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I don't know for sure but I would say the 11.1 since it starts out higher it would take longer to reach the shut down voltage of the regulator. You did say "all things being equal" right?
That's is not what I am looking for, the lipos shut down on there own at their low voltage cutoff (protected). My question is related to the regulator, is it more efficient stepping down 11.1v or 7.4v down to 5v or because it has to step down more voltage it works harder and is less efficient.
I would think a step down regulator is designed for a certain amount of input voltage.
I'm not sure about this, but a step down transformer rated at 120v-24v would give 48v when input is 240v. I sometimes use a 240v-24v transformer to replace 120v-12v as 12v 40VA are hard for me to find.
That being said, maH is maH, so the battery storage should be the same I think.
I'm not sure about this, but a step down transformer rated at 120v-24v would give 48v when input is 240v. I sometimes use a 240v-24v transformer to replace 120v-12v as 12v 40VA are hard for me to find.
That being said, maH is maH, so the battery storage should be the same I think.
Still not what I am looking for. I have have made over a dozen mods with the LM2596. Just curious if putting 3 14500 instead of 2 would last longer, 11.1v instead of 7.4v.
http://www.e-cigarette-forum.com/forum/battery-mods/259577-just-lm2596-users.html
Two things -
If the mAh of the packs are the same, but the voltage of one is higher, then the pack with the higher voltage would have more useful energy equaling longer run times.
If the energy of the packs are equal (i.e., the Watt/hour rating), then it depends on the input vs output efficiency of the regulator. On the OKR module I use, the higher the input voltage vs output voltage, the lower the efficiency. The W/hr of the packs being exactly equal would mean that I would get less run time with a higher voltage pack.
edit-
I forgot to explain the Watt/hour calc-
To calculate the watt-hour of the pack, you multiply V x A. So a 11.1v pack at 2200mAh would be 24.42W/hr and a 7.4v pack at 2200mAh would be 16.28W/hr. The 11.1v pack has more energy.
A 7.4v pack with bigger cells, like 3000mAh would have 22.2W/hr of energy, close to the 11.1v pack. Even though it has less voltage, it would offer comparable run times in an e-cig.
If the mAh of the packs are the same, but the voltage of one is higher, then the pack with the higher voltage would have more useful energy equaling longer run times.
If the energy of the packs are equal (i.e., the Watt/hour rating), then it depends on the input vs output efficiency of the regulator. On the OKR module I use, the higher the input voltage vs output voltage, the lower the efficiency. The W/hr of the packs being exactly equal would mean that I would get less run time with a higher voltage pack.
edit-
I forgot to explain the Watt/hour calc-
To calculate the watt-hour of the pack, you multiply V x A. So a 11.1v pack at 2200mAh would be 24.42W/hr and a 7.4v pack at 2200mAh would be 16.28W/hr. The 11.1v pack has more energy.
A 7.4v pack with bigger cells, like 3000mAh would have 22.2W/hr of energy, close to the 11.1v pack. Even though it has less voltage, it would offer comparable run times in an e-cig.
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LOL I thought it was a trick question and I was just playing along. I don't know the answer but what meatsneakers wrote sounds good. But I can tell how to find the answer, just breadboard it and see which runs the longest. 
Thanks, you answered my question.. I think. The second part of my question was if the stepdown regulator like a 2596 works harder to stepdown 11.1 to 5 v than 7.4 to 5v and this harder work reduce battery life.
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It depends on the module. I never read the data sheet for the 2596 but it's usually the case that the larger the divide between the input and output voltage, the less efficient the converter is. On a switching converter it's only a few % though, so I wouldn't worry about it.
What really matters with a switching converter like the 2596 is the Watt/hour capacity of the pack. Unlike a linear converter, it isn't just burning away the voltage so you're getting 90%+ of the energy out of the pack.
What really matters with a switching converter like the 2596 is the Watt/hour capacity of the pack. Unlike a linear converter, it isn't just burning away the voltage so you're getting 90%+ of the energy out of the pack.
You have to sum capacities of all your batteries. Say, if you use 2 batteries in series 1 a-h each, you get 2 a-h. If you use 3 batteries in series 800 ma-h each, you get 2.4 a-h. Then compare. In my example the second design gives more capacity. Of course you also have to consider effectiveness of your DC-DC converter, but in common this rule works.
Also in common better to have bigger difference between input and output voltage (depends of a board). So 11 volts sometimes could be more effective.
But charging of 3 cells simultaneously... I don't like it
Also in common better to have bigger difference between input and output voltage (depends of a board). So 11 volts sometimes could be more effective.
But charging of 3 cells simultaneously... I don't like it
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It actually doesnt work as hard stepping down from a higher voltage using a switching regulator. IF you hooked a Amp meter up to the input side of the regulator you would see it would be using less amps bucking down at 11.1 volts and more amps at 7.4 volts. So in the case of bucking down to a lower voltage the 11.1 pack is going to get around a 1/3 longer run time then the 7.4 pack.
Thanks guys, finally got an answer.....
Making another docking station to snap onto my VV LM2596 PT box and was wondering if three 14500 was better than two in series. No problem slimest I never charge in box. Since the PT is in a 3AA box I plan to snap another 3AA box to the back of it. From all your responses 3 14500's in series will give more vaping time than two in series.
Making another docking station to snap onto my VV LM2596 PT box and was wondering if three 14500 was better than two in series. No problem slimest I never charge in box. Since the PT is in a 3AA box I plan to snap another 3AA box to the back of it. From all your responses 3 14500's in series will give more vaping time than two in series.
This has already been stated, but it didn't sound quite right to me so here's how I'd put it;
Switching regulators are more efficient when input voltage is closer to output voltage, but it's not a huge amount. Probably less than 5% between the two scenarios. Strictly in terms of regulator efficiency, it would be better to use a 2S (7.4V) LiPo pack than a 3S (11.1V) LiPo pack.
One thing that may be confusing with LiPo packs is that charge capacity is specified per the value of a single cell in the pack. So, for example, a 2200mAh 2S pack has two 2200mAh cells. A 2200mAh 3S pack has three 2200mAh cells. Since switching regulators conserve power, you have to look at things in terms of energy capacity. A 2S 2200mAh pack has 16.3 Watt-hours (2200mAh x 7.4V). A 3S 2200mAh pack has 24.4 Watt-hours (2200mAh x 11.1V). In that case, the 3S LiPo would provide approximately 50% more run time than the 2S LiPo. It wouldn't be quite 50% more since regulator losses would be a little higher using the higher input voltage.
Switching regulators are more efficient when input voltage is closer to output voltage, but it's not a huge amount. Probably less than 5% between the two scenarios. Strictly in terms of regulator efficiency, it would be better to use a 2S (7.4V) LiPo pack than a 3S (11.1V) LiPo pack.
One thing that may be confusing with LiPo packs is that charge capacity is specified per the value of a single cell in the pack. So, for example, a 2200mAh 2S pack has two 2200mAh cells. A 2200mAh 3S pack has three 2200mAh cells. Since switching regulators conserve power, you have to look at things in terms of energy capacity. A 2S 2200mAh pack has 16.3 Watt-hours (2200mAh x 7.4V). A 3S 2200mAh pack has 24.4 Watt-hours (2200mAh x 11.1V). In that case, the 3S LiPo would provide approximately 50% more run time than the 2S LiPo. It wouldn't be quite 50% more since regulator losses would be a little higher using the higher input voltage.
The difference between 16.3 watt hours and 24.4 watt hours is 33% or 1/3. So a S3 11.1 volts pack will give you around 33% longer run time then a a 7.4 volt S2 pack, bucked down to the same output voltage.
It's just semantics. If you look at 16.3 Watt-hours as the baseline, then 50% more would be 24.4 Watt-hours. If you look at 24.4 Watt-hours as the baseline, 16.3 Watt-hours would be 33% less.
Don`t forget about some PCB protection for that li-po, otherwise will not last long enough
Yes, good you brought that up. LiPos absolutely need protection when used to power an e-cig mod. The 2S and higher packs are sold primarily for use in powered RC models and do not include protection. The motor controllers they use with them provide over-discharge protection, but that's it. The RC guys are aware of the risks and handle the cells accordingly. For an e-cig, they are way too hazardous as is. Add a protection PCB or at least a PTC fuse and charge the cells in a safe manner.
Love this forum: A simple question becomes and education.
I have no problem with charging always use balancing chargers from my RC's but what should I use on the PV to protect from over discharge? I use an RC 11.1V RC 20C 850 mAh lipo in my PT dock. Normally just recharge when voltage gets below 11v.
I have no problem with charging always use balancing chargers from my RC's but what should I use on the PV to protect from over discharge? I use an RC 11.1V RC 20C 850 mAh lipo in my PT dock. Normally just recharge when voltage gets below 11v.
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That's the tricky part. For a single cell, you can easily make a cutout with a voltage detector and a MOSFET. However, voltage detectors are not available with high enough trip points for two or more series cells. I could be wong, but I have yet to see any over 4.5V.
You have to come up with your own cutout. A simple circuit with a zener, resistor, and MOSFET might work. I don't know for sure because I've only been doing single cell mods and have not tried to make a cutout for a 2S or 3S pack.
The problem is your cutout should shut down current as much as possible, but the cutout requires some amount of power to monitor battery voltage. Ideally, it should draw only a few µAmps at most. Voltage detectors are perfect for that. The ones I use for my mods (powered by a single LiPo cell) draw only a tenth of a µAmp.
Some of the switching regulators just happen to have an under-voltage lockout that's good for a 2S pack. However, it's too low for a 3S pack.
Of course, the easiest thing to do is just add a protection PCB which will cover all the bases. There's a wide selection of them here for 2S and 3S packs.
You have to come up with your own cutout. A simple circuit with a zener, resistor, and MOSFET might work. I don't know for sure because I've only been doing single cell mods and have not tried to make a cutout for a 2S or 3S pack.
The problem is your cutout should shut down current as much as possible, but the cutout requires some amount of power to monitor battery voltage. Ideally, it should draw only a few µAmps at most. Voltage detectors are perfect for that. The ones I use for my mods (powered by a single LiPo cell) draw only a tenth of a µAmp.
Some of the switching regulators just happen to have an under-voltage lockout that's good for a 2S pack. However, it's too low for a 3S pack.
Of course, the easiest thing to do is just add a protection PCB which will cover all the bases. There's a wide selection of them here for 2S and 3S packs.
The scary part about multiple battery mods is that from what I've heard, all meltdowns reported lately while vaping were stacked mods. It's a shame we can't just use an inline fuse instead of individual protection PWBs. That doesn't stop a battery that's decided to go thermal, though.
I expect to see more safety devices incorporated as ecig technology grows and develops. Just saying ...
That doesn't stop a battery that's decided to go thermal, though.I expect to see more safety devices incorporated as ecig technology grows and develops. Just saying ...
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