stop yields a very large supply, so I suspect the answer is somewhere between the 3A breaker and the continuous current of all the magnets. I'd be very grateful for some pointers.

Thanks!

[AllenAnalog]

See Michael's answer below. Just be sure to get a 13.8 Volt unit - Astron also makes 28 Volt supplies.

[Pipeorganbuilder]

I would go on *bay and look for a Astron power supply with a rating of 45 amps or more. This is what I use for most power supplies now days.

Michael

[viscount_hw]

Larry - good point! The 3A breaker is on the 230VAC input. Duh! There is a 15A 'T3' (ie. slow blow) fuse on the output (which is at 17.5V). It still sounds a bit small, but they are only small 15mm stroke stops so between that and the capacitors perhaps that's all it needs. Also they're pulsed, which must help. I've managed to pop the 3A breaker on the input a few times, but quite how that's possible without popping the 15A DC fuse I don't know... I assume it's got a bit trip-happy with age.

Michael - I'll look at Astron. If I don't need quite such a big current do you think I could get away with a less 'full on' supply? eg. for each jamb of 30 stops:

https://www.meanwell.com/webapp/prod...prod=UHP-200(R)

yielding about 440mA for each stop @15V.

Thanks both!

[Pipeorganbuilder]

Thanks Larry for mentioning the voltage of the two units.
The Astron 30 amp. power supply should work just fine. You will not be switching every stop action magnet at the same time. These power supplies have large filter capacitors inside that will take the momentary current draw.

Michael

[John Drabik]

To summarize what others have said, and add a bit:

- The 3A fuse is on the 230V side; the output side is 17V (transformer ratio of about 13:1). As a rule of thumb, the current scales the opposite way, by the same ratio (i.e., it could *theoretically* supply up to 13*3=39A on the output side, give or take. The 17V is unregulated on most supplies of this type so consider that too.)
- It is unlikely that most (and rarely all) stops switch together, so it's unlikely you'll experience a full current load (you might come close with a Sforzando switching to All Off)
- The capacitors can supply peak currents when needed, if they are still in good condition. They age. Replace them after 15-20 years.
- If the capacitors have gone south, you could trip a breaker (if only certain caps are shot) or the main fuse (if most/all are gone). This is because the power supply now has to supply nearly all the current for the drawknobs. If any of the capacitors have shorted (in the pulse section) the circuits for them will continuously draw excess current, adding to the load. You may be able to detect this with in the form of an overheating power resistor in those circuits.
- You can trip a breaker when you consider the switching load plus the capacitor re-charging required after a drawknob change. Unlikely, but if it does happen, it will most likely be on the primary (3A / 230V) side since each of the other circuits has at least some surge capacity already