What is considered a good voltage drop?

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sonicbomb

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There is no magic number. Voltage drop is constantly variable depending on the resistance. The lower resistance the greater the drop, though this is partially/largely due to battery sag under increased load.

Eg.
SMPL @ 0.6 ohms ~ 0.17 volts
SMPL @ 0.33 ohms ~ 0.42 volts

You can measure it, but it's more for comparison between your own devices and builds. There are some tweaks you can do to reduce drop. Make sure the mod is spotlessly clean and use a good battery. I used copper tape on the inside of my Panzer to 'bridge' the electrical path between the ends of the tube.
Panzer @ 0.6 ohms ~ 0.7 volts before, 0.3 volts after taping

Voltage drop is an inescapable factor with mechanicals, along with their other peculiarities. If you want efficiency use a regulated mod.
 

Kaezziel

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Voltage drop across the coils isn't really very useful in my eyes. It tells you absolutely nothing about the mod. A true measure of a mod's voltage drop should be done with either no atomizer on it, or for the most realistic case, check the drop at the posts with no coils installed. That would give you the true voltage drop of your equipment. :2c:
 

edyle

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Hi,

I want to hear you guys opinion, what do you guys consider a good voltage drop? like between what range? My friend told me some numbers but I'm not convinced. I apologize for such a newbie question, I already tried searching around to get some answers but all I'm finding just an explanation what voltage drop is. Thanks guys! :D

I'd want to keep voltage drop less than 10%.
So for 4 volts that would be 0.4 volts.
 
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suprtrkr

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+1 to @Kaezziel . Voltage drop across a resistance coil doesn't tell you much. Voltage is supposed to drop across a resistance, see Ohm's Law for a complete statement. What you're actually interested in is losses, specifically I^2R losses in the equipment; the voltage drop across the coil is work, ie. heat on the coil, and not a loss. The question mekkies are asking when they talk about voltage drop is "how much power is my mod/atty wasting, instead of using it to heat the coil," and Kaez is right: you find that out by measuring at the posts with no coil installed, and comparing this value to battery voltage. BTW, .18 is lower than I would care to build on 25Rs in a $20 parallel box. That draws 23+ amps. If you get a bad connection and are only working one battery, you are begging for a vent.
 

Kaezziel

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+1 to @Kaezziel . Voltage drop across a resistance coil doesn't tell you much. Voltage is supposed to drop across a resistance, see Ohm's Law for a complete statement. What you're actually interested in is losses, specifically I^2R losses in the equipment; the voltage drop across the coil is work, ie. heat on the coil, and not a loss. The question mekkies are asking when they talk about voltage drop is "how much power is my mod/atty wasting, instead of using it to heat the coil," and Kaez is right: you find that out by measuring at the posts with no coil installed, and comparing this value to battery voltage. BTW, .18 is lower than I would care to build on 25Rs in a $20 parallel box. That draws 23+ amps. If you get a bad connection and are only working one battery, you are begging for a vent.

Thanks bro. I was hoping that I came across the way I intended to... sometimes my thoughts don't translate into words very well. I've been a bit unfocused the last couple of days, and it's always worse when I'm like this... :lol: I appreciate you clearing it up a bit for me! :toast:
 
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edyle

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+1 to @Kaezziel . Voltage drop across a resistance coil doesn't tell you much. Voltage is supposed to drop across a resistance, see Ohm's Law for a complete statement. What you're actually interested in is losses, specifically I^2R losses in the equipment; the voltage drop across the coil is work, ie. heat on the coil, and not a loss. The question mekkies are asking when they talk about voltage drop is "how much power is my mod/atty wasting, instead of using it to heat the coil," and Kaez is right: you find that out by measuring at the posts with no coil installed, and comparing this value to battery voltage. BTW, .18 is lower than I would care to build on 25Rs in a $20 parallel box. That draws 23+ amps. If you get a bad connection and are only working one battery, you are begging for a vent.

errr.. guys? you got something mixed up.
the op measured the voltage drop correctly.
voltage drop = (battery voltage) minus (voltage accross the coil under load)
the battery voltage can be measured as the voltage between the posts with no coil installed
 
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suprtrkr

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Thanks bro. I was hoping that I came across the way I intended to... sometimes my thoughts don't translate into words very well. I've been a bit unfocused the last couple of days, and it's always worse when I'm like this... :lol: I appreciate you clearing it up a bit for me! :toast:
I thought it did. If mine was also helpful, so much the better. We strive to explain complex and non intuitive concepts; understanding them ourselves makes it easy to skip over some of the basics that are, to us, obvious, but to others impenetrable. I'll tell you what, though: in my youth, for my sins, I spent 10 or 15 years working electrician. Not your electronic stuff, but if you need somebody to go up in a bucket truck to replace a 138kV insulator tower, I'm your man. Still, I do believe vaping has sharpened my appreciation of the interconnected nature of Ohm's Law, particularly in the low volt, low watt regime. If you're hooking up a 600v, 3ph, 50 horse AC motor, voltage drop in the switch is meaningless. I mean, you don't even think about it. You've got power out the wazoo, you just bulldoze through it and, so long as it doesn't melt or catch fire, who cares? That dam motor costs $150 an hour to run anyway. What's a few watts lost to ambient heat? But when your power is a pair of VTC4s... it makes a difference. A big difference, for all the math is identical :)
 
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suprtrkr

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errr.. guys? you got something mixed up.
the op measured the voltage drop correctly.
voltage drop = (battery voltage) minus (voltage accross the coil under load)
the battery voltage can be measured as the voltage between the posts with no coil installed
depends on what you're measuring. We're arguing semantics. If you want to know sag under load, you're right. If you want to know throughput efficiency, we are. The voltage measured at the posts with no coil is not battery voltage; it is battery voltage minus I^2R losses in the mod/atty combination.
 

edyle

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depends on what you're measuring. We're arguing semantics. If you want to know sag under load, you're right. If you want to know throughput efficiency, we are. The voltage measured at the posts with no coil is not battery voltage; it is battery voltage minus I^2R losses in the mod/atty combination.

With no coil, I=0.

If you get less voltage accross the posts with no coil compared to the battery voltage that says more about the measuring instrument than anything else.
A dmm would read correctly because it's high impedence.
 

suprtrkr

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With no coil, I=0.

If you get less voltage accross the posts with no coil compared to the battery voltage that says more about the measuring instrument than anything else.
A dmm would read correctly because it's high impedence.
Have it your way, I won't argue. I do agree, entirely, that if you measure the same voltage at the battery terminals you do across the posts, it says something about your instrument. "There is no such thing as a zero ohm resistor."
 

Kaezziel

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With no coil, I=0.

If you get less voltage accross the posts with no coil compared to the battery voltage that says more about the measuring instrument than anything else.
A dmm would read correctly because it's high impedence.

I still stand behind my previous statement and agree with @suprtrkr. I have measured different mods with the same calibrated Fluke meter that we use at work. On my stainless steel Corsair mod with a clone Hobo rda (no coils) I measured a 0.032 voltage difference between the mod/atty (at the posts) and the battery alone. On my Praxis (faux) hybrid with a Derringer (all copper for both) I measured a 0.011 voltage difference between the mod/atty (at the posts) and the battery alone. That is the amount of voltage that is lost and is not being used to generate heat in my coils. Granted, in both cases it is negligible and doesn't really amount to anything as far as producing vapor goes, but if you had dirty, nasty threads and contact points then you could be looking at upwards of a 0.2 volt loss (potentially) which could be significant as you continue to vape. If your battery is holding 3.8V and you're losing .2 or so before it even gets to the coil, then you're changing batteries earlier than you truly needed to. It is a strong indication that you need to clean your mod.
 
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Kaezziel

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I thought it did. If mine was also helpful, so much the better. We strive to explain complex and non intuitive concepts; understanding them ourselves makes it easy to skip over some of the basics that are, to us, obvious, but to others impenetrable. I'll tell you what, though: in my youth, for my sins, I spent 10 or 15 years working electrician. Not your electronic stuff, but if you need somebody to go up in a bucket truck to replace a 138kV insulator tower, I'm your man. Still, I do believe vaping has sharpened my appreciation of the interconnected nature of Ohm's Law, particularly in the low volt, low watt regime. If you're hooking up a 600v, 3ph, 50 horse AC motor, voltage drop in the switch is meaningless. I mean, you don't even think about it. You've got power out the wazoo, you just bulldoze through it and, so long as it doesn't melt or catch fire, who cares? That dam motor costs $150 an hour to run anyway. What's a few watts lost to ambient heat? But when your power is a pair of VTC4s... it makes a difference. A big difference, for all the math is identical :)

LOL! Yeah, I remember the first time I replaced a ceiling fan... apparently electricians and electronics think differently. For electronics, black is typically ground (or common... whatever you wanna call it)... I hadn't bothered to kill the breaker, I just turned off the switch... well, it was a sliding dimmer switch and apparently it wasn't all the way off... not enough voltage to hurt, but that tingling of electricity running down your arm when you expect none is still quite startling! :lol: That's when I learned that black is hot and decided to kill the breaker... I don't even consider playing with 3ph or 220/440v stuff... that stuff scares the crap out of me!
I know what you mean about the big voltage motor though... 50 watts give or take is trivial at that level.
 
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suprtrkr

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LOL! Yeah, I remember the first time I replaced a ceiling fan... apparently electricians and electronics think differently. For electronics, black is typically ground (or common... whatever you wanna call it)... I hadn't bothered to kill the breaker, I just turned off the switch... well, it was a sliding dimmer switch and apparently it wasn't all the way off... not enough voltage to hurt, but that tingling of electricity running down your arm when you expect none is still quite startling! :lol: That's when I learned that black is hot and decided to kill the breaker... I don't even consider playing with 3ph or 220/440v stuff... that stuff scares the crap out of me!
I know what you mean about the big voltage motor though... 50 watts give or take is trivial at that level.
Nothing like making a mistake like that to liven up your day. If you survive :)
 
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daviedog

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Have it your way, I won't argue. I do agree, entirely, that if you measure the same voltage at the battery terminals you do across the posts, it says something about your instrument. "There is no such thing as a zero ohm resistor."
I hope you are joking? 0 ohm resistors have been used for decades in automatic insertion machines for PCB manufacturing..
 

daviedog

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Have it your way, I won't argue. I do agree, entirely, that if you measure the same voltage at the battery terminals you do across the posts, it says something about your instrument. "There is no such thing as a zero ohm resistor."
I hope you are joking? 0 ohm resistors have been used for decades in automatic insertion machines for PCB manufacturing..
 

suprtrkr

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I hope you are joking? 0 ohm resistors have been used for decades in automatic insertion machines for PCB manufacturing..
Oh, I know they exist. I nearly laughed my behind off the first time I saw one because of the color code. The point I had hoped to make is if you measure one, and it reads exactly 0 ohms, you need a more sensitive meter. All conductors have some impedance to current, no matter what. This is implicit in Ohm's Law. AFAIK, this is true even of cryogenic "suprconductors," even though it gets way, way down there. It's like absolute zero. You can't ever get there, and if you could, you couldn't measure it because your meter wouldn't work.
 
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