There has been much discussion on the istick thread regarding the istick's technology. I realize that it may be a bit much to ask everyone to read through nearly 8000 posts to discover what has been learned previously. Rehashing the debates over topics that have been settled 5000 posts before tends to annoy many. So, here is a compilation of posts that have come before with some added commentary...
Rather than Direct Current as we see directly out of a battery, the iStick utilizes pulse-width-modulation (PWM) to fire our coils.
So what does this all mean for iStick users?
Below is a screen-grab from Phil Busardo's iStick review...
What does this chart tell us?
1.) The iStick is incapable of firing below 4.1V (at full battery charge).
2.) The iStick is capable of firing it's maximum Amperage (4.5A) and voltage (5.5Vavg or 5.6Vrms).
3.) The iStick is capable of firing above 20W - 5.1Vrms into 1.1Ω is 23.65W (V²/R=W - Ohm's Law).
Next is a screenshot from PicoScope6 of the iStick firing at a displayed 3V...
This tells us:
1.) The iStick is utilizing PWM, with a Vpk of 5.8 and frequency of 48Hz (times per second).
2.) The iStick is definitely tuned to Average (mean) Voltage output - Vavg.
3.) The iStick is incapable (at full battery charge) to fire below 4.065Vrms.
We also know that the iStick's firmware, at approximately 2/3 battery charge, lowers the peak voltage (Vpk) in its PWM cycle to 4.8V unless a higher output is set on the display. In which case, the Vpk returns to 5.8V. Why does it do this? Probably to extend battery life. Smart tuning actually. But it requires us to redo the math for voltage outputs of 4.8 and below.
Next, from PicoScope6, the iStick's output; 4.7V setting @ approximately 66% battery charge:
1.) Peak voltage (Vpk) is reduced to 4.8
2.) Output is now 4.64Vavg or 4.7Vrms
Next, from PicoScope6, the iStick's output; 4.8V setting @ approximately 66% battery charge:
1.) Vpk is still 4.8
2.) Vavg & Vrms values are the same @ 4.781
Next, from PicoScope6, the iStick's output; 4.9V setting @ approximately 66% battery charge:
1.) Vpk returns to 5.8.
2.) Vrms = 5.2
What else does this tell us? When at approximately 2/3 battery charge or less, the iStick fires at a minimum of 3.8Vrms.
If you want to see Phil Busardo's review you get that here:
https://www.youtube.com/watch?v=_W1G7p_fCJw
Please note that there has been some confusion regarding Phil's review because he doesn't spell things out in detail...
1.) On the screen titled "Minimum/Maximum Allowable Wattage Settings" (shown below), Phil discuses what settings are allowable by the iStick's firmware in Variable Wattage mode. This is not a display of what the iStick is actually capable of outputting.
2.) On the screen titled "iStick - 20 Watts" (shown below), Phil clearly demonstrates the iStick fires 5.1Vrms into the 1.1Ω coil. According to Ohm's Law (and Joule's Laws), this dissipates 23.65W at the coil.
Phil doesn't test at resistances between 1.1 & 1.6Ω or at 1Ω. Unfortunately, this range happens to be the iStick's "sweet spot". From 1 to 1.5Ω the iStick can not only hit 20 Watts, it can exceed it. At 1.6Ω, the iStick is very close with a 19.6W output.
I hope this clears up any confusion regard this brilliant, yet controversial device.
Thanks for reading!
Rather than Direct Current as we see directly out of a battery, the iStick utilizes pulse-width-modulation (PWM) to fire our coils.
aldenf;14316506 said:Just a primer on how PWM works...
With very few exceptions, PWM boosts the battery voltage to a set level, usually the device's highest voltage, sometimes a bit higher. Then it pulses that voltage several times per second to obtain the overall voltage that's been set. In the case of the iStick, it boosts voltage to 5.8V. Then it pulses 5.8V 48 times per second (48 Hz). Those 48 pulses per second can be very short or much longer until the output voltage looks constant on test equipment. The percentage of time that the voltage is on (vs. off) is called it's duty cycle.
The below image shows a device with a peak of 5V firing at 75%, 50% & 20% duty cycles.
Here's where it gets kind of tricky... If we multiply the peak voltage (Vpk) by the duty cycle (C%) we get the average voltage (Vavg, shown above). We know that firing a Vavg of 3.5V into our 1.8Ω coil creates much higher Wattage at the coil than a constant 3.5V.
For example, using the iStick's specs:
Ohm's Law (V²/R=W) tells us that a constant 3.5V into a 1.8Ω coil will give us 6.8W.
We also know a different formula is used to determine Watts from a PWM signal:
(Vpk²/R) * C% = W or in our case, (5.8²/1.8Ω) * (3.5/5.8) = 11.3W
6.8W vs. 11.3W is a big difference.
We use RMS (root-mean-square) Voltage to obtain the Watts that constant Voltage provides.
aldenf;14327936 said:
So what does this all mean for iStick users?
Below is a screen-grab from Phil Busardo's iStick review...
What does this chart tell us?
1.) The iStick is incapable of firing below 4.1V (at full battery charge).
2.) The iStick is capable of firing it's maximum Amperage (4.5A) and voltage (5.5Vavg or 5.6Vrms).
3.) The iStick is capable of firing above 20W - 5.1Vrms into 1.1Ω is 23.65W (V²/R=W - Ohm's Law).
Next is a screenshot from PicoScope6 of the iStick firing at a displayed 3V...
This tells us:
1.) The iStick is utilizing PWM, with a Vpk of 5.8 and frequency of 48Hz (times per second).
2.) The iStick is definitely tuned to Average (mean) Voltage output - Vavg.
3.) The iStick is incapable (at full battery charge) to fire below 4.065Vrms.
We also know that the iStick's firmware, at approximately 2/3 battery charge, lowers the peak voltage (Vpk) in its PWM cycle to 4.8V unless a higher output is set on the display. In which case, the Vpk returns to 5.8V. Why does it do this? Probably to extend battery life. Smart tuning actually. But it requires us to redo the math for voltage outputs of 4.8 and below.
Next, from PicoScope6, the iStick's output; 4.7V setting @ approximately 66% battery charge:
1.) Peak voltage (Vpk) is reduced to 4.8
2.) Output is now 4.64Vavg or 4.7Vrms
Next, from PicoScope6, the iStick's output; 4.8V setting @ approximately 66% battery charge:
1.) Vpk is still 4.8
2.) Vavg & Vrms values are the same @ 4.781
Next, from PicoScope6, the iStick's output; 4.9V setting @ approximately 66% battery charge:
1.) Vpk returns to 5.8.
2.) Vrms = 5.2
What else does this tell us? When at approximately 2/3 battery charge or less, the iStick fires at a minimum of 3.8Vrms.
If you want to see Phil Busardo's review you get that here:
https://www.youtube.com/watch?v=_W1G7p_fCJw
Please note that there has been some confusion regarding Phil's review because he doesn't spell things out in detail...
1.) On the screen titled "Minimum/Maximum Allowable Wattage Settings" (shown below), Phil discuses what settings are allowable by the iStick's firmware in Variable Wattage mode. This is not a display of what the iStick is actually capable of outputting.
2.) On the screen titled "iStick - 20 Watts" (shown below), Phil clearly demonstrates the iStick fires 5.1Vrms into the 1.1Ω coil. According to Ohm's Law (and Joule's Laws), this dissipates 23.65W at the coil.
Phil doesn't test at resistances between 1.1 & 1.6Ω or at 1Ω. Unfortunately, this range happens to be the iStick's "sweet spot". From 1 to 1.5Ω the iStick can not only hit 20 Watts, it can exceed it. At 1.6Ω, the iStick is very close with a 19.6W output.
I hope this clears up any confusion regard this brilliant, yet controversial device.
Thanks for reading!
