12v outlet/3-in-1 adapter Question

Conversations between dc/ac are very inefficient. A Cobra inverter is around 80%, (a bit more at low usages, less at peek). efficient. this means every 80 watts used in ac cost 100watts DC. 400 watt 12 outlets inverters are way less efficient then a cobra 1500. The ac adapter for the fridge in not more then 70-80% efficient either. The fridge is a dc unit and using the ac adapter is less efficient. If the fridge uses 8 amps @ 12 volts thats 96 watts DC. Now the ac adapter is roughly 75% efficient so now we need 128 watts AC to power the 96 watts DC. Since we plug that into an inverter at approx 75% efficiency, we need 170 watts Dc to power the inverter which outputs only 128 watts AC, which powers the adapter, which output only 96 watts DC. The extra power is lost in heat in both conversions. Now the actual amount lost will vary, but 75% is not an unreasonable estimate. 170 is 1.77 times 96 so my inital number of 1.5 times as much power could be a little low. Depends on efficient, but the double conversion is never a good idea.

Now, also consider, 170/12 is 14.6 amps. He cant plug anything else in without blowing the truck fuse since it should be 15 amp. I never understood 400 watt inverters since you always run out of amps on the socket long before 400 watts. 400watts is roughly 33 amps. I dont know any cigeret lighter wired for 33 amps.

 

Cobra 400

Specifications
Continuous output power: 400W
Surge rating: 800W
Peak efficiency (12V – 1/2 load): > 88%
Efficiency (full load, 12V): > 83%
No load current draw: < 0.5A (12.6V)

At half load it is still outputting 352 watts. My laptop (19v/9.5a) needs 180w to run. I used a Cobra 800 which has the same efficiency off the cigarette lighter in the front with no issues.

 

Your laptop could use a max of 180. it doesn't normally require that unless you run your cpu at 100% and your graphics at that.


laptop charger can produce a max of 180 watts. Your laptop wont ever use that much. Also thats the MAX output of your laptop power adapter in DC. Plug it into a wall meter with the output maxed out and it will use more then 180watts AC. You can check this by plugging into an ac watt meter. i use the "kill-a-watt" meter.

Even assuming it only needs 180 AC under max (which is wrong)....that 88% is lab conditions, not real world. Even at 88% you need 205watts DC to make 180 AC. That is 17 amps @ 12 volts which is more then a 15 amp fuse in your 12 volt outlet. So, either your running a 20 amp fuse or have never pushed your laptop to its max. The only way to requier all the power is run "toast" (which will max out cpu) and "furmark" (which will max out you GPU) and a hard drive access test with a dead batt so its trying to charge while running comp on max. Then, maybe you will get the fuse to pop. Long story short, you will never get close to 400watts out of the inverter unless you have a larger amp wiring and fuse. 200 is about your max on 15 amp. Your laptop hasnt tripped it yet becuase you have never required the 180 on the DC side. The charger is capable of 180, but wont have enough dc-->ac-->dc power to run at max. Most of us double convert with our laptops, but its much more efficient to get a dc-dc converter for your laptop. These plug into the cigerett lighter and bump up whatever input voltage you have (10-16ish) to 19 volts. You can then run your comp with only one fairly efficient conversion.

 

neither of those draws anywhere near 400 watts. Last you told us you had 20 amp fuses as well (which is bad) allowing you a max of (14.4v*20a) 288 watts providing the wiring doesn't fry.. Chances are you never pulled more then 288 watts.

Mac book pro is around 180 when fully cooking and cell is almost nothing.

 

X-Country, see if you can get your shop to put a few extra 12v outlets in the bunk area. Some heavy wire, kind of like the amplifier power cables for car stereos, a small distribution/fuse block and a line to each outlet.

Wouldn't be all that hard to do.

 

You always have a safety factor build in. You can ask ten people and get ten different answers. It is HIGHLY suggested you do not change the fuses just because the lower amperage blows. All it takes is one time to overheat and catch fire. Then when they look as to why and find the reason, you can be held liable for the damage.

Do as I and others suggested. Stop by your companies shop and ask them to wire in a new connector with a better amperage load for your cooler. This way if anything happens, it falls back on the shop wiring it.

The 3/1 or 4/1 are wired in Parallel and will only draw the current needed.

 

all it takes is one time. You need to be on the safe side and have your shop wire in an extra socket for the cooler.