Fusebox question...

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Feb 17, 2001 | 09:56 AM

larryV

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From: Chicago, IL

Fusebox question...

For my boost guage, I used a mini fuse #8 (telephone) on the panel. I don't have the phone option and the fuse originally on it is 5 amps. I plugged in an add-a-circuit from pep boys with a 10 amp fuse (max for the mini size fuse) and connected my boost guage to that.

Is there a problem here?

I know, stupid question but I dunno much about electrical stuff but is there something wrong with putting in a 10 amp fuse on something that originally had a 5 amp fuse.

Thanks.

Feb 17, 2001 | 10:00 AM

James R.

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Not a problem unless the wires that lead away from that fuse were

scaled for those currents. How hot a wire gets is related to the resistance of the wire and how much current flows through it...and then finally how much surface area that wire has (determines the actual temp in degrees) the other two tell you how many watts of energy the wire will dissipate I^2 * R = P

Anyhow...more likely than not that 5 Amp fuse was there because that was the max current they wanted the phone device to draw...but to play it safe you could dump a 5 A fuse back in there. 5A fuse makes for 69 Watts...your 10A makes for fusing at 138 Watts...do you think your boost gauge has a 138 Watt lightbulb inside? ;-)

Regards,

James R.

2001 A4 1.8TQMSXP (StopTech A4 Brakes, StopTech SS Front - AWE SS Rear Lines, Oettinger Pedal Set + Dead, Oettinger RE's 17x8, Yoko AVS Sports 225/45/R17, European Xenon Housings, Bailey BPV & RS4 Grill)

Feb 17, 2001 | 10:05 AM

larryV

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From: Chicago, IL

James, if you got a minute...

Ed P isn't around so can you look at Ed P's boost guage FAQ and the schematics with the eagle editor included to see if a 15 amp fuse is absolutely necessary as he mentioned in the FAQ or is a 10 amp fuse feasable?

The add-a-circuit I found was only available in the mini size which can only use a max fuse of 10 amps.

If this is a problem, I may have to hunt down the bigger version add-a-circuits.

Thanks.

Feb 17, 2001 | 10:15 AM

James R.

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Muhahahaah sheesh...I could die laughing...ok there are 10 LED's I'm not even gonna look

at the schematic...I got sick of looking at that thing after I helped Ed redo the upper and lower scaling since they snatched the circuit from an App diagram for a different pressure sensor their scale was all wonky...I helped him fix it.

Anyhow 10 LED's at 20mA MAX each would be 200mA say toss on another 200mA for the rest of the circuit (way to generous) and you're drawing like 400mA I'd say a 1 or 2 amp fuse is what you should run 10A is waaaaaaaaaaaay to high the board would be smoldering on fire in front of you and the fuse would never even think about blowing...trust me.

Regards,

James R.
2001 A4 1.8TQMSXP (StopTech A4 Brakes, StopTech SS Front - AWE SS Rear Lines, Oettinger Pedal Set + Dead, Oettinger RE's 17x8, Yoko AVS Sports 225/45/R17, European Xenon Housings, Bailey BPV & RS4 Grill)

Feb 17, 2001 | 10:19 AM

larryV

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From: Chicago, IL

lol! I kinda figured that....

wondering why Ed said to use a 15 amp circuit in the FAQ.

Must've been hitting the pipe the day he wrote it

or was I reading that wrong?

Feb 17, 2001 | 11:26 AM

James R.

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Hittin' the pipe would be my guess...15A would fuse at a 207 Watt load...actually higher

cause fuses rarely pop at their rating...they'll handle surges well in excess of their rating. I would try to find something on the order of a 2 amp fast blo if they have such a thing for cars. That circuit should never draw more than 500mA if it does something is clearly wrong...so even a 1 amp fuse would make sense...but a 15A fuse is IMHO downright unsafe. You know one of the primary reason they have fuses in cars is to prevent electrical fires from starting when components supplied by that fused line fail in a shorted or low impedance state!!!

Regards,

James R.

2001 A4 1.8TQMSXP (StopTech A4 Brakes, StopTech SS Front - AWE SS Rear Lines, Oettinger Pedal Set + Dead, Oettinger RE's 17x8, Yoko AVS Sports 225/45/R17, European Xenon Housings, Bailey BPV & RS4 Grill)

Feb 17, 2001 | 03:37 PM

WClark

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Biigger than needed...probably wont protect gauge from melt down

That gauge draws under an amp in operation. The fuse just needs to be big enough to not fatique and not so be as to not protect the product (or the car) from failure. 2A-5A is plenty big. Larger fuses will still blow if you have dead short in the circuit or wiring but a 10A will allow the unit or wiring to heat at up to 120W during a less-than- short-condition defect before the fuse blows.