> Date: 8/1/00 6:53:12 PM Central Daylight Time > From: cstann@home.com (CHRIS STANN) > > [Discussing the power requirements of an RV air conditioner] > > 30 amps max at startup. Much less when running. It would be like running > your high beams on with aux. lights. Yep, a 90 amp alternator would be > nice. The amps don't do you any good unless they're supplied at the necessary voltage. The A/C wants 30 amps at 120 volts, but the alternator's putting out 90 amps at only 12 volts. You can trade amps for volts by running the alternator output through some sort of power converter; what stays constant is the wattage, which is amps x volts. (You can only get more watts by getting a more powerful alternator.) So, the A/C wants 30 amps at 120 volts, which is 3600 watts. But the alternator puts out 90 amps at only 12 volts, which is just 1080 watts - less than a third of what the A/C needs. Looked at another way, we could take that 12 volt, 90 amp output from the alternator, and run it through a power converter that would convert it to 120 volts (that's 10 times the voltage) and 9 amps (one-tenth the amperage). Same result as before - less than a third of what the A/C needs. To run the A/C (and nothing else), you'd need a 300 amp alternator, which I suspect might be a bit taxing for the engine. These calculations assume a 100% efficient power converter; real-life power converters lose a bit of power during conversion. Also, the air conditioner runs on "AC" ("alternating current"), whereas the alternator (oddly, given its name) puts out "DC" ("direct current"), so the power converter you'd use would actually be an "inverter", which converts DC to AC (sort of) along with converting 12V to 120V. -Steven Sittser |
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