author
1Instructables32,589Views48CommentsJoined October 6th, 2006

Tell us about yourself!

Complete Your Profile

Achievements

10K+ Views Earned a bronze medal
  • przemek commented on Steve Willson Kujur's instructable Build a Power Bank in $21 year ago
    Build a Power Bank in $2

    You're right that one can't let the Lithium batteries get out of the narrow voltage range---that's why Li charger systems are tricky and can't just be a 'diode and lightbulb' circuit from the lead-acid era. The Li chargers measure individual battery voltage by having individual 'balancing' connections to each level of the serial stack.The problem with the parallel setup is this: the Li cells have small internal resistance and narrow voltage tolerance. Small cell differences result in huge balancing currents. Healthy cells that don't differ much will, as you say, just balance out their charged state, but if a cell goes out of spec, at best you just waste the charge out of the good cell, and at worst you can burn up the bad cell with the excessive current flowing from the good ones. Yes y...

    see more »

    You're right that one can't let the Lithium batteries get out of the narrow voltage range---that's why Li charger systems are tricky and can't just be a 'diode and lightbulb' circuit from the lead-acid era. The Li chargers measure individual battery voltage by having individual 'balancing' connections to each level of the serial stack.The problem with the parallel setup is this: the Li cells have small internal resistance and narrow voltage tolerance. Small cell differences result in huge balancing currents. Healthy cells that don't differ much will, as you say, just balance out their charged state, but if a cell goes out of spec, at best you just waste the charge out of the good cell, and at worst you can burn up the bad cell with the excessive current flowing from the good ones. Yes you can mitigate that by having balancing resistors and/or fuses on each battery, but why bother f you can just throw a series stack balancing charger on the problem? In either case, you need some sort of monitoring circuit because as you say, you can't let the Li battery charge/discharge out of its design voltage window.Simply saying, the Li battery chemistry is much less forgiving than the lead acid, so you need fancy charger, and series stack is just easier to handle.

    View Instructable »
  • przemek commented on Steve Willson Kujur's instructable Build a Power Bank in $21 year ago
    Build a Power Bank in $2

    The batteries already have tabs welded to them---when you disassemble the packs, just cut the tabs in the middle. This will result in tabs hanging off with the sufficient length that soldering to them will not heat the battery enough to cause damage. On the other hand, soldering directly to battery end-buttons is liable to transfer enough heat to melt the plastic between and around the internal electrodes, which could lead to catastrophic shorts and spectacular failures. Similar damage was causing the Samsung Note battery fires last year.Another issue: LiIon batteries are more voltage-sensitive than other batteries.. They should not be paralleled---especially if cells have different histories. I haven't seen many commercial packs that have more than 2 cells in parallel, and they use fr...

    see more »

    The batteries already have tabs welded to them---when you disassemble the packs, just cut the tabs in the middle. This will result in tabs hanging off with the sufficient length that soldering to them will not heat the battery enough to cause damage. On the other hand, soldering directly to battery end-buttons is liable to transfer enough heat to melt the plastic between and around the internal electrodes, which could lead to catastrophic shorts and spectacular failures. Similar damage was causing the Samsung Note battery fires last year.Another issue: LiIon batteries are more voltage-sensitive than other batteries.. They should not be paralleled---especially if cells have different histories. I haven't seen many commercial packs that have more than 2 cells in parallel, and they use fresh/new cells. The safe way is to put cells in series, and have individual balancing connections going between stages. It's trickier and more expensive but most chargers support that.

    View Instructable »
  • przemek commented on sam's instructable Wooden Candle Holder1 year ago
    Wooden Candle Holder

    I'm sorry to be a stick-in-the-mud, but a wooden candle holder is NOT a good idea. My cousin ended dead with her children because of a candle that burned down the house. There HAS to be a fireproof container under the candle: metal, ceramic or glass.

    View Instructable »
  • Measure The Moisture Content Of Your Firewood With A Multimeter

    You're right that part of the latent heat released by burning the wood goes to boiling off the water, but hopefully that water doesn't go into your room---that would be a failure of your chimney system. The fire heats your house by radiation and heat transmission from the hot fireplace and chimney. The water lowers a little bit the burning temperature, but the main effect is that it depresses the combustion of the volatile compounds which promotes creosote deposition. Another bad thing is water condensation in the chimney leading to lining damage.

    View Instructable »
  • DIY: Squeeze Extra Capacity From Old NiCd Batteries

    When you cut up the chain, just cut the metal tabs half way between the batteries, leaving stub tabs attached to the batteries. This way, when you reassemble the cells you can solder the tabs (perhaps using a bridging piece of wire across both tabs). It'll be much easier to solder because you will be heating just the tab rather than the entire battery, which by the way tends to damage it.

    View Instructable »
  • przemek commented on pinchan's instructable Use your tablet as Raspberry Pi screen2 years ago
    Use your tablet as Raspberry Pi screen

    It's possible to use the TCP/IP over USB, where you connect RasPi and the tablet by a USB cable; which of course takes care of charging the tablet battery. Caveat: I did it on a Beaglebone, but it should work on RasPi as well.By the way, VNC is one way to do it, and you can also install and run an X server on the tablet and display remote X11 protocol.

    View Instructable »
  • przemek commented on Paige Russell's instructable How to Chop an Onion3 years ago
    How to Chop an Onion

    That's not right---oxalic acid is C2H2O4, so where would sulphuric acid get its sulphur? Onions emit a volatile enzyme 1-sulfinylpropane, which by itself irritates nerve endings in the cornea: no sulphuric acid involved, and thanks goodness or else I've been blinded long ago (I love onions)http://www.scientificamerican.com/article/what-is-the-chemical-proc/

    View Instructable »