Yet another Fusible link question.

[enoniam]

Amps are amps, but volts are volts and volts*amps = wattage or power.

It DOES make a difference... 

The actual total power/wattage is what the wire is rated for which is the volts*amps.

Without taking into account the resistances/capacitance etc you SHOULD be pretty close by looking at the radio of the rated voltage and what you want to use.

Thus a wire rated for 20 amps at 120 volts SHOULD work at 200 amps at 12 volts.

Due to factors such as resistance of the wire and capacitance though you really should look at 12 volt rated wire for proper power capacity. 120 volt rated wire may NOT quite carry 10x the amperage at 12 volts.

Unless they changed how they rate wiring in the 30 years since I went to tech school... I could be getting "old" too I suppose but this is the way I remember it..

Rodney

As an electrical engineer I advise all to NOT follow the above advice.  Voltage rating applies to the insulator material around the current carrying core.  Current rating applies to the core.  They are not a tradeoff.

 

[Calicak89]

Voltage rating applies to the insulator material around the current carrying core.  Current rating applies to the core.  They are not a tradeoff.

That's what I was thinking but I wasn't totally sure so I didn't want to say anything. I knew the insulation has something to do with the voltage rating as when I worked for Mc-Graw, we had various cable of the same size, for example 300, or 350mcm, but different Voltage ratings, and the only difference was the thickness of the Crepe insulation wrap on it. Thanks for the clarification

 

[MS03 2500]

This is why I love this forum, if you don't know ask the question someone will reply. Now if you believe them or not is another question. LOL..


Thanks for the link Calicak89 I just notice it, that was the circuit breaker I was looking at.

One of my main problems is the 2 air compressor I have mounted in the bed that kept melting the wires both power and grounds. I'm going to run a big azz wire back there and keep the run to them short then ground them to the frame.

Thanks again folks.

 

[Randy]

I think that chart is more for stereo amps and speaker wire sizing..

Direct current (DC) is different, what's important is length . The chart on that web site is a little misleading, that's kind of a best case, short length of wire.. What's missing on that one chart is the length. I tend to go bigger than I need just to be safe.

120 Volt AC you could you could run a 20 amp circuit 100 ft 12ga with no issues, you couldn't do that with 12 Volt DC. With DC you would would need 8 ga or maybe 6ga just to go 50 ft, but drop that to 3 ft and you could use 14ga or even 16ga.


Just look up "12 volt wire amp rating chart", there's a lot of sites with similar info..

 

[MS03 2500]

I think(know) you are spot on about the length, the compressors said to use 10 gauge but it was 17 feet long. The fuses did not even blow until they wires melted together and shorted out.

 

[Randy]

That's one of the reasons I put a power tap when I ran the power cable to my amps. It gives a place to tap 12 Volts to a compressor in the middle of the truck and at the rear.

Then just use a relay if you want to switch it on and off, that way you don't have to run a large gauge wire to the rear..

 

[MS03 2500]

I'll have to look into that Randy

 

[MS03 2500]

I decided to actually test the power draw from the stock(well stock as I could get it) system.


Running no lights on. about 31-32 amps.

Headlights on.

The 6 lights on(Both headlight and fogs) the LEDS brights did not add much of a draw.

All lights on and AC compressor

AC on no lights

Next Replace the ground and see if anything changes

 

[redheadedrod]

One thing to be aware of is that you will notice that your alternator wire is smaller than the rest of them.

Remember that the alternator just charges the battery so they generally size the wire a little smaller. still needs to be sized to the output it can carry. Your Battery cables are bigger because it can discharge far more instantaneous energy than the alternator can. 

Over sizing an alternator is never a bad thing. Just gets more costly.

What alternator did you end up going with? I believe based on the new belt I got that I have a 145 amp alternator in my truck but with the planned upgrades for next year I am looking at going to a 250 or better myself.

Did you also turn on the seat heaters when testing? Those suckers suck up a alot of power.

The fusible links were used by the factory because they are cheaper than fuses/circuit breakers and are not likely to "blow" under normal operation.

I have circuit breakers in mine that I can open the circuits in so I don't have to disconnect the battery when I park it for long periods of time. I can just open the breaker. Breakers and fuses do wear out eventually but easier to replace than a fusible link.

 

[MS03 2500]

I'm not sure what you mean the alternator just  charges the battery but mine certainly does more than that.

 

[redheadedrod]

Guess it depends on how you look at your system...

Factory system and any power using system should be connected to the battery NOT the alternator. Your battery can provide much more immediate power than the amplifier can. If you note the power wires running from your battery go to the starter and the under hood power distribution block directly.

Also note that all after market systems hook directly to the battery NOT the alternator for their power source...

At least in MY truck the alternator is hooked to the starter wire realistically only out of convenience. We all know the alternator doesn't provide power to the starter since it doesn't do any power generation during starting up.

The battery provides boosts of power when you have things like winches or stereo amplifiers. When you have these big power drains the alternator works a little harder but does not provide the initial power, it can not react as fast as a battery. So in theory as long as the alternator can provide more than the average usage of your battery the battery stays charged. If not the battery will discharge. The alternator provides charging power based on how the battery requires it. In newer vehicles you can see this when the alternator stops charging when the battery is fully charged. When vehicles started using electronics for everything the battery became a necessary cog in the electrical wheel. It acts as a smoothing capacitor for the spiky output of the alternator and is considered the main source for your power. While older vehicles could run on just the alternator and really just needed the battery to start the car this is not true with newer vehicles. If you attempt to do so you can cause dramatic damage to your electronics and in some cases I have heard some vehicles won't run without the battery in the system for this reason.

Feel free to debunk this if I am inaccurate but it is as I understand it.