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Old 04-08-2012, 04:26 PM   #1
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Adding of a 1000w Inverter

I have purchased a 1000 watt pure sin wave inverter and am looking to instal it in my trailer. I have found a decent spot in which I can mount it and access the wires from the battery before they enter the power centre of trailer. My plan was to run wires of the same size that come from my trailer (#6 cu) and have them feed my inverter.

Now after reading a post on this forum "Very Long - My 12v electrical Modifications and Solar Power System Installation" I have begun to question my process. According to the calculations on that post I would need #1cu wire. I don't think the lugs on my inverter would be large enough for the wire. I am an electrician so I understand why one rates wires and such and why one has to be safe. I guess my questions are is it bad idea if I just use #6cu wire (fused)? Am I just oversizing the wire to the inverter due to voltage drop? (since 1000 watt inverter will only draw 9amps. 1000w/115v= 8.6)

My run of wire to my inverter would be approximately 15 feet.
Thanks


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Old 04-08-2012, 05:54 PM   #2
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You are on the wrong side of the inverter in your calculation. The wire size is required for the 12VDC wiring.

1000 watts / 12 VDC = 83.3 amps.
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Old 04-08-2012, 05:58 PM   #3
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Remember fusing is to protect the conductor. You can use smaller than necessary conductors if they are properly protected, however if you approach the limit of your inverter, or during a surge, you will be replacing fuses.

And remember that 12V is a nominal value, and not a number you would use for any conductor or protection calculations.

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Old 04-08-2012, 06:22 PM   #4
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IMHO 15 feet is way too long of a run for inverter wiring. Keep it to about 4 feet maximum. And as for wire go to the welding supply store and buy yourself some O or OO welding cable. Get some solder lugs and go at it.
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Old 04-08-2012, 06:25 PM   #5
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Quote:
Originally Posted by RJHuser View Post
You are on the wrong side of the inverter in your calculation. The wire size is required for the 12VDC wiring.

1000 watts / 12 VDC = 83.3 amps.
Nope I think your wrong on your calculation there. That is 1000 watts @120VAC. If it were 83 amps DC you would drain your battery bank in a matter of seconds.
1000 watts AC= 10 amps AC approx. if my math is correct.
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Old 04-08-2012, 06:56 PM   #6
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You are correct in that 1000 watts at nominal 120 VAC is about 9 amps. However, 1000 Watts at 120 VAC means at least 1000 Watts input to the inverter (actually, it's higher because the inverter is only 92% to 94% efficient. So, 1000 Watts input at 12 VDC is about 84 amps.

8.3 amps X 120 VAC = 1000 Watts = 1000 Watts / 12 VDC = 83.3 amps

Simple high school physic.

And, yes you're correct, most batteries (about 100 amp-hour capacity) would only last about an hour or a little more. That's why most coaches with inverters will have two, four or more large amp-hour batteries to get 400 to 600 amp-hour capacity. Also why you don't find large inverters in fivers and travel trailers -the. Battery weight eats up all your load capacity.
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Old 04-08-2012, 07:47 PM   #7
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Stephan, You are getting very good advice here from folks who know.

In fact 3 feet to the inverter from the battery bank is max IMHO and #4 gauge the optimum size for a 1000 watt inverter (although 8 is what I would consider the minimum).

Yes, it really is that many amps. In fact, as the battery loses capacity from use the voltage drops. As the voltage drops, assuming the AC load is constant, the amps required from the battery bank goes UP so fuse and wire accordingly.

Most Inverters will drop off line at 10.5 DCV so using that voltage and the required 1000 watts, your amp load on the battery will be 1000/10.5 or about 95 amps. Fuse and wire for that load.

Yes, Virginia, if you have a 95 AH battery fully charged and use the entire 1000 watts AC; your battery it will last about 25 minutes till dead.

Deep Cycle Battery FAQ

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Old 04-08-2012, 08:20 PM   #8
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What Herk said is correct. I simplified it in my reply. A size 24 or 27 battery will give you about 25 minutes operation at the 1000 watt load (you get less than the hour I said because the battery, at high loads, has actually a lower capacity than the rating).
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Old 04-08-2012, 09:09 PM   #9
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Thanks for all the advice. Now I am starting the rethink the location for my inverter. I guess the next question is what would the max length of wire for the load size of the inverter. The location I chose would have close to what the only things that I would use.



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I was hoping to put the inverter by the door by the bedroom. After all of this great advice would I be better off mounting the inverter behind my power supply and run #12 for a new outlet box? My inverter has a remote. My main power centre is under my fridge.
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Old 04-08-2012, 09:24 PM   #10
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My 1800 watt MSW inverter called for a maximum of 5 feet with a minimum of 2/0 wire, this distance included a switch and fuse. The shorter the better.
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