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[HELP] Trying to build very specific portable battery!

Discussion in 'Power Electronics' started by JML, Dec 24, 2015.

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  1. JML

    JML

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    Dec 24, 2015
    I want to build my own portable battery. Hoping someone here would be able to point me in the right direction. This is some of the things that I'd like to include.
    1: On/off switch
    2: Output would be a house hold outlet 3 prongs (AC outlet?) (need to draw 111 watts minimum)
    3: possible 2nd switch for small CPU type fan to blow hot air out of battery container vent. (Don't know how hot the batteries/container would get, container would be 3D printed ABS plastic)
    4: Batteries have to be able to handle 220-240 V / 50-60 Hz or 110-120 V / 50-60 Hz. (I have to double check for what the item i want to power specifically, but it would be nice if the one battery pack could work for both?)
    5: Would like to maximize the portables battery life but want to limit the size of the portable battery to 7.9 inches in diameter X 2-3 inches tall. (so it would be a flat cylindrical shape portable battery)

    I think that covers the basics of it! Any help from what components, the math i would need to do, any heat sink problems, how to wire up the switches, anything at all would be very much appreciated! Merry Christmas!!!
     
    Last edited: Dec 24, 2015
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    ok that's esy

    ok so you want a DC to AC inverter to power AC devices plenty of those on ebay that you can add to a battery
    you need to give info on power requirements

    not a problem

    Batteries take and are DC voltage ..... your sentence doesn't make much sense ... please clarify

    again that depends on what output power you expect/need at 120/220V
    but as a starter, that small size isn't going to accomplish much
     
    Martaine2005 likes this.
  3. JML

    JML

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    Dec 24, 2015

    Okay so for the batteries the item i want to power usually plugs into wall outlet, but i want to run it from batteries. It draws 111 watts total of power total, between the heating element and fan.

    What size would i need to get 1-3 hours of life?
     
  4. davenn

    davenn Moderator

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    you first need to specify what AC voltage you are going to use ..... 120 or 220, it affects the calculations
    and also the type of inverter you need to buy


    VERY large battery, car battery or bigger
     
    Martaine2005 likes this.
  5. davenn

    davenn Moderator

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  6. JML

    JML

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    Dec 24, 2015
    Okay i will check into the 120v/220v tonight and get back to you. Okay and huge ass battery. hmmm once i figure out the 120/220v is there a way to look at battery size vs run time? as in I don't want to lug around a car battery, but wouldn't be opposed to something a little smaller.


    Would running a bunch of lipo batteries in parallel be able to achieve the same affect as the car battery. I'm trying to optimize the amount of space/weight, and need the over all shape of the portable battery to be round.
     
  7. davenn

    davenn Moderator

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    yes there is :)
     
    Martaine2005 likes this.
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    111W for 3 hrs = 333Wh. A 100% efficient inverter powered from 12VDC would therefore need a capacity of 333/12 = 27.75Ah. Allowing for inefficiencies you'd need around 40Ah @12V (or 80Ah @ 6V). Hence the car battery, or equivalent.
     
    Martaine2005 likes this.
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    It has wheels, so is portable. Box it all up and you're good to go:)

    upload_2015-12-24_23-16-20.jpeg [​IMG][​IMG] upload_2015-12-24_23-24-25.jpeg :p

    Martin
     
    Bluejets likes this.
  10. JML

    JML

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    Dec 24, 2015
    okay so i got the low down on what i need,
    "110-120 V / 50-60 Hz, 120 W" that's what it says on the underside of the unit i want to power
     
  11. JML

    JML

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    Dec 24, 2015
    "110-120 V / 50-60 Hz, 120 W" hahah okay so lets say i want an hour, can i rig up some lipos in parallel or what would you do if i want to make this portable unit compact as possible?
     
  12. Martaine2005

    Martaine2005

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    An example here
     
    Bluejets likes this.
  13. JML

    JML

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    Dec 24, 2015
    Okay guys so what if I put two of these together then just hooked it up to one of the small AC car converters that usually plugs into the cigarett light like in a car. (cause then the converter would already have a fan in it ect)

     

    Attached Files:

  14. davenn

    davenn Moderator

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    Sep 5, 2009
    its NOT going to provide anywhere near the power you require !
    reread post #8 from Alec_t ..... for the power requirements, a couple of 6V lantern batteries strapped together
    aint going to do it


    Dave
     
  15. JML

    JML

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    Dec 24, 2015
    Thanks for working with me still, much appreciated. I realize that the video i posted and those batteries wouldn't work for what i want to do. I was talking about applying that idea to a larger battery or two larger batteries. Like a battery for a riding mower. I'd be willing to cut down my run time to 30minutes-1hour if I can use a smaller power source. (even smaller than a tractor battery)

    Going off of Alec_T's math:

    120W x 1hr = 120Wh
    120W / 12 vdc = 10Ah

    Are there any batteries that can match what i need for this?
     
  16. Bluejets

    Bluejets

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    Oct 5, 2014
    For your calculations, Alec_T did say you must also look at the inefficiency.
    Efficiency( approx 67%) and select a power source capacity from that.
    So your calculation of 10Ah needs to be much higher.

    Having a run time from 30 minutes to 1 hour means you will have to calculate at 1 hour as it is double the requirements.

    If you want specifics, you have to be specific.
     
  17. JML

    JML

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    Dec 24, 2015
    So if I'm understanding this correctly this inverter would be able to handle the amount of power I need it to be able to convert.
    "10.5vdc-15.5vdc
    400 Watt Max 200 Continuous"

    And now I just need to find a 12v battery to hook up to the inverter and depending on how many Amp hours or mila amp hours it is that will determine how long it can power the item?

    So if i can find a 10Ah battery I should be able to power this thing for one hour?
     

    Attached Files:

  18. JML

    JML

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    Dec 24, 2015
    Okay so lets say i want 1 hour out of a item that draws 120Watts. Can you please show me the math behind this?

    humor me, how big of a battery would i have to hook up to this inverter to run the item for 1 hour?
     
  19. hevans1944

    hevans1944 Hop - AC8NS

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    Why don't you buy an AC inverter and try it out? You are gonna need an inverter no matter what "battery" you come up with to power it, so you might as well get that out of the way now.

    I do think you will be disappointed in the "run time" you get from a pair of 6V lantern batteries. Even the 12 V 22 AH sealed lead-acid will only provide 100 watts a power for about an hour before you have to stop and re-charge it. Deep discharge of lead-acid batteries is not recommended, even for the ones labeled as such, or labeled as suitable for marine duty. Other battery chemistries are not as sensitive, but always follow the battery manufacturer's recommendations concerning discharge and re-charge parameters. Oh, and why does the battery have to be a flat cylindrical shape?

    A few years ago I bought an inverter for the sole purpose of powering up my HP laptop while on long road trips. I probably could have found some sort of "adapter" that would plug into the cigarette lighter socket, or into the auxiliary power socket, to provide the right voltage to my laptop, but since I already have a line-operated thingy to recharge the laptop battery, I figured why not plug that into an inverter and power the inverter from the cigarette lighter socket? Plus, I would then have 115 VAC power available for other purposes while "on the road".

    Usually the laptop goes into the hotel room for the night and I connect it to an HDTV in the room with an HDMI cable, powering up the laptop from a convenience outlet. Using the hotel wireless WiFi, I call up Netfilx or Amazon Video on the laptop and stream movies from the laptop to the big-screen TV provided by the hotel. I have never had a bandwidth problem doing this, but your mileage (or kilometers) may be different. On the road, I don't use the laptop much, especially if I am driving. My wife insists on it. So, it turned out not to be a very useful purchase after all since I gave up on my Sprint "hockey puck" hot spot because it was seldom used and very expensive on a month-to-month basis.

    It might help if you told us what you actually want to do with your rig. That is, describe the problem instead of what you think might be a good solution. For example (theoretical only): "I have diabetes and during long road trips my feet become swollen and I need to plug in a foot-warmer with built-in massage magic fingers. The Diabetes-R-Us store had a really spiffy model on sale which I purchased, but unfortunately it requires 110 - 120 VAC, 50/60 Hz, 120 watts and I need to power it for portable operation.... I am a long-haul truck driver with in-cab 12 VDC electricity available to power this puppy.... yada, yada, yada."

    Hop
     
    Last edited: Dec 25, 2015
  20. BobK

    BobK

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    Jan 5, 2010
    To answer your question. A 120W appliance operated for 1 hour need 120 Watt Hours.

    From a 12V battery this is equivalent to 10 Amp Hours.

    But,

    1. Efficiency will likely be about 80%, so 10 / 0.8 = 12.5AH.

    2. Batteries of this size are rated when discharged over 20 hours. At higher discharge rates they do not have as much capacity. At a discharge rate of 1 hour, the capacity is likely 1/2 the rated capacity. So 25 Amp Hours.

    So, to run your device for 1 hour off a 12V battery, I would expect it to take a battery rated at about 25AH.

    Bob
     
    hevans1944 likes this.
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