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Electrical Load ?

How much can be "loaded"(not sure if it is the right word) on the Stock Electrical System.

I'm looking at a aftermarket modification that is  uses a AC only Unit (will need an large inverter to run).

The device Operates on 150  or 230 VAC 50/60HZ and has a consumption of 715 W.

Weight will be in issue but this is not the correct forum.

With a large inverter, can the stock system handle this? or should I  dedicate a 2nd alternator and seperate wiring to it alone ?

Electrical Load ?

Reply #1 –
Thats just 4.8/3.1 amps, is it not? I think you'd be fine as long as you run the inverter wires directly to the battery. Headlights themselves draw more current than this (65w/12v*=5A+ each)
1988 Thunderbird Sport

Electrical Load ?

Reply #2 –
P=V*I
 
I(current in amps)=P(in Watts)/V(voltage)
                        =715/12
                        =60 amps
 
That's a lot of current to draw from a 12V system.

Electrical Load ?

Reply #3 –
Quote from: thundergrowl
P=V*I
 
I(current in amps)=P(in Watts)/V(voltage)
=715/12
=60 amps
 
That's a lot of current to draw from a 12V system.

He is correct but if your using an inverter you need to find out that its consumption is.  most inverters are vehicle safe.  depending on the consumption.

Electrical Load ?

Reply #4 –
but that is 715w at 12v...the item he's using is 715w at 150/230v.  Then again, thats on the output of the inverter. Guess I was thinking about the wrong side of it, not the input.

Either way, with that much current draw, I'd try a 200w alternator with a nice, thick cable going to the battery
1988 Thunderbird Sport

Electrical Load ?

Reply #5 –
715 watts is 715 watts, regardless of the voltage. The difference is the amperage. At 110 volts it takes about 7 amps to produce 770 watts (I'm using 770 watts for the sake of easy math - watts equals volts X amps, so 110 volts X 7 amps = 770 watts). To get that same 770 watts out of a 12 volt system you need about 65 amps. The inverter circuit will actually consist of a high current/low voltage side (the cables to the battery) and a high voltage/low current side (the AC lines to the load).

Just like light bulbs - a 60 watt headlight bulb requires about 5 amps at 12 volts, but a 60 watt household bulb uses about a half an amp at 110v. As voltage goes up, amperage goes down to get the same work (and watts is a measurement of work). It also applies to heavy trucks. Their starters are at 24 volts, but the windings inside those starters are actually smaller (thinner wire) than in a 12 volt starter.

That, however, is assuming your inverter is 100% efficient, which it isn't. You will lose some power through the circuitry of the inverter (that heat that comes off the inverter is power loss). Truthfully, the best way to decide what your current draw will be is to look at the manual that comes with the inverter. In the manual's specifications section it should list peak and average current draw. And don't buy a 750 watt inverter to power a 715 watt load - your inverter will not last long operating at 95% capacity. You should run at least a 1000 watt inverter.
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

Electrical Load ?

Reply #6 –
you are correct with your theory, but you are leaving out something, a inverter will take the 12V run it through a coil to up the amperage and voltage then run through a rectifier to convert to AC, you will have some losses but not drastic ones see the scheamtic for a basic inverter.  Most inverters can be run on 12V with a stock alternator. Granted if he is running a 700+ watt device i would still recomend getting an alternator but not necisarily needed.

Electrical Load ?

Reply #7 –
Would a 2nd alternator dedicated to the device be necessary? seems like a lotta juice ...

Electrical Load ?

Reply #8 –
No just get an upgraded alternator and youll be fine, no need to run 2.

Electrical Load ?

Reply #9 –
The coil ups the voltage, but not the amperage. The highest amperage is on the low voltage side of the circuit, and even a fairly small inverter like my 300-watt model draws a lot of current (mine has blown a 20-amp fuse while powering a 150-watt laptop battery charger). If that 20 amps were available on the high voltage side the inverter would generate 2200 watts instead of the 300 it's capable of (110 volts X 20 amps = 2200 watts). That 300 watts is really only about 2.5 amps worth of current at 110v AC

Just think of an automotive battery charger - it's kind of like a reverse inverter. It takes low current high voltage AC and converts it into high current low voltage DC. It has to be low current high voltage because the wall plug is only rated at 15 amps, but the DC side can generate over 100 amps at 12 volts. That's why the charger has a little bitty 14 gauge input cord but heavy duty 4-gauge output leads.

I've installed a lot of inverters in cop cars, RV's and tractor trailers, and I can assure you, if you try to power a 700 watt load off a stock 65-amp 2-G alternator you will kill the alternator very quickly. A 130 amp 3-G might last a bit longer, but if this is a continuous load instead of something you only use occasionally, even the 3G will live a very short life. If the inverter is constantly drawing 65 amps, then you add all of the car's accessories (heater fan, headlights, wipers, fuel pump, EEC, injectors, ignition system, power windows/locks/seats, stereo, etc) the 2G won't have a chance, and the 3G will be running a very high duty cycle, high enough to significantly shorten its life.

Hell, I've installed a second alternator AND battery into brand new GM trucks owned by the fire department to power 1500 watt inverters because the stock alternator and battery couldn't handle the loads of the inverter and the truck. GM even offers a second alternator as a factory option on the diesel trucks (and has recently started offering onboard AC power in its "hybrid" trucks)...
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

Electrical Load ?

Reply #10 –
You guys listen to the Chicken, he knows what he's talkin' about...

Electrical Load ?

Reply #11 –
Quote from: TurboCoupe50
You guys listen to the Chicken, he knows what he's talkin' about...

Yup!

Electrical Load ?

Reply #12 –
mhm, know he does
1988 Thunderbird Sport

Electrical Load ?

Reply #13 –
Well definally it wont be  constantly, it's just for car shows etc. Its strictly a show off device and to run it constantly would be a waste. I 'll definally upgrade the Alternator and hope for the best I guess. And Yes I always listen to Thunderchicken and anyone else on this board. :D

Electrical Load ?

Reply #14 –
so now can we ask what you are doing? or is it a surprise?