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Old 06-29-2010, 08:22 AM   #15
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The Installation Manual for my 3000 Watt (Model RV3000) Xantrex Inverter calls for a 300 amp fuse between the inverter and the battery bank in-line on the 2-gauge positive battery lead.

Keep in mind your 1500 watt Inverter is also a very large current battery charger. Probably somewhere around 80 to 90 amps. My RV3000 puts out 150 amps of charging current to the batteries.
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Old 06-29-2010, 08:53 AM   #16
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You would normally fuse (actually, use a circuit breaker) the 120vac output line for the max output it can handle, which is 20A in this case (limited by your choice of 12 gauge wiring). 20A x 120v = 2400 watts, which exceeds the constant load of the inverter but is within its 3000W surge rating. If you ever actually pulled 2400 watts from the inverter, it would draw 200 amps from the batteries to do so. That was the rationale for using a 200A fuse rather than 125 or 150. Using a 125 amp fuse limits the whole inverter system to no more than 1500 watts, so you should probably choose a similar restriction for the 120vac output, which would be roughly 15A (1875 watts). Personally, I would use 150A or 200A fuse on the DC input and make sure the wire gauge was a suitable size to handle that (2/0 gauge works for a 5-6 foot distance).

Your 900 watt microwave will indeed need the 12.8A you referenced in your earlier post. The 900W is the microwave output, but it takes more amps & watts for input to produce that much output. Stick with the amp figure shown on the rating plate on the microwave.

The Motomaster inverter in use here does not have a battery charge function - it is an inverter only.
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Old 06-29-2010, 01:17 PM   #17
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To the original poster.. Go back to my last post and do not forget to UPGRADE your wire.. The post links to a site that tells you how much of an upgrade you need.

I would go at least one wire size larger than they suggest to reduce voltage drop

Also the two (negative and positive) tie, loom or tape them together as much as possible to reduce inducatance when the inverter first kicks in.

NOTE: The fuse is usually a bit larger than the max RUNNING draw of the inverter
The inverter needs a bit of extra amprage for starting up

DO read the manual and use the proper size fuse .
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Old 06-29-2010, 03:10 PM   #18
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BadBoy,
I've read and considered the subsequent post to my last one and if the loads you posted, in watts, are accurate, I stand by everything I told you. If you want to increase the wire size I would suggest 1/0(0) copper but 2/0(00) is overkill and a waste of money but if it make you feel comfortable be my guest. Whatever your decision, I recommend you try to get welding cable, it will be very difficult to train and bend it if you don't.

The type of fuse used on the the 120 volt side is faster acting and will blow before the class T fuse. So if you run both coffeemaker and Microwave at the same time by mistake the 15 amp breaker will trip before the class T fuse. Why change out a $20 fuse when you can simply reset a circuit breaker.

Again, I think your battery bank is the weak link here so I recommend you try this setup in your driveway so you can monitor battery temperatures and get a feel for how long you'll realistically be able to use it.
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Old 06-29-2010, 06:27 PM   #19
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Quote:
Originally Posted by BadBoy View Post
Gotcha, I have plenty of room as I designated a full side box to the inverter. That box is 5 feet from the battery bank so the heavier cable (2ought) is prob best. I'll do the 125 amp t-fuse on the dc side (as close to batteries as possible and go for the 15 amp fuse on the AC side mounted as close to the inverter as possible.
Hope that will do the trick!
I'd strongly suggest a 200 amp fuse on the dc side.

With 15 amp protection at the output and an 85% efficiency factor on a loaded inverter AND 12.0 volts at the input(typical of a loaded 12 volt wet cell bank) the input dc current will be much higher than 125 amps!

Example calculation:
(15amps ac X 120 Volts ac)/ (12 volts dc X .85)=176 amps dc

Every time you forget to limit the loads, you will burn up an expensive t-fuse.

Why not just go to Xantrex's website and get all this info directly from them?

Marty
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Old 06-29-2010, 08:41 PM   #20
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Marty,
You make a good point about the efficiency requirement of the inverter. We don't know what kind of inverter he has except that it's 1500 watts and the efficiency can be as low as 80%. I agree with you about increasing the fuse size to 200 amps since that's the next fuse size up and it will coordinate better with the 15 amp fuses upstream.
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Old 06-30-2010, 10:44 AM   #21
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That inverter should be better than 90% efficient anywhere near its peak loads.
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Old 06-30-2010, 11:24 AM   #22
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Originally Posted by RV Roamer [Gary] View Post
That inverter should be better than 90% efficient anywhere near its peak loads.
Gary
With newer inverters possibly, but in the absence of specs for that inverter, I used the numbers provided with mine. Main point was the consideration of efficiency in determining input currents for fusing.
Mine states full load effic=85% and peak effic=92%.

Also , not enumerated is that as battery voltage decreases, the input current will increase as the regulation circuitry will try to maintain the 120 volt ac out level. In the case of my inverter that is maintained within 5%

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