Circuit Breaker can be used in battery operated devices?

Discussion in 'The Projects Forum' started by Lightfire, Dec 27, 2010.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    Well, I'm back. It's me again, Lightfire.

    Well, I am planning to have a project about circuit breaker on how it's operates... But, I don't want to test it in electricty as for sure my parents will not allow me to do that...

    So, may I know if it can be done by 12 volts battery or lower??? and how to use it? :p

    p.s. ARE YOU FAMILIAR WITH "Dynamo"?

    Lightfire xD
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
    Cars are full of them nowadays, auto parts stores have them or they can be ordered from almost anywhere. For a demonstration purpose you'll want one that deals in low amperage so you won't have to put much of a load on it to demonstrate how they work. 2 or three switchable 12V RV light bulbs and an inexpensive motorcycle or any sort of 12V gel cell battery would make a nice supply that can be recharged. Get a breaker rated to take one but not two of the light bulbs, then switch them on one at a time to show that one won't kick the breaker but adding the second will after a brief amount of time while three will kick the breaker much faster.

    If this is for a science fair or something school related you may get extra points if you also illustrate common fuses as well as polyfuses.

    A polyfuse is a self-resetting circuit breaker that are not only extremely handy for some designs but also quite intriguing to most people because so few have ever seen one.
  4. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010

    So, if some of my devices accidentally short circuit no matter its accident or not, the battery will not explode as circuit breaker will take care about it, I mean will automatically shutdown? Isn't it???

    Are you familiar with watt hour meter (which is given by your electric company, I mean the one that provides you electric supply)? Is there any like that operated only by battery??? :pPPPPPPPPPPPPPPPPPPPP
  5. k7elp60

    Distinguished Member

    Nov 4, 2008
    The following words are of caution.

    Both a circuit breaker and a fuse require some time to open the circuit when a short occurs. A lot depends on the ratings of both items. Fast blow fuses are usually faster than a circuit breaker as the circuit breaker needs a short time to heat up.
    A typical 10A fast blow fuse will safely pass 10A forever without opening, but if the current increases to 15A it can take from 15 to 20 seconds for to open. If the current thru the fuse increases to 40A, the fuse will open in 0.1 sec.

    A typical thermal circuit breaker has the following specs:
    100% load----no trip
    145% load----trip in 1 hour
    400% load----trip in 1.5 to 6.0 seconds
    1000% load---trip in0.15-0.65 seconds

    The short circuit current is affected by the resistance of the short, the current capabilities of the battery. If resistance of the wire can always affect the current depending on the size of the wire and the length of wire from the battery.

    I have used a lot of sealedl-lead acid batterys in various capacities. I always use a fuse between the battery and the load. I didn't use a fuse one time and I had a short that caused a fire, as the connecting wire got red hot and burned the insulation completely off. Some batteries will supply over 10 times their AH capacity when a short occurs. For example
    a 7AH battery can supply about 700 amps for a short time.
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    No, the battery won't explode unless you try using some sort of unreasonably large circuit breaker, keep it close to the load of the circuit that's being powered. Just to be safe go ahead and include a hidden fuse somewhere, certainly can't hurt.

    Your second question is a good one, they're basically a cumulative amp meter that operates only off of AC by a motor driving the indicator dial setup. The higher the amperage through the motor the faster it spins.

    The only thing I know that would be close for DC may not even be available anymore, it was a long glass tube filled with a metallic compound (probably mostly mercury) + an electrolyte that was used to measure hours according to the current that was passed through it. If you've got access to a chemistry lab you may be able to duplicate the idea with more common metals and glass tubing but they're rather slow in response depending on design. tube hour meter&f=false

    [EDIT:] You'll need to start a page or two up in that link to the old book.
    Last edited: Dec 29, 2010
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
    I found something similar but at about 4x that price. I'm sensing he's on a limited budget.

    A bit of further research proves that people have made devices out of common laboratory glass tubing with metal at each end and an electrolyte inbetween but in his case it seems to me that a simple ammeter and a stopwatch would serve the same purpose.

    One of these days I'm going to do a little quartz glass blowing myself. I need to rig up a furnace, no problem for me as I've made them before, then do a little glass welding to separate a cathode end, a reservoir for some CuBr, some mild gas replenishment fittings and all the internals including an isolated discharge tube and Brewster windows for the main tube ends. Care to guess what I'm making in time?

    I've already got most of the parts, just never have the time nor need for it.