You can go to .2 without problems. Imho if you Go much Lower than that and you start to get issues with variability of resistance dipping into danger zones. Others may disagree on this one.
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If you read all the responses to your question you saw;
8.4v /.3Ω = 28a, doesn't matter if that is .3Ω ( three tenths of an ohm) or .300Ω or .30000Ω the amp draw is the same.
A stacked battery mechanical with no venting holes to relieve pressure if something goes wrong is not something to learn on.
8.4v /.3Ω = 28a, doesn't matter if that is .3Ω ( three tenths of an ohm) or .300Ω or .30000Ω the amp draw is the same.
A stacked battery mechanical with no venting holes to relieve pressure if something goes wrong is not something to learn on.
Huh?,
The OP is asking about a stacked cell mechanical. 2 cells stacked one on top of the other which doubles voltage, keeps the same mah and amp rating of one cell.
8.4v / .2Ω = 42a
Even with voltage sag & drop;
7.4v / .2Ω = 37a
There are no 18650 cells that can safely support this amp draw and use the word 'safe' in the same sentence, or even paragraph.
This thread is in the new members section where safe & sane advice should be given, obviously the OP has very little to no experience using a mechanical.
Using any cell above its CDR is not safe or sane.
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Well that's Good.
So now the question is How Accurately can you Measure the Ohms of what you are going to use?
Because 8.4v / .30 Ohms = 28 Amps.
That is Right on the Edge for a Dual Mech running in Series. And leaves No Room if your Brand New 30A batteries are Not Performing at their Peek Performance.
But if you Ohm Reader is Off by 0.1 Ohms (Not Unheard of by any means) then the Amps jump to...
8.4v / .20 Ohms = 42 Amps.
That's a Big Jump in Amp Draw for a VERY Small change in Ohms. And Now you are Exceeding what Brand New 30A Batteries are supposed to be able to handle by a Significant Amount.
You Need to Build Higher to give yourself a Little Safety Margin.
That is Just Too Low for a Dual Mech running in Series.
Excellent points for novices to know.
Some folks take it for granted that a $10 ohm meter will be as precise and accurate as a $3000 Fluke digital multimeter. At the range that we are measuring for sub-ohm coils, precision and accuracy are critical. Super sub-ohm is right on the edge of being a hard short (0.0 ohm).
Then we have the issue of aftermarket batteries. Also called "re-wraps" or rebranded batteries. How often have novices been using what they thought was a 30 - 40 amp battery only to find that they are actually using a ridiculously over-rated battery? For example, below are Mooch-tested batteries from Imren. That's not to mention batteries from Efest or MXJO or AWT among others.
Imren Orange 30A 2100mAh 18650 Bench Test Results...only a 20A+ battery[/COLOR]
Imren Purple 40A 2500mAh 18650 Bench Test Results...a 20A cell that runs very hot
Imren Yellow 40A 2000mAh18650 Bench Test Results...a decent 20A battery, may be an HD2
Imren Leopard 50A 2600mAh 18650 Bench Test Results...just a 20A rewrap
Imren 40A 3000mAh 18650 Bench Retest Results...only a 17A battery, damaged at 30A
Imren Gold 30A 3000mAh 18650 Bench Test Results...a ridiculously overrated battery
Imren Green 40A 3200mAh 18650 Bench Retest Results...just 17A, the purple Imren 3000mAh rewrapped!
Imren Green 40A 3200mAh 18650 Bench Retest Results...now 10A, shame on you Imren!
Imren Yellow 25A 3400mAh 18650 Bench Test Results...just a 12A battery
The green 30A 3500mAh Imren is a 10A battery!
Are You Using a Rewrap (Rebranded) Battery?
That's why it makes good sense to build with a margin of safety in mind and to only use batteries from Lg, Samsung, or Sony.
Imren Purple 40A 2500mAh 18650 Bench Test Results...a 20A cell that runs very hot
Imren Yellow 40A 2000mAh18650 Bench Test Results...a decent 20A battery, may be an HD2
Imren Leopard 50A 2600mAh 18650 Bench Test Results...just a 20A rewrap
Imren 40A 3000mAh 18650 Bench Retest Results...only a 17A battery, damaged at 30A
Imren Gold 30A 3000mAh 18650 Bench Test Results...a ridiculously overrated battery
Imren Green 40A 3200mAh 18650 Bench Retest Results...just 17A, the purple Imren 3000mAh rewrapped!
Imren Green 40A 3200mAh 18650 Bench Retest Results...now 10A, shame on you Imren!
Imren Yellow 25A 3400mAh 18650 Bench Test Results...just a 12A battery
The green 30A 3500mAh Imren is a 10A battery!
Are You Using a Rewrap (Rebranded) Battery?
That's why it makes good sense to build with a margin of safety in mind and to only use batteries from Lg, Samsung, or Sony.
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Excellent points for novices to know.
Some folks take it for granted that a $10 ohm meter will be as precise and accurate as a $3000 Fluke digital multimeter. At the range that we are measuring for sub-ohm coils, precision and accuracy are critical. Super sub-ohm is right on the edge of being a hard short (0.0 ohm).
...
I agree.
Sometimes there is a Big Disconnect between the Mathematical World where Accuracy can be defined Absolutely. And the Real World where All Accuracy is Relative.
And things like Measurement Error or even how Numbers are Display via Round Up, Round Down, or being Truncated isn't considered.
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