Question about the Accessory Power Outlet mod...

[T-Bone]

I am going to do the mod to my GS and I was wondering what fuse I should use.  I would think a 15amp but I am not too sure.

[sledge]

The rating of the fuse will have to depend on the amount of current the accessory draws and the current it draws will depend on the power it consumes.
More power=higher current=bigger fuse.
What are you thinking of powering off it and what is its wattage?

[T-Bone]

just a cell phone or maybe a GPS for long trips.  I am not sure the power that they would use.  I dont have a GPS unit yet to check.

[walkingman]

I just added an outlet today, and I used a 20 amp fuse. I power a GPS with the setup, and the adapter that belongs to the GPS (that plugs into the outlet) has a much smaller inline fuse as well. So, the 20-amp leaves headroom in case I want to do something else later on.

Really, 20 amps is probably more than is needed, but it's just what came with the little kit I picked up.

[John Bates]

I am going to do the mod to my GS and I was wondering what fuse I should use.  I would think a 15amp but I am not too sure.

The max load that you anticipate determines the max current draw. 

The wire size is then chosen to safely carry the max current.

Then the fuse size is determined to protect the wiring. 

It goes something like this:

12 ga wire, 23 amp fuse
14 ga wire, 17 amp fuse
16 ga wire, 13 amp fuse
18 ga wire, 10 amp fuse
20 ga wire, 7.5 amp fuse

These number are just to give you an idea of how it works.
The actual numbers depend on several factors, such as the type of insulation on the wire and the location of the wires.

 

[RedShift]

John's post reminded me that there are several posts herein that explore the amount of "surplus" power that can be drawn without harm to the charging system.

If memory serves, there is no more than 100-120 watts of available power for a stock GS500.  At 12 volts nominal power, that would make 8-10 amps that one could draw before you're robbing Peter to pay Paul.

So I'd use a 10 Amp fuse even if you have a wire thicker than 18 gauge.

(Where's StarWalt.  He knows more than me about this stuff.)

[3imo]

John is on the right track but I believe his wording is misleading.

Then the fuse size is determined to protect the wiring. 

the fuse size is determined by

the amount of current the accessory draws

And the size of the wiring.

Remember, a fuse in this part of the circuit will be protecting everything after it. In other words, it's sole pupose is to protect anything you use with the accessory oulet. Although it will protect your bike if your accessory shorts and pulls too much current, the determining factor is the max current pull of the accessory.

You must chose a fuse to protect the wiring and your accessory. I doubt anything you use will require more than a 10 amp fuse, and If so (as Redshift put it) you will be robbing Peter to pay Paul.

[John Bates]

John is on the right track but I believe his wording is misleading.

Then the fuse size is determined to protect the wiring. 

the fuse size is determined by

the amount of current the accessory draws

And the size of the wiring.

I think you have restated what both sledge and I have said, which is fine.

Remember, a fuse in this part of the circuit will be protecting everything after it. In other words, it's sole pupose is to protect anything you use with the accessory oulet. ..........

I have to disagree with you here.  For motors and such that don't have internal protection and where the operation of the device, stalled or overloaded, can pull damaging current, yes.   But for most electronic stuff, no, you don't usually protect them and the wiring with the same fuse.  Most electronics have a small internal fuse for self protection.
The inline fuse in generally for wire protection only.

[3imo]

Then we agree to disagree. 

either way it doesn't really matter. As far as his GPS or Cell charger goes, I have seen the adapter plugs with fuses built in and some without.

In my line of work I generally take into account both the gage of wire and current draw of the load when designing a circuit, but like you said most "loads" I mean to protect do not have any other means of protection.

I didn't mean to offend, just clarify. We still pals? 

[John Bates]

Then we agree to disagree. 

Why not, that's life, right?