by miseli » Thu Mar 31, 2011 10:10 am
Hello baty92,
If you have 25 modules of 1V and 0.415mA available (are these futurlec cells by the way?) then why don't you make a panel using around 15 or 16 of these connected in series?
I am currently putting together a low power panel (around 6W) for the AIMSCC using around this number of futurlec modules to see if they're any good because they're so cheap. If they end up being half decent then that's a quality model solar car panel for like 60 AUD.
If your intended application is some kind of model solar car then the 2232 6V motor will easily handle the extra voltage from a solar panel and have no problems running a little overspeed. In fact, many teams competing in the AIMSCC will have the 2232 running at over 15000 rpm by the end of a race in good sunlight. Dynamometer tests have even taken this motor beyond 20000 rpm for short periods of time without damage.
The cars that finished 2nd, 3rd and 4th in Australia in 2011 all used panels that had maximum power voltages of around 18V or 19V without any problems. Of course, having such a high panel voltage doesn't however necessarily mean that the motor voltage has to get (or will ever get) that high though.
The maximum voltage that the 2232 will see throughout a model solar car race will depend on the gearing of the car and so one can pretty much set things up to get almost whatever voltage (up to the panel voltage) is wanted across the motor no matter what voltage the panel is. For example you could have a 10W, 20V@0.5A panel where the gear ratio limits the motor voltage to only 10V at top speed. If it is assumed that the Automax is 100% efficient (not quite but let's pretend) then that means a 1A motor current. Similarly, a gear ratio could instead be used to give 5V across the motor at top speed with a 2A motor current or 15V@0.67A.
Anyway, I won't go into the specifics but, in general, the maximum voltage seen across the 2232 at the end of a single lap race is somewhere around the 15V mark for a fast car in good sunlight. Stray too far below this and the higher motor currents will result in higher resistive losses in the motor and also lower electronics efficiencies during a race. Conversely, going too far above this (for a higher voltage panel where the motor voltage is still less than the Vmp) will result in higher no-load motor losses and possible overspeed damage to the motor. Getting the motor voltage above the panel Vmp means a sharp drop off in panel power and so going much beyond this should be avoided. In other words, for a panel that has a Vmp of 15V the motor voltage shouldn't really be allowed to get above 15V.
Taking all of this into account I would therefore suggest starting off with a 15 - 16V (Vmp) panel, the Automax, a 2232 6V motor and around a 5:1 or 6:1 gear ratio with a 50 - 60mm drive wheel diameter. Follow that up with some testing to fine tune things. For a fast car, that should get the motor voltage up to somewhere around 15V (Vmp) by the end of a race in good sun (voltage will be lower for a slower car). This same car setup can then more or less be left unchanged for most weather conditions.
With a high voltage panel (20V is beginning to get a little high) I would advise teams not to go free-running their drive wheel without applying a load or otherwise risk damage to the 2232.
miseli
