Battery woes



  • edited April 2017
    No reason why you can't as long as you have a suitable interface circuit. You then have the advantage of being able to adjust the cut off voltage within the code. We do something similar by using a small Picaxe board to drive a motor controller.
  • Prove the discharger works before adding intelligence. Finding the root cause of any fault will help you much more than just trying something else. I once made a discharger that logged ampere-hours until the volts dropped to 10.5. It was complex, and I had to question the real benefits. I would recommend the BobC method since it will give you an accurate indication of the relative storage capacities between all the batteries you test (so that you match up similar pairs), and its a simple to understand device that you don't need a degree in electronics to build.
  • Sage advice Old Timer
  • Just the result of too much time spent in the garden shed workshop with things that broke, caught fire or blew up. Learning by doing - its the best way - you remember things better and it allows you to match theory with practice. Plus there are no exams at the end!
  • Here's the latest version using a programmable low voltage disconnect unit from REUK set to 10.8 volts actuating a 30 amp automotive relay. Seems to work perfectly with a new battery discharging a 16 amps for 1hr 43mins and cutting off at exactly 10.8 volts. Data logged by a Maplin 30 volt
    photo 54B2F329-CE05-4AAA-A910-E93CAF916DE9_zpsylnpmpuv.jpg
    photo 301B078B-8D01-4B13-8DA8-CC9AD231CCCD_zpseonrc6lz.jpg
  • Looks a good nadger. Well made. Every team should make one!!
  • They are only about £11 and come ready made. Add a relay £8 for 5 complete with socket and short loom connect that to the resistors and Bob's your uncle !
    Program the cutoff voltage with button presses and your away.
  • You're not your, pay attention at the back !!
  • whswhs
    edited May 2017
    Bob's you are uncle? .............. I jest ;-)

    Anyway, when it comes to discharging, Bob is everybody's Uncle. Cheers Uncle Bob, and OldTimer.
  • Always willing to share knowledge. Just remember this, "If you don't measure it, you can't control it". Once you have learned each battery's capacity then you can match them up knowing that they will both reach their 10.5 V minimum at a similar time. That way the risk of damaging one due to undervoltage is reduced. Also, you can confidently choose your best batteries for the race. You will also observe that manufacturing tolerances can show capacity differences, sometimes as much as +/- 10%. When you are striving for a small percentage increase in mileage range the battery capacity can make a large difference. Put a unique serial number on each battery and keep a log of each capacity check. Good luck.
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