The Ford Barn

Frank Miller · 11-02-2017, 10:57 AM

Yeah but if you put 12 volts to a 6 volt circuit it will carry twice as many amps as it was designed to. You need the bigger wire because there is not as much energy to push the current through.

flatheadmurre · 11-02-2017, 11:30 AM

But in a points ignition system the current is the same since the limitaion is the points burning...and they can take the same current no matter what voltage.
So same size of cable is needed in 6v or 12v.
What you can get with 12v is more energy in the coil.

Frank Miller · 11-02-2017, 11:46 AM

Not sure if it is me or you but someone has confused the shit out of this. In a 12 volt ignition system a resistor is added to limit current. That resistor will give off heat so energy is split between that and the coil. If you have a 2ohm coil it will flow 3 amps in a 6 volt system and 6 amps if you put the full 12 volts to it. That is the theory anyway. Other factors may change numbers slightly. Think of a water pipe with 30psi pressure. When you turn on the valve it will flow a certain amount of water and the dynamic pressure may change depending on the source. If you increase the pressure to 60 psi it will flow twice a smuch water given other values remain the same. It might not really be twice as much bit I'm using that for this argument. The points can probably handle 10 amps because they are just contacts. all they care about is how much current goes through them. When the current gets high enough it will create heat in them much like any wire that is not sized big enough for the circuit it is on. A short circuit has no resistance and will flow as many amps as possible. Forcing too many through a small wire creates heat and burns stuff up or down. This is why you need heavy wires on a starte motor. It creates a short until it starts spinning. But that's a complicated subject for another day.

Crankster · 11-02-2017, 12:11 PM

So long as we're off in the weeds here, so to speak, is there really such a thing as a 6 volt coil? 6 volt condenser? 6 volt points? It's my understanding that when the OE manufacturers switched to 12 volts, Ford at least basically kept the ignition system, as well as dash gauges, the same. The difference was the addition of a ballast or voltage dropping resistor in the primary circuit. The idea of course was to limit the current through the points, and perhaps the coil?

flatheadmurre · 11-02-2017, 12:25 PM

There´s nothing like a 6v or 12v coil....but with more voltage available you can have more windings in the coil or a ballast resistor.
More windings and bigger core gives you more energy available.

tubman · 11-02-2017, 12:35 PM

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Quote:

Originally Posted by Frank Miller

Yeah but if you put 12 volts to a 6 volt circuit it will carry twice as many amps as it was designed to. You need the bigger wire because there is not as much energy to push the current through.

I think you have amps and watts mixed up. Trying to push twice the amps at twice the volts will increase the watts by a factor of 4 which would not be good for the wiring harness.

rotorwrench · 11-02-2017, 02:45 PM

With more electromotive force (voltage) you don't need as much conductor wire cross sectional area (American Wire Gauge) to flow current. A 6-volt system needs very low resistance conductors for them to flow the required amperage that is drawn by a given circuit. A 16-AWG conductor wire is average for a low amp draw circuit like a small lamp bulb in a 6-volt system. The same bulb in a 12-volt system would only require an 18-AWG conductor wire. The aircraft I work on are mostly 24-volt systems so they the average conductor wire size is 20-AWG.

Wire size in automotive or aircraft systems depends on the length of the run of the wire and the amount of current draw of the electrical component or components in the circuit. I use a chart in one of the FAA advisory circulars to get the correct wire size for a new circuit being added. The wire size can be calculated but it's easier to just use the chart and choose the appropriate circuit breaker rating for the wire size utilized.

Frank Miller · 11-02-2017, 04:03 PM

Okay here is a better picture using lightbulbs
A 24 watt bulb will draw 4amps at 6 volts. It will have a resistance of 1.5ohms. 1.5 x 4 =6volts. Current squared x resistance also = watts. 4x4x 1.5 =24. We can agree on that.
Now let us put 12 volts to that bulb. Volts/resistance = amps. 12/1.5 = 9 So if you put 12 volts to a bulb rated for 6 volts it will not last long and you may overheat the wire.
A 24 watt bulb rated for 12 volts will have a resistance of 6ohms resulting in a flow of 2amps. The power is equal because of the increased voltage. Because wire is rated for amps you can use a smaller wire. Voltage ratings are tied to the insulation. We are a bit off topic but hope this helps explain wht we do not put 12 volts to 6 volt coils and why 12 volts has smaller wire.

36fordguy · 11-02-2017, 04:58 PM

A light bulb is used because it has a "negative" resistance coefficient meaning when the bulb is not shinning it has a lower resistance. Thus a greater voltage across the inductor that will saturate the inductor faster, as the core saturates the inductive reactance decreases, more current will flow thru the inductor, the bulb will light brighter the resistance increases, limiting the current thru the inductor so you do not burn the inductor (coil) up. This provides a current source to coil 36fordguy

11-02-2017, 10:57 AM	#81
Frank Miller Senior Member Join Date: May 2010 Location: Auburn, MA Posts: 2,106	Re: Condenser Capacitiance. Yeah but if you put 12 volts to a 6 volt circuit it will carry twice as many amps as it was designed to. You need the bigger wire because there is not as much energy to push the current through. __________________ “The technique of infamy is to start two lies at once and get people arguing heatedly over which is true.” ~ Ezra Pound

11-02-2017, 11:30 AM	#82
flatheadmurre Senior Member Join Date: Apr 2015 Location: Sweden Posts: 3,045	Re: Condenser Capacitiance. But in a points ignition system the current is the same since the limitaion is the points burning...and they can take the same current no matter what voltage. So same size of cable is needed in 6v or 12v. What you can get with 12v is more energy in the coil.

11-02-2017, 11:46 AM	#83
Frank Miller Senior Member Join Date: May 2010 Location: Auburn, MA Posts: 2,106	Re: Condenser Capacitiance. Not sure if it is me or you but someone has confused the shit out of this. In a 12 volt ignition system a resistor is added to limit current. That resistor will give off heat so energy is split between that and the coil. If you have a 2ohm coil it will flow 3 amps in a 6 volt system and 6 amps if you put the full 12 volts to it. That is the theory anyway. Other factors may change numbers slightly. Think of a water pipe with 30psi pressure. When you turn on the valve it will flow a certain amount of water and the dynamic pressure may change depending on the source. If you increase the pressure to 60 psi it will flow twice a smuch water given other values remain the same. It might not really be twice as much bit I'm using that for this argument. The points can probably handle 10 amps because they are just contacts. all they care about is how much current goes through them. When the current gets high enough it will create heat in them much like any wire that is not sized big enough for the circuit it is on. A short circuit has no resistance and will flow as many amps as possible. Forcing too many through a small wire creates heat and burns stuff up or down. This is why you need heavy wires on a starte motor. It creates a short until it starts spinning. But that's a complicated subject for another day. __________________ “The technique of infamy is to start two lies at once and get people arguing heatedly over which is true.” ~ Ezra Pound

11-02-2017, 12:11 PM	#84
Crankster Senior Member Join Date: Oct 2017 Posts: 563	Re: Condenser Capacitiance. So long as we're off in the weeds here, so to speak, is there really such a thing as a 6 volt coil? 6 volt condenser? 6 volt points? It's my understanding that when the OE manufacturers switched to 12 volts, Ford at least basically kept the ignition system, as well as dash gauges, the same. The difference was the addition of a ballast or voltage dropping resistor in the primary circuit. The idea of course was to limit the current through the points, and perhaps the coil? Last edited by Crankster; 11-02-2017 at 12:17 PM.

11-02-2017, 12:25 PM	#85
flatheadmurre Senior Member Join Date: Apr 2015 Location: Sweden Posts: 3,045	Re: Condenser Capacitiance. There´s nothing like a 6v or 12v coil....but with more voltage available you can have more windings in the coil or a ballast resistor. More windings and bigger core gives you more energy available.

11-02-2017, 02:45 PM	#87
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,426	Re: Condenser Capacitiance. With more electromotive force (voltage) you don't need as much conductor wire cross sectional area (American Wire Gauge) to flow current. A 6-volt system needs very low resistance conductors for them to flow the required amperage that is drawn by a given circuit. A 16-AWG conductor wire is average for a low amp draw circuit like a small lamp bulb in a 6-volt system. The same bulb in a 12-volt system would only require an 18-AWG conductor wire. The aircraft I work on are mostly 24-volt systems so they the average conductor wire size is 20-AWG. Wire size in automotive or aircraft systems depends on the length of the run of the wire and the amount of current draw of the electrical component or components in the circuit. I use a chart in one of the FAA advisory circulars to get the correct wire size for a new circuit being added. The wire size can be calculated but it's easier to just use the chart and choose the appropriate circuit breaker rating for the wire size utilized.

11-02-2017, 04:03 PM	#88
Frank Miller Senior Member Join Date: May 2010 Location: Auburn, MA Posts: 2,106	Re: Condenser Capacitiance. Okay here is a better picture using lightbulbs A 24 watt bulb will draw 4amps at 6 volts. It will have a resistance of 1.5ohms. 1.5 x 4 =6volts. Current squared x resistance also = watts. 4x4x 1.5 =24. We can agree on that. Now let us put 12 volts to that bulb. Volts/resistance = amps. 12/1.5 = 9 So if you put 12 volts to a bulb rated for 6 volts it will not last long and you may overheat the wire. A 24 watt bulb rated for 12 volts will have a resistance of 6ohms resulting in a flow of 2amps. The power is equal because of the increased voltage. Because wire is rated for amps you can use a smaller wire. Voltage ratings are tied to the insulation. We are a bit off topic but hope this helps explain wht we do not put 12 volts to 6 volt coils and why 12 volts has smaller wire. __________________ “The technique of infamy is to start two lies at once and get people arguing heatedly over which is true.” ~ Ezra Pound

11-02-2017, 04:58 PM	#89
36fordguy Member Join Date: May 2010 Posts: 73	Re: Condenser Capacitiance. A light bulb is used because it has a "negative" resistance coefficient meaning when the bulb is not shinning it has a lower resistance. Thus a greater voltage across the inductor that will saturate the inductor faster, as the core saturates the inductive reactance decreases, more current will flow thru the inductor, the bulb will light brighter the resistance increases, limiting the current thru the inductor so you do not burn the inductor (coil) up. This provides a current source to coil 36fordguy