Battery safety check

[GoBlue88]

Hey folks,

Just validating that I am running my brand new sigelei 75 safely.
I'll be using Sony VTC4s. Is .5 ohms a safe resistance for me to run at 75 watts?

My calculations suggest that since:

Watts=VI

&

V=IR

I=squareroot(watt/R).

So if I run at 75 watts and .5 ohms I'll be about 12-13 amps?


Does that look right/safe?

Thanks in advance for the advice.

 

[dhood]

Should be safe. I believe those are rated at 20 (or more) amps continuous discharge. Battery life won't be great at that rate, though. Better get some spares.

 

[edyle]

Hey folks,

Just validating that I am running my brand new sigelei 75 safely.
I'll be using Sony VTC4s. Is .5 ohms a safe resistance for me to run at 75 watts?

My calculations suggest that since:

Watts=VI

&

V=IR

I=squareroot(watt/R).

So if I run at 75 watts and .5 ohms I'll be about 12-13 amps?


Does that look right/safe?

Thanks in advance for the advice.

The calculation is:
watts = volts x amps

your battery needs to put out 75 watts
your battery might be as low as 3 volts

amps = watts/volts
amps = 75/3
amps = 25 amps.

When the battery is fully charged, voltage is 4.2 volts
at 4.2 volts the amp draw is 75/4.2 = 18 amps

 

[Completely Average]

There isn't a supported setting on that mod that is unsafe with a VTC4 battery. You can run the lowest supported ohm at the full 75W and it will be safe for the battery.

As for using a .5ohm coil at 75W, that's a meager 12.25A draw on the battery, and the VTC4 is a 30A continuous drain battery. You could run a .1ohm coil at 75W and still be below the 30A battery limit.

 

[edyle]

So if I run at 75 watts and .5 ohms I'll be about 12-13 amps?
.

That is 12-13 amps going through the coil at 6 to 7 volts.
That is not the amps draw from the battery.

 

[GoBlue88]

Ahh, is this in regards to the difference between the voltage of the device and the voltage of the battery?

 

[Completely Average]

The calculation is:
watts = volts x amps

your battery needs to put out 75 watts
your battery might be as low as 3 volts

amps = watts/volts
amps = 75/3
amps = 25 amps.

When the battery is fully charged, voltage is 4.2 volts
at 4.2 volts the amp draw is 75/4.2 = 18 amps

His battery will never be as low as 3V. The mod stops firing at 3.2V.

The mod also boosts/bucks voltage as needed. It's not a mech mod. It can output 7.5V from a battery with a 3.3V charge. It can also output 0.5V from a battery with a 4.2V charge.

 

[Completely Average]

That is 12-13 amps going through the coil at 6 to 7 volts.
That is not the amps draw from the battery.

And if it's drawing 18A from the battery and only delivering 12A to the coil, what exactly is happening with the other 6A?

 

[GoBlue88]

His battery will never be as low as 3V. The mod stops firing at 3.2V.

The mod also boosts/bucks voltage as needed. It's not a mech mod. It can output 7.5V from a battery with a 3.3V charge. It can also output 0.5V from a battery with a 4.2V charge.

So what is the difference between battery output voltage and a batteries voltage charge, as you are referring to it

 

[GoBlue88]

There isn't a supported setting on that mod that is unsafe with a VTC4 battery. You can run the lowest supported ohm at the full 75W and it will be safe for the battery.

As for using a .5ohm coil at 75W, that's a meager 12.25A draw on the battery, and the VTC4 is a 30A continuous drain battery. You could run a .1ohm coil at 75W and still be below the 30A battery limit.

It sounds like you are using the same calculation that I am, I=squareoot(watt/R), which at max amperage rating of the batteries (30 amps) would be .08ohms.

The manual says the suh 75 fires down to .05 ohms, so that would suggest it could be run unsafely using VTC4s, and a 35 amp battery would be required below .08 ohms. That is, unless I'm really misunderstanding this (which is a very real possibility).

 

[Completely Average]

So what is the difference between battery output voltage and a batteries voltage charge, as you are referring to it

The difference is what is called Boost and Buck converters. Boost converters take a set input voltage and increase it, Buck converters take a set input voltage and decrease it. The Sigelei 75W is capable of both boosting and bucking voltage so it can deliver voltages to the coil that are different from what the battery can provide.


And I think edyle is making a fundamental mistake not taking that into account. According to what he is saying if you took two of these mods, ran one with a .1ohm coil at 75W and ran the second with a 2ohm coil at 7W then both would last the exact same amount of time on a single battery charge because both are drawing the exact same amperage from the battery at all times. That is demonstratively false. You'll get more than twice the battery life running the 2ohm coil at 7W compared to the .1ohm coil at 75W which is only possible if the mod is capable of altering the amp drain from the battery.

 

[Completely Average]

It sounds like you are using the same calculation that I am, I=squareoot(watt/R), which at max amperage rating of the batteries (30 amps) would be .08ohms.

The manual says the suh 75 fires down to .05 ohms, so that would suggest it could be run unsafely using VTC4s, and a 35 amp battery would be required below .08 ohms. That is, unless I'm really misunderstanding this (which is a very real possibility).

I could be wrong on this, but I don't think the 75W fires kanthal below .1ohms. I think everything below .1ohms is for Temperature Control mode.

 

[GoBlue88]

I could be wrong on this, but I don't think the 75W fires kanthal below .1ohms. I think everything below .1ohms is for Temperature Control mode.

Ahh that could be it, the manual doesn't specify temp control vs. non temp control min. resistance.

I'll look into this boost and buck more, thanks for the advice.

 

[GoBlue88]

I could be wrong on this, but I don't think the 75W fires kanthal below .1ohms. I think everything below .1ohms is for Temperature Control mode.

Also, as long as you're in this thread and knowledgable, do you have any advice on determining that my VTC4s are legit? I got them from ecig avenue, but they just came in a hard plastic case, not wrapped with a Sony logo or anything like that.

 

[Boden]

On a regulated power supply you can ignore the resistance if the coil when calculating battery draw.

It's really simple

At fully charged the battery voltage is ~4.2V

Just before it needs recharged it is ~3.2V.

75W at 4.2V = 17.86A draw
75W at 3.2V = 23.44A draw

So no matter what the resistance of the coil, that will be the amp draw at those battery conditions at 75W.

 

[edyle]

And if it's drawing 18A from the battery and only delivering 12A to the coil, what exactly is happening with the other 6A?

Their are two separate circuits.

The mod draws 18A at let's assume 4 volts from the battery. 72 watts pumped into the mod/chip.
The 18A flows from the battery to the chip/circuitry and back again to the battery.

The mod/chip outputs lets say 6 volts to the 0.5 ohm coil.
Current flowing from the mod/chip to the coil and back again is 12 amps.
Power to the coil is about 72 watts.

 

[edyle]

It sounds like you are using the same calculation that I am, I=squareoot(watt/R), which at max amperage rating of the batteries (30 amps) would be .08ohms.

The manual says the suh 75 fires down to .05 ohms, so that would suggest it could be run unsafely using VTC4s, and a 35 amp battery would be required below .08 ohms. That is, unless I'm really misunderstanding this (which is a very real possibility).

Yes you are misunderstanding.

In a regulated mod the current (and the voltage) from the battery is different from the current (and the voltage) to the coil.

 

[edyle]

His battery will never be as low as 3V. The mod stops firing at 3.2V.

The mod also boosts/bucks voltage as needed. It's not a mech mod. It can output 7.5V from a battery with a 3.3V charge. It can also output 0.5V from a battery with a 4.2V charge.

1: "His battery will never be as low as 3V. The mod stops firing at 3.2V."
Correct.
I just used 3 as a round number, not 3.0, 3.1, 3.2, or 3.3
We are already ignoring the efficiency loss of the regulated mod chip which might be like 10%, probably better.

2: "The mod also boosts/bucks voltage as needed. It's not a mech mod. It can output 7.5V from a battery with a 3.3V charge."
Correct.

3: " It can also output 0.5V from a battery with a 4.2V charge"
Based on the numbers I'm seeing at:
$62.22 Authentic Sigelei 75W Temperature Control VW Variable Wattage APV Box Mod - 5-75W / aluminum alloy at FastTech - Worldwide Free Shipping
using 0.05 ohms and 5 watts
v x v = 5 x 0.05 = 0.25
v = 0.5 volts
Oh!
Correct again.
I didn't know any mod went that low.
That would be because of nickel coils.

 

[GoBlue88]

On a regulated power supply you can ignore the resistance if the coil when calculating battery draw.

It's really simple

At fully charged the battery voltage is ~4.2V

Just before it needs recharged it is ~3.2V.

75W at 4.2V = 17.86A draw
75W at 3.2V = 23.44A draw

So no matter what the resistance of the coil, that will be the amp draw at those battery conditions at 75W.

How are you calculating those numbers?

 

[Boden]

How are you calculating those numbers?

W/V = A

Or 75W/3.2V = 23.4375A