power supply for organ

[duncan webster 1Participant @duncanwebster1]

[duncan webster 1Participant @duncanwebster1]

The topsy type organ I've built needs 12v @ 1.6A to drive the pallet valves and decoder and 24v @ 1.5A to drive the fan. I'm currently running it on a 0-12-24 transformer (nominal). Smoothing the 12V gave too high a voltage for the decoder, so that has a 12v regulator (7812), and the 24V to the fan is controlled by a variable mark/space ratio controller. The transformer is all a bit heavy.

I've searched the interweb for a 0-12-24 switch mode supply to no avail. I'm now proposing to buy a 12v @ 5A switch mode **LINK**

and feed the fan controller via a second 12-24 switch mode booster. I can then get rid of the 12v controller. Can anyone think of a reason this won't work? Do I need a capacitor between the 2 switch modes to provide some reserve?

[Martin KyteParticipant @martinkyte99762]

Can you not get 2off 12V floating output supplies and stack the outputs.?

regards Martin

[Keith Rogers 2Participant @keithrogers2]

Hi Duncan,

Why not get a 24v Power supply and drop to 12v with your regulator.

(you'd probably need a heatsink)

Keith

[Les Jones 1Participant @lesjones1]

I would suggest getting a 24 volts switch mode regulator of at least 3 amps rating and a switch mode regulator module such at this to regulate down to 12 volts. Using the switching regulator to drop the 24 volts down to 12 volts avoids having to disipate about 20 watts in a linear regulator. You can get these modules cheaper direct from China but it takes about 4 weeks.

Les.

[BazyleParticipant @bazyle]

Just no sense in using one psu. 12v powerplugs are dead common as just about every techie toy uses 12v so volume = cheap, say £5. 24v is a lot less common but available for under £15. This also keeps fan motor noise off the electronics.

Alternatively have a look at 3D printer websites a they want electronics at low voltage and a higher level for the steppers.

[Neil WyattModerator @neilwyatt]

+1 for Les' solution.

[duncan webster 1Participant @duncanwebster1]

Martin, I'd need 12v at ~4A plus 12v @ ~2 A, so certainly no cheaper than my solution

Keith, I'm trying not to have a linear regulator pumping out about 18W. The one I've got should by rights have died by now, it is working above it's nominal max current

Les, your solution seems to be very similar to mine except if I start with 12v I can run off a battery if I need to, plus I've already got the 12 to 24 left over from a previous project, I just wanted to know if there was an issue running one inverter off another

Bazyle, I like that idea, I'm looking into 24v supplies, not as rare as I had imagined, and about £11.50

Thanks for all your replies

[Les Jones 1Participant @lesjones1]

Hi Duncan,
I have to confess that I did not read you first post fully. I see no problem with what you propose. The only think I would say is that you will be running the 5 amp (60 W) power supply above it's rating. If we assume 80% efficiency in the boost converter then it will take 3/0.8 = 3.75 amps at 12 volts and the rest of your 12 volt load is 1.6 amps so 1.6 + 3.75 = 5,35 amps. I notice that the advert offers an 80 watt unit (6.66 amps.) so that would be a better choice. (And 50p cheaper)

Les.

[duncan webster 1Participant @duncanwebster1]

Les

I'm glad I read your post carefully. Prompted me to actually measure the input current to my boost converter. 4.8A with the motor on full chat drawing 2A, which I suppose isn't that bad. I'd forgotten that step up draws a lot more than the output, if it didn't we'd be into perpetual motion. If I'd gone down my planned route I would have released the magic smoke. I'm adopting your approach with one of these **LINK**

and the step down thing you suggested.

Thanks again

[Martin KyteParticipant @martinkyte99762]

Posted by duncan webster on 11/08/2017 17:40:45:

Martin, I'd need 12v at ~4A plus 12v @ ~2 A, so certainly no cheaper than my solution

Probably. I was really pointing out that you can 'stack' floating output switch mode supplies like batteries to obtain different supply rails.

regrads Martin

[Nick_GParticipant @nick_g]

.

Jasons Tidman organ steam engine was designed for such originally.

Nick

[Martin NewboldParticipant @martinnewbold]

You said you cant locate a switch mode supply have you tried RS Electronics

[duncan webster 1Participant @duncanwebster1]

I've implemented Les's solution, but laptop has now died, so I'm fighting to get my new one to do what I want. They don't make it easy, but I have several willing friends who understand these things

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