Power supply with more current?

[xGx]

Hello, I am working on a project that has several circuits, and I had intended to power them all using a MFOS + / - 12V Wall Wart Power Supply with the suggested 12 VAC 1000 mA Wall Wart. However, I realized that one circuit requires 3 or 4 amps. Is there a way I can adapt the Wall Wart Power Supply to provide more current, for example by using a different wall wart and regulators? Would I need to change any other components / values? I have looked around, but it seems like most beginner DIY bipolar power supply projects provide 1 - 2 amps. It would be great if I could use the existing Wall Wart PCB. Thank you so much for your help!

[PHOBoS]

Is it really just one single ciruit or a combination of ciruits ? 3~4 amps is quite a lot. For a standard linear regulator, which is used in the MFOS wall wart PSU,
it is advised to have an input voltage that is 3V higher than the output. That would be 9-12 Watts that's dissipated in heat, if a voltage regulator could handle
that current in the first place. There are some linear regulators that can handle more current but they can be harder to find for negative voltages.
It is also possible to add a power transistor for more current but you will still have a lot of energy loss in heat. If it's not a single circuit you could use several
regulators powered by the same unregulated DC voltage to spread the power consumption and heat. So, In theory if you can find suitable regulators you could
use the MFOS supply but you will need some BIG heatsinks (and more capacitors). Finding a wall wart for that kind of current might get difficult too.

A better option would probably be a switched supply which can usually handle a lot more current with less loss but that depends a bit on the circuit.

[xGx]

Thank you for the welcome and the reply, PHOBoS!

The project is combination of several circuis:

1. a piezo mixer / preamp requiring a bipolar +9 / -9V supply (schematic attached - note the original schematic had 5 channels, but I only need 4)
2. a SparkFun Red Board https://www.sparkfun.com/products/13975 requiring 7-15V;
3. a Big Easy Driver https://www.sparkfun.com/products/12859 requiring 8-35V driving this stepper motor https://www.sparkfun.com/products/13656

The Big Easy Driver documentation states the power supply "...should be a 6V to 30V, 3A (or more) power supply that is clean (low ripple)." http://www.schmalzhaus.com/BigEasyDriver/

Note SparkFun offers different requirements: "You can use any kind of power supply (desktop, wall adapter, battery power, etc.), but verify that whatever choice you go with is capable of providing up to 2A and falls in the range of 8V to 35V." https://learn.sparkfun.com/tutorials/big-easy-driver-hookup-guide

I was hoping to connect everything in parallel to one supply as in the attached block diagram (using the positive and ground of the biploar supply to power the Red Board and Big Easy Driver).

I have everything built and working; I am currently powering the Big Easy Driver with this supply https://www.amazon.com/gp/product/B073QTNF9F/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 the RedBoard is powered via the USB of my laptop, and the mixer is powered by my bench power supply. I now want to mount everything permanently in my project box so that I have a single cord and on/off switch.

Not to complicate things, but the mixer schematic calls for +/-9V, whereas I was considering using +/-12V. The AD820 can handle up to +/-15V, so I think that is OK? If not, the MFOS power supply could be configured as +/-9V supply.... I just didn't want to be at the bottom of the voltage requirements, particularly for the Big Easy Driver.

Is there any chance the Wall Wart Power supply or something similar could work? It sounds like I may be able to get away with 2 amps if I go with SparkFun's requirements. Does that simply things? Do you think a linear supply is still plausible? I haven't yet found a good resource that introduces slightly more complicated power supply management, so any guidance would be much appreciated.

Thank you for your help!

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[JovianPyx]

It looks like the current hog is the Big Easy Driver which wants 3 amperes.

In my opinion, the Big Easy Driver needs it's own PSU. It would be unwise to drive all three circuits from one supply. I would create a 3 ampere supply for the Big Easy Driver and use a separate supply for the other two. The mixer should need very little current. The Red Board also, I'd predict fairly low current. LM350T is a 3 ampere regulator which could be used for the Big Easy Driver. Note that your transformer for this needs to supply at least 3000 mA. You might not be able to find a wall-wart transformer that provides that much current. It's voltage should be about 12 volts AC for a 9 volt regulator. If the input DC voltage is more than 12, you will experience more heat coming from the regulator. I would also plan on a substantially sized heat sink for it.

The Big Easy Driver needs to dump large currents into the stepper motor coils and could push noise back into it's supply. Using a separate power supply for it will help quash noise that could easily come from it.

[PHOBoS]

[JovianPyx]

Oh and for the Big Easy Driver PSU, I would use on with a single secondary coil transformer feeding a full-wave rectifier. No sense throwing away half of the AC cycles.

[xGx]

Thank you JovianPyx and PHOBoS! Would it make sense to have the LM350T PSU power both the RedBoard and the Big Easy Driver since they need to be connected (Arduino code on the RedBoard controls the Big Easy Driver) and both only need a unipolar supply? And then a separate bipolar supply for the mixer? That would totally isolate the audio circuit from the rest.

I will research possible circuits using the LM350T, but what I'm not quite sure of is how to implement two power supplies but still have a single cord and on / off switch for everything.

Is the attached sketch at all close? Mains power feeding two transformers in parallel.... one for a unipolar PSU and one for a bipolar PSU? The unipolar would maybe use the LM350T, and the bipolar perhaps the LM317 and LM337?

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[JovianPyx]

That depends on how close to the 3 amperes the Big Easy Driver goes. If there is enough current headroom, the Red Board could work. If not, it could operate erratically.

I don't know how much current the Red Board needs and I don't know how much headroom the Big Easy Driver allows with a 3 amp supply.

[PHOBoS]

[xGx]

[JovianPyx]

Hmmm. My understanding of SMPS is that an oscillator is used to generate an input AC voltage to a transformer. The frequency is higher than 50Hz or 60 Hz to keep the size and weight of the transformer lower (50 kHz to 1 MHz). Note that the higher the switching frequency, the easier it is to filter out the switching noise. The transformer is fed a rather low voltage of AC from a DC source and a transistor "interrupter". The voltage can then be increased as high as 300 volts by the transformer. The output voltage is controlled by using phase control of the AC voltage fed to the transformer. The last stage is to use another transformer to lower the voltage to something useful. This is generally the design used in PC power supplies, but there can be many ways to design SMPS, I described only one.

Personally, I don't like to play around with voltages that high. I would buy a commercial SMPS rather than try to build one. I would attempt it only if the specs of the design you're trying to build do not include voltages that high. Please be careful, this could be a dangerous thing while trying to build and troubleshoot. I would seriously suggest purchasing this piece of gear from a commercial source.

[PHOBoS]

Yeah I agree with Scott, I wouldn't try to build the SMPS myself, unless you really really REALLY want to.
Could just use the one you already have (unless you need it for something else) just keep in mind that if you
would build it in a case it needs some ventilation.

An AC wallwart is just a transformer, with a (thermal)fuse if it is a proper one. So you can just use a transformer
for that, just make sure everything is properly insulated. That's one of the main advantages of using a wallwart,
you don't have to deal with the mains part and it's already in an enclosure.

If you have enough space there is an easy solution. Use a socket strip and plug in a wallwart and a SMPS, wire that
to a switch. You could even use one of those mains inlets with a build in fuse and switch, something like this.

[xGx]

Thank you both again! I agree that building a SMPS is not a good idea. But I think a see a Plan taking shape, based on your advice. It involves using the SMPS I am currently using.

1. Build the MFOS Wall Wart Power Supply

2. Buy one of these or similar: https://www.amazon.com/dp/B01C7OE868/?coliid=I195ASGHQ2L9FM&colid=1F32SLWJVP2SL&psc=1&ref_=lv_ov_lig_dp_it

3. Buy one of these or similar: https://www.amazon.com/dp/B078N95379/?coliid=I17W0LLVXHB1YE&colid=1F32SLWJVP2SL&psc=1&ref_=lv_ov_lig_dp_it

4. Cut the single "prong head" off the "cable leader" in step 2. Separate the wires.

5. Mount the switch from step 3 to my project case.

6. Solder the exposed wires from where the prong head was to the switch, so the two sockets are inside my case.

7. Mount the MFOS WWPS and the store-bought SMPS that I am currently using into my project case, ensuring adequate ventilation.

8. Plug the MFOS WWPS and the SMPS into the "cable leader" receptacles.

9. Use one of these to connect between the switch socket and the wall: https://www.amazon.com/dp/B00FBA1UHG/?coliid=I32UQ4G42YP3S1&colid=1F32SLWJVP2SL&psc=1&ref_=lv_ov_lig_dp_it

I am a bit nervous about steps 4 and 6, but is this the general idea?

[blue hell]

Genral idea will work.

add step 10 (or a little earlier better :-) ):

re 4. and 6. and so, use shrink wrap tubing over the solder connections of the mains wires, and make it so that the mains wires can't move anywhere even when a single failure occurs (like a not-so-good solder connection comming loose, or the device falling down from some height, stuff like that) - tie wraps may work well for that.

add step 11:

In the hand drawn schematic above, on the secondary sides of the supplies: connect '-' of PSU1 to 'GND' of PSU2 close to the PSU's (or otherwise they'll either float with regard to each other or there will be a ground connection anyway trough other connection not drawn but in a less defined way).

[PHOBoS]

step 6: I'd use (insulated) faston/crimp connectors instead of soldering which is what those switches are designed for. Soldering directly to the
switch requires quite a bit of heat which could potentially damage it (depends a bit on the quality). You could also solder to those connectors
instead of crimping on the wires, but it can be a bit tricky.

step 8: not exactly sure how you are planning to do that. Those aren't mains sockets. I mean voltage wise yes but you can't plug something
like a wallwart in them. There might be cables for that purpose available though.

and yes, make sure everything is properly secured.

[xGx]

Hey PHOBoS,

Maybe I misunderstood... I thought step 8 was essentially the crux of your suggestion.

Rather than have two power cords dangling off the back of my project, mount a mini split extension cord inside the project box. Wire one end to a switch, and plug both the MFOS wall wart bipolar power supply and the store-bought SMPS in to the female ends of the split extension cord (inside the box).

I have attached a drawing, which I hope makes sense.

If this isn't what you meant please let me know. If it is, then I have an additional idea I'll run by you.

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[PHOBoS]

It's not that the idea is bad but I highly doubt you will be able to find a wallwart with a 'IEC-320' connector.
I think what you'd need is a 'nema 5-15' connector which looks a bit similar but is something else.
There are probably splitter cables for those, let's see,..
this should work https://www.amazon.com/Pro-Techgroup-Premium-14AWG-Outlet-Splitter/dp/B002MGT72C
at least if that is indeed the type of mains connector you use.

nice drawing btw

[xGx]

Ah yes, thank you.... I actually hadn't noticed that the link I sent wasn't a normal power cord. This all makes sense now.

However.... I did want to see if this simplification would work. I have attached another drawing.

This plan would use the MFOS Adj. LM317/LM337 power supply: http://musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=POWERSUPPLY2009/POWERSUPPLY2009.php&VPW=2358&VPH=1053

Here are the steps:

1. Build the MFOS Adj. LM317/LM337 power supply.
2. Cut the plug off the store-bought SMPS.
3. Solder zip cord to the primary of the MFOS supply.
4. Solder the positive and ground of the SMPS supply and the MFOS supply together.
5. Connect the junctions of the MFOS and SMPS to zip cord. Tape and shrink tube everything.
6. Connect the zip cord to switch using faston / crimp connectors. Tape and shrink tube.

This is a bit more challenging, but it is essentially the same as the previous plan but with fewer parts, correct? Is this closer to how things are usually done when one project has multiple power requirements?

Thanks for your help!

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[PHOBoS]

LM317/LM337 supply with an actual center-tapped transformer is an improvement over the standard wallwart supply
but does require you to wire up a transformer. A toroidal type might be the safest to use and easy to mount with the
correct hardware.

[mph]

Hello
If you need a 5Amp PSU why don't you use the same regulator for each rail?
A simple pair of LM338, link them as you would do with 2x9V batteries to achieve symmetrical output.
V+
0 linked to the second V+
second 0 (which became V-)

I think it's better to use the same regulator on each rail because they will behave the same way under load.

[xGx]

[PHOBoS]

[xGx]

[quote="PHOBoS"]

[PHOBoS]

ah I see, great. I was actually expecting the switch to be 'pre-wired' just like the fuse is, but this makes it more versatile.
Yes, those instructions are correct.