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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Topic: Question about ptr08100 V adjust resistors
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Author Topic: Question about ptr08100 V adjust resistors  (Read 2750 times)

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Offline kortt

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Question about ptr08100 V adjust resistors
« on: April 29, 2013, 10:28:58 PM »
I'm a noob when it comes to figuring this stuff out so please bear with me.  I'm hoping to get my head around this.  I've been planning a mod using the 8100 and want it to adjust from 3.2 to 5.5 volts output.

According to the resistor chart of the datasheet, 3.2v requires a 453ohm resistor and 5.5v requires a 241ohm resistor To adjust in the range I stated I would need to use a potentiometer of 212ohm and a resistor of 241ohms in series.  Is this correct?

Most mods I see with the 8100 are using a 200ohm pot and a 240ohm resistor which by the chart would be a range of 3.3 to 5.5 but it seems that people always say the output is something like 3.6 to 5.5.  Am I missing something? 

-a confused noob :D

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Re: Question about ptr08100 V adjust resistors
« Reply #1 on: April 30, 2013, 10:05:10 AM »
Using a 200ohm pot and a 240ohm resistor  would be a range of 3.3 to 5.5. Yes but you have to consider the parts tolerance. If the pot measured EXACTLY 200 ohms and the resistor was EXACTLY 240 ohms that would be true. Try to get a fixed resistor that has a tolerance of 1%. It will be hard to find a pot to your liking with a low tolerance. Most pots/trimmers are 10% - 25%. When the pot is zeroed out (low end of the voltage range) it would come close to hitting the 3.2v to 3.3v mark. The high end of the voltage range with the pot at full deflection, you will see the max voltage either higher or lower than the chart max.

Offline kortt

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Re: Question about ptr08100 V adjust resistors
« Reply #2 on: April 30, 2013, 12:19:59 PM »
Ah, ok.  I had forgotten about tolerance. 

Is the way I'm looking at the calculations correct?  So if 3v was required for the low end output voltage you would replace the fixed 200ohm resistor with say a 250ohm? (according to the table 3.0v is 491ohm)

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Re: Question about ptr08100 V adjust resistors
« Reply #3 on: April 30, 2013, 12:54:13 PM »
Ah, ok.  I had forgotten about tolerance. 

Is the way I'm looking at the calculations correct?  So if 3v was required for the low end output voltage you would replace the fixed 200ohm resistor with say a 250ohm? (according to the table 3.0v is 491ohm)

A general note: The higher the resistance, the lower the voltage output and visa-verse.
So... 3v low end would require the pot at full resistance range plus the fixed resistor for a total resistance of 491 ohms or close to it. Using a 240 ohm fixed and a 200 ohm pot would be what you are looking for (440 ohms).
A 200 ohm pot w/ 10% tolerance can be any thing between 180 ohms to 220 ohms. That would make your total between 420 ohms to 460 ohms. And don't for get about the 1% fixed resistor tolerance of 237.6 ohms to 242.4 ohms

On some of my projects I had a bag of 200 ohm trimmer pots and I hand picked a pot that was as close to 200 ohms as possible.

So... to summarize, a 200 ohm trimmer and a 240 ohm fixed resistor would give you approximately, depending on tolerance, of 3.35v to 5.5v
Note, you mentioned replace the 200 ohm fixed resistor, did you mean pot? The fixed resistor will change both the high and low output range being it is always in the picture.

Offline kortt

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Re: Question about ptr08100 V adjust resistors
« Reply #4 on: April 30, 2013, 01:03:34 PM »
Thanks Breaktru, that cleared it up nicely  :thankyou:

yeah, after reading your reply and getting my head around it I did mean the pot.
Much appreciated!

Offline CraigHB

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Re: Question about ptr08100 V adjust resistors
« Reply #5 on: April 30, 2013, 01:26:14 PM »
One thing you can do if parts are cheap enough is buy a bunch of them and just pick out the ones that have tolerance within your requirements.  I've done that before.  It's actually the same thing the factory does with components.  They split them up into groups by tolerance and than price them accordingly.   Usually, the only difference between say a 5% and 10% part is how they tested out at the factory.

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Re: Question about ptr08100 V adjust resistors
« Reply #6 on: April 30, 2013, 05:26:04 PM »
Didn't know that the factories do that too. I picked through a bag of 200 ohm pots and measured every one and separated them according to the read resistance.
As far as the pot, it will only effect the top end voltage output. With the values that I use it only means the difference of achieving 5.9v to 6.2v.
With the low end of the voltage output, using a 1% fixed resistor will pretty much get you want to where you want to be.

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