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you'll juice out your battery almost instanly
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Posted by Siegfried (more from Siegfried) on Thu, 29 Nov 2012 13:43:39 Share Post by Email
In Reply to: Using power inverter with my 99 9-3, Skip, Thu, 29 Nov 2012 12:56:37
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Skip,
When the engine is idling the alternator is able to give you 20 amps at its best (20A x 14.4V ~=300W), probably less. You can take all those watts off your car, but they'll be coming from your battery which you'll have to juice back up later. Better say: very soon. Modern batteries with 60-66 Ah rating will be giving you 25A only within 1-2 hours even when in good condition and fully charged. Batt capacity depends on the discharge current: with 0.1A of discharge current you will measure ~200Ah, with 6A discharge - 60Ah, with 25A - 50Ah. And finally with something like 200A (which turns to 2.5kW at batt's 12V of voltage) it gonna be only 5Ah.

And fwiw, you've got to refer to the specs for particular alternator, but general rule of thumb is that they (modern ones) reach their amperage rating only when the engine is revving at 5000-6000 rpm, 75% rating is available starting around 3000 rpm.

So if you aren't planning using it for 5-15 minutes of work, then the best idea is to use some portable (CNG-, diesel- or gas-powered) generator.

Good luck,
Zig

posted by 188.134.4...

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