Likely stupidly simple questions about power

[feetsdr]

Care to field these simple questions?

I have a gadget that uses 2 AAA batteries. I want to run it on AC. I have loads of 12v power supplies from external hard drives, old routers, etc.

1) How would you recommend I get 3V out of those 12v power supplies?
2) Or that would cost as much / more than just buying a 3v power supply? From Amazon or is there somewhere else you like? Like this one?

https://www.amazon.com/GMJYC-120-240V-5-5x2-5mm-Decorations-Fountains/dp/B09W9B8RLP

3) And I need a floor pedal / (on-off). again, you guys like amazon? Or is there a place that's cost effective for electronic components / devices?

4) maybe appropriate to ask here? A different project has an electric motor (think sewing machine motor) with a thin shaft. I need to attach a longer rod to it (to effectively extend the length of the motor shaft). Anyone know where you'd get a coupling or similar to connect the motor shaft to the extension. haven't measured both yet, but likely something like 1/8" diameter for each. The extension is only a couple inches.

I am envisioning a sleeve with a hex set screw at each end? I have no idea where to get something like that.

THANKS!!

 

[rjenkinsgb]

For the coupling, just search "3mm shaft coupling" on ebay etc.
Examples - rigid:

Golden 3mm-3mm Brass Shaft Coupling Coupler Motor Transmission Connector | eBay

Size: 3mm. Material: brass. Great accessories for RC Model motor, such as airplane boat model.

www.ebay.co.uk

Flexible, for eg. if the extension has its own bearings:

Flexible Shaft Coupling Coupler Stepper Motor CNC 3D Printer 3 4 5 6 7 8 10mm + | eBay

These couplers join stepper motors to leadscrews for any DIY CNC project. Flexible Shaft Motor Coupling Coupler for CNC / 3D Printer. Flexible Shaft Motor Coupling Coupler. Each coupler orderincludes the necessary grub screws.

www.ebay.co.uk

Imperial sizes are less common, but you should be able to drill a 3mm to 1/8" if needed.

For the 3V unit, what current does it need?

There are numerous versions of buck converter modules available, that could be used - but be aware the power or current ratings in adverts like these are often rather exaggerated, eg. possibly the current they can stand for a fraction of a second. Always use one that is advertised ate 2 - 3 times higher than you actually need!

Also, if a motor is involved, the initial current can be far higher than the measured running current, so you need a power supply that can take at least five times the normal current, for a short time.
This type is OK for very low currents, but I've had one fail at well under 1A...

5pcs/set Mini 3A DC Adjustable Converter Step Down Power Supply Replace LM2596! | eBay

Output Current: lowering the value of 3A, long 1.8A. Mini-360 (ultra small size DC-DC synchronous rectifier buck module). Module Properties: non-isolated buck. Load regulation: ± 0.5%. Output ripple: 30mV (no-load).

www.ebay.co.uk

This style is fine for possibly a couple of amps:

LM2596 Step Down Module Adjustable Power Supply PSU Buck Converter 3V-35V -UK | eBay

(LM2596 DC-DC Buck module. Power (3-40V), power indicator light, the module is working properly. Can't booster). Output Current :3A( Max). Output ripple: <30mV.

www.ebay.co.uk

 

[Pommie]

If it's using AAA batteries then the current shouldn't be high and the buck converters linked above should suffice. Do you have a meter to set the output voltage?

Mike.

 

[feetsdr]

Thanks sooo much guys! Great links and info!

 

[DrDoggy2]

LOL, and ensure the volts are all the way down before you hook it up!