Fuse differences

[yellow85cj]

What is the difference in these 3 fuses? All blade type, all 20 amp.

Do they have different melt times?

Found this pic on a site.

 

[Torxhead]

I remember when they all used the glass tube type, and they worked just fine. Now they come in all shapes and sizes.

 

[Captainlance]

All 3 are 20A fuses, although they are physically different, the electrical characteristics are all the same. As time has moved forward, manufacturers have made them smaller in an attempt to save space, material, and of course $$$$$

 

[Peanut Butter]

What is the difference in these 3 fuses? All blade type, all 20 amp.

Do they have different melt times?

Found this pic on a site.

What you have in order is a MAXIE, ATO or Regular, and a Mini. All are rated at 20 amps, but the big difference is the amount of heat they can handle and most Maxie fuses are rated for 20 to 80 amps. ATO is 2.5 to 40 amps. Mini are same as ATO in amperage. The amount of heat a fuse can dissipate is significant since larger amps create more heat as the fuse acts like a resister which creates heat. In a short the fuse heats up to a point where the metal inside melts. Just as a 22ga wire cannot carry the current that a 4ga wire can, the fuses are the same.

In a different look the wire used to power a starter is larger than a wire used to power a radio, the fuses must also be larger. Trying to pull enough current through a small wire from a battery to a starter will melt it, the fuse is the same. Think about the amount of pressure in two different sizes of water hoses. The pressure can be the same, but the volume will be different.

Hope you're totally confused now..........

 

[Peanut Butter]

All 3 are 20A fuses, although they are physically different, the electrical characteristics are all the same. As time has moved forward, manufacturers have made them smaller in an attempt to save space, material, and of course $$$$$

Not necessary true. The mini and the ATO maybe, but the Maxie can be found under the hood of most modern vehicles. The are used for the Air Conditioning system, and other large capacity systems.

 

[yellow85cj]

You are correct PB... I'm more confused.

20 amps is 20 amps, whether it is running though a 2 ga wire or a 10 ga wire.

Don't the amps create the heat?

The question comes up from my trying to use an XJ PDC for a relay box (lights,fan, etc).

There is a line of maxi fuses. They are powered from a bus bar. They are feeding wire that ranges from, at the most 14 ga to probably 6 or 8 ga. Maxi size fuses run from 20 to 60 amps.

Now if what you are saying is that a maxi fuse is more of a fusible link wire type fuse, where it can take the over rated amps (surge) for a longer period of time, before melting, that would make sense. Maybe a modern day fusible link?

From past electrical posts, you should know that you are not explaining it to a dummy, you are explaining it to an electrical idiot.

 

[Peanut Butter]

You are correct PB... I'm more confused.

From past electrical posts, you should know that you are not explaining it to a dummy, you are explaining it to an electrical idiot.

Sorry, I guess I'm not the best at explaining this.

So let's look at the hose comparison: In the Fire Department they use a 1 1/2 inch hose and a 2 1/2 inch hose. Both are set at 100psi from the Fire Engine, but the amount of water they put out or volume is different. Also the amount of friction or heat going through the 2 1/2 is less than the 1 1/2 inch line.

Now think about a small 22ga wire and a 4ga wire. Both are 12 volts. Both fuses are 20 amps, but the 4ga wire pulls that 20 amps easier than a 22ga wire due to size. In order to maintain the 20 amp max current, the 4ga wire needs a bigger fuse in size to not over heat. It is the amount of resistance going through that fuse that makes it blow. Resistance can be thought of as heat, like an electric stove top. The round element heats up due to the resistance. So the Maxie fuse can handle more heat as the device being used attempts to pull more juice through the wire.

In a vehicle the horn usually has a large fuse and a relay because a small beep doesn't pull much current. But when you lay on the horn, that horn wants to pull more juice the longer it is on, and that creates heat. If the wire is too small it will melt, if the fuse is an ATO in might blow, but if it is a Maxie, it can take more heat before it blows. The fuse size has to follow the wire size.

Also Maxie fuses are the only ones that go as high as 80 amps. ATO's only go to 40 amps. Also that's why you PDC box will have a number of relays in it. Most switching is done with very small wires, because they all go to a relay.

 

[BusaDave9]

20 amps is 20 amps, whether it is running though a 2 ga wire or a 10 ga wire.
Don't the amps create the heat?

You're exactly right. 20 amps is 20 amps. Anything above that and the fuse blows.

The difference is how fast the fuse blows. The Mini fuse is a fast blow fuse and the Maxi is a slow blow fuse. There are some electrical components, such as motors, that draw more current as they start up. Then once they are running they draw less current. A motor is more likely to use a Maxi fuse. If a mini fuse is used it may blow when there is nothing wrong.

Here's more info on the topic from a fuse manufacturer: http://www.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdf

the MAXI Fuse has more time delay than the MINI Fuse, compare their opening times at an overload of 100A. Despite the fact that the fuses are the same rating, the MINI Fuse opens in about 0.1 seconds while the MAXI Fuse opens in about 2.2 seconds.

 

[Lumpy Grits]

The mini will blow faster than the maxi.
The lg one will handle the heat better than the others. One of the reasons Maxi is common under the hood.
LG

 

[mstar]

The application you describe may be a good use for a circuit breaker.I use them on things that have a spike like you describe. My electric fans (dual),a/c fan, etc are a couple places I use circuit breakers.They are also used on some headlight switchs. Just a thought. mike

 

[Peanut Butter]

You are correct PB... I'm more confused.

20 amps is 20 amps, whether it is running though a 2 ga wire or a 10 ga wire.

Don't the amps create the heat?

You're exactly right. 20 amps is 20 amps. Anything above that and the fuse blows.

The difference is how fast the fuse blows.

Yes 20 amps is 20 amps. Amps are the amount of current going through a wire. BUT, resistance is HEAT. Resistance in the Maxie Fuse allows for more heat than an ATO fuse, but the size of the wire makes a big difference too. That's why we use different wire sizes and different fuse sizes. Resistance has to be factored into every circuit. In a circuit like BusaDave talks about when that circuit tries to pull more current upon startup it creates more heat. That additional amount of heat would melt the ATO fuse but not the Maxie fuse.

 

[BusaDave9]

I think we are detracting from the issue here. The Mini fuses are fast blow fuses and Maxi Fuses are slow blow fuses. Period. That's what the manufacturers say. It's true that high current causes the metal link in a fuse to melt and open the circuit. It gets hot with high current but the manufacturers don't say to use Maxi fuses in high heat areas such as under the hood. They say use Maxi fuses when you need a time delay.
No need to complicate a simple issue.

I gave one source from Littel Fuse Company, a major manufacturer of fuses. If anyone thinks this fuse manufacturer is wrong I would like to see a respectable source, such as another fuse manufacturer.

I searched and found other reliable sources:

Fuses Unlimited Blade - Mini® Fuse

Automotive blade MINI Style fuses are fast acting

Fuses Unlimited Blade - Maxi? Fuse

The MAXI style automotive blade fuse is a time delay fuse

 

[Peanut Butter]

I don't disagree with you, I'm just trying to explain why it is a slow blow fuse. Basic electrical properties.