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Power Inverter Question

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Posted by Barry on December 2, 2005, 9:40 pm

Have considered getting a large power inverted for mobile power in an
emergency.  My question is what effect do they have on a vehicles
battery/charging system.  If an inverter can supply 2500-3000 watts, that
seems like it would be  an incredible drain on the vehicles battery/charging
system.  I imagine most alternators can't put out that kind of current.  ( I
could be wrong ).  Would you burn  out the alternator after the battery was
drawn down? Would the inverter just not function?  Am I wrong about the
alternators ability to supply that kind of current?



Posted by Chris Hill on December 2, 2005, 10:31 pm

On Fri, 2 Dec 2005 16:40:30 -0500, "Barry"

Nope.  Not wrong at all.  Even the alt on my f350 diesel is only like
a 120a model which would be about 1440W maximum output.  Also, a big
inverter needs big cables.  I've thought of putting a 500 or 1000 unit
under the hood to run an electric impact wrench, just haven't found
the space yet.  Brief bursts probably wouldn't kill an alternator,
full time 3kW probably would.

Posted by Harry Chickpea on December 2, 2005, 10:32 pm

It is, and inverters of that size aren't designed for use with car
batteries, but for use with deep-cycle batteries.

An average car alternator is good for about 75 watts (less than 7 amps
at 12 to 14 volts).

It can happen.

Many cut out when the battery can only supply around 10 volts.
(voltage drops as the charge is drawn out of the battery)

It is all a matter of time.  Add a couple of trolling motor batteries
to the car battery and connect everything with good welding cable to
provide for the increased current, and your alternator can charge the
batteries for long time to provide enough energy to run a high-wattage
appliance for a short period of time.  You cannot run a high wattage
appliance continuously, because you have to take less out of the
system than you put in.

Posted by Ulysses on December 3, 2005, 4:47 am


I think you mean 750 watts.  A 100 amp alternator can supply about 1300-1400

Combined with the battery it would be possible to provide more power but
only for a limited time as it would run down the battery.  I would suggest
to the OP to limit the inverter to around 700-800 watts unless additional
deep cycle batteries are installed and seperate from the vehicle battery.

Posted by Bruce in Alaska on December 3, 2005, 6:57 pm

 hchickpeaREMOVEME@hotmail.com (Harry Chickpea) wrote:

It isn't the battery that is the limiting factor here, it is the
alternator. Car Battery or Deep Cycle will not have any effect on the
inverter as long as the alternator can keep up with the inverter draw.
Even if the alternator can't keep up, the difference between Car Battery
and Deep Cycle will not be significant except for some slight effect on
cell integrity under large discharge conditions.

Bruce in alaska
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