9V batt project - even need a fuse?

Discussion in 'The Projects Forum' started by bio88, Aug 14, 2011.

  1. bio88

    Thread Starter Member

    Feb 17, 2011
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    0
    Got a small 9V battery project that is basically a switch and a small DC solenoid. Would you recommend a fuse and if so what size?
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    If those small 9V 500mAH batteries then no need of a fuse.Just keep it simple.But using a fuse will not do any bad, so if you want to add it you have to tell us the current rating of the solenoid.

    Good Luck
     
    bio88 likes this.
  3. bio88

    Thread Starter Member

    Feb 17, 2011
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    Thank you - the small 12V solenoid has a 40 Ohm coil powered by the 9V.
     
  4. debjit625

    Well-Known Member

    Apr 17, 2010
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    So that gives us 9/40 = 0.225A or 225mA,their are fuse available but I don't think you will need any fuse for that unless you are using a very large battery capable of delivering a huge amount of current which could cause fire in a situation of short-circuit .Else if it's a small battery like used multimeters then not much will happen in a situation of short-circuit just the battery may warm up a bit and drain all the charge.

    Good Luck
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    It may be useful to consider what a short working life you can expect from such a battery. 9V applied to a nominally 12V coil relay will barely pull it in - in fact it may not work, even when the battery is new. The battery voltage surely cannot fall far before the relay will not work.

    Unfortunately, you are proposing to use the battery with a much bigger current drain than it is suited for. Even taking its capacity at its face value, you could only hope to get a couple of hours, and to make matters worse the Ampere-hour capacity gets worse at excessively high current drain. You might therefore get less than an hour of function with a PP3. If that is not acceptable, use a bigger battery.
     
  6. bio88

    Thread Starter Member

    Feb 17, 2011
    34
    0
    Thanks for the help! The solenoid only needs to energize/actuate to end of stroke. 9V gives me just barely the ness. mechanical force. Although more force is always better!

    Need to keep the circuit very safe and consumer level battery-wise. Don't want to burn anything down : )
     
  7. rmnorton2

    New Member

    Oct 12, 2011
    1
    0
    bio88-
    sounds like you might have already done what I am trying to start. What stroke is your solenoid? Where did you find it?
    I need a simple push solenoid with a stroke of an inch or more and would like to run it off a 9v battery. Will need to push a few pounds for a brief moment. Is this realistic?
     
  8. Butterworth

    Active Member

    May 6, 2009
    135
    3
    I think it would be more realistic to use 8-AA cells, rechargable if you must, but those will only give you about 9.6V (at a mAh rating from 800-1000mAh), if you use Alkaline, you will get about 12V(+/-) at a regular mAh rating (around 500mAh or less?).

    So its up to you to try:
    1. More voltage @ lower mAh capacity, or,
    2. Slightly higher voltage @ higher mAh capacity?
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    If you put a small signal diode such as a 1N4148 you can get reverse voltage protection (if you put the battery in backwards) and it may also act as a fuse when need be.
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    To consider the worst case, assume the user uses a 9V rechargeable and manages to short it. I think the old nicad batteries will deliver the highest sustained current. I suspect shorting one actually would create some risk of burns or even fire. A fuse is never a bad thing, except for the cost and footprint.
     
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