Wire gauge & Amps questions

[STBernard]

I want to modify my trickle charger harness and quick disconnect to handle a high draw accessory. The harness made by Yuasa is 16 gauge wire and has a purple spade-type fuse with an "3" on it. The accessory I want to hook up is a small air compressor that may draw 15 amps, and has a cig socket plug on it. I know the stock socket hooked up to the quartet harness will not handle the draw.

I cut off the end of the wire on the compressor and soldered on the quick disconnect in place of the cig plug and it ran for a second and blew the fuse.

I do not know what amp rating on that fuse, but was wondering how big of a fuse it would handle with the 16 gauge wire. The compressor says it will inflate a car tire in 3 minutes, so the high draw would not be for a long period or time if I get a flat, but I do not want to fry the wiring.
This is the compressor:
http://www.harborfreight.com/12-volt...sor-96068.html

Do I need to put a 12 guage harness on the battery, or can I just replace that existing fuse with a 15 amp rated one?

[sennister]

16 gauge wure maxes out at about 13 amps. So no I wouldn't simply put a 15 amp fuse on there. I would run 12 or 10 gauge wire run to the battery. However another thing to consider is what the max rating is on the cig adapter. What about a powerlet? These connections have a larger contact area and can handle more power. You could use the port for trickle charging, air compressor as well as heated gear or other things while riding. Unless you are going to try and put air in the tires while underway or trickle charge while riding.

The only problem is that you need to get a powerlet socket as well as a couple plugs to convert the compressor and trickle charger over.

If you are on a budget I would convert them to 2 pin SAE. They are avaialbe at Ace or other hardware stores.

[ChipSTer]

There is a table (maximum CYA amps/gauge) in Handbook of Electronic Tables and Formulas published by/for American Wire Gauge that will tell you what gauge wire to use... I would probably err on the side of caution and for 15 amps, I would use 10 gauge wire... And I wouldn't recommend just upping the fuse to 15 amps... You might end up with a red-hot wire burning through all kinds of stuff in the harness... At 15 amps, it wouldn't take but a few seconds to do serious damage... I am not an expert in this field, but I have stayed at a Holiday Inn Express...

[Old2wheeler]

http://www.windsun.com/Hardware/Wire_Table.htm This is a link to all the info you need. What it comes down to is that a given size of wire can carry a given amount of current (Amperes - or Amps) (Think of current as analogous to VOLUME of water coming out of a hose). Your fuse with the #3 on it will allow three Amps of current to pass through it... more than that will melt its conductor and it will become a blown fuse. Think of Volts, or Electromotive force (the PRESSURE it takes to make electrons move from one molecule of the conductor (usually copper) to the next and so on. In the chart on the link, if you go down to the 12 Volt chart and look at the 15 "Amps in wire" column, and follow it across you'll find that there is a 6 (meaning one can conduct 15 Amps at 12 Volts up to 6 feet in #14 gauge wire (By the way, as the gauge #'s get larger the wire gets smaller, ie: the next one over is #12, which is larger wire and can handle the same current up to 8.5 feet). So, you can start your project by considering how far you want to put the connecter from the battery, probably only a foot or two? By looking at the smallest wire size, #14 which is common at auto parts stores, you see that it is safe to carry 15 Amps up to 6 feet. So, if you use that size, you will be plenty safe and you can put a 15 Amp fuse in the circuit, and it will be unlikely to blow. If a properly sized fuse does blow, consider it a warning that the circuit is being asked to carry greater current than it was designed for. Going back to the chart, you'll see red blocked in under 20 Amps for #14. That means that if you put a 20 Amp fuse in a circuit of #14 wire that is, say, 7 feet long, you will be setting the protection (the fuse) at a current level (20 Amps) that is 5 Amps more than the wire can safely carry. So, in the event that you plug in something that draws more than the wire is rated to carry, the wire will get hot. The wire will get very hot. The wire will get hot enough in some cases to cause your motorcycle to catch fire. This is not good, thus one would be wise to understand fuses and what they do, etc.

Hope this helps...

Rod

[STBernard]

S
Thanks, but I do not know why the attached power cord with the cig plug is only 16 gauge also? BTW, I am using the 2 pin SAE connector for both the charger and the compressor. What happens if I had a 10 amp fuse where it calls for a 15 amp? Would it consistantly blow each time I used it?

I am pretty sure I will have to make a 12 gauge harness and protect it with a 15 amp fuse, but if the rest of the (stock) power cord is 16 gauge, what's up with that?

[Old2wheeler]

S
Thanks, but I do not know why the attached power cord with the cig plug is only 16 gauge also? BTW, I am using the 2 pin SAE connector for both the charger and the compressor. What happens if I had a 10 amp fuse where it calls for a 15 amp? Would it consistantly blow each time I used it?

I am pretty sure I will have to make a 12 gauge harness and protect it with a 15 amp fuse, but if the rest of the (stock) power cord is 16 gauge, what's up with that?

If you put the 10 A fuse in and run the compressor IF IT really draws 15 A, it will consistently blow that size fuse. However, lots of things get over-engineered, and it is possible that its current draw is less than 15 A, and it might not blow the fuse. Brings up a good point, when adding wiring it is wise to fuse it at the lowest current that is required as the fuse is THE SAFETY "valve" in your system or subsystem. On the other hand one needs to plan ahead and fuse it for what you will NEED to use as you are looking at your flat tire, for example, on the side of the road. As to the 16 gauge question... It's like there are two separate circuits. One is the one you put in with a plug on the end (And, by the way... Sennister... GOOD POINT about the capacity of the plug one chooses!!) and the other is the one the compressor engineer designed that assumes you have supplied her plug with sufficient current capacity. That #16 wire is to me a clue that they MIGHT have over engineered things a BIT. However it is safer to over engineer it than the reverse.

You are right on to use #14 with a 15 A fuse... as the wire gets bigger, it gets harder to work with. By the way again, http://www.posi-lock.com/index.html these Posi tap connectors are the coolest and easiest way to hook up stuff if you aren't going to use heat shrink tubing on soldered connections.

Rod

[RaYzerman]

You should be able to run a 10 amp fuse in 16 ga. Actually, just try it with the compressor under load blowing up a tire. Worst case the fuse blows. But my bet is the compressor won't ever see 15 amps., and the actual design load is much lower. I don't think any of us would understand why they put a 15 amp fuse in there.
However, the simple answer is make up a new harness for the bike portion, 14 ga. and you're good to go.

[Tom Mac 04a]

snip... purple spade-type fuse with an "3" on it. snip...for a second and blew the fuse.
I do not know what amp rating on that fuse, snip?

That was a 3 amp fuse... and under rated for the pump.

Replace the wire with 12g and add a 15a fuse and it will be fine and you and the bike will be safer.

PS... fuse the lenght of wire as close to the battery as possible!
(nothing worse than wire shorting out before a fuse and burining/melting from the high current, esp near a gas tank)

[Old2wheeler]

"PS... fuse the lenght of wire as close to the battery as possible!"
Tom Mac 04a

[sennister]

As for the small gauge wire on the compressor. Remember what was stated above in the post where it stated 15A 12 V with 14 gauge wire was good for 6 feet. How long is the cord? Probably about 6'.

I kind of doubt it pulls 15A as well but it is probably a little bigger than it needs to be because the last thing you want is your compressor popping fuses when you are on the side of the road. If you are in your garage chances are you are not using an emergency inflator as they are designed to be.

Also keep in mind that when your engine is running it isn't 12V it is in the 14V range.

I would agree with the comment about keeping it larger to accomodate not only this but other things in the future.