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DevMike

AAE - Amps Are Everything

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I've fielded multiple trouble tickets and calls this past week about loads and misconceptions about draws.  In fact, the title of this post suffers from the same misconception.  Let's have a lesson on how electricity works.

 

Electricity, just like your local river, is described as having (or being) 'Current', and current really has *2* distinct parts.  Let's stay with the river for a moment.  

 

The amount of water going past a single point is controlled by 2 things:  The volume of water that can be handled somewhere downstream (how deep is the river?), as well as the speed of the flow (how fast is the river?).  For example, a very shallow river running very fast can give a volume of water that may equal a very deep river running very very slowly.  If we want to, we can call these things 'Pressure' (the measure of how fast it is running), and 'Volume' (the amount of water discharged per unit of time).

 

Electricity is the same thing, except we use the words 'Voltage' to refer to the pressure and 'Amperage' to talk about the quantity of electrons being consumed.  If you notice, you can NOT separate the 2 when talking about CURRENT.  You MUST know both the pressure, and the volume that can be handled.  

 

In 1827 this relationship was described by Georg Ohm, and is called 'Ohm's Law' to this day.  I=V/R.   We could at this point have a huge discussion on Ohm's law.  In fact entire college classes are dedicated just to that single simple equation.  

 

While not 100% technically correct, I find it is easy to think about electricity this way:  Amperage is the VOLUME of ELECTRONS I can get past a single spot in a circuit.  Voltage is a measure of the PRESSURE behind those electrons.  Keep this in mind.

 

Ok, so that is all well and good but what we really need to know is how much work we are doing.  James Watt gave us an easy way to figure that out, and it's part of his work with (believe it or not) steam engines.  In the electrical world, which is what we are most interested in and will be talking about, Watt's law is W=V*A.  

 

A watt is a unit of work, and you will notice that it is deeply connected to both the pressure (voltage) as well as the volume (amperage).  To do 12 Watts of work, I can use 12 volts at 1 amp, (12*1=12), 6 volts at 2 amps (6*2=12), 1 volt at 12 amps (1*12), or any of other of the infinite solutions to the problem.  Yes, producing light is considered work (in the scientific sense).

 

I know you are familiar with the Watt.  We use wattage all the time to describe how much power is being consumed.  A 60 Watt Light bulb consumes... Wait for it...  60 Watts.  Your hair drier consumes 1500 Watts.  An LED light bulb may consume 9 Watts.  We are so used to talking about Watts that we forget that there are 2 components to it.  

 

What about our poor friend VOLTAGE?  See, I purposefully mislead you.  A 60 Watt bulb will ALWAYS produce 60 Watts of WORK.  A 60 Watt bulb DRAWS 1/2 amp at 120V, but what if we reduce the voltage to 12 volts?  That 60 Watt bulb now consumes 5 WHOLE Amps.  Think about it this way:  At 120 V, 4 60W bulbs will consume 2A.  We can safely run that on Christmas Light Wire (22/24 AWG).  2A @ 120V is a very fast, but shallow river.  

 

Now make those 4 bulbs run on 12V.  Holy crow!  Those 2A @ 120V are 20A @ 12V!  TWENTY AMPS.  Go ahead and try to run 20A through a Christmas Light string and tell me what happens.  Just please do it somewhere away from flammable materials and wear thick rubber and fireproof gloves.  That wire will just about IMMEDIATELY melt the insulation  and glow RED HOT!  What you have there is a need for a slow but VERY DEEP river, but you've only given it a shallow river (small wire) to run through.

 

Which brings us back around to the reason I stated this post.  Some of you are not considering VOLTAGE when it comes to your loads.  Before the advent of low cost RGB low voltage lighting, we could simply talk about Watts or Amps because we knew that voltage was always going to be 120.  Today it  is a much different story.  Maybe you have a string of LEDs that consumes 10W.  6 of them consume 60W - and think "that's NOTHING!".  Well, you are wrong.  At 120V that is nothing, but at 12V that is 5 AMPS.  

 

...Or you come at it the other way.  For example, our CMB24 is rated at 4 Amps per channel.  "WOW! that's a ton." you say.  Well, not really.  It's 4A @ 12V.  Hook up those 6 of those 10W strings and the transistor goes kapow!  Just like a Triac on an AC controller since 60 is greater than 48.

 

...And as I said above, don't think that because you are dealing with low voltage, you can get away with using any scrap of wire you have laying around.  You can just as quickly burn down your house at 12V as you can at 120V.   if you don't believe me, pop the hood on your car and take a look at the wires running to the battery.  Your car runs on 12V.  The Battery is 12V, but look at the size of those wires!!!  They are going to be AT LEAST 4AWG, if not 2 or even into the aughts.  

 

So why do I say that Amperage is Everything, if actually everything is related?  Knowing the AMPERAGE of something forces you to know the VOLTAGE you are working with.  We are so used to talking Wattage at 120V, that can NOT talk about amperage without instinctively saying 'At what VOLTAGE'?    Get used to doing that now.  If you catch yourself saying 'N' Watts, stop and say 'X' AMPS at 'Y' Volts.

 

You can always find the missing parameter if you know the other 2.  Use the Formula W=V*A

 

What's that?  Forgot your high-school algebra?  ->

Know Voltage and Amperage?  W=V*A

Know Wattage and Voltage?  A=W/V

Know Amperage and Wattage?  V=W/A

 

Congratulations!  Your hobby requires both science and math! :)  Your 8'th grade physics teacher is proud of you!!! :D

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