Average Reviews:
(More customer reviews)This is a very good unit, for what it is designed to do. It is up to Cobra's usual high quality standards. There are a few things you should know before you buy it though.
There are a couple of comments about the unit not putting out full voltage - however, if you go to the Cobra website and read up on this unit you will see that a standard voltage meter will not read the voltage correctly due to the sine wave configuration, instead it will read low voltage. Measurement requires a specialized meter, an RMS if I recall correctly. I have read also that some electronics work fine with the modified sine wave and some pick up some interference. It would probably be worth the time and energy to research which would be the case for your particular electronic application, before buying.
Another quite important thing to know is that this unit, while rated at 1600 watts, will only run at 800 watts continuously. The 1600 watts provides room for start up surge, but not for running more than a few seconds. I bought mine to use in my car. First thing I tried was a 1500 watt heater, and it would run for a few seconds and then stop. Then I tried a 750 watt heater and it ran just fine. So check your application and see if it will be 800 or less watts, if more, get a bigger unit.
Another important thing to watch for on automobile installations is the output of your alternator. Many cars have alternators with as little total output as 60 to 75 amps. You can calculate the amp draw by dividing the AC watts by 12 and then multitplying by 1.1 - so in my case the 750 watt heater draws 69 amps from the battery/alternator. If I had a 60 or 75 amp alternator then there would be a serious problem. Probably the battery would be drained while driving and I would end up with a dead battery, at night, in the middle of nowhere, surrounded by zombies pounding on the windows....
I have a 135 amp alternator, but since I am not sure exactly how much amp draw my car uses while running at night with headlights (most of my driving is after dark) then I am not completely sure how much reserve/overage I have for the inverter. As a result I only run the heater intermittently so the battery won't drain. If your application pulls enough amps to cause the charging system to run at system capacity so that the alternator continuously puts out 100%, the alternator will not last nearly as long as normal. I never run my heater when the engine is idling, at idle the alternator puts out about 40% less.
If you are going to use this in a running car, try and find the total amp draw needed for the car,(I found that my alternator runs at about roughly 60% when idling so I am guessing that my total draw would be about 50% of the total capacity of the alternator at full speed, or 68 amps in my case, but that is a guess) subtract that from the total output of your alternator, and then compare your alternator's power reserve with the draw from the inverter with your application, to make sure you have enough total capacity with some margin. Mine would, based on this theory, run a 2 amp deficit. Or do what I do and run the application only intermittently so the battery gets charged up and the alternator isn't running at 100% capacity all the time, and never while the engine is idling.
If you are going to use this in your car while driving, the supplied cables are not going to work for you, they are too short. The inverter is not weather proof so it can not be mounted under the hood where water can splash up on it, or dust get into it. It needs to be in a weather tight environment with good air circulation, it also doesn't like heat. I took a pair of heavy jumper cables and soldered bolt connectors on each end and ran these to my cars interior. I added an in line 100 amp fuse in case of a short in the cables.
If you are going to use this on a battery only, there are formulas to determine how long the battery will supply the load you need - you can find the info with a goole search easily. It would most likely be worth your time to run the formula before buying, to make sure that you are going to get sufficient run time from the battery you have or plan to get. If frequent recharging is in your future, consider deep cycle batteries.
In summary, this unit works, within it's limitations, and I am happy with it. I would have given it 5 stars, but the Amazon description of the unit's true continuous run capacity should be more detailed than it is.
August 2009 - I see that the description has been changed so that it better represents the 800 watt continuous capacity. Kudos to whoever made that honest change!
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Cobra CPI 875 800 Watt 12 Volt DC to 120 Volt AC Power Inverter with USB portThe Cobra CPI 875 is a 12 volt DC to 120 volt AC power inverter with 800 watts continuous power handling and 1600 Watts peak power.This unit contains a 5 volt USB output, modified sine wave, thermal shutdown, reverse polarity protection, low voltage shutdown, low voltage alarm, external fuse, 2 grounded AC receptacles, and includes a carry case, and direct- to battery cables with clips.
Click here for more information about Cobra CPI 875 800 Watt 12 Volt DC to 120 Volt AC Power Inverter with USB port
