Help With Camping Project

Discussion in 'The Projects Forum' started by Epiales, Sep 7, 2014.

  1. Epiales

    Thread Starter New Member

    Sep 7, 2014
    3
    0
    Hey all,

    I've VERY new to anything dealing with electronics, but I have been reading about circuits and other things the last few weeks, and have become very interested in learning. I currently have some battery boxes that I use to store 18650 batteries in for portable power to charge my cell phones and such. But I am wanting something to like run a 12v coffee pot while I'm outside and have no place to get any. I'm a devil without my coffee lol...

    I have a question about battery storage first.... If I were to use this circuit board,

    http://www.ebay.com/itm/2PCS-5V-Min...132?pt=LH_DefaultDomain_0&hash=item4856410194

    Would that allow me to just parallel any amount of 3.7v 18650 Lithium batteries together? Since it doesn't change the Voltage, I wouldn't think the amount of batteries would matter? Like if I wanted to run 15 of the 18650 batteries to store more power, it would be okay?

    Secondly, to run serial on the 18650's, what type of circuit would I need? I'm assuming it would have to have 12v capacity to run a 12v coffee pot?

    Like I said, extremely new, but very fast at learning. Any help would be appreciated.

    Blessings,

    Epiales!!!
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    First of all, the charger isn't made to charge a bunch of batteries in parallel. Although the voltage is (theoretically) the same, the current requirements go up with each battery that is connected. You can only feasible charge one battery at a time.

    Second, the power requirements for the particular coffee maker will determine how to configure your battery setup. You won't get much power out of a single string of batteries connected in serial to make 12V. Most likely, you'll need to parallel sever strings, and I'm not sure how practical that's gonna be. You just have to read the wattage requirements and see how many batteries it's going to take to get that wattage, plus a certain percentage more to make up for losses. Actually, you should have twice the amp-hour capacity that you're going to need, at least.

    PS: Welcome to the forums.
     
  3. Epiales

    Thread Starter New Member

    Sep 7, 2014
    3
    0
    Hi Brownout, thank you for your response and in welcoming me :)

    I did not plan on charging batteries with the circuit I show in the link, but just wanted to store power. So instead of using like 6 of the 18650's which work well in the charger/storage box I currently have, I wanted to build my own box that holds like 15 or more of the 18650 batteries. Just parallel them all the way down and then soder to the circuit. Is that possible anyway, using the above circuit?
     
  4. Epiales

    Thread Starter New Member

    Sep 7, 2014
    3
    0
    As far as the coffee pot, it would be 12v/13amp/156 watt current draw....

    Does that mean that it will take 156 watts per hour to run it? Like I said, fairly new here.... Or does it mean it takes that many watts to do one pot of cofee?

    Now in order to get 222 watts off 18650 batteries, I estimated 25 batteries run serial. Now based on cost effectiveness, I could get a 12v / 30amp battery and that would work?

    Sorry for the noob questions, but I will learn quickly. Thank you!
     
    Last edited: Sep 8, 2014
  5. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Watts is power (Joules per second) and is equal to V * A - so 12V*13A = 156W

    So it tells you very little about how much power you need to heat a given quantity of water. Basically it is related to the resistance of the heater element so you supply 12V and the element will draw 13A. To work out how much battery power you need to heat a given quantity of water you need to look at the specific heat capacity of water - 4.187 kJ/kg/K so you need 4187 Joules to heat 1kg (=1 litre) by 1 degree. Assuming you want to heat half a litre (bit less than a pint) by 80 degrees you need 167480J assuming no losses. There are going to be losses so you can probably double that figure in reality.

    Warning, it's early here, I haven't had much coffee so the calcs above may be wrong, however the theory is right, but I get at best 17 minutes to boil the kettle!
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    There's a reason that camping gear usually uses liquid fuels to produce heat. The energy density is just so much higher - no need for heavy batteries and all the stuff that goes with them.

    I'd save the batteries for the electronics and use fire for making heat. Even solar heating would be a good choice if the timing was better matched. Unfortunately you likely want your coffee before there has been a lot of sun to warm it for you. That's why I build a fire first thing out of the tent. Well, second thing.
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Let's do a little math. You want 12V, so you need to stack enough (and just enough) to get 12V. I'm not familiar with 18650's so I'll just use 1.5v cells as an example. So, for 12V:

    N=12/1.5 = 8. So, you need 8 batteries in series for 12V. But what about current?

    156W/12V = 13A. Now, I made another assumption, which may or may not be correct. Let's say each battery is capable of delivering 1A. So, now each stack will deliver 12V @ 1 A, and so you'll need:

    13A(required)/1A(per stack) = 13 stacks. So, you have 13 stacks in parallel of 8 batteries, for a total of 104 batteries. Wait, we're not done yet.

    Now let's say it takes 20 minutes to make your coffee. So, you require 13A*.3h = 3.9AH of energy. That would divide between each stack, so that's ~.3AH per stack. Now assume that each battery has a .3AH rating. So you're good, right? Well not quite. The problem here is, your batteries are most likely destroyed after just the first pot you make. You really need to have double the AH for your application, so now, you're looking at 26 stacks of 8 batteries, or 208 batteries.

    I made a lot of assumptions, and you can plug in your own numbers. I avoid the whole issue by packing a 100AH deep cycle marine battery whenever I go camping. It runs my coffee pot, lights and my tent fan, because who the heck can stand to be in a hot-ass tent in the summer without at least a fan!?
     
    Last edited: Sep 9, 2014
  8. tom_s

    Member

    Jun 27, 2014
    285
    333
    side comment as its no (well, maybe) help to the OP.

    been a long time since i've been camping, but the general idea was to get away from all the hustle and bustle of the city. you took whatever you had in the backpack and walked for km's (that's miles for the imperial countries) until you found a camping spot and spent a night or few out in the wilderness. first 2 that were always done first, tent up, collect a bit of wood and a fire lit.

    i have 4 x 100AH marine batteries sitting here (4 x 90AH sla's as well, a little lighter admittedly), somehow i can't see myself carrying even one of those too far. here's me thinking camping was to get away from it all. cook and boil water on the fire for the coffee, food....

    how 741 of me :)
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    The campground I like is over 11,500ft - that's 3,500 meters in those unimperial countries - and so a cooling fan is not needed! It feels like there's not enough air for a fan to push around anyway. And NO WAY would I want to carry around the weight of a battery at that altitude. Snickers bar yes, battery no.
     
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