The reason being is that that is a constant 120v source. There are no variances surges or anything at your house. with a battery the voltage can be anywhere for 10 to 14 easily and the power sent out varies even more. The fuse will help make sure that the device does not get surged which is the reason why the manual tells him to use a 1.5 A fuse. A DC battery circuit and a AC house circuit are nowhere near analogous. Just keep with the 2 A fuse and you will be good to go!
I'm not sure what kind of entry level electronics class you took in school, but you clearly do not understand the purpose of fuses. And even less about the relationship of AC to DC. It was not my intent to post this to start an argument, only to clear up some things. People come to this forum (myself included) to learn new things, and hopefully learn the RIGHT things. Unfortunately, there are no entrance exams to qualify to post information. This is the first topic I felt compelled to reply to because it is a topic I know very well, not because I was bored and needed to talk. So let me try to explain this one more time.
Let me try to do this in order of how you stated it:
All electricity (AC or DC) is subject to variations in voltage. This is known as voltage drop, and it is present whenever a load is running. The higher the load, the higher the voltage drop. I do not know why you think AC has no voltage drop, but it does, just like DC.
Secondly, as far as variations and surges go your house is FAR more likely to experience a voltage variation or surge than your car or bike. The reason for this is simple, you, and all of your neighbors, are sharing the same power. The voltage in YOUR house will easily DROP if some of your neighbors are running very high load demands. Sometimes just your own AC unit, or high powered circular saw, or maybe even your well pump if you have one, is enough to cause the lights to dim in your house while it kicks on. This is a variance so large you can SEE it. If you measure the voltage coming in to your house at different times of day, and different times of year, I assure you you will get different results. Typically house voltage varies between 110-120 volts easily. And as far as surges, it is well known that lightening can easily go through a houses electrical wiring and fry anything in its path. This is why you can (and should) buy surge protectors for anything you want to plug in to your house and not fry in a lightening storm. Now as far as the bike, the only person using that power is YOU, so you are not going to see any loads that you did not put there, making that source of power much more consistent that that of your house. Also, you will not be subjected to a lightening surge through your car or bike, making these systems immune to that as well. So I'm not sure why you think a surge is a problem on a bike?
And third, here is a point you REALLY need to understand: FUSES ARE FOR PROTECTING THE WIRING, NOT THE EQUIPMENT. This is not something I made up, this is a fact. Fuses do NOT prevent surges, fuses do not control voltage, fuses do not limit the power going to the load in any way, shape, or form UNLESS it blows. There are devices that filter and condition voltage, but a fuse is NOT that device. What this means, in basic terms, is that a GPS running off of a line with a 7 Amp fuse will draw EXACTLY the same load as that same GPS running off of a 2 Amp fuse. The amount of current that is drawn by the running GPS is determined by the GPS unit, and ONLY the GPS unit. It will draw the EXACT same load no matter if a 2 amp fuse is used, or if a 20 amp fuse is used. The only purpose for the fuse is to keep the wire from melting and causing a fire, or other hazzard as a result of a failure of the insulation. This is the purpose for matching a fuse to the gauge of wire being used. Now, some manufactures may choose to use a smaller fuse than the wire gauge will allow, lets say they use a 5 amp fuse instead of a 10 amp fuse. They do this only to create a little extra saftey margin for the wire because they know that the load they intend to operate will not exceed that amount, NOT to protect the equipment being used.
And, just because I think you are missing this point, I will separate it on its own. The GPS will NOT draw more power that it is designed to draw UNLESS it has ALREADY suffered a malfunction. In which case, it may THEN cause the fuse to blow. The fuse WILL NOT prevent the GPS from "blowing up" first. This is why the fuse does NOT protect the equipment, just the wire.
And there is nothing wrong with using a house analogy to shed some light on the bike wiring. Electricity is electricity. Unless you want to start talking things like induction circuits, or EMF, or other things that are AC specific, all of that which I have used for explanations are perfectly analogous.
Having said all of that, I will end basically the way I ended my first post. And that is to say that there is no problem with using the 2 amp fuse to power the GPS, it will not hurt anything. However, there is NO REAL BENEFIT either, just the wasted time of changing it. If you want to change it, that is certainly your perogative to do so, but I at least would like you to understand the reason you are changing it, and the reason you do not need to change it, so you can make an informed decision and do it for the right reason, not because of some false sense of security you feel you are gaining.
Kevin
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