Questions about Power Inverters

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2,431
Location
Toronto, Canada
I am thinking of buying this Cobra 2500W inverter. http://cgi.ebay.ca/BRAND-NEW-COBRA-CPI-2...A1%7C240%3A1318 My questions are: 1) Are Cobra inverters of good quality? 2)This inverter has a surge rating of 5000w. I measured the start-up current of my portable 120v air compressor with a scope and it drew 50 amps for 200 milliseconds. 50 amps translates to 6000w, does that mean that this inverter will not be able to start up my compressor? Thanks in advance for any input.
 
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2,340
Location
La.
I think it means the inverter is too small. Sounds like you may need a generator. Almost all small inverters are made by the same company, no matter what the brand. I can't remember the name!
 
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12,385
Location
Northern CA
+1 I think cheap inverters (it's cheap) tend to handle less than they are rated for. IIRC, Pablo used to work for a 1st class Inverter mfr before they got hosed by China. If he doesn't stumble in here, PM him.
 
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7,430
Location
beaver land EH?
I use Xantrex invertor products exclusively. All others like Victor, etc. are all junck and not worth the money spent. Of course, MortarMaster (from Crrappy tires) are OEM'ed Xantrex units and worth pursuing when CT is having a sale. Q.
 
Messages
125
Location
Ohio
 Originally Posted By: George7941
My questions are: 1) Are Cobra inverters of good quality? 2)This inverter has a surge rating of 5000w. I measured the start-up current of my portable 120v air compressor with a scope and it drew 50 amps for 200 milliseconds. 50 amps translates to 6000w, does that mean that this inverter will not be able to start up my compressor? Thanks in advance for any input.
I'm new to these forums so I don't know much, but I always shy away from using inverters for such loads as it gets much more expensive than a generator when you start pulling hundreds of amps from a battery for continual loads. 5000W from a 12V source is a bit over 416 Amps and 6000W is 500A at 12V both assuming 100% efficiency. In reality the more expensive units barely make 90% efficiency. Common would be 70-80%. We're talking big honkin' battery(s) with power cables the size of welding cables and a heavy duty alternator that may get lucky and provide a 1/3 of what the inverter is wanting at those loads. If determined, I would suggest a sine wave inverter for such high loads for less harmonics and a cooler running motor. Quasi or modified sine is acceptable, but recommend any attached electronic equipment have common mode noise rejection capability. Electronics with internal clocks referenced to the line frequency would be erratic as well with quasi/modified sine.
 
Messages
36,112
Location
ME
If you want air from your car get a dedicated 12v compressor or a pulley drive system like serious off-road jeeps have rigged up. OTOH cheap compressors with somewhat fewer CFM than you're used to may come in under the surge rating of your favorite invertor.
 
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10,738
Location
Nokesville, VA
 Originally Posted By: MolaKule
A sine wave inverter (Prosine) is needed for computers, etc.
Most computer UPSs don't have sine wave inverters in them, they are modified sine wave inverters. So a computer does not need a sinewave inverter.
 
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