Portable DC & AC power

I would really appreciate some advise on this topic. This is my first step on saving a little power off the grid.
I want a portable power system to power a few 12 V DC and 120 V AC items like computer, cell phone, PDA, XM radio, etc. The local Home Depot, Sears, and Wal-Mart have some units that may work out well for me. These things are made for jump starting cars and pumping air into tires also. They are:
Home Depot - Husky - about 300 Amps - 400 watts AC - $90
Sears - Diehard 1150 - ? Amps, 400 watts? - $110
Wal-Mart - Black & Decker 400 - 300 amps - 400 watts (12V 19AH) - $99

Any experience with any of these? Can I charge any of these by plugging a small solar panel into the 12 V outlet? Any other (better?) options within $100 to $500?

Thank you very much! You may reply off list of course.


  • BB.BB. Super Moderators, Administrators Posts: 33,080 admin
    Re: Portable DC & AC power

    First, realize that standard lead acid batteries really don't store much power for their weight...

    A standard car sized storage battery can store about 100 amp*hours (or about 1 kWatt*hour) and you should only draw down to about 50% of capacity before recharging--or you will quickly distroy the battery.

    My older laptop takes about 20-30 watts while running, add 80% efficiency of the inverter, a 500 watt*hour car sized storage battery would support it about:

    Hours=500 Watt*hours / [25 watts / 80%] = 16 hours

    Run one of those 400 watt inverters at full blast, you would be lucky to get 1 hour out of a car sized storage battery before you killed it... (400 watts / [11 volts * 80%] = 45 amps out of your battery)...

    If you protable power, you really have only two options... 1) Identify your needs and go for conservation/specialization--i.e., small laptop, LED lights, propane powered fridge, etc.... and 2) get a small generator like a gasoline Honda eu1000i/2000/3000 (peak watts) and a gallon of gasoline will give you the equivalent energy of 10 car sized storage batteries (that 5 gallon gas can would be the equivalent of 50 car batteries). If you your portable power is long term, you can look to diesel or other type of fuel for the generator.

    The small "jumper battery" type of units are practically junk... I used one on a car to jump a dead battery and it never worked again (I don't trust the batteries inside are really storage type batteries--and in anycase, they are not rated for the type of currents that a jump or 400 watt inverter would draw). I would assume that you can get only about 1/10 the power as a full sized car battery (i.e., 50 watt*hours or 4 amp*hours) of useful power before recharging (or damage to battery).

    I am not trying to rain on your parade--there are many places batteries/solar/alternative power is a great thing to have and use. And there are many other types of batteries and sizes of batteries besides "car sized storage batteries." I just used that as an example of size that most everyone is familiar with (and about the maximum size/weight that anyone would concider to be portable)...

    Your best bet is to first identify your loads/requirements (with conservation and backup/alternative sources of power in an emergency--if needed). Then, look for solutions that may fit your needs. It may be a hybrid system... Good battery bank, charger, inverter with generator (run generator for a couple hours a day to charge, and on batteries the rest of the time), and as your budget allows, add solar panels (or wind generator) to reduce your dependence on the fossil fuel generator. But don't look at this as a portable system unless it is on a trailer or RV.

    Good luck!
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Portable DC & AC power

    Yeah, Bill is right. I've seen the guts in these things and they are mostly junk that the box stores have to sell. Many just have two small motorcycle starting batteries in them.
    These things are hyped up to the point where many people think they are capable of running everything but the hot water heater for extended power outages, and some aren't too sure about the water heater. I've had one guy curse me when I told him they wouldn't run his fridge during power outages. He learned the hard way, it wouldn't even START the fridge.
    The unfortunate thing is that people are sucked in, discover how useless they are, and think that that's the story on Solar.
  • System2System2 Posts: 6,290 admin
    Re: Portable DC & AC power

    I agree with the quality of the total package but remember... it's mostly for my PDA, cell phone, XM radio, and "maybe" my portable computer. It is not for my normal inside the house stuff... last month I used about 2,500 KWH so I know that little 19ah battery will not help me there! :)

    But I do appreciate all the advise. My long term plan is a solar PV system once the price drops a little. I live in deep south Texas and we get lots of sun. It has rained about 4 inches this year (normal should be 7 by now)... not many clouds here!

    Thanks again,
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