Mech Mod Voltage drop - why it is important :) UPDATED

[robby]

Jun 21, 2014 23:23:23 GMT hijack said:

Well written robby and worth bearing in mind when using a mech with a rebuildable that performs best within a certain window.
So does this mean that when working out the drain on your battery when sub ohming, this effect of the added resistance reduces the Amp drain on the battery?

Yes it does slightly due to the slightly lower current flowing through the mod hijack

[robby]

I have just tested three batteries, the Panasonic NCR18650B 3400mah battery(green), the Panasonic NCR18650 2900mah (grey) and the LG ICR18650HE2 2500mah (red)

The no load voltage of the 3400mah Panny battery is 4.15V. The voltage with a .8 ohm coil firing is 3.6V. It has an internal resistance of <100 milliohms which is .1 ohms
The no load voltage of the 2900mah Panny battery is 4.12V. The voltage with a .8 ohm coil firing is 3.8V. It has an internal resistance of <60 milliohms which is .06 ohms
The no load voltage of the 2500mah LG   battery is 4.18V. The voltage with a .8 ohm coil firing is 4.01V. It has an internal resistance of <16 milliohms which is .016 ohms

So even though the three of them are good quality batteries, the difference between the best and the worst is almost half a volt which is very significant in terms of vaping performance and flavour.

[tomj777]

Curiosity piqued, I wondered about comparative resistance and found this chart (from 2012)


I found this comment on internal resistance and why it drops over time - it might be useful to someone

Lithium-ion batteries lose capacity through cell oxidation (cholesterol), a process that occurs naturally during normal battery use and aging. As the battery ages, internal resistance (cholesterol) increases as well. This increase in cholesterol (internal resistance) leads to plaque build up and when sufficient build up occurs. This results in a plugged artery/battery or, a battery that can no longer deliver current sufficiently to meet the workload. Not dissimilar to someone having a heart condition having difficulty going up a flight of stairs.

(source www.happyvaper.com/Articles.asp?ID=240)

So the implication is that by measuring the internal resistance of a battery one can tell how viable it is (or should it be recycled) without using a subjective measure.
And I guess that leads to three questions

• How a layman measures internal resistance with a multimeter
• If there is a table out there giving internal resistances when new of batteries (or should one measure and record when new) ?
• How does one tell what an acceptable change in internal resistance is ?

I know this is a bit of a digression - any thoughts? Knowledge?

[robby]

Brilliant resource tomj777 !!

[tomj777]

Jun 22, 2014 10:01:15 GMT robby said:

Brilliant resource tomj777 !!

 Thank you (but note that it's a very old chart)

[robby]

I`m sure there is a way of measuring the internal resistance of a battery, but you would need a very accurate test bed to do it I think. You can usually find it if you Google it. In the case of the LG battery I quoted, it`s a very small amount of resistance, putting a meter across it would not work because of the 4.2 volts there. It could be done with calculation and a good test bed I think tomj777

[tomj777]

Jun 22, 2014 10:06:28 GMT robby said:

I`m sure there is a way of measuring the internal resistance of a battery, but you would need a very accurate test bed to do it I think. You can usually find it if you Google it. In the case of the LG battery I quoted, it`s a very small amount of resistance, putting a meter across it would not work because of the 4.2 volts there. It could be done with calculation and a good test bed I think tomj777

I understand. Ah well  -I shall learn to mark my batteries and work on subjective measures (how long before voltage drops to an untenable level)

[robby]

allaboute-cigarettes.proboards.com/thread/41507/last-cheap-voltage-drop-device?page=1&scrollTo=721203

Might interest you tomj777

[tomj777]

Jun 23, 2014 10:59:43 GMT robby said:

allaboute-cigarettes.proboards.com/thread/41507/last-cheap-voltage-drop-device?page=1&scrollTo=721203

Might interest you tomj777

Ah - my first purchase from FyneMods
Useful for telling how much charge remains in the battery and also the voltage drop on the Mech (which in turn indicates how clean the threads are, including the 510 connector on the atty and the 510 connector on the meter).

Not sure how it would tell me the health of the battery (internal resistance increases as the battery ages and the ?electrolyte? is ?oxidised? ) or to put it another way, how far through the advertised charge cycles / personally acceptable charge cycles the battery is.

I could be being a bit slow though - Tom has good days and Tom has...

[robby]

Easier to understand if we separate the battery resistance and place it in circuit visually.









VMeter 2 is the coil voltage, VMeter0 is the Battery voltage loss due to internal resistance and

VMeter1 is the combined voltage loss of the Mod, Switch, Connectors etc

Imeter0 is the current flowing through the circuit.













VMeter 2 is the coil voltage, VMeter0 is the Battery voltage loss due to internal resistance and

VMeter1 is the combined voltage loss of the Mod, Switch, Connectors etc

Imeter0 is the current flowing through the circuit.



So, the top setup would give you 15.9 watts (3.57V available to the coil) and the bottom setup would give you 18.8 watts (3.88 available to the coil) because of the difference in battery internal resistance. The bottom battery was a high output LG (20AMP).



In the case of the bottom setup, Power = Volts X Amps which gives us 3.88 X 4.84 = 18.8 watts.

[robby]

Look at the difference it makes when you use an average resistance coil (2.4 ohms)




Now over 4 volts available to the coil and the battery resistance and mod resistance much less significant. The important thing is the relationship between the coil resistance and all other resistances combined.

[tomj777]

I'm learning more and more. This means others as well. Thanks