ksander wrote:... it stay recharging a long time and do not run. ...
If the robot was actually applying high-rate charging to your test-battery, I think there is a good chance that it got way over-charged; and, way too hot!
Did you happen to touch any of the AA cells after charging had been in progress for a couple hours? They might have been very hot to the touch!
R3-Roombas have several means (I think) to terminate high-rate charging. The most often used method is to cut off charging when the thermistor temperature reaches a specific value. I don't think we know that exact number, however I ran three hi-temp cut-off trials on either a 510 or 560 main_PCA and determined that high-rate charging is halted when thermistor temperature reaches the mean temperature of: <66.4 C>. General thinking is: That number is about 20 degrees Celsius higher than is safe for NiMH cells!
Your test cells were not thermally connected to the thermistor
, so the thermistor remained cool while the cells could have gone way high in temperature. I believe that R3-Roomba's have a time-out feature that come into play when none of the planned means to terminate charging are invoked.
Now then, I think I have an answer to this posed problem:
ksander wrote:... it ... do not run. ...
Roomba does not run because it senses a dead battery as soon as its motors become powered.
When Roombas sense a battery voltage of 12 volts, or less, it stops all motors and signals a need to re-charge. "How can the 530 'think' the battery is dead? I measured its no-load terminal voltage as 15.3V !", you might say.
The following is what is very likely going on:
A) First, you need to grasp several of Roomba's operating values:
1) You have just learned that Roomba stops the Clean Mode when battery voltage is sensed to be nominally 12-volts or lower.
2) You also must recognize that Roombas draws between 1.5 to 2 amperes dc current from its battery while sweeping floors.
3) It is also useful to know that high-rate charging current of a depleted battery begins at about 1.3A (for a 1.25A, nominal charging PSU). As battery charge rebuilds over the charging period, charging current diminishes.
B) You have chosen to use "battery-holder" to grasp and serially connect your 12 cells. This choice is the core of your operational problem
. vic touched on it, but detailed the effect for charging (as I recall), not for Clean Mode. There is no fault with the holders
mechanically grasping groups of cells, but there is a huge problem with the holder's contact resistance to each cell terminal. This is how it goes:
1) Each cell terminal has two terminals, and there are 12 cells, hence 24 terminals, 24 contact points, altogether.
2) We can't know the value range of contact resistance for your cells and cell-holders without actually measuring each one, but as I recall the number can be on the order of tenths of an ohm per contact for a spring-force electrical contact. Let's use 0.1 ohm as a trial.
3) The overall series resistance attributable to contact-resistance is then: R_cntcs ~= 24 * 0.1 = 2.4 ohms.
4) I think we now have everything we need to calculate the total voltage drop within your test-battery when it tries to support Roomba's Clean Mode current. I presume you are familiar with the Ohm's Law expression: E(volts) = I(amps) * R(ohms), or, for this case, I can say: E_terms ~= I_cln_md * R_cntcs; followed by applying values from (A,2) and (B,3), to get: E_term ~= 1.5A * 2.4 ohms = 3.6V.
5) Finally, you must appreciate that as Roomba is switched into Clean Mode the 1.5 to 2A current will be drawn from the battery and the initial battery terminal voltage, E_ini_term, of 15.3 will fall by the E_term voltage dropped across the summation of contact resistances. IOW, E_BAT ~= 15.3 - 3.6 = 11.7V; and, it is then that Roomba declares battery voltage is now less than 12V and halts operations.
Similarly, battery charging is impacted by the sum of contact resistances. The net result is battery terminal voltage is a few volts lower than its could be if contact resistance was made closer to zero by spot welding metal tabs between cells.