questionscan anyone tell me how to compare amps to volts?

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The short answer is - you can't compare amps to volts. It's like comparing gallons per minute of water flow rate to PSI in a pressurized water line. They measure different things.

This wiki article helps some but it's probably more technical than you want...
http://en.wikipedia.org/wiki/Volt

In an attempt to answer your question - a 12 amp vacuum would probably run (in America) on a standard 110 volt circuit. A 12 volt vacuum would suggest it runs on battery power, perhaps? If you're using power usage to compare vacuum sucking potential, it's probably not as important of a measurement as the design of the vacuum... but generally speaking, a vacuum that plugs in will be more powerful than a portable battery powered one.

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Oo boy... Here goes, though it will likely be several posts (1000 characters is not very much).

Electric current is the flow of electrons down a wire. The number of electrons per second going past a specific point is the current. This is measured in AMPeres. If I use the "standard" analogy of water flow, AMPs are like gallons per minute.

Voltage is basically how hard those electrons are being pushed down the wire. Think of it like water pressure.

With more water pressure (voltage), you get more gallons per minute (amps) going past a point if everything else remains the same.

Power, or the amount of work that can be done, by the water is therefore based on how much water there is and how much pressure that water has behind it. Same for electricity: power (wattage) is basically the voltage multiplied by the amerage (this ignores something called power factor but I'm not going there in this context and it doesn't matter that much for your purposes).

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As @liquidblue1 points out, it is meaningless to compare volts to amps, just as it is meaningless to compare miles per hour to seating capacity (when talking about cars).

As far as suction strengh goes, there are factors other than the voltage the vacuum is designed to use & the number of amps that it draws at that voltage. We can call these other factors the efficiency of the vacuum.

So, the voltage multiplied by the amps tells you about how much power the vacuum uses. Multiply this by the vague efficiency factor from above & you get suction power (why do I suddenly feel like I'm in a Dyson commercial?)

However, as a general rule, it is likely that a vacuum that plugs in will be at least as good and probably much better than the 12 volt one (which certainly runs on batteries).

As for sales people, I rarely expect them to know very much about how things work, though I have been pleasantly surprised on a few occasions.

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I agree with all of the above. the "water" analogy is very common way to describe the difference between volts and amps and watts. And the simplified basic equation is as stated watts=volts x amps. The only time that isn't good enough is for people that REALLY understand how even a standard copper cord puts some restiance on the electricty running through it. For your average joe all you need to remember is don't put a wet finger in an electrical outlet.

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In either event, the vacuums that advertise on the strength of their motors (10 Amps of power!! or 1200 watts strong!!) are using a bit of sleight of hand. This is only representing the amount of electricity that the motor uses. It may or may not relate to the strength of the suction that comes out of the machine. Note to the non geeks: since P=IE (power is current x volts, in the US (120 V), the two claims are the same.

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Wow. Thanks to all of you for your responses. For someone who still doesn't understand how electricity works (sorry to say), I am impressed at the knowledge you wooters have. I can't say I "get it" all, but I know now enough not to try to compare suction power by comparing amps to volts. Thanks! Susan