electrical gurus?

**750Y** · 1st July 2005, 18:57

Hi guys/gals, just need a heads up before hooking up the battery to my fishfinder. It says in the manual to use a 3amp fuse between the positive lead from the battery & the display unit.(failure to do this will void the warranty). I'm using a 12 volt motorcycle battery for power.
the problem is I went to dick smiths & bought a fuse holder & a pack of 'easy blow' 3 amp fuses. I wired in the fuse holder but when i opened the fuse pack & looked closely, they say 3amps at one end & 250v at the other.
Is this gonna be a problem? i haven't gone live yet just in case.

**scooterboynz** · 1st July 2005, 19:36

hi ya , i am a sparky and 3 amps is 3 amps whether at 12 volts or 230 volts ,,, the voltage marked on the fuse is its maximum operating voltage ,, its quite ok to use at 12 volts

**750Y** · 1st July 2005, 19:59

Originally Posted by scooterboynz

hi ya , i am a sparky and 3 amps is 3 amps whether at 12 volts or 230 volts ,,, the voltage marked on the fuse is its maximum operating voltage ,, its quite ok to use at 12 volts

YES! cheers scooterboynz, that's exactly what I wanted to hear, i'm off to power it up now & test, ready for the dawn patrol tomorrow...
laterz

**Jackrat** · 1st July 2005, 20:57

So ahhhhh,where we goin' fushin' mate.

**FROSTY:Me** · 1st July 2005, 21:21

no scooterboys is wrong --You must use $%$%$% brand fuses.(insert name of fishfinder company) These fuses are 29.95 each and all warrantys are void if ya dont use em.
OHH Im sorry I forgot it isnt a bike

**Ixion** · 1st July 2005, 21:25

Originally Posted by FROSTY

no scooterboys is wrong --You must use $%$%$% brand fuses.(insert name of fishfinder company) These fuses are 29.95 each and all warrantys are void if ya dont use em.
OHH Im sorry I forgot it isnt a bike

You didn't mention that delivery time is 6 weeks. From the distribution centre in Godfsakenistan

**750Y** · 1st July 2005, 21:42

well she's all good to go.. yehoo! tested a-ok. just add water 8-)
i know it's not a bike, but it does have a bike battery,2 cylinders & goes brrrm brrrm. 8-(

**Redstar** · 1st July 2005, 22:14

p=vxa

p = 240x3

720watts

12vX3

36watts

Umm.. a melt down like cronoble is on the cards...

**scooterboynz** · 1st July 2005, 22:40

Originally Posted by Redstar

p=vxa

p = 240x3

720watts

12vX3

36watts

Umm.. a melt down like cronoble is on the cards...

well you are right and you are wrong , if the manual says use a 3 amp fuse then thats what you use 3 amps , 12 volts or 12,000 volts it doesnt mater , the 240v or what ever marked on the fuse is the maximum voltage to use that fuse , trust me i didnt spend 3 years at tech and 15 odd years doing electrical work to not have a clue about things , and where the hell is cronoble? i thought it was chernobyl??????

**riffer** · 1st July 2005, 23:02

Exactly scooterboy.

It doesn't matter what the fuse is rated at voltage-wise, as the device will only draw a certain amount of current anyway.

Where you would come unstuck is if you had voltage of >12v or current of >3A going in to the device.

As the battery puts out 12v that's not likely, so the fuse will cut out if the device draws more than 3A.

Even though, at 36W its a pretty thirsty little device.

**GeorgeR** · 1st July 2005, 23:13

Originally Posted by Redstar

p=vxa

p = 240x3

720watts

12vX3

36watts

Umm.. a melt down like cronoble is on the cards...

umm, so you're assuming a fuse should be connected directly between 12v/240v and gnd?
A fuse has a set resistance (assuming constant temp) - meaning that at a constant current there will be a specific voltage drop across it.

So....

R = 0.1ohms (for example)
I = 3A

Vdrop = I*R = 0.3v

P = V*I = 0.9W

(or simply P = I^2 * R = 0.9W)

Note that the power dissipated is independant of supply voltage.