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Blown fuse

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william linvill

10-15-2001 19:21:35




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I have a 1966 IH cub turn lights on all work bright, dim, rear red flash and rear work light must have been set up for road crew. when the engine is started the fuse blows. have taken instrument panel loose and can see wireing and have found no shorts any ideas ?




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Jon Hagen

10-16-2001 15:14:49




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 Re: blown fuse in reply to william linville, 10-15-2001 19:21:35  
Check your charging system voltage with the engine running fast. System voltage should less than 15 volt. If voltage is too high,acessories will draw much more than normal amps. Also if more lights have been added then the stock fuse may be too small. You may need to add 2-3 amp larger fuse for each additional light.



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Dusty

10-16-2001 06:32:24




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 Re: blown fuse in reply to william linville, 10-15-2001 19:21:35  
If you are starting the engine while the lights are on, the starter draws a large load causing a voltage drop this will cause a larger amperage draw to the lights which could cause the fuse to blow.
Dusty



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How?

10-16-2001 09:04:38




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 Re: Re: blown fuse in reply to Dusty, 10-16-2001 06:32:24  
How could a lower voltage cause a higher amperage draw?

RD



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BB

10-16-2001 10:16:19




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 Re: Re: Re: blown fuse in reply to How?, 10-16-2001 09:04:38  
It can't. Current is equal to voltage divided by resistance. Since the resistance cannot change without something in the circuit changing, the current will drop as the voltage drops. That's why you will see your lights dim when you are starting your tractor or car or any other vehicle.
I can only guess that there is a relay somewhere in the circuit that gets picked up when the engine starts. There may be a short or miswire in that circuit that grounds out the lamp circuit when the relay gets energized.

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Thanks

10-16-2001 12:21:26




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 Re: Re: Re: Re: blown fuse in reply to BB, 10-16-2001 10:16:19  
For a minute there I thought they had repealed Ohm's law and I missed it in the news.

RD



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Old Sparky

10-18-2001 18:51:47




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 Re: Re: Re: Re: Re: blown fuse in reply to Thanks, 10-16-2001 12:21:26  
Actually, lower voltage frequently results in higher amperage draw. In the case of incandescent lamps, the filament when cold has much lower resistance than when hot. The lower voltage=cooler filament which draws more amperage. Too-small wire causes voltage drop and sometimes, blown fuses. Same thing happens with electric motors, especially induction type. Lower voltage results in lower impedance, the effect of which is measured in ohms, although the unit of impedance is "henry".

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Red Dave

10-22-2001 08:44:56




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 Re: Re: Re: Re: Re: Re: blown fuse in reply to Old Sparky, 10-18-2001 18:51:47  
Sparky, Your point that an incandescent bulb filament becomes more resistive as it heats is correct, but if the amperage through the filament did increase, the filament would have to get hot, thereby increasing resistance, but that is probably not what is happening here.
There isn't much data to go on, but I think Jon Hagen is on the right track.
You are also correct in pointing out that an AC induction motor, running undervoltage, will draw more amps. However, the incandescent light circuit in question is a purely resistive DC circuit. Inductive reactance would not be a factor since it is only associated with AC circuits. In a resistive DC circuit, when voltage across the circuit drops, amperage must also drop. BTW - the "henry" is the measure of inductance, not inductive reactance, which is measured in Ohms.
I don't wish to start a pi$$ing contest here, just clear up a few misconceptions about electricity and electrical terminology.

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