Sunday, November 11, 2012

Roomba 4xx test batteries - manual

Having a lot of Roomba batteries for the series 4xx (third and fourth generation), before to trash them in the recycle kit I just received,  I needed a way to see if a battery is good or bad.

To test a battery there are some steps to follow :

  • measure the voltage of the battery - if below 15V the battery can have problems
  • discharge the battery
  • charge the battery
  • discharge the battery on a calculated load - it should last a fixed amount of time depending the type of the battery. At least 1 hour for the older NiCd
Using the external iRobot charger modified (for manual), I did set up this environment.

The dis-charger is a 12V lamp.
I'm experimenting with a 12V 50W and a 12V 34W lamps.


Building the contraption is easy.
The only trick is to pay attention to the polarity of the wires.
It would be great to use red/black cables, but as usual I use whatever I have around in my junk box.

 Here I'm using a 12V 50W lamp, but as soon as I find a socket for the other lamp, I'll try to use the 12V 34W lamp.
The ideal it would be to use a load that simulates the Roomba load. People doing this before me estimated that a 12V 25W lamp is a perfect load.
One of these days I'll try in different places to find the lamp, for now this is what I have around.

For mechanical reason, I put the switch (Switch A) in plastic box (of course re-used many many times for different projects).

The switch is actually a 3 position switch, so the label indicates ch (Charger), off (Off :) ) and dis (Dis-charger).
Because of that, there is really not need of the Switch B, since is enough to put the switch A in the Off position to measure the battery voltage with no load.
But for "logical" reasons, the Switch B still exists.
Let say that "Switch A in Off position",  is equivalent to say "Switch B open".

Here the contraption connected to the modified external charger.


In order to see if a battery is OK or not, here Step by Step list of things to do.

  1. set the Switch A on Off (or set  the Switch A  to connect the battery to the dis-charger and set the Switch B of the dis-charger  open).
    In this way is possible to measure the voltage of the battery without load.
  2. put the battery on the battery holder of the iRobot external charger.
    Low reading at this stage can already indicate if a battery is dead.
    A healthy battery should give a reading around at least 14.4V.
  3. set the switch A on dis (Dis-charger) or set the Switch B On.
    Simply keep connect the battery to the dis-charger until the lamp is on.
    When the lamp goes off :
    - if lasted at least an hour for the NiCD and two hours for the NiMH the battery is OK (assuming a load of 12V 25W, less for bigger loads)
    - if last less the battery is not good anymore, however at least one charge cycle must be performed before to decide the battery is no good.
    Go to the point 4 if the battery needs to do at least a charge cycle
  4. toggle the Switch A to connect the battery to the charger.
    If the battery has a chance to be OK, the battery charger is engaged (green LED ON).
    The charge operation can last up to three hours, depending the type of battery.
    - If the green LED flash, the battery must be dead. Discard it.
    - If the green LED goes OFF in few minutes, the battery could be dead.
      Check if the battery is warm. If not the charger refused to charge it. The battery is dead.
    - If the green LED goes OFF after at least 1 hour (black battery) or 2 hours or more (yellow battery), go back to the point 1

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