When V does not equal IR...

[dragginfly]

Still trying to wrap my head around the effects of current,
power, and temperature on vaporization/flavor in cartos.

My best flavor is currently with a KR808D1 PT and Nhaler HR mega cartos.

Assuming 3.4 ohm resistance and 5 volts, the current demand
would be around 1.47 amps.

V=IR

So far, so good, right?

I'm using the PT on my desktop computer front panel USB port.

Just read another thread (now closed) in this expert section
about the current delivery from many USB sources being limited
to 500 mA, or 0.5 amps.

If the USB only delivers 0.5 amps, then at a 3.4 ohm resistance
the voltage drop across the carto is only 1.7 volts. No where
near the 5v potential output of the USB.

So what are we really looking at here?

Is the actual operating voltage of the USB reduced to 1.7 volts
when the current is limited?

I thought 5 volts DC is 5 volts DC is 5 volts DC is 5 volts DC.

 

[rolygate]

The trouble is that USB is a low-power *signal* technology, not for supplying power to devices. The fact it can handle 500mA is just to enable the use of longer cables or cheap ones with high resistance. In theory, no PC USB port can power an ecig without implications. It's why people have burnt out their USB ports (part of the mainboard) doing this.

Using a separate wall socket to USB adapter is safer, you can get 2 amp ones.

To answer your question about the voltage, what will probably be happening is that the ecig will pull more than 500mA out of the USB port. How much you can't know without testing, which I wouldn't do anyway due to the risk of blowing a USB port...

There might be some voltage drop, not sure - but probably the atty will not get all the power it is asking for, is all. One way or another it most likely isn't delivering the theoretical 7.35 watts your numbers should give. Or perhaps it is, and your PC is very well made and can supply that juice to the USB ports (at least, up to now). That seems quite likely as it goes, because a 3.4 ohm atty/carto is more or less dead at the standard ecig's 3.2 volts on-load or whatever, at least as far as most people's taste goes today, they won't stand for the puny hit that used to be the norm.

Also I don't know anything about the KR8 PT - some of these things only charge the battery, they don't provide the 5 volts straight-thru.

Get a wall power socket USB adapter anyway, you know it makes sense.

The main factor in your own sweet spot or taste is the watts drawn by the device, the power it uses / delivers. The old benchmark was 4 watts but now more people prefer about 7 watts. Some go for 10 or even 12 or more, here you're talking about the same sort of big hit as a Capstan Full 'Navy cut' full-strength plain cig, halfway down the cigarette, mega strong.

Although the wattage is the main factor, it is further modified by the atty/carto type (some are hotter/cooler), the e-liquid type/flavor, and even whether the 8 watts or whatever is achieved by using low-voltage and LR atties or hi-voltage and HV atties. The wattage is king though.

 

[Kent C]

Still trying to wrap my head around the effects of current,
power, and temperature on vaporization/flavor in cartos.

My best flavor is currently with a KR808D1 PT and Nhaler HR mega cartos.

Assuming 3.4 ohm resistance and 5 volts, the current demand
would be around 1.47 amps.

V=IR

So far, so good, right?

I'm using the PT on my desktop computer front panel USB port.

Just read another thread (now closed) in this expert section
about the current delivery from many USB sources being limited
to 500 mA, or 0.5 amps.

If the USB only delivers 0.5 amps, then at a 3.4 ohm resistance
the voltage drop across the carto is only 1.7 volts. No where
near the 5v potential output of the USB.

So what are we really looking at here?

Is the actual operating voltage of the USB reduced to 1.7 volts
when the current is limited?

I thought 5 volts DC is 5 volts DC is 5 volts DC is 5 volts DC.

Rolygate is right: "Using a separate wall socket to USB adapter is safer, you can get 2 amp ones." In fact at the Vapor4Life forum you'll find that a 2amp plug is considered a 'requirement' for the V4L PT. But that's to run it and has little to do with your 'vaping experience' which has more to do with Wattage than amperage.

A recent post from our 'resident expert' Scottbee explains:

"Current does not directly correlate to "heat". Power, or Watts does. I can flow a substantial amount of current and still not generate any heat.

And manufacturers generally don't play with resistance to balance battery draw. The play with the resistance to vary the heat generated by the atomizer or cartomizer.. since heat correlates to power, and power = E**2/R."


Also see this post and chart on wattages:
http://www.e-cigarette-forum.com/fo...cts-maam-no-chit-chat-please.html#post1687242

 

[Papa Lazarou]

USB 1.1 and 2.0 specifications call for 0.5A/500mA @5v per port (0.9A on USB 3.0). This is not enough to power any passthrough other than the type which have a battery built in. However in practice I think most ports will deliver more than this. Often two ports together share the same header on the motherboard, so it seems possible that if both ports are not being used with high power devices, that more than 500mA can be provided on one port.

Also I think many PC manufacturers are wise to the fact that USB is used more and more as a power source as much as a communication interface. For example, several Gigabyte motherboards have a feature called "3X USB Power Boost" which they say allows much more power to be provided by the USB ports. Due to power requirements for charging phones a new USB Battery Charging Standard is now in place which allows up to 1.8A @ 5.25v to be provided through USB on PC's which support this standard. More here - Universal Serial Bus - Wikipedia, the free encyclopedia

But yes a AC-USB adapter is safer overall and I have heard of people damaging PC's using passthroughs.