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  #1  
Old 08-16-2005
optikal illushun's Avatar
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Hard wiring a power inverter.

Picked up a 750W rms/1500W surge power inverter. i wanna hard wire it. im gunna use it to power a nebulizer, maybe a 15.6V drill charger...nothing huge.

question is, which method is the best? i was gunna use an amplifier wiring kit for a stereo. if i do that, which size kit would i use and what size fuse?
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Old 08-16-2005
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Does it have a fuse ( the power inverter ), from the fuse size and length needed to be ran the wire size can be found.
I looked up some of your specs on ebay, looks like about 10 gauge wire. 10g wire has a max rating of about 60 amps, so 60 or 50amp fuse sounds good.

An amplifier kit would work great, since it comes with a fuse and holder, but you don't need all the rca's and other junk it comes with. Go to a car audio shop and get bulk wire and they may have a low-amperage fuse and holder as you need.

Last edited by rideac1; 08-16-2005 at 06:45 PM.
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  #3  
Old 08-16-2005
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local audio shop, lol. i wont give them any business. bunch of ********.

it has two 40 or 50 amp fuses on the side of the inverter. im more worried bout the power spike from some devices. i was gunna go with 8 awg and a 80 amp anl style fuse.
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Old 08-16-2005
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Forget about the shop then.
I'm not sure what the 'spike' is you're talking about.
If you're talking about the surge/max taking place, the amps should be less than the fuses on the inverter, and everything is swell.
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Old 08-16-2005
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the start up draw, i was reading for a split secnd somew devices have a spike or start up draw like an electric fan...
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Old 08-16-2005
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OK, I'm sure the inverter is made to handle it, I don't think it would hurt anything with the normal wire setup you're planning.
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  #7  
Old 08-16-2005
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Id get 4gauge wiring kit off ebay. Inverters are sensative to voltage.
However it would probably run fine on 8gauge.
are you sure its not 30amp fuses.. I have rarely seen blade fuses larger than 30A

I got a 1200watt(2400surge) continuous coleman.. its very nice. I wired it with 4gauge.

the thing is 8gauge is fine for 60amps.. but if you have a 14ft run.. you will have serious voltage drop. 750/12=62amp.. I'd go with a 60-75amp underhood fuse.
Rand
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Old 08-16-2005
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ya it will be quite a lenghty run, estimate 15 foot. but the power inverters rock. its all coming together now...i know what size wire and fuse to use. im just worried about the start up draw on some devices...
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Old 08-16-2005
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startup draw is normally for something like.. an a/c compressor.. or an air compressor etc. Or a washing machine, laser printer...etc
Alot of the newer tools have capacitors and such to reduce the "startup draw"
Most stuff like battery chargers etc have no startup draw or very little.

IMO 6gauge would be a good wiring size but 4gauge rarely costs more...
thats why I recommended 4gauge. Also you could always split 4gauge to wire something else.. like a cb etc.. although I will warn you Inverters put off ALOT of noise (for cb's etc)

Rand
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Old 08-16-2005
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The wattage that can handle on AC is NOT equal to the wattage it draws on 12 volts. If it was, you wouldn't need to cooling fans on it :) You can either read the specs on it or see what it is fused at. Either way is fine. Size your wire to work with that amperage.

http://www.kb1fpd.com/wire-gauge.pdf will help you.
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Old 08-17-2005
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Quote:
Originally Posted by FireRanger
The wattage that can handle on AC is NOT equal to the wattage it draws on 12 volts. If it was, you wouldn't need to cooling fans on it :) You can either read the specs on it or see what it is fused at. Either way is fine. Size your wire to work with that amperage.

http://www.kb1fpd.com/wire-gauge.pdf will help you.
What do you mean... Power is Power... Wattage is Wattage... Only the voltage and current are changing. So Wattage on AC IS equal to Wattage it draws on 12 volts (unless you start taking into account PF which isn't really necassary here).

I have a 2500W inverter on my truck, and used parallel 4awg wires with 2 slow burn 80amp fuses. The best place to buy the stuff (IMHO) is at a boat shop. They had all the large style fuse holders (only way to get an 80amp fuse that I found), Waterproof 200A disconnect switches, and all the crimp on connector that you'll need for the wire ends. This way is going to be a lot cheaper than buying a wiring kit, and you can make the wire the length you need.

As far as the surge power, I run vacuums, air compressors, saw-zall, skill saws, blenders, and none have ever taxed the system more than half capacity. The general rule I use, take the 120V AC load given on the nameplate of the motor, and multiply it by 10. Example, my shop vac has a load of 7amps on the nameplate, so it will be drawing about 70 amps from the battery/alternator.

I'm not sure if this is clear, but let me know if you'd like more info.



I
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  #12  
Old 08-17-2005
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Well a 4gauge wiring kit on ebay goes for about 30$.. with fuse holder..etc.. and you even get a bonus set of long rca cables :)

Fireranger.. your thinking is flawed. a 1200watt inverter isnt how much power it can draw.. its how much it can convert to ac.

Now if you have say.. 3 30amp fuses=90amps
90amps x.75 (conversion effeciency) =67.5Ax12=810watts.
so if you were saying something like that and I misunderstood your 1 line sentance.. I would agree to that. :)

Rand
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  #13  
Old 08-17-2005
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Quote:
Originally Posted by Rand
Fireranger.. your thinking is flawed. a 1200watt inverter isnt how much power it can draw.. its how much it can convert to ac.
I'm saying exactly that. Many people think that 1200 watts out on AC = 1200 watts draw on the 12 volt system. That is not the case. It is not 100% efficient. All that heat getting blown out of the inverter by the fans is power being wasted as heat, not AC. So, the inverter can concievably draw more watts on the 12 volt side than is can supply on the AC side. Same thing with two-way radios and stereo amplifiers.

It is not simply watts to watts while changing only the voltage and current. If it was only that simple.
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Old 08-17-2005
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FireRanger- I obviously misunderstood your statements as well... I don't know what a standard efficiency rating of a small inverter would be, but I would think it was upwards of 95%? Does that sound right? If so, it's pretty much negligible.

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  #15  
Old 08-17-2005
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Quote:
Originally Posted by elmo_4_vt
What do you mean... Power is Power... Wattage is Wattage... Only the voltage and current are changing. So Wattage on AC IS equal to Wattage it draws on 12 volts (unless you start taking into account PF which isn't really necassary here).
The problem is that the inverter disapates some of that energy (power) while doing it's thing. This is usually disapated as parasitic heat. As Matt said, this is why you often see cooling fans on larger inverters. No inverter ever made is 100% efficient, so it is always going to draw more power than it puts out.. disapating the rest as heat. There is no free lunch..
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  #16  
Old 08-17-2005
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Quote:
Originally Posted by elmo_4_vt
FireRanger- I obviously misunderstood your statements as well... I don't know what a standard efficiency rating of a small inverter would be, but I would think it was upwards of 95%? Does that sound right? If so, it's pretty much negligible.
Honestly, I have no idea off the top of my head. I could find some spec sheets and do the math later on. 95% is probably pushing it.
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  #17  
Old 08-17-2005
optikal illushun's Avatar
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interesting debate guys!
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  #18  
Old 08-17-2005
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the most efficient a modified sine wave inverter could possibly be (generally)
is around 80-82%.. under a light load.. no fans etc.
Under a load close to its capacity it can drop downwards of 70% or so.
I used 75% as a general rule its close.

If you have a pure sine wave inverter (expensive) those run about 50-65% efficient
So for instance.. charging my drill and running my laptop... <250watts total on my 1200.. its probably high 70's for efficiency.
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  #19  
Old 09-30-2005
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Ok, dumb question so don't yell to much. I'm a ME not a EE :) Can one of these 2500W inverters be used as backup power for a fridge or freezer during a blackout? We had one last week for 2+ days and I went and rented a generator from Home Depot so our food would spoil. The fridge is 12 Amps and the freezer is 5. I have a 200 Amp alternator. 2500W based on 12V is 208 Amps but 21 Amps at 120V. Would this frag my alternator?
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  #20  
Old 09-30-2005
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It probably would eventually kill the alternator... That and I doubt that you'd want to run your truck for 2 days straight.

You be better off buying a small generator I think.

Don
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  #21  
Old 09-30-2005
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The advertised wattage on the inverter is the AC side of things. So you have 2,500 watts of AC at 120 volts. That happens to be 20.8 amps. Convienient number, that is what most household electrical circuits are rated for. If the Fridge is 12 amps and the freezer is 5 amps, that is a total of 17 amps. If you use the 125% rule, you would want a circuit that can handle 21.25 amps. The 20.8 from the intverter is close enough for this purpose. So, to answer one half of this question, yes the INVERTER can handle it.

Now, can the truck handle the inverter? That is the other half of the question. I'm going to assume the inverter is only 80% efficiant. Based on that, I'm figuring an additional 500 watts on the 12 volt side of things. 3000 watts @ 13.8vdc is 217 amps. Again using the 125% rule, you want 270 amps to spare on your truck for this to work properly. Don't forget, you also need some juice to run the ignition and other stock electrical devices on the truck. Running BOTH the freezer and fridge is not going to work properly with a 200 amp alternator, ESPECIALLY AT IDLE when you're never going to get all 200 amps.

I did some more math, some helpful tidbits:
Running just the refridgerator is about 156 amps on the 12 volt side. Running just the freezer is about 80 amps on the 12 volt side. Both of those are with the 125% rule So, you could run just the fridge or just the freezer safely and not stall out the truck or pop fuses. Running one at a time would also let you plug in a few small lights to see at night. Keep some small 20 watt bulbs around, they draw nothing so you can use a few of them and see plenty in the dark.

You're going to need a big **** extension cord for this. DO NOT use the 200ft long 16/2 extension cord. You need one of those big beefy ones, no less than 12/2, 10/2 if you can find it. If you use a cheezy extension cord, your going lose more power to heat from the resistance than you'll have to supply the load.

Also keep in mind that idling a gas engine for 3 days is not a good idea. Generators are designed for this use, not our vehicle engines. I would give it a break now and then, take for a drive around the block, etc.
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  #22  
Old 09-30-2005
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Ok, thank you for the reply. I'd also eyed those generator kits for trucks that have an a/c alternator that's engine driven. They showed it on Trucks TV a few years ago. I'm just trying to save some space in the garage and costs of a unit :)
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