question on dual coils

[bunglebear]

hi all,

built my first jenny and pleased with results, im running an ikarus hybrid which can have dual coils. 
My question is: why do dual coils half the ohms/resistance of a single?

so if i run two coils at 2.1 ohms each, total would be roughly 1ohm...right?
is it because the same amount of power is being diverted into 2 therefore halfing it??....no that sounds stupid!

TIA

[Deleted]

That is essentially it ... the current drawn is split equally through the two equal resistances.

If you take a simple example of 2 x 4 ohm resistances in parallel with a voltage drop across them of 4 volts then the current drawn by each of them will be v/r = 4/4 = 1 amp. So 1 amp through each resistance means 2 amps total and 2 amps flowing through a circuit with a total voltage drop of 4 volts means that the overall resistance is 2 ohms ie: a half of one of the two equal resistances.

The resistances don't necessarily have to be equal as the equation is Rt = (r1 x r2) / (r1 + r2)

[markm]

If you think of resistance like water flowing through a pipe,
The bigger the pipe (or number of pipes) then the lower the
Resistance to the flow, ie more water gets through. That also
Helps you understand what you get with lower resistance, change
The word water for heat. The lower the resistance the hotter it gets.

[bunglebear]

Jan 20, 2014 21:28:04 GMT markm said:

If you think of resistance like water flowing through a pipe,
The bigger the pipe (or number of pipes) then the lower the
Resistance to the flow, ie more water gets through. That also
Helps you understand what you get with lower resistance, change
The word water for heat. The lower the resistance the hotter it gets.

nice metaphor....thanks

[Dan]

Jan 20, 2014 20:25:06 GMT @freefromsmoking said:

That is essentially it ... the current drawn is split equally through the two equal resistances.

If you take a simple example of 2 x 4 ohm resistances in parallel with a voltage drop across them of 4 volts then the current drawn by each of them will be v/r = 4/4 = 1 amp. So 1 amp through each resistance means 2 amps total and 2 amps flowing through a circuit with a total voltage drop of 4 volts means that the overall resistance is 2 ohms ie: a half of one of the two equal resistances.

The resistances don't necessarily have to be equal as the equation is Rt = (r1 x r2) / (r1 + r2)

*dons the dunce hat*

That has gone so far over my head that I feel like putting my hand up.. "please sir"

Anyway of putting it any simpler?

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?

[VapingBad]

If you don't understand the maths then always measure the resistance of the atty (always a good idea anyway).

I = V / R
3 Amps = 4.2 volts / 1.4 ohms

P = V x I = 4.2 x 3 = 12.6 Watt

20 W @ 4.2 V R about 0.9, but I would advise against pushing it to the limit.

[Dan]

Jan 27, 2014 16:51:15 GMT VapingBad said:

If you don't understand the maths then always measure the resistance of the atty (always a good idea anyway).

I = V / R
3 Amps = 4.2 volts / 1.4 ohms

P = V x I = 4.2 x 3 = 12.6 Watt

20 W @ 4.2 V R about 0.9, but I would advise against pushing it to the limit.

Thankyou for replying.

My biggest problem is that my mod is purely vw. It doesn't display voltage output..

I check the ohms everytime I power the device up by the way..

mod has a non replaceable meltable 8amp fuse so don't want to exceed 7amps to be safe..

[boyofford]

I'm a bit lazy to learn the maths, I can follow it but lazy lol!

Can use this link to work out what you need, just add two figures and it calculates the rest.....www.onlineconversion.com/ohms_law.htm

Best to leave yourself a safe margin on these things too though.

[VapingBad]

Dan most VW mods won't fire a resistance below an ohm, some 1.2 ohm and some limit to 1.5 ohm. Try and find the spec for yours and I would imagine that it likely refuse to fire anything with too low resistance.

[boyofford]

Jan 27, 2014 17:10:05 GMT Dan said:

Jan 27, 2014 16:51:15 GMT VapingBad said:

If you don't understand the maths then always measure the resistance of the atty (always a good idea anyway).

I = V / R
3 Amps = 4.2 volts / 1.4 ohms

P = V x I = 4.2 x 3 = 12.6 Watt

20 W @ 4.2 V R about 0.9, but I would advise against pushing it to the limit.

Thankyou for replying.

My biggest problem is that my mod is purely vw. It doesn't display voltage output..

I check the ohms everytime I power the device up by the way..

mod has a non replaceable meltable 8amp fuse so don't want to exceed 7amps to be safe..

Just reread your post...doh...didn't get what you ment.

Using online calc I linked earlier, putting in 1.4 ohms and 20w gives amps of 3.78 (and Voltage of 5.3 which it will do automatically I guess if you put to 20watts)...... would like someone to check this though as don't want to be responsible for your mod going pop!

[Deleted]

Jan 27, 2014 16:39:37 GMT Dan said:

Jan 20, 2014 20:25:06 GMT @freefromsmoking said:

That is essentially it ... the current drawn is split equally through the two equal resistances.

If you take a simple example of 2 x 4 ohm resistances in parallel with a voltage drop across them of 4 volts then the current drawn by each of them will be v/r = 4/4 = 1 amp. So 1 amp through each resistance means 2 amps total and 2 amps flowing through a circuit with a total voltage drop of 4 volts means that the overall resistance is 2 ohms ie: a half of one of the two equal resistances.

The resistances don't necessarily have to be equal as the equation is Rt = (r1 x r2) / (r1 + r2)

*dons the dunce hat*

That has gone so far over my head that I feel like putting my hand up.. "please sir"

Anyway of putting it any simpler?

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?

Dan  

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?
At 20 watts a 1.4 ohm coil will draw 3.77 amps current

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?
The lowest resistance you could go to at 20 watts drawing 7 amps would be 0.4 ohms

[Phoenix .]

Jan 20, 2014 20:25:06 GMT @freefromsmoking said:

That is essentially it ... the current drawn is split equally through the two equal resistances.

If you take a simple example of 2 x 4 ohm resistances in parallel with a voltage drop across them of 4 volts then the current drawn by each of them will be v/r = 4/4 = 1 amp. So 1 amp through each resistance means 2 amps total and 2 amps flowing through a circuit with a total voltage drop of 4 volts means that the overall resistance is 2 ohms ie: a half of one of the two equal resistances.

The resistances don't necessarily have to be equal as the equation is Rt = (r1 x r2) / (r1 + r2)

Pardon?

[Dan]

Jan 27, 2014 18:15:38 GMT VapingBad said:

Dan most VW mods won't fire a resistance below an ohm, some 1.2 ohm and some limit to 1.5 ohm. Try and find the spec for yours and I would imagine that it likely refuse to fire anything with too low resistance.

It will take anything down to 0.7ohms to 15w and 1.1ohm+ to 20w..

I know what it's capable of with single coils, but dual coils I'm not so sure..


So using the linked calculator, a 1ohm coil at 20w gives a current draw of 4.47amps.

So a dual coil at 1ohms needs a 9amp draw (more than the chip can handle!)

This is confusing!!

[Dan]

Jan 27, 2014 18:27:16 GMT @freefromsmoking said:

Jan 27, 2014 16:39:37 GMT Dan said:

*dons the dunce hat*

That has gone so far over my head that I feel like putting my hand up.. "please sir"

Anyway of putting it any simpler?

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?

Dan  

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?
At 20 watts a 1.4 ohm coil will draw 3.77 amps current

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?
The lowest resistance you could go to at 20 watts drawing 7 amps would be 0.4 ohms

So it makes no odds whether its single or dual coil?

Coolio! Gonna try one at 1.2ohms then.. heat a bit quicker and not need so much oomph!

[Deleted]

Jan 27, 2014 21:07:50 GMT Dan said:

Jan 27, 2014 18:27:16 GMT @freefromsmoking said:

Dan  

I have a dual coil of 1.4ohms readout. How can I work out what amp draw that will give?
At 20 watts a 1.4 ohm coil will draw 3.77 amps current

how can I work out the lowest ohms (dual coil)I can go at full power (20w) eithout exceeding 7amps?
The lowest resistance you could go to at 20 watts drawing 7 amps would be 0.4 ohms

So it makes no odds whether its single or dual coil?

Coolio! Gonna try one at 1.2ohms then.. heat a bit quicker and not need so much oomph!

That's right Dan  ...  it's the overall resistance matters, not each individual parallel resistance  .... just remember that the overall resistance is half of one of the two equal resistances  .... two 2.4 ohm coils in paralell will give 1.2 ohms overall.