Nobody likes math on a weekendHey I owe you an apology for not acknowledging your point was valid, I was just addressing the term I've not seen used in electrical engineering. Some good discussions and I stayed out of the math talk because it's the weekend and I don't so math on weekends haha
Don't forget about Watts Law
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I'm just going to hit a few random points and I'm leaving a lot out intentionally because the post is way too long as it is.
Read a dozen college/university level books or a vocational one like Delmar's and you'll find a chapter covering ohm's law, power and energy in all of them under the same umbrella. Look up the ohm's law calculations and every chart includes the power calculations. You'll have an easier time finding Bigfoot than you will "Watt's Law" in any book at that level.
Though some high school teacher's slide show messing up terms doesn't even raise an eyebrow. I at least understand where that bad knowledge is coming from and even forgive it...
...a teacher changing things up in an attempt to make it easier to learn. OP got screwed by the education system there.
Try going to electriciantalk, eeweb or the eeevblog forums and see how "Watt's Law" flies there. Those guys can use some entertainment.
Here are some of the most simplified and straightforward explanations I've ever seen on the subject of DC-DC converters, Boost Converter and Buck Converter. That guy just does a fantastic job of it. Just keep in mind these are about as bare bones as it gets. If you want to take it further, I'd recommend watching Dave Jones' EEEVblogs, then maybe picking up Brown's Power Supply Cookbook, a book written by a practicing design engineer for practicing design engineers. Of course a few prerequisite books covering general electronics would be necessary. Getting into VW/VV mods generally requires going well outside standard specs for most PMIC (power management integrated circuits) chips and require advanced knowledge.
As far as mods being able to draw more than a battery is capable of, sure its possible i.e. a budget priced product like anything eleaf (or it may very well have a good PMIC battery chip for all I know...I've never tested one) might over draw from a battery, but most quality boards incorporate a PMIC battery management chip that prevent the mod from overpowering the battery, put in a 10A battery and it will limit the mod to drawing 10A from the battery. They're dirt cheap chips and easy to implement. P Busardo and others have demonstrated those capabilities in practical testing on some mods like the DNA40 and SXMini, it would be a simple thing to test for.
While isolation from battery to load is theoretically possible, isolation typically increases size and costs of a DC-DC converter from 120% to 250%, also peak efficiency suffers by up to 10% depending on topology chosen so it will never reach a peak efficiency even close to 90%.
When you consider most mods are designed to be as physically compact and efficient as possible with peak efficiency commonly reaching the mid to high 90s, it places them squarely in non-isolated buck, boost and buck/boost circuitry templates.
DC-DC converter theory and some basic battery management 101 that is as plain as day to anyone familiar with the subject. The very minimum knowledge I would expect of anyone handing out professional advice and making definitive statements.
There's nothing wrong being a professional and saying so, there's nothing wrong with handing out advice, even getting it wrong when going out on a limb and making it clear that it's an educated guess. And of course the honest mistake can be forgiven.
But when someone runs around making definitive statements of fact as an authority, stressing they are a professional repeatedly, while being consistently so far off the mark across the board that its almost comical, it leads to some unflattering places....
Read a dozen college/university level books or a vocational one like Delmar's and you'll find a chapter covering ohm's law, power and energy in all of them under the same umbrella. Look up the ohm's law calculations and every chart includes the power calculations. You'll have an easier time finding Bigfoot than you will "Watt's Law" in any book at that level.
Though some high school teacher's slide show messing up terms doesn't even raise an eyebrow. I at least understand where that bad knowledge is coming from and even forgive it...
...a teacher changing things up in an attempt to make it easier to learn. OP got screwed by the education system there.
Try going to electriciantalk, eeweb or the eeevblog forums and see how "Watt's Law" flies there. Those guys can use some entertainment.
Here are some of the most simplified and straightforward explanations I've ever seen on the subject of DC-DC converters, Boost Converter and Buck Converter. That guy just does a fantastic job of it. Just keep in mind these are about as bare bones as it gets. If you want to take it further, I'd recommend watching Dave Jones' EEEVblogs, then maybe picking up Brown's Power Supply Cookbook, a book written by a practicing design engineer for practicing design engineers. Of course a few prerequisite books covering general electronics would be necessary. Getting into VW/VV mods generally requires going well outside standard specs for most PMIC (power management integrated circuits) chips and require advanced knowledge.
As far as mods being able to draw more than a battery is capable of, sure its possible i.e. a budget priced product like anything eleaf (or it may very well have a good PMIC battery chip for all I know...I've never tested one) might over draw from a battery, but most quality boards incorporate a PMIC battery management chip that prevent the mod from overpowering the battery, put in a 10A battery and it will limit the mod to drawing 10A from the battery. They're dirt cheap chips and easy to implement. P Busardo and others have demonstrated those capabilities in practical testing on some mods like the DNA40 and SXMini, it would be a simple thing to test for.
While isolation from battery to load is theoretically possible, isolation typically increases size and costs of a DC-DC converter from 120% to 250%, also peak efficiency suffers by up to 10% depending on topology chosen so it will never reach a peak efficiency even close to 90%.
When you consider most mods are designed to be as physically compact and efficient as possible with peak efficiency commonly reaching the mid to high 90s, it places them squarely in non-isolated buck, boost and buck/boost circuitry templates.
DC-DC converter theory and some basic battery management 101 that is as plain as day to anyone familiar with the subject. The very minimum knowledge I would expect of anyone handing out professional advice and making definitive statements.
There's nothing wrong being a professional and saying so, there's nothing wrong with handing out advice, even getting it wrong when going out on a limb and making it clear that it's an educated guess. And of course the honest mistake can be forgiven.
But when someone runs around making definitive statements of fact as an authority, stressing they are a professional repeatedly, while being consistently so far off the mark across the board that its almost comical, it leads to some unflattering places....
Help out a layman here @Mike 586
After reading twelve pages of this thread (and else where on ECF) saying that in a VW Mod the battery doesn't see the resistance of the coil as it's on a different circuit (and so amp draw is our only concern), are you now saying this is wrong?
That it's one circuit with a PMIC? And that the PMIC will limit power to the CDR limit of the battery?
Or am I completely miss understanding you?
I'd like to know, as until I read your post I completely accepted the separate circuit explanation.
After reading twelve pages of this thread (and else where on ECF) saying that in a VW Mod the battery doesn't see the resistance of the coil as it's on a different circuit (and so amp draw is our only concern), are you now saying this is wrong?
That it's one circuit with a PMIC? And that the PMIC will limit power to the CDR limit of the battery?
Or am I completely miss understanding you?
I'd like to know, as until I read your post I completely accepted the separate circuit explanation.
If you have a mod that can register what the max amp the battery can handle that's pretty impressive, also they are too seperate circuits, watts law is seperate from ohms law, if you reference the Delmars again and pay attention you'll see that their definition of ohms law is strictly the relationship between volts, amps and resistance. Power is in the same chapter and is not referenced as watts law I will admit that watts law is not a universally used term some just call it power formulas but it is not ohms law. Also the circuits are seperated, the board sees the battery voltage, then bucks or boosts to dictate what the coil sees, the coil never sees the nominal voltage of the battery
Ok can anyone find an example of a regulated mod blowing up? Just curious... because I could not... im sure it is possible but i would guess its from gross stupidity like putting in a 5 amp battery in a 200 watt mod....
What im saying is common sense will cover your .... with a regulated mod. With the rare exception of mr murphy...
What im saying is common sense will cover your .... with a regulated mod. With the rare exception of mr murphy...
Ok for example wismec dna200. Ok 3 cells in series... will drain to 3.3v before shutoff... so 3.3v×3 cells, 9.9 volts... plug in 200 watts and 9.9 volts and you need a minimum of 21 amp batteries... unless someone sees an error here... I=P/V.
so i go put 25 amp batteries in, and done... no more calculating.
so i go put 25 amp batteries in, and done... no more calculating.
I'm not concerned if we are dealing with Ohms Law or Watts Law, or Power Formula. Most of this thread seems to be dealing with symantics at any rate.
I understand the simple expression:
VW Mod
I=P/V/0.9
I'm only concerned that @Mike 586 seems to be calling into doubt the separate circuit theory that is the basis of ignoring the coil resistance for VW Mod builds, and only focusing on the amp draw.
I like the separate circuit theory as it is simple to apply, frees me from worrying about the resistance of the coil, and seems to make sense in a world full of VW Mods with TC Protection for builds that are often 0.1ohms and lower.
But just because I like it, doesn't make it right, and I don't have the technical knowledge to question the theory. That's what I rely on you guys and girls, and ECF for.
I hope he comes back and clears up his early post, because it's
confused me without giving me an alternative method to check the safety of my builds.
I understand the simple expression:
VW Mod
I=P/V/0.9
I'm only concerned that @Mike 586 seems to be calling into doubt the separate circuit theory that is the basis of ignoring the coil resistance for VW Mod builds, and only focusing on the amp draw.
I like the separate circuit theory as it is simple to apply, frees me from worrying about the resistance of the coil, and seems to make sense in a world full of VW Mods with TC Protection for builds that are often 0.1ohms and lower.
But just because I like it, doesn't make it right, and I don't have the technical knowledge to question the theory. That's what I rely on you guys and girls, and ECF for.
I hope he comes back and clears up his early post, because it's
confused me without giving me an alternative method to check the safety of my builds.
You don't need to worry about it. You already know the formula to keep you within the safe limits of your battery. @Mike 586 is right most of the mods will not have a true isolated output because of the cost and size, and efficiency issues he mentioned. Most of the mods will have the negative or ground sides of the output circuit and battery connected to the outer part of the 510 either directly or via the metal case. So not a true isolated circuit but it makes no real difference to the key thing you need to know on any device:- The maximum current draw on the cell(s) This is important as I don't know of any mod that can identify the cell that an end user has put into it. Most will measure the cell voltage, some may measure and even limit the input current to the regulator circuit for safety, but this only ensures safety if the appropriate cell is chosen in the first place. Much less of an issue when regulated devices were 20-30W as the input current was always lower. Current 75W devices are capable of pushing 20A cells beyond what I would be comfortable with. We may see more issues with regulated devices as time goes by.
There is something lost in this thread... regardless of the accuracy of your application of Ohm's law, there is no assurance a particular battery labeled 20A will safely put out 20A, even if it is made by the most reputable of makers. There are other issues, such as sample variation, internal hidden damage, or simply aging that affect that.
Someone here suggested it is as simple adding up the CDR's of a multiple cell battery pack and we're done. I don't think he considered what happens when one of those 2 or 3 batteries (in his example) can't put out the same current as the other battery or two, or the effects of aging.
Real engineers apply a healthy margin of conservatism to all this, to account for those often unknown and unknowable variances. But here people simply assume an ideal world and have at it. Given that attitude I'm surprised myself at the apparent safety record of at least the regulated mods. Stuff happens and the law of large numbers can be cruel. I use a 50% number for my adjustments for the sake of conservatism. So I don't regularly run my own mods and batteries at more than 50% their rated CDR capacity. You can tell me I'm overly conservative but no one ever vented a battery because he ran it well below it's CDR.
Someone here suggested it is as simple adding up the CDR's of a multiple cell battery pack and we're done. I don't think he considered what happens when one of those 2 or 3 batteries (in his example) can't put out the same current as the other battery or two, or the effects of aging.
Real engineers apply a healthy margin of conservatism to all this, to account for those often unknown and unknowable variances. But here people simply assume an ideal world and have at it. Given that attitude I'm surprised myself at the apparent safety record of at least the regulated mods. Stuff happens and the law of large numbers can be cruel. I use a 50% number for my adjustments for the sake of conservatism. So I don't regularly run my own mods and batteries at more than 50% their rated CDR capacity. You can tell me I'm overly conservative but no one ever vented a battery because he ran it well below it's CDR.
There are no separate circuits as far as the battery is concerned. Electronically the complete unit
is made with multiple circuits. A power supply sees all the multiple circuits as one circuit in the
form of total impedance.
Regards
Mike
My 
good enough version
(W out + 10% W out)/cell min V = ~Amp draw
So for 100W from random dual series box with cutoff at 3.2V per cell.
(100W+10W)/6.4V = ~17.19A
This thread amuses me, carry on.
good enough version(W out + 10% W out)/cell min V = ~Amp draw
So for 100W from random dual series box with cutoff at 3.2V per cell.
(100W+10W)/6.4V = ~17.19A
This thread amuses me, carry on.
There's a problem with that. The "Cutoff" you're looking at is open-circuit or "no load" cell voltage. But under load, the cell voltage is quite a bit lower and thus the current to get x watts needs to be proportionately higher. Since most battery manufacturers specify 2.5V as their cut-off voltage under load, I figure most regulator boards use that as the actual threshold, thus I'd use it in the calculation.My
(W out + 10% W out)/cell min V = ~Amp draw
So for 100W from random dual series box with cutoff at 3.2V per cell.
(100W+10W)/6.4V = ~17.19A
So you don't understand input voltage from output voltage ?
If you contact John, I think he can elaborate alot better for you, and with far superior credentials than any here
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You have a problem with an imaginary mod?Of course I'm talking about cut off under load. What mod would use the resting voltage?
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