Ti-8100 & vv

[Cool_Breeze]

I've assembled a TI-8100 in a 1 x 2 x 3 RS box. It formerly housed the madvapes VV board. It has two 18350 batteries in series.

I'm attempting to obtain voltages from 4 to 5 Volts, though beyond that range is fine.

Overlooked by myself was the fact that the output of the 8100 is logarithmic. The trimmer pots I've found are linear. While I've installed a linear trimmer, it is very difficult to make any type of fine adjustment. I've checked Digi-Key and a little at Mouser and I've found no log trimmers. I've also not located a possible rotary switch in very small size for possible use with a series of fixed resistors. The value needed is 0 - 200 Ohms. A 240 Ohm resistor makes up the required difference.

...any thoughts on (not too complicated or space consuming?) methods for obtaining 0 - 200 Ohms in a logarithmic fashion?

 

[asdaq]

Mine has a little blue pot that is multi turn. About 20 turns, not so sure. The nice part is that one turn give s 1 tenth of a volt change, I could even dial in to hundredths, but no need.

sent from my HTC genisis using Tapatalk

 

[Cool_Breeze]

Mine has a little blue pot that is multi turn. About 20 turns, not so sure. The nice part is that one turn give s 1 tenth of a volt change, I could even dial in to hundredths, but no need.

sent from my HTC genisis using Tapatalk

Thanks, asdaq.

Does the 1 tenth of a volt per turn seem fairly consistent through the 20 turns?

 

[jhonutz]

yep that multi turn trimmer is all you need. good luck

 

[Robert T]

I think the Ever cool variable voltage mod thread has a parts list or PM BigBlue he would know.

Robert

 

[Cool_Breeze]

I think the Ever cool variable voltage mod thread has a parts list or PM BigBlue he would know.

Robert

Thanks...!

 

[Robert T]

You're welcome!

 

[asdaq]

Don't hold me to exactly 20 turns, it was correctly rated and the shop wasn't sure if it was even multi, but yes .1v for each and every revolution and I've stayed between 4.0 and 5.6.

 

[Robert T]

I bumped the Ever Cool thread up for you.

Robert

 

[WillyB]

I'm attempting to obtain voltages from 4 to 5 Volts, though beyond that range is fine.

Well if that's the range you want why don't you tweak your values a bit (check my numbers in the datasheet).

If you went with 260Ω for your limiter = ~5V, Add a 100Ω trimmer for 360Ω total = ~3.9V. You now would have reclaimed all the degrees of the trimmer for your range. Basically with the standard setup the degrees (of rotation) over 5V and under 3.9V are now regained making for a less 'twitchy' (better granularity) adjustment. Perfect? No, but better.

This isn't exactly correct but it illustrates the point.

If you want to stick with the 200Ω the multi-turns folks are talking about will also help, I'd go for a 12 turn though.

3266W-1-201LF Bourns Trimmer Resistors - Through Hole

Digi-Key - 490-2974-ND (Manufacturer - PV37W201C01B00)

 

[Cool_Breeze]

Yes, WillyB - the range you indicated is fine. ...and apparently available at Digi-Key. That's a big plus as I'm hoping to obtain some tantalum capacitors there as well.

Thank you so much!

 

[WillyB]

Yes, WillyB - the range you indicated is fine. ...and apparently available at Digi-Key. That's a big plus as I'm hoping to obtain some tantalum capacitors there as well.

Thank you so much!

You got room in that thing?

Peruse the datasheet from TI.

http://www.ti.com/lit/ds/symlink/ptr08100w.pdf

Some tidbits.

CAPACITOR RECOMMENDATIONS FOR THE PTR08100W POWER MODULE

Electrolytic Capacitors
When using electrolytic capacitors, high-quality, computer-grade electrolytic capacitors are recommended.
Aluminum electrolytic capacitors provide adequate decoupling over the frequency range of 2 kHz to 150 kHz,
and are suitable when ambient temperatures are above -20°C.

Tantalum, Polymer-Tantalum Capacitors
Tantalum type capacitors may only used on the output bus, and are recommended for applications where the
ambient operating temperature is less than 0°C. The AVX TPS series and Kemet capacitor series are
suggested over many other tantalum types due to their lower ESR, higher rated surge, power dissipation,
and ripple current capability. Tantalum capacitors that have no stated ESR or surge current rating are not
recommended for power applications.

The main considerations when selecting input capacitors are the RMS ripple current rating, temperature stability,
and maintaining less than 100 mΩ of equivalent series resistance (ESR).
Regular tantalum capacitors are not recommended for the input bus.

If you look at page 10. Table 3 they have a list of recommended caps. May be best and easiest to just use one that TI has found acceptable, for both input and output with no caveats.

Like these Panasonics, which are also cheap.

EEU-FC1V181 Panasonic Electronic Components Aluminum Electrolytic Capacitors - Leaded

They are a little bigger (10 mm Dia. x 12.5 mm L), so check your room.

Food for thought.

 

[Cool_Breeze]

Thanks for pointing my attention to TI's data on capacitors. I do have room, but I'm not in the direct location of the module. I'll give it a closer look and do a little head scratching.

What is the reason for utilizing 25 to 35 Volt capacitors rather than 10 to 16 Volts?

Also the referenced capacitor at Mouser is 180 microfarad vs. the 100 TI has indicated. (?)

Thanks again.