I've been looking into building some low ohm coils, and I've been reading up on ohm's law. I'm using three aspire 18650s rated at 40a (I've read some tests online and apparently an assumption of a safe max discharge rate would be around 30a on these) and I'm wondering if running multiple batteries changes what my overall max discharge rate is, or if it just increases capacity.
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Does using multiple batteries affect maximum discharge rate?
- Thread starter udawg34
- Start date
Depends on how they're configured. There are two possibilities.
The first is a parallel configuration. Most mods wired like this will have both "+" and "-" ends on the same sides of the sled... ...as in, two positives on the top and two negatives on the bottom or vice versa. The batteries sit side-by-side in the circuit and essentially share a single positive and negative connection point, so the amp load is split between the two. A coil that draws 10A total will draw 5A from either battery. This means your amp ceiling and capacity are doubled, while output voltage remains the same as that of one battery.
In practice, it's not going to be exactly double, but it will be close. A lot of people pretend that it's 1.5 times to give themselves headroom, which would give you 45A as a max from two 30A batteries, but even that is conservative imo.
Parallel is common only in unregulated box mods, as it makes up for the fact that low-end sub-ohming (as most mech users do) is not power-efficient in that it requires a lot of current in order to reach a given wattage. If you want to sub-ohm below .3 on an unregulated device, then this is the safest and most effective option. It allows you to have a high-powered sub-ohm vape with a reasonable capacity at their rather low native voltage output level. Regulated boxes have long since shied away from this, as it is more efficient to cut voltage down to current than it is to turn current into voltage.
The second is a series configuration. Unlike parallel, both ends of the sled will have one plus and minus on the top and bottom. Back in the day, people used to call it stacking in reference to the batteries being on top of each other. The positive on the first battery connects to the negative of the second, so the current travels from one to other, rather than leaving each battery separately and converging afterwards. This doubles the voltage, but leaves the capacity and amp limit the same as that of either battery alone.
You will see series most often used in high-powered regulated boxes because the higher voltage output makes them much safer and more power efficient, as you can attain the same wattage for just half of the current when you double your voltage. They use a buck converter between the batteries and atty to exchange voltage for current as dictated by ohm's law, meaning that a coil that draws say, 38A to hit 150w (.1) can get it in exchange for only 20A from the batteries. The voltage you get from running the batteries in series is what makes it possible to safely vape at .1 on a regulated box.
This principle somewhat applies to unregulated boxes as well, though it's less common, as not very many people seem to like building coils that can take 8v... ...even something as high as a .3 @ 8v yields a whopping 213w at 26A. People are intimidated by them, though they can be made to run what are quite debatably much safer and more efficient high-powered vapes than parallel mech mods, as you can vape at 100w and only draw 12A from your batteries. There's no need to go deep into the sub-ohm territory. People generally build at .5-2.0 to get something similar to a .1-.5 vape on a single battery or dual-parallel mech.
I should also add that if you're running a regulated box, then it's probably running in series. With those, the current draw from the batteries is determined by the wattage setting, not the resistance. No matter what coil you're dropping onto it, it will always need to pull ~20A from fresh batteries to power whatever build you have at 150w.
If it IS one of maybe 2 or 3 obscure ones that runs in parallel, then it will need to pull ~40 amps to in order to hit 150w, which in practice still means 20A from either battery. So it's not a matter of what the resistance of the coil is or how the batteries are configured. It's all about the wattage setting.
The first is a parallel configuration. Most mods wired like this will have both "+" and "-" ends on the same sides of the sled... ...as in, two positives on the top and two negatives on the bottom or vice versa. The batteries sit side-by-side in the circuit and essentially share a single positive and negative connection point, so the amp load is split between the two. A coil that draws 10A total will draw 5A from either battery. This means your amp ceiling and capacity are doubled, while output voltage remains the same as that of one battery.
In practice, it's not going to be exactly double, but it will be close. A lot of people pretend that it's 1.5 times to give themselves headroom, which would give you 45A as a max from two 30A batteries, but even that is conservative imo.
Parallel is common only in unregulated box mods, as it makes up for the fact that low-end sub-ohming (as most mech users do) is not power-efficient in that it requires a lot of current in order to reach a given wattage. If you want to sub-ohm below .3 on an unregulated device, then this is the safest and most effective option. It allows you to have a high-powered sub-ohm vape with a reasonable capacity at their rather low native voltage output level. Regulated boxes have long since shied away from this, as it is more efficient to cut voltage down to current than it is to turn current into voltage.
The second is a series configuration. Unlike parallel, both ends of the sled will have one plus and minus on the top and bottom. Back in the day, people used to call it stacking in reference to the batteries being on top of each other. The positive on the first battery connects to the negative of the second, so the current travels from one to other, rather than leaving each battery separately and converging afterwards. This doubles the voltage, but leaves the capacity and amp limit the same as that of either battery alone.
You will see series most often used in high-powered regulated boxes because the higher voltage output makes them much safer and more power efficient, as you can attain the same wattage for just half of the current when you double your voltage. They use a buck converter between the batteries and atty to exchange voltage for current as dictated by ohm's law, meaning that a coil that draws say, 38A to hit 150w (.1) can get it in exchange for only 20A from the batteries. The voltage you get from running the batteries in series is what makes it possible to safely vape at .1 on a regulated box.
This principle somewhat applies to unregulated boxes as well, though it's less common, as not very many people seem to like building coils that can take 8v... ...even something as high as a .3 @ 8v yields a whopping 213w at 26A. People are intimidated by them, though they can be made to run what are quite debatably much safer and more efficient high-powered vapes than parallel mech mods, as you can vape at 100w and only draw 12A from your batteries. There's no need to go deep into the sub-ohm territory. People generally build at .5-2.0 to get something similar to a .1-.5 vape on a single battery or dual-parallel mech.
I should also add that if you're running a regulated box, then it's probably running in series. With those, the current draw from the batteries is determined by the wattage setting, not the resistance. No matter what coil you're dropping onto it, it will always need to pull ~20A from fresh batteries to power whatever build you have at 150w.
If it IS one of maybe 2 or 3 obscure ones that runs in parallel, then it will need to pull ~40 amps to in order to hit 150w, which in practice still means 20A from either battery. So it's not a matter of what the resistance of the coil is or how the batteries are configured. It's all about the wattage setting.
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