Testing NiCad batteries...

Discussion in 'Getting Started' started by steamhead, Jun 26, 2008.

  1. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    What kind of a load would be appropriate to use to test 1.2v, 2300mAh NiCad rechargeable batteries to determine their "usefulness"..?? I'm currently using a 6v light bulb, but gauging brightness is not really a good indicator, except when the bulb doesn't light..I know the battery is dead....I could use a voltmeter, but I need to place some sort of load to determine if the battery still has some muscle to it...

    Any and all suggestions welcome..!!
  2. seanm

    seanm Member

    Joined:
    Oct 11, 2004
    Messages:
    376
    Likes Received:
    0
    Gus,


    Sounds like what you want is a fuel gauge for a battery. This is a dificult thing to accomplish NiCad and other advanced batteries have a very flat discharge curve untill they hit a critical point and then volts drop off pretty fast. I know this from my days flying electric RC planes. The only real way to tell is to make a discharge curve at a given load and then compare where you are on the curve to what you see on the meter. This takes some pretty expensive equiipment.

    The only other way I would siggest is by time as long as you have a constant draw from the battery.

    Hope this helps.
  3. seanm

    seanm Member

    Joined:
    Oct 11, 2004
    Messages:
    376
    Likes Received:
    0
    I guess I didn't answer your question. Best load is as close a to the load you are planning on using it for as possible. As far as how to determine that, I am not that smart. :-(
  4. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    Tennis...anyone..??

    Ooopsss...wrong forum. :mrgreen:

    Well, anybody else want to take a crack at this..?? What I'm looking to get, I think, is the value of a resistor that would put a good load on the battery being tested, just for a brief time, long enough to take a voltage reading, and see how it "degrades" over time....
  5. Mountain Man

    Mountain Man Active Member

    Joined:
    Jan 20, 2007
    Messages:
    1,705
    Likes Received:
    0
    Could the company that makes them provide any data?
  6. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
  7. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    Thanks Mikey....I flew R/C aircraft for close to 22 years..(my age is showing..... :mrgreen:) so I'm quite familiar with the indications made in the article. Back then I had a battery meter, like the one described in the article, and that helped a lot to keep planes flying. Unfortunately, I sold all my stuff off when I got out of the hobby (though the hobby didn't get out me....) so I'm back to square one. The batteries I want to test are batteries for a couple of power tools that have conked out. I rebuilt one with a bunch of batteries I got on eBay (@ $1.90/ea...!!), and am attempting to rebuild another one, so I have to see which cells have gone bad, and which I can keep.
    Just before I read your post, I had thought of posting my question in the R/C forum....I think I will, as I'm sure someone there may have the info I need.
    Thanks to all that responded...I appreciate it..
  8. Squidbait

    Squidbait Recovering ALCO-holic

    Joined:
    Jan 27, 2007
    Messages:
    1,257
    Likes Received:
    0
    Gus,

    You need to find someone with an advanced battery charger/discharger, that will let you discharge a battery at a set amp draw. You can track the voltage as the cell is discharged, see how many milliamps have been pulled out, and how long it takes.

    Being an avid electric RC flyer, I've got a couple, but the Electrifly Triton is a good one for that sort of thing. They're available cheap secondhand (less than $50) these days, since they've been surpassed by newer, more flexible, more powerful chargers.
  9. Biased turkey

    Biased turkey Active Member

    Joined:
    Apr 10, 2006
    Messages:
    1,019
    Likes Received:
    0
    This link might help:
    http://www.rcbatteryclinic.com/ESVbyHoff.html

    I'm not a R/C modeller at all.
    The author of the article plotted the discharge curve at 200 mA.
    The resistor value should then be V/I or in that case 1.35 / 0.2 = 6.75 Ohm.

    Jacques
  10. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    Thanks Squidbait...I'll look into one of those...or something similar.

    I looked into the R/C forum....Not much going on there...I think I'm one of the most prolific posters...and I'm not even into R/C nowadays....
  11. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
    I was poking around my workshop and found my old R/C battery pack discharge circuit... It was for the NiCd battery I had in the early 80's it was 7.2V 2300mah

    I have a 200 Ohm 10W resistor in the circuit with a 15V panel meter for measurement.
  12. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    Jacques...We must have been writing at the same time....I didn't see your post 'till now....Very informative. Thanks...

    Mikey...Any chance of posting that circuit..? Thanks again...
  13. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
    I thought of that after I posted last... All I have is the meter and the resister..... But I do remember the meter was across the resistor.. and i did find the dropping resistor 22 Meg for the meter's protection..

    You'll have to change it to something smaller around 3 or 4 meg ohm since you're working with 1/6 the voltage.

    Attached Files:

  14. steamhead

    steamhead Active Member

    Joined:
    Apr 17, 2005
    Messages:
    2,527
    Likes Received:
    0
    Mikey....That's precisely rhe set-up I was thinking of doing (without the dropping resistor...) so I wasn't far off....I just needed the value of the resistor across the leads...Thanks a bunch..!! :thumb:
  15. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
    Glad i could help.. Even more glad i could find it in all my junk :D :D :D

    Just remember to check the resister value to the meter :) :)
  16. ezdays

    ezdays Out AZ way

    Joined:
    Feb 3, 2003
    Messages:
    6,590
    Likes Received:
    0
    I hate to jump in here so late, but why the resistor to the meter? If you're using a VOM, there's enough protection in it already, and a series resistor is just going to screw up your reading. I wouldn't use one unless you were measuring with just an plain old panel meter by itself. Most VOM's have an input impedance of around 10 meg, so a 22 meg series resistor will give you about 1/3 the actual reading.
  17. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
    It's a panel meter - just a Volt meter with a 15 v scale... The instructions said to put a resistor in series - i have no idea why it's so large and what size it should be for 1.2 volts :( :(

    but yeah - if you use a real meter it's protected...
  18. ezdays

    ezdays Out AZ way

    Joined:
    Feb 3, 2003
    Messages:
    6,590
    Likes Received:
    0
    Panel meters are very sensitive to current and do require a series resistor to limit the current and a shunt resistor to bypass a large % of that current. The shunt resistor is probably built into the panel meter already.
  19. Biased turkey

    Biased turkey Active Member

    Joined:
    Apr 10, 2006
    Messages:
    1,019
    Likes Received:
    0
    By definition, a voltmeter is just a galvanometer ( current meter ) with a very high resistor in serie ( the higher the resistor, the better ) . So ( as ezdays ) I'm puzzled too about the resistor in serie with the panel meter .
    But of course if that NiCad battery checking circuit floats your boat who care.
    Just the thought of a ( retired ) electronic technician
    Jacques
  20. N Gauger

    N Gauger 1:20.3 Train Addict

    Joined:
    Dec 20, 2000
    Messages:
    7,260
    Likes Received:
    0
    Well 220 Ohm is "big" :D :D

    I really dont remember :) This circuit was built 24 years ago :eek::eek::eek::eek: