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Old 27th January 2009, 23:41   #1
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Thumbs up How to Determine the Fuse/Wire Size for YOUR Project.

Came across these interesting articles on the internet. Thought it would be helpful.

Calculating the Fuse Size

A common car audio question I get is, "What size should my fuse be?". This is almost always in regards to the main power fuse. The most important component you'll install in a car audio system. This is the fuse that protects the system and your vehicle and is located within inches of the battery. Choosing a fuse size that is too large will not provide adequate protection and choosing one that is too small will cause a lot of blown fuses. Here's a few guidelines you need to know when locating and sizing the main power fuse for your car audio system.
  1. Location - The only function of the main power fuse is to protect the main power wire. This in turn protects the vehicle. Without the fuse a short in the main power wire could cause excessive current to ignite the wire and eventually the vehicle (it's happened). This is why you want the distance between the battery clamp and the main power fuse as short as possible. Any length of cable between the fuse holder and the battery clamp will be unprotected. The general sound off rule is eighteen inches but the shorter the better.
  2. Current Handling - The fuse needs to handle the power that will flow through the cable under maximum operating conditions (full power) and no more (ideally). To determine the maximum amount of current that will be needed you will need to know the current draw of each part of the system that draws power from the main wire. For example, if you have two amplifiers that draw 30 amps and 50 amps respectively you'd want to use an 80 amp fuse.
  3. Fuse Type - There are three main types of fuses used in car audio. The most common is the barrel (cylindrical) fuse which may be an AGC or AGU type. The second most common is the blade fuse which is the type most often found in your vehicle's fuse box. Large blade fuses are used in some fuse holders and may be referred to as a MAXI fuse. The least common type of fuse is the ANL or "wafer" fuse. These are used in the larger fuse holders when high current handling is required. Typically 100 amps and higher. The type you use will depend on the current capacity needed and your own preference. For draws of less than 100 amps expect to use a barrel fuse. For currents larger than that you'll probably be looking at the more expensive wafer fuse.
  4. Fuse Size - Using the method in item two you'll be able to choose the size of the fuse you need. But what if you have a current draw that is greater than one value of fuse but less than another (i.e. 125 amp). In this case you have the option of either choosing a 100 amp fuse or a 150 amp fuse. I always go for the larger fuse to reduce the chance of accidental fuse blows. However you may choose to go with a smaller fuse for greater short circuit protection. Just keep in mind that if you keep blowing fuses you'll probably need to move up to the next size. But if you're blowing fuses and you've sized it correctly for your current draw you may have another problem. Time to break out the multi-meter and check for problems.
Doing those four things will help you choose the right fuse the first time. It may also save your car from a fire in the event of a short circuit. Car audio power wires can carry a lot of power so make sure you're fusing properly to prevent disaster.
Source : Car Audio Fuse Selection

Determining Fuse Size.

The question of determining fuse size has been a common one lately so we decided to make a quick write up on choosing the correct fuse size. One common misconception about choosing the correct fuse size is that itís dependent the load of the circuit. Actually, the load of the circuit should have nothing to do with choosing a fuse size. The fuse size should be based on the SMALLEST wire (largest gage number) in the circuit. Here is how to correctly choose the right fuse size for your circuit.

1) Determine the wire gage you already have by locating it on the package or measuring it, you can also look at the topic this was posted in on Oznium forums for a step by step guide to finding the amperages for common products at the Oznium store.

2) Use the following table to determine the maximum current for whatever wire gage is being used.

3) Take the maximum current value obtained from the table and find the largest fuse you can find that still falls within the limitations. DO NOT EXCEED THE VALUES ON THIS TABLE! Common automotive blade-style fuses exist at 5A-20A in 5A Increments. Ex: 5A,10A,15A,20A

Determining the Total Amperage of your Circuit

So you just bought your stuff at Oznium and are getting ready to plan your installation while USPS gets it to your door. One of the first questions to ask when planning your installation is what size wire to use, which will later determine what fuse to use.

Don't worry if you're lost, you're at Oznium, we're helpful here.

Current is measured in Amperes, abbreviated to Amps or just the letter A. Because of the low-current nature of the products at Oznium, most of the products, and the table that I've developed, have current listed in milliamperes or mA for short.

1A is equal to 1000mA

To find the total amperage in your specific installation, refer to the table below. Find the items that you are installing and their current requirements. Add the values and divide by 1000 to get your total current in Amps. You can this use this value in the table above to determine the minimum wire size required.

Here's an example.

Say you bought a cold cathode kit for each side of the dash (2 Transformers), 5 superflux LED's for your vents, and a 4.7" Flexible LED strip for your center console.

If you want to put all of these on a single circuit, you'll need to know the current. Based on the table above, each transformer draws 700mA, each Superflux LED draws 80mA, and the LED strip draws 80mA

If you add up (700*2)+(80*5)+(80*1) you would get 1880mA total.

Divide this by 1000 to come up with 1.88A.

Put 1.88A into the top table in this post. That table tells you that you should have no smaller than 21 gauge wire for your circuit.

Personally I would go with the 20 gauge wire and a 2.5A fuse.
Source : How to Determine the Fuse/Wire Size for YOUR Project
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