Friday, 3 December 2010

Ac-dc Converter - ac-dc converter, cobra


This review is in response to some comments regarding wire and fuse size selections for this inverter and others like it.



In response to other review quoting a table from the National Electric Code (NEC). While the table that was posted is correct for 115VAC (household voltage) is does not translate directly to 12VDC (automotive voltage). When dealing with a 12 volt system there is less concern with wires overheating, at least in the way that the NEC considers it, and far more concern with voltage drop. When running wiring a reasonable distance (a couple hundred feet or so) there is little concern with voltage drop with AC power. But when dealing with DC, simply increasing your wiring distance 5-10' can have a drastic effect on voltage drop. That is why this inverter should be wired with, at the very least, #4 wire and really should be installed with #2 or thicker, especially if you need to run wire 15 or 20 feet or more.



The purpose of a fuse in a DC system is to protect the rest of your electrical system in the event of a short. That is why you always want to install your fuse as close to the battery as possible (no more then 3' if you can help it). As far as the amperage goes, there is a really good quick reference chart for automotive wire size that can be found at Tessco's web site here:[Turns out I can't link to an outside page so I'll paste the contents of the table at the bottom]. But to boil it down, you can safely fuse a 12VDC circuit at 150, or 200 amps, or more on #4, #2 or #0 wire.



Now this unit at full load is something like 85% efficient. So if you do the math -- 1500 Watts / 12 Volts / .85 efficiency = ~147 amps, A 150 AMP FUSE IS REQUIRED. If you take peak power into account you would need to double that to a 300 amp fuse, but because the inverter cannot run at peak power for more then a moment, a slow-blow 150amp fuse may work just fine, or perhaps you could step up a 200amp. I wouldn't go all the way to a 300 amp fuse unless you really found that you needed it and had the inverted is wired in such a way that it could handle that level current (read: installed using very heavy gauge wire). Now if your vehicle is running while your inverter is working the amperage will be a little lower because your dealing with 14.4 VDC rather then 12 volts (watts = volts x amps -or- amps = watts / volts). But at the very least, a 150 amp ANL fuse is very good idea and not at all over sized.



Just a FYI on fuses, most car stereos are installed with AGU style fuses, but they only go up to 100 amps.



You will need an ANL style fuse to get one rated at 150 amps or more. See these links for examples:

Kicker 09ANL150 150 Amp ROHS Compliant ANL Fuse - Package of 2

Scosche EWFH Single ANL Fuse Holder



Wire Gauge Selection Table 12 Volt Circuit



Wire Distance

AMPS 3' 5' 7' 10' 15' 20' 25'

---------------------------

<5 18 18 18 18 18 18 18

6 18 18 18 18 18 18 18

7 18 18 18 18 18 18 18

8 18 18 18 18 18 16 16

10 18 18 18 18 16 16 16

11 18 18 18 18 16 16 14

12 18 18 18 18 16 16 14

15 18 18 18 18 14 14 12

18 18 18 16 16 14 14 12

20 18 18 16 16 14 12 10

22 18 18 16 16 12 12 10

24 18 18 16 16 12 12 10

30 18 16 16 14 10 10 10

40 18 16 14 12 10 10 8

50 16 14 12 12 10 10 8

100 12 12 10 10 6 6 4

150 10 10 8 8 4 4 2

200 10 8 8 6 4 4 2 Cobra CPI 1575 1500 Watt 12 Volt DC to 120 Volt AC Power Inverter

This product works great, I have a microwave, flatscreen tv, and a toaster i hook up to it and there is no problems. One thing I wish would have been mentioned somewhere is that you need to purchase a 150 amp inline fuse to put in the power wire from the battery to the inverter. So plan on getting one of those and have it ready so you can install it. I didnt know about it and spent some time in North Dakota trying to find one. Enjoy.

The inverter is working for me exactly as described and as I hoped. I drive a truck and have it installed to replace an older, smaller model. I run a number of things including my laptop, external speakers, printer, TV and a coffee pot. The low input warning works great, and will shut down the inverter if necessary. I will be adding things soon, such as a microwave.

The meter is a great feature which lets me see how much power is being drawn by each device attached as well as the input voltage.

I highly recommend this inverter.

Other reviewers don't seem to have had the problem I did, so this might be a good product but I must tell you my experience with it. I am very familiar with inverters and how to hook them up having lived off of solar power now for over ten years. When I first set up this inverter, the input voltage showed 12.3 volts, the same as my battery voltage but undr a 110 watt load the output wattage meter showed 0 (zero) watts. What I had plugged into the inverter was working fine (a small TV), so I assumed this meter was just broken. If that was all that was wrong I could have lived with it. The next morning I turned it on, turned on the same TV and within 20 minutes the picture on my TV slowly shrank down to a pinpoint and then shut off. There were no low voltage warning sounds. I checked my battery level and it was at 12.2 volts, the same 12.2 volts showed on the input meter on the inverter, output still showed zero, as it always did. I checked the output at all three of the outlets on the inverter and they showed zero. I turned the inverter off and then back on with the voltage meter still in one of the outlets and watched my meter go from 119 volts down to 30 volts, up to 80 volts and then back to zero. The whole time there were no warning sounds coming from the inverter. This fluctuation could very easily damage anything that was plugged into the inverter!!!!



The good news, Amazon's return system is very easy, didn't cost a penny to return it and I got a refund quickly. I thought of getting a replacement instead of a refund because of all the good reviews but decided not to press my luck, no equipment was damaged this time but why risk it again. If I could rate Amazon I would give them five stars but the inverter gets zero xtars since it didn't function as advertised, went dead under much lower load than it is rated for. - Cobra - Ac-dc Converter - Inverter - Power Inverters'


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