What if my power source has too many amps?

I have purchased a stepper motor and a solenoid. For both of them I have also purchased controllers (a chopper driver for the stepper motor and some other chip for the solenoid). Both motor and solenoid are rated at 24 volts.

I also have lying around a transformer from an old door bell I think. On the front it says “24V 20VA”. I think that means 24 volts and 20 amps.

My question is this: Can I use this power source with my other stuff? Or will the large amperage burn them out? Or will the controllers regulate the power?

Thanks a lot!


Tim

VA means Volt*Ampere, which is Watt (ignoring power factor for now). So this transformer will give you 24V RMS (AC) and about 0.8A (AC as well).

If you are willing to accept advice, throw it into a box and forget about it for now. Get yourself a good regulated DC power supply. Find out how much current your application will need and do a parametric search at your favourite electronics shop. Some laptop power supplies will provide 24V and don't cost a fortune.

Consult the datasheets to see what your controllers need. Don't assume anything.

Not salvage prices, but low.

Too many amps? If you connect things wrong then it will burn more up. Other than that, not a problem.

GoForSmoke:
Not salvage prices, but low.
Power Supplies | All Electronics Corp.

Also note that mains AC voltages can seriously upset your heartbeat and will eventually kill you.

And you really don't want to find out what that feels like. Therefore I discourage using open-frame power supplies.

If your current requirements are moderate, a laptop power supply is the safest choice.

GoForSmoke:
Too many amps? If you connect things wrong then it will burn more up. Other than that, not a problem.

OK. I apologize for my raving ignorance, but I would really like to know something. Is this the way it works? If I have a component that is rated at 0.6 amps and I connect it to a 2 amp power supply, what will happen? Will the component just happily only draw 0.6 amps and work perfectly fine, with 1.4 amps left over for something else? So if I get a power supply that produces 10 amps, does that actually mean it produces up to a maximum of 10 amps depending on how much is drawn out of it?

Google / consult wikipedia for 'Ohm's Law'. It is quite simple and very useful.

The Amp-rating on power supplies states how much amperage it is capable of providing - if the attached load requires it. Normal power supplies don't force the load to 'take' x-amps. It's like a bank account, you can withdraw everything, but don't have to :wink:

If I have a component that is rated at 0.6 amps and I connect it to a 2 amp power supply, what will happen?

Lets put it this way, you have an AC outlet in the wall of your home, it's rated at 20 amp max before it will trip the circuit breaker. You can however plug in a night light that requires only 7 watts of power, or 60 ma of current. You can plug in a 7 amp vacuum cleaner and it too will work fine. The load determines how much current will flow, the supply just has a maximum value rating that it can supply if the load demands it.

Lefty

OK. I apologize for my raving ignorance, but I would really like to know something. Is this the way it works? If I have a component that is rated at 0.6 amps and I connect it to a 2 amp power supply, what will happen? Will the component just happily only draw 0.6 amps and work perfectly fine, with 1.4 amps left over for something else? So if I get a power supply that produces 10 amps, does that actually mean it produces up to a maximum of 10 amps depending on how much is drawn out of it?

Congratulations, you have figured it out correctly!

Don

If I have a component that is rated at 0.6 amps

There are two types of components, those designed to work at a fixed voltage and those designed to work at any voltage.

Normally we reserve the word rated for those components that are designed to work at any voltage, like a light bulb, resistor or diode.

Those designed to work at a fixed voltage don't have a rating they have a current draw. That current is defined at the working voltage, and as long as you only apply the working voltage that is what they will draw. They normally work only in a narrow range of voltages like logic chips. Most of these work at only 5V and have a fixed amount of current they draw. We do not say they are "rated".

madworm:
Also note that mains AC voltages can seriously upset your heartbeat and will eventually kill you.

And you really don't want to find out what that feels like. Therefore I discourage using open-frame power supplies.

If your current requirements are moderate, a laptop power supply is the safest choice.

Actually it is the 60 Hz that upsets the heart into fibrillation that is the big danger. From what I understand the 50 Hz system is far safer. Why we have 60 Hz? To run the clocks!

I'm more afraid of the big caps in those things. Even disconnected from power they can bite. Lucky for me I have my trusty steel-shaft with insulated handle screwdriver to short those caps before getting my mitts on them!

24V.......

I just bookmarked this PS. It costs a bit more but has power-connect tips and USB power and can run from house or car. $19.90:

  • Power: 100W
  • AC input: AC 110~240V
  • DC input: DC 12V
  • Output: 12V/15V/16V/18V/19V/20V/24V
  • USB output: DC 5V
  • Included USB port can supply power for any available devices with USB port (cellphone/camera/PDA/MP3/MP4/PSP etc.)
  • 8 connectors: 6.3 x 3mm, 6 x 1mm, 5.5 x 2.5mm, 5.5 x 2.1mm, 5.5 x 1.7mm, 4.8 x 1.7mm, 4 x 1.7mm, 3.5 x 1.35mm
  • Easy and safe to use
  • Package includes:
  • 1 x Universal power supply
  • 8 x Connectors
  • 1 x Power cable (2-round-pin plug / 140cm cable length)
  • 1 x Car charger (40cm cable length)

From the Allelectronics page I posted, at $14.75:

Elpac# MW6524F. Input: 100-240V 50/60Hz, 1.75A. Output: 24Vdc, 2.71A. Enclosed table-top switching supply, 130 x 77 x 34mm. Enclosure is white. Power cord may not match enclosure. 6' output cord with 5-pin male DIN plug. Includes detachable IEC power cord. CE, TUV, RoHs.

There is also a good selection of enclosed efficient switching power supplies that can easily drive Arduino and projects. 9V at 1A for example, only $10.50 though I'd rather have a 12V 1A which BTW I do, somewhere here. What I really like are the nice multi-voltage supplies.

Power from wall warts is about 50% to 70% (if that) efficient. From switching power supply is more like over 90% efficient. The switchers are worth the extra cost and weigh less too.

GoForSmoke:
Actually it is the 60 Hz that upsets the heart into fibrillation that is the big danger.

As they say, "It's the hertz that hurts." I once saw this guy, live, do this with a million volts: http://www.wondersofscience.org/sfs/MILLION.HTM And the video: Million Volt Man - Dean Ortner - YouTube