Battery not powerful enough

Discussion in 'The Projects Forum' started by James1402, May 30, 2013.

  1. James1402

    Thread Starter New Member

    May 30, 2013
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    Hello.

    I made a fire alarm system panel that is currently being supplied by 4v coming from the mains. I now want to use a battery as a source instead of using the mains but when I connect even up to 6 volts there is not enough power to run the panel (the light will barely light up and the sound is very weak)

    I have tested the batteries and I got a 5.37v reading.

    Any suggestions? Thanks :)
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Is that battery voltage reading made while they are under load?

    Is your supply 4V AC ?
     
  3. James1402

    Thread Starter New Member

    May 30, 2013
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    It's without the load, I didn't want to try any higher voltage battery incase it blew the circut.. (It's all hardwired, no circut board) so should I try increase the voltage until I get a 4v reading under load?
     
  4. wayneh

    Expert

    Sep 9, 2010
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    NO, a higher capacity battery would be a better strategy if the voltage is sagging under load. Batteries have a capacity specification, usually in amp-hours or milliamp-hours. A larger battery will have a lower internal resistance and be able to supply more current at a given voltage.

    I wouldn't expect the panel to require a "high" current, but without any details on the panel or the batteries, my guess is that is what is happening. The needed current is too high for the battery and the voltage sags.

    I'll ask again: How sure are you that the panel needs DC and not AC? If it's running fine on a mains-powered power supply, you can measure the running voltage.
     
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
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    To me that sounds like an odd voltage for a battery..
    Is it a 6 volt battery that's not fully charged? Or is it just an old battery?
    What is the battery voltage when it's connected to your alarm?
     
  6. circuitfella11

    Member

    May 10, 2013
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    5

    same with wayneh, i think its in the current, the batteries are not capable of providing it..

    hmmm, and also you have that hard wired circuit.. so its the best cue to measure a running voltage..
     
  7. James1402

    Thread Starter New Member

    May 30, 2013
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    I still need to buy more batteries (as I ran out :rolleyes:) My only worry with adding more current was it frying the circuit while the alarm was not sounding.

    It was using AC current from the mains But I didn't think that was a problem with this type of circuit.

    I have 4 AA batteries (1.5v each) and they where brand new. Perhaps there was slight resistance in the wires? I haven't had the chance to test the circuit while under load as Im currently in work.

    I will mesure the voltage reading while under load when I get home. I'm still fairly new with circuits and electronics so until now I believed having the same voltage coming from batteries just like the mains would still work :p

    Here is a quick schematic I drew last night of what I have made. Its very basic so some parts may be laid out wrong.

    Basically the switches on the bottom right are the smoke alarms and call points (break glass/pull stations) which, when closed, makes a relay which the panel off sounding the alarm. The [1, 2, 3] part on the top left is a 3 way switch turns on/off sounders as well as the buzzer in the panel.

    [​IMG]
     
  8. wayneh

    Expert

    Sep 9, 2010
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    No worries. A circuit only draws what it needs. Having a high current capacity does not mean that you will have any higher actual current. It's like having a thick garden hose with a spray nozzle on the end. The water flow is controlled by the nozzle, not the hose.
    This is still confusing. AC mains are 120V AC. You said your panel uses 4V. We don't know if that is 4V AC or 4V DC, or how the step down in voltage is accomplished. If it's meant to run on AC and you supply DC from a battery, it might cause a problem.
    Wire resistance is tiny compared to internal resistance of the battery. Big batteries have lower internal resistance and can supply larger currents without dropping voltage.
     
  9. James1402

    Thread Starter New Member

    May 30, 2013
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    So it wont blow the LED's if I add a higher voltage to the circuit (with resistors placed infront of each LED)?

    Ok so so when I created the circut it was running on a 4v AC power supply coming from the mains. (it was not converted to DC)

    When I changed the supply to 4v batteries, the supply is now 4v DC. I didnt think this would have being a problem as the only load on the circuit was a buzzer, speakers (controlled by a chip forgot to include that on the schematic thing) and the LEDS. Would that be a problem with this circuit?
    Thats weird then.. Maybe Ive being robbed 1v from one battery? :p
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Whoa! We were talking current, now you've switched to voltage. In the water analogy, voltage is like pressure. More pressure could burst your hose or nozzle, so you need to keep it in the right range.
    Ahhh, as I suspected. So you have just a transformer that converts mains to 4V AC? How is that 4V measured, is it simply written on the transformer?

    Now the question is why DC from your battery isn't working. Measuring the battery voltage under load is a first step, since the answer could be as simple as the battery being too small.

    Beyond that we'll need a better schematic and maybe detailed photos would be better.
     
  11. James1402

    Thread Starter New Member

    May 30, 2013
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    Its starting to make sense now. Never knew there was a difference, but hey I'm still learning :D

    So I need a barrery with a higher current output?

    Yes. This is what is written on the transformer:
    Input: 100-200v~
    50-60hz0.15A
    Output: 4v==0.56A

    Unfortunately the multimeter I was using had to be returned to my friend who was using it. Until I get my hands on my own I cant measure the readings :mad:
    I have done the schematic via a program I found online. I still don't know if it will make sense to you but here it is:

    [​IMG]
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Not so much. Lots of shorts as drawn. Since you've said the panel works, it must not be like the drawing, which absolutely would not. Maybe some detailed pictures would be a better way to go.
     
  13. James1402

    Thread Starter New Member

    May 30, 2013
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    That's a shame.. I need to get better at making These drawings. I need to take apart the panel before I take shots of it.. Ill try get it up tonight

    Edit:[\B] after looking at the diagram I've just made, I see the problems. I will just upload an image of the actual thing
     
    Last edited: May 31, 2013
  14. gerty

    AAC Fanatic!

    Aug 30, 2007
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    What is the coil voltage of your relay?
    What are you using for "lamp" and sounder, voltage/wattage?
    A picture will really help, we'll see how many errors on the drawing are really in the circuit.
    Your first drawing you show "end of line" is that supposed to be end of line resistor, and it's missing in the second drawing.
     
  15. James1402

    Thread Starter New Member

    May 30, 2013
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    I've attached an image of it below. As you can see its quite the mess. I've after breaking two of the switches so I will have to re-wire the whole lot. Hopefully I will do it cleaner this time
     
  16. wayneh

    Expert

    Sep 9, 2010
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    :eek:
    Understatement of the day.

    I recommend getting a clean and solid schematic before you begin building again. There's a reason people - even skilled designers - follow that workflow. Enough bad things happen even WITH a good plan.
     
  17. James1402

    Thread Starter New Member

    May 30, 2013
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    Ill attempt another schematic today (after reading tips on how to do them) then order more components online. Hopefully things will go right this time :rolleyes:
     
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