Author Topic: x VDC @ y A  (Read 3350 times)

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ABCD

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x VDC @ y A
« on: June 27, 2011, 02:36:33 am »
When looking at kits, I see some say something like 12VDC @ 15mA.  So if I have a power supply that outputs 12VDC but at 1A, then this is no good.  How would I reduce the current, since if I did, I'd also be reducing the voltage.

A kit built power supply I was looking at, for example, can output from +/- 1.35 to +/- 15 VDC @ 1A.  So in a circuit that I see as taking 12VDC @15mA, this supply would give too much current, right?  Or am I looking at this the wrong way?

ivan747

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Re: x VDC @ y A
« Reply #1 on: June 27, 2011, 02:42:38 am »
When looking at kits, I see some say something like 12VDC @ 15mA.  So if I have a power supply that outputs 12VDC but at 1A, then this is no good.  How would I reduce the current, since if I did, I'd also be reducing the voltage.

A kit built power supply I was looking at, for example, can output from +/- 1.35 to +/- 15 VDC @ 1A.  So in a circuit that I see as taking 12VDC @15mA, this supply would give too much current, right?  Or am I looking at this the wrong way?

No. Your power supply will just keep the voltage. The current flowing through the circuit will be determined by the kit. Go and Google for Ohm's law, you will understand the relationship between voltage, current and the load (resistance).

w2aew

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Re: x VDC @ y A
« Reply #2 on: June 27, 2011, 02:47:43 am »
When looking at the spec for a kit, it tells you the REQUIRED supply voltage, and the current that IT will DRAW from that supply voltage.

When looking at a spec for a power supply, it will tell you what voltage it can produce, and the MAXIMUM current it can provide at that voltage.

The circuit will draw what it needs.  So, if your circuit only needs 15mA and your supply is capable of 1A - you're golden.  If your kit needs 500mA and your supply can only do 200mA, then you have problem (not enough capacity in your supply).
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Wartex

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Re: x VDC @ y A
« Reply #3 on: June 27, 2011, 03:44:28 am »
When looking at kits, I see some say something like 12VDC @ 15mA.  So if I have a power supply that outputs 12VDC but at 1A, then this is no good.  How would I reduce the current, since if I did, I'd also be reducing the voltage.

A kit built power supply I was looking at, for example, can output from +/- 1.35 to +/- 15 VDC @ 1A.  So in a circuit that I see as taking 12VDC @15mA, this supply would give too much current, right?  Or am I looking at this the wrong way?

Current is a consequence of voltage, not other way around. Power supply provides 12v DC and can provide UP TO 1A, but the actual current (15 mA) will depend on the resistance of your device, which in this case is ~800 Ohms (12/0.015 = 800).

Mechatrommer

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Re: x VDC @ y A
« Reply #4 on: June 27, 2011, 04:38:18 am »
So if I have a power supply that outputs 12VDC but at 1A, then this is no good.
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ABCD

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Re: x VDC @ y A
« Reply #5 on: June 28, 2011, 12:09:36 am »
When looking at the spec for a kit, it tells you the REQUIRED supply voltage, and the current that IT will DRAW from that supply voltage.

When looking at a spec for a power supply, it will tell you what voltage it can produce, and the MAXIMUM current it can provide at that voltage.

The circuit will draw what it needs.  So, if your circuit only needs 15mA and your supply is capable of 1A - you're golden.  If your kit needs 500mA and your supply can only do 200mA, then you have problem (not enough capacity in your supply).

That's what I thought, that the circuit is using what it needs, so I guess I was reading it the wrong way -- the way you put it made it crystal clear.  Thanks.

wardenclyffe

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Re: x VDC @ y A
« Reply #6 on: June 29, 2011, 03:49:32 pm »
If you use a supply capable of 1A on a kit that only requires 15mA it will work, but you may have some voltage regulation issues because of the light loads. Also, the supply will likely be operating at its lowest efficiency. These may not be important for the kit to function....just something to think about.

Smf