Battery Question

[tony46113]

I'm using (and have been for several months now) Samsung 25R's in my RX200's at 75W. Coil resistance is 0.15ohms. Ohms law calculator calculates the current at 22.36068 amps.

The Samsung 25R's are rated at 20A ... My question is that do you triple the max current to 60A, since the RX200's have three batteries or am I operating right above the line at 75W?

 

[smacuser]

 

[NU_FTW]

Pulled this well written essay from reddit

PSA: You Don't Calculate Current Draw on Regulated Mods Like You Do on Mech Mods • /r/electronic_cigarette

Multiple Battery mods:

Some mods will run multiple batteries in series or parallel. First we need to explain the difference:

A series connection will treat the two batteries as one. The advantage of a series connection is the voltage doubles (from 3.7v nominal to 7.4v nominal). This means you will, in a sense, be putting less stress on the battery. For instance, if you were to run 100w with a 3.7v battery, you are drawing 27 amps on a fresh battery. If, however, you have two batteries in series, you will only be drawing 13 amps. Remember, in series, the two batteries behave as one. Therefore, the amp limit of one battery is the amp limit of both batteries (25R's in series still have a 20 amp limit). However, with the doubled voltage, you don't need as much current to achieve the desired power. So, even though the amp limit hasn't magically doubled, the need for those amps has decreased.

Parallel configurations do not double the voltage. Two 3.7v batteries in parallel still only provide 3.7v. However, the capacity of the cells (amp hours) is doubled. This also means that the amp limit will also double (from 20 amps for one battery to 40 amps for two, and so on). So, if you want 100 watts with parallel batteries, you will still only be applying 3.7v to achieve it, which means you are drawing 27 amps on a fresh battery. But since you have two batteries with a 20 amp limit, the 27 amps is well within that 40 amp margin of safety.

Essentially, as far as current draw is concerned, series and parallel achieve the same thing. It's just the way they achieve it is different. Series achieves it with more voltage (which decreases the need for more current), while parallel achieves it by doubling the amp hours (increasing the available current).

Example: You are running your Sigelei 150 at 150 watts and you want to know the amp draw on your batteries.

I = 150/ 7.4v = 20 amps

Since your two batteries become a single battery in series, the nominal voltage effectively doubles. This means you don't need as much current to hit that 150 watts.

TL;DR: Don't confuse output voltage for input voltage on regulated mods. If you want to determine your current draw from the battery on a regulated mod, here is the only correct way to do it: I = P/V. That means your current will equal your watt level divided by how much charge you have on your battery. If you don't know the charge, then just plug in 3.7v (as that's the nominal rating). Atomizer resistance has nothing to do with the current being drawn from your battery on a regulated mod.

EDIT: Looks like I was late. Another guy wrote this same PSA a while back. I recommend reading his as well.

EDIT #2: /u/D-juice comments are also relevant:

max amps = max watts/2.5v

For multi-battery mods divide that by the number of batteries (the maths works the same in parallel and series).

His equation provides a bit of a safety margin, so you can use 2.5v as a "rule of thumb" number to calculate the amperage being drawn from an almost depleted battery. Also, you need to factor in efficiency (~10% overhead) as well depending on the board (check your board's specs for efficiency).

 

[Ryedan]

I'm using (and have been for several months now) Samsung 25R's in my RX200's at 75W. Coil resistance is 0.15ohms. Ohms law calculator calculates the current at 22.36068 amps.

The Samsung 25R's are rated at 20A ... My question is that do you triple the max current to 60A, since the RX200's have three batteries or am I operating right above the line at 75W?

I use the Steam Engine battery drain calculator for these calcs. It's easy (takes care of most of the variables involved) ... and I like easy

Click on 'regulated' and 'power regulation (VW)', enter 75 watts in the 'Power (wattage) setting' field, and enter 9.3 volts for 'Battery voltage' (minimum combined voltage with 3 batts in series at 3.1V each). Click enter.

Under 'Battery drain - what taxes your battery' you'll see 8.96A for each battery. Change the resistance and you'll see battery drain does not change. Change the battery voltage to 12.6 for fully charged cells at 4.2V each and you'll see what happens to the amp draw. For one battery use 3.1V, for two in series use 6.2V.

For multiple batteries in parallel you leave the battery voltage at 3.1V and manually divide the amp draw by the number of batts in the mod.

Hope that helps.

 

[tony46113]

I assume that the RX200 is a parallel config since the batteries are side by side? I don't really see that stated on the Wismec site, but maybe that is basic battery/electronic geek stuff, that I don't know about. However, I do know the definition of parallel.

Thanks for the link to the Steam Engine site ... It helps me, but that is way too overwhelming for the aveage person. Way too many variables there.

Also ... this guy on Reddit who's article that was mentioned ... I feel like he is doing it backwards. I don't have a mod that I can adjust voltage, do you? ... We adjust wattage and control resistance depending on the coil/build.

 

[NU_FTW]

I assume that the RX200 is a parallel config since the batteries are side by side? I don't really see that stated on the Wismec site, but maybe that is basic battery/electronic geek stuff, that I don't know about. However, I do know the definition of parallel.

Thanks for the link to the Steam Engine site ... It helps me, but that is way too overwhelming for the aveage person. Way too many variables there.

Also ... this guy on Reddit who's article that was mentioned ... I feel like he is doing it backwards. I don't have a mod that I can adjust voltage, do you? ... We adjust wattage and control resistance depending on the coil/build.

Pretty sure the RX is series not parallel. The mod adjusts the voltage based on your desired wattage. Increase your watts and the mod will increase the voltage draw on the battery. Now the voltage calculation you use is based on what the batteries are capable of so as stated with the low end of the voltage being 3.1 per you multiply that by the 3 batteries in the mod to equal 9.3 divide your desired wattage by 9.3 and you will get the power draw on the battery. Most mods consider 3.1 to be a dead battery to protect under volt. 4.2 being the high side you will see your best case scenario with 12.6v being the most you can have which lowers the amp draw on the batteries when full. The website works with the exact same calculations. The resistance of the coil means nothing on regulated mod. Absolutely Nothing.

 

[tony46113]

Then your parallel and the definition of parallel mean two different things. Parallel means "side by side". Perhaps that physically side by side doesn't mean parallel in the electronics world? I guess I will revist this tomorrow ... My RX200 reads 0.16ohms, 75w, and 3.46v ... batteries are half full.

My original question was that of how much current is safe to pull from that config ... One battery is rated at 20A continuous ... I'm pulling over 20A, I would assume, based on an ohms law calulator at 75w and 0.16ohms. Should I consider myself to have 60A (Three 20A batteries) and theoretically have the ability to safely pump that mod up to 225W (if that were even possible)?

 

[Train2]

Then your parallel and the definition of parallel mean two different things. Parallel means "side by side". Perhaps that physically side by side doesn't mean parallel in the electronics world? I guess I will revist this tomorrow ... My RX200 reads 0.16ohms, 75w, and 3.46v ... batteries are half full.

My original question was that of how much current is safe to pull from that config ... One battery is rated at 20A continuous ... I'm pulling over 20A, I would assume, based on an ohms law calulator at 75w and 0.16ohms. Should I consider myself to have 60A (Three 20A batteries) and theoretically have the ability to safely pump that mod up to 225W (if that were even possible)?

 

[tony46113]

This thread is exactly why people don't understand or care to learn. I understand the difference on the inside ... How do you tell the difference by looking at it?

 

[Jim_ MDP]

This thread is exactly why people don't understand or care to learn. I understand the difference on the inside ... How do you tell the difference by looking at it?

This is easy...

In general... if the batteries are flipped end for end in the sled, it's a series configuration. This is because the wiring is just plain easier that way, and if they are wired parallel the pos and neg ends will be together ( + with +, - with - ). Look at some dual batt mech mods (the interiors are generally open to view so you can see the wiring connections) and you will see... simple convenience (or at least in the mech's case... shorter wiring/lower internal resistance/higher efficiency. Desirable but less important in a regulated).

Two things... parallel in a regulated mod is far rarer than series (the Eleaf i100 and i100 TC are good examples of parallel).

And when in doubt... simply insert a single battery and try to turn it on.
If the mod comes to life... it's parallel. A series circuit won't function with one of the batteries (in series) missing. That leaves a rather large "open" in the circuit.

Make sense?

eta: By the way... all of our RXs are series.

 

[NU_FTW]

Then your parallel and the definition of parallel mean two different things. Parallel means "side by side". Perhaps that physically side by side doesn't mean parallel in the electronics world? I guess I will revist this tomorrow ... My RX200 reads 0.16ohms, 75w, and 3.46v ... batteries are half full.

My original question was that of how much current is safe to pull from that config ... One battery is rated at 20A continuous ... I'm pulling over 20A, I would assume, based on an ohms law calulator at 75w and 0.16ohms. Should I consider myself to have 60A (Three 20A batteries) and theoretically have the ability to safely pump that mod up to 225W (if that were even possible)?

No just because they are side by side does not mean anything. They are in series meaning positive to negative to which their voltages add up unlike in series where it is positive to positive where the voltage is equivilent to one battery but the amps are added up. Ohms law does not apply here, the coil is not pulling the power, the chip is supplying a precise amount of power in this case being 75w from at a minimum of 9.3 volts.. Ohms law would apply if the COIL was the deciding factor such as in a mechanical mod build. I am not trying to mock you or anything trying to reiterate it in perhaps a way you will understand, to me it makes perfect sense and ill admit i am not the best teacher. you have a .16ohm coil being supplied 75w of power from the chip, the only action the ohms play a role is deciding how hot to get from that exact amount of power. The coil cannot dictate the amps being drawn, that is the whole purpose of the chip inside that makes it a regulated mod.

 

[Train2]

I meant the little drawing to answer this comment:

Then your parallel and the definition of parallel mean two different things. Parallel means "side by side". Perhaps that physically side by side doesn't mean parallel in the electronics world? ?

This thread is exactly why people don't understand or care to learn. I understand the difference on the inside ... How do you tell the difference by looking at it?

Hard to be sure "by looking" with the wiring hidden - but the RX is in a series - because it's got more volts available, that's how they get to the higher watts - and to have more volts available, it has to be in series.

I'm not the right guy to answer the full original question - was just trying to chime in on that one bit...

 

[Jim_ MDP]

...
Hard to be sure "by looking" with the wiring hidden - but the RX is in a series - because it's got more volts available, that's how they get to the higher watts - and to have more volts available, it has to be in series.

Or by using a boost transformation
This increases current draw, but it's spread across the available batteries. It's also slightly less efficient, which may be part of the reason parallel isn't used as often, or for our higher wattage mods.

IIRC... the 100/120 W dual parallel i100s I mentioned go to 10 volts. Not sure how many Ohm I'd use that on, I don't build that high.

 

[mongo74]

It's a series mod. I've never personally run into a parallel regulated mod.

You're well below the CDR of 25r's on an RX200. You divide your wattage+10% for device inefficiency by the cut-off voltage of the device(usually 3.2v) times the number of batteries in the mod in order to get current draw on the batteries.

SO: 75w+10%=82.5w/3.2*3(9.4v)...82.5/9.4v=roughly 8.8a per battery. You're within their rated max sustained discharge rate up to about 165w.

 

[tony46113]

Thank you, mongo. That's exactly what I was looking for.

 

[mongo74]

Welcome. Also remember, unlike mechanical mods, coil resistance isn't a factor in regulated mods.

 

[KenD]

It's a series mod. I've never personally run into a parallel regulated mod.

You're well below the CDR of 25r's on an RX200. You divide your wattage+10% for device inefficiency by the cut-off voltage of the device(usually 3.2v) times the number of batteries in the mod in order to get current draw on the batteries.

SO: 75w+10%=82.5w/3.2*3(9.4v)...82.5/9.4v=roughly 8.8a per battery. You're within their rated max sustained discharge rate up to about 165w.

The iStick tc100w is a parallel mod, but other than that I can't really think of a parallel regulated mod.

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[mongo74]

Ah, thanks @KenD I can say I have now. lol

 

[Jim_ MDP]

Ah, thanks @KenD I can say I have now. lol

Got me on ignore or somthin'?

 

[KenD]

Got me on ignore or somthin'?

Of course not, missed that you already mentioned that you already mentioned the tc100w in my desire to be a know-it-all

...and responded even though the post was for mongo74 due to my advanced narcissism

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