power drop from battery

[jlinder]

Re: power drop from battery

Sorry but that is incorrect because: The 12V DC circuit supplying current does create less heat in the same conduit than a 110V AC voltage supply, provided that the currents are the same.

Sorry, but you have it wrong. This is something that people get confused.

The heat created in the wire is due to the voltage ACROSS THE WIRE times the current. It has nothing to do with the voltage across the other elements in the circuit like the battery or the load. If I pass 20 amps through a 10 ft. long 12 gauge wire the amount heat generated is based on the voltage drop (.653 volts in this case x 20 amp = 13 watts).

You might have it connected to a 12 v battery or you could have 440v AC supply - it does not matter to the wire.

Yes, for the 12v supply you would have 20A supplied at 11.35v to the load and it would dissipate about 227watts, and at 440v you would dissipate about 880 watts, but that is in the load (or from the supply).

No matter what you still have 13 watts of heat in the wire.

 

[bruceb58]

Re: power drop from battery

The 12V DC circuit supplying current does create less heat in the same conduit than a 110V AC voltage supply, provided that the currents are the same.

Totally incorrect. You need to stop reading that link you posted.

 

[sasto]

Re: power drop from battery

Sooooo....what size wire does our guy here need to meet his needs?

 

[Silvertip]

Re: power drop from battery

No calculations necessary. IF the OP wants a safe installation, he moves the battery wherever he likes, makes the power extensions using the same gauge or larger than the battery cables going to the engine. Simple! If a smaller gauge wire was ok, the engine manufacturer would have used it to save money. What's not to understand here?

Can the OP "bet by" with smaller gauge wire? The answer is "It depends how safe he wants to be!"

 

[bruceb58]

Re: power drop from battery

deleted

 

[halas]

Re: power drop from battery

Sorry, but you have it wrong. This is something that people get confused.

The heat created in the wire is due to the voltage ACROSS THE WIRE times the current. It has nothing to do with the voltage across the other elements in the circuit like the battery or the load. If I pass 20 amps through a 10 ft. long 12 gauge wire the amount heat generated is based on the voltage drop (.653 volts in this case x 20 amp = 13 watts).

You might have it connected to a 12 v battery or you could have 440v AC supply - it does not matter to the wire.

Yes, for the 12v supply you would have 20A supplied at 11.35v to the load and it would dissipate about 227watts, and at 440v you would dissipate about 880 watts, but that is in the load (or from the supply).

No matter what you still have 13 watts of heat in the wire.

You have completely lost me there. I guess one of us are not able to follow the concept being discussed.

 

[bruceb58]

Re: power drop from battery

I guess one of us are not able to follow the concept being discussed.

What part of voltage drop x times current = watts are you missing. The voltage drop across the wire is resistance times current. Totally independent of what the voltage at the source of the wire is.

 

[halas]

Re: power drop from battery

No calculations necessary. IF the OP wants a safe installation, he moves the battery wherever he likes, makes the power extensions using the same gauge or larger than the battery cables going to the engine. Simple! If a smaller gauge wire was ok, the engine manufacturer would have used it to save money. What's not to understand here?

Can the OP "bet by" with smaller gauge wire? The answer is "It depends how safe he wants to be!"

That is the best advice I would go with. Just like to add that good solid connections are important.

 

[jlinder]

Re: power drop from battery

No calculations necessary. IF the OP wants a safe installation, he moves the battery wherever he likes, makes the power extensions using the same gauge or larger than the battery cables going to the engine. Simple! If a smaller gauge wire was ok, the engine manufacturer would have used it to save money. What's not to understand here?

Can the OP "bet by" with smaller gauge wire? The answer is "It depends how safe he wants to be!"

To put numbers on this, the original is probably 4 gauge. With the longer wires you need bigger. 2 gauge might do it, but you really should go with 0 gauge. (IMHO)

 

[fisherguy123]

Re: power drop from battery

Well I guess I really started a great topic here judging by all the responses. After all this advise I think I would be safer to leave the battery where it is and I can`t make a mistake and burn everything out !!!!!

 

[99yam40]

Re: power drop from battery

Electricity is really quite simple.
the smaller the wire gauge the more resistance per foot, the larger the gauge wire the less resistance there is per foot.
The more resistance there is in a circuit at a given voltage and amperage the more heat is produced. Increase any of the three and you get more heat.
On set resistant loads like electric heaters it just means less heat out put at the heater as the whole circuit resistance is pretty well defined If the voltage source is stable then the more resistance in a circuit will cause an amp drop at the load, because of the less voltage there is available to the load.
But in a motor that needs to produce a certain amount of force( hp/watts) to do a certain job( turn over the main motor) the lower voltage will cause it to draw even more amps to get the hp needed to do the work. Thus over heating the cables/ wires even more if not rated to the proper size to handle the amount of amps.
The charts that you see for wire size/amps ratings are for what a wire can carry constantly without over heating the wire past it's insulation temperature rating, rated open air or in cables or in conduit. That is because of the ability of the wire to dissipate the heat generated by the current it is carrying in free air will allow more heat to be removed/ dissipated when nothing else is around it than inside conduit or cables.

The other thing that should be looked at is what amps are being pulled and how far the voltage is dropping during start.

But going larger than the factory size would be a must for longer cables, they(factory) are taking into consideration your battery will not be charges up completely every time you try to start just to cover themselves

 

[jlinder]

Re: power drop from battery

Well I guess I really started a great topic here judging by all the responses. After all this advise I think I would be safer to leave the battery where it is and I can`t make a mistake and burn everything out !!!!!

Don' worry about it. Use the heavier gauge wire to do it right and you will not have any problems.

The problem comes with people who ignore the need for heavier wires to compensate for the longer distance or try to save some money by buying smaller wires. Just don't cheap out and you will be fine.

 

[tbird175]

Re: power drop from battery

Electricity is really quite simple.
the smaller the wire gauge the more resistance per foot, the larger the gauge wire the less resistance there is per foot.
The more resistance there is in a circuit at a given voltage and amperage the more heat is produced. Increase any of the three and you get more heat.
On set resistant loads like electric heaters it just means less heat out put at the heater as the whole circuit resistance is pretty well defined If the voltage source is stable then the more resistance in a circuit will cause an amp drop at the load, because of the less voltage there is available to the load.
But in a motor that needs to produce a certain amount of force( hp/watts) to do a certain job( turn over the main motor) the lower voltage will cause it to draw even more amps to get the hp needed to do the work. Thus over heating the cables/ wires even more if not rated to the proper size to handle the amount of amps.
The charts that you see for wire size/amps ratings are for what a wire can carry constantly without over heating the wire past it's insulation temperature rating, rated open air or in cables or in conduit. That is because of the ability of the wire to dissipate the heat generated by the current it is carrying in free air will allow more heat to be removed/ dissipated when nothing else is around it than inside conduit or cables.

The other thing that should be looked at is what amps are being pulled and how far the voltage is dropping during start.

But going larger than the factory size would be a must for longer cables, they(factory) are taking into consideration your battery will not be charges up completely every time you try to start just to cover themselves

Very good explanation. Look at the size of the electrical wires on service poles, the single conductors in open air are much smaller that the conductors entering your house because of their ability to dissipate heat. This is why overhead electrical transmission lines are bare unbundled conductors.

 

[Jerryh3]

Re: power drop from battery

You also have to conisider most of those wires are before the step down transformers so they are probably around 400V.

 

[jlinder]

Re: power drop from battery

You also have to conisider most of those wires are before the step down transformers so they are probably around 400V.

What ??????

 

[bruceb58]

Re: power drop from battery

What ??????

What he is saying is that because they run at a higher voltage, they can drop the diameter of the wire accordingly since the current is inversely proportional to the voltage. That is one of the main reasons that transmission wires are extremely high voltage...the current is less and thus the wires are a smaller diameter than if you run lower voltage.

 

[jlinder]

Re: power drop from battery

I understand that, just could nof figure out where the response came from since we were not talking about that in any of the replies.

BTW - not sure what is typical but pretty sure the voltage on the power poles (before the transformer) is a lot more like 9600 volts and higher. 400 volts would not be nearly enought of a step up from the 240 volts delivered to the house.

9600 to 240 is a 40 to one ratio, so the current at 9600v would be 1/40th of that at 240 volt.

To get an idea of how high the voltage is take a look at the length of the insulator. The longer the insulator the higher the voltage

 

[bruceb58]

Re: power drop from battery

I understand that, just could nof figure out where the response came from since we were not talking about that in any of the replies.

Someone stated the reason the wires were smaller on transmission lines was that they were cooler because they were in open air which is a minor reason.