On Nov 9, 5:59*pm, wrote:
On Fri, 9 Nov 2012 06:38:47 -0600, "HeyBub"
wrote:









harry wrote:
On Nov 9, 2:37 am, "HeyBub" wrote:
From a blog post:

---

Folks considering inverters should first check their automobile s
alternator capacity to figure out how much they can power long-term
from an inverter without discharging the battery.

Making rough calculations, your Mazda RX-8 probably came stock with
a 100 Amp alternator (at 13.8V) = ~1400 Watts, so anything much more
than that is overkill (not to include peak rating). You can get
aftermarket high output alternators, usually in the 160-200A range;
my older Toyota only has a 60A alternator.

But some of that power is needed to run the car (20-40 Amps), so for
a 100A alternator the best case is 1100W available for the inverter.
These output ratings are at normal driving engine RPMs and at idle
you are lucky to get 75% of the rating (and as low as 50%) so we re
now down to 800W (max, probably lower), which will provide you with
~7A @120V AC, enough to run the refrigerator (130-200W) and more.

You ll need at least a 750W inverter ( peak 1500W inverters typically
have a peak rating 2x the normal rating) to handle the starting surge
current for starting the refrigerator (~1200W) with the extra energy
coming from the battery regardless of how much power your alternator
produces.

To run a 3000W inverter continuously without discharging the battery
you need a 300A alternator, what you would typically find on a fire
engine.

---

Tch. What drivel.
Automotive alternators are not continuously rated.
You *only get the full output at fairly high engine revs anyway.

Can you work a pencil?

Depends on what you mean by "full output." Car alternators are connected to
voltage regulators which hold the output voltage (almost) constant,
irrespective of RPM.

Why is 20-40 amps needed to run the car?

A 2000-watt amplifier will use (at least) 170 amps. Add headlights, a/c fan,
cigarette lighter, and, of course, the engine, and you'll be above 200 amps.

A 2000 watt amplifier will draw PEAKS of 170 at full volume - average
current well less than 100 amps - and 2000 watts is INSANE.

Big thing is a few amps to run the alternator field, another 10-ish
for ignition at full bore, and another 17-25 for EFI including fuel
pump - then add cooling fan, heater fan, and air conditioning clutch.

60 amps will barely keep up.

All that is nonsense. Except for lighting, 10 amps will cover
everything.
The alternator is larger to recharge the battery which takes a few
minutes only.
Which is why they have no need to be continuously rated.