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3a fuse blows but 5a doesnt.

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tomhanaway

Joined: 12 Aug 2006
Posts: 111
Location: Murphy, NC

Posted: Fri Feb 11, 2011 2:26 pm Post subject: 3a fuse blows but 5a doesnt.

I have led warning lights for doorâ€™s being latched (20awg).  Iâ€™m also running a stall warning wire (18awg) to the same fuse.

 

If I use a 3 amp fuse, it blows immediately when power turns on and  both led lights go out.

If I put in a 5 amp, the system works as designed and lights stay on indicating doors not latched.

 

I traced and found the short to ground (part of an ongoing installation-problem solved) but I donâ€™t understand why one fuse pops immediately and one slightly larger doesnâ€™t.

 

As stated above, running a  20 and 18 awg at this fuse.

 

Thanks in advance,

Tom Hanaway

RV-10

Boynton Beach, FL

  [quote][b]

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nuckolls.bob(at)aeroelect
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Posted: Fri Feb 11, 2011 4:14 pm Post subject: 3a fuse blows but 5a doesnt.

At 05:16 PM 2/11/2011, you wrote:

 	  Quote: 	
		  I have led warning lights for door's being latched (20awg).  I'm 

also running a stall warning wire (18awg) to the same fuse.



If I use a 3 amp fuse, it blows immediately when power turns on 

and  both led lights go out.

If I put in a 5 amp, the system works as designed and lights stay on 

indicating doors not latched.



I realize I'll want to go in and trace all the wires to make sure I 

don't have an unintentional ground but I don't understand why one 

fuse pops immediately and one slightly larger doesn't.


	


    how much current flows in the protected circuit.

    If you had a unintentional ground, no fuse would

    stay intact. >But if you had, say 4A of current

    flowing in this circuit, then a 3A would blow

    quickly and a 5A would hang around.



    Can you scan and publish a schematic of the

    system you're trouble-shooting?

   Bob . . .

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tomhanaway

Joined: 12 Aug 2006
Posts: 111
Location: Murphy, NC

Posted: Fri Feb 11, 2011 4:51 pm Post subject: 3a fuse blows but 5a doesnt.

Bob,

It was an unintentional ground.  I hadn't hooked up the final stall warning

buzzer and the wires were lying on the bottom of the fuselage. I don't have

a schematic of this portion of the system, just coded wires.  

Tom



--

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_________________
RV-10. Built and sold
RV-8a. Building

gpabruce(at)gmail.com
Guest

Posted: Fri Feb 11, 2011 6:01 pm Post subject: 3a fuse blows but 5a doesnt.

Rather than use fuses to guess at your amperage, use an ammeter and put in series. It's not a short, so no need to trace wiring. Its simply how much current is being used. The fuse is sized to protect the wire. The wire is sized to supply the device. I don't know off hand the protection required for a 20awg and an 18 awg. I also don't know the nominal current required for your devices. You must begin there. Is the device using more current than it is designed to use? In the case of multiple devices, the device currents must be added to know the total current. Then is the wire capable of handling all devices or must they be wired and fused separately. Begin at the device . . . read what the specs are, measure the current with an ammeter not a fuse.

    

 On Fri, Feb 11, 2011 at 2:16 PM, Tom Hanaway <tomhanaway(at)comcast.net (tomhanaway(at)comcast.net)> wrote:

 [quote]   

I have led warning lights for door’s being latched (20awg).  I’m also running a stall warning wire (18awg) to the same fuse. 

  

If I use a 3 amp fuse, it blows immediately when power turns on and  both led lights go out. 

If I put in a 5 amp, the system works as designed and lights stay on indicating doors not latched. 

  

I realize I’ll want to go in and trace all the wires to make sure I don’t have an unintentional ground but I don’t understand why one fuse pops immediately and one slightly larger doesn’t. 

  

As stated above, running a  20 and 18 awg at this fuse. 

  

Thanks in advance, 

Tom Hanaway 

RV-10 

Boynton Beach, FL

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