Wishful "thinking", at best. You have said nothing about how you intend to point the panel at the sun. If you use a fixed angle support frame that aims the panel's normal south, then you might obtain the above result for 15 minutes before and after your solar noon (before and after the sun crosses your meridian).Prof. Prevaricador wrote:Vic:
I was thinking in a solar panel with these specs:
- Maximum Power: 10.3W
- Maximum-power Voltage: 17.8 V
- Maximum-power current: 0.58 Ampere
I'm thinking that maybe two of these in parallel I would probably get in most sunny days 15-16 Volts with 0.8-1 amp.
How do you define an "entire day" , or a "full day"? Would that be local sunrise to sunset, or fewer hours? Even if you actively point your solar panel at the sun over that large angle (say by use of an az/el panel-mount having clock motor drives on each axis), the panel will not likely output a mean half-amp throughout the "full day". But, if you could guarantee a 0.5A charging current for seven hours the amp*hour input would be 3.5A*h, which would be almost enough to recharge a 3000mAh battery. However, if, during that long period the panel becomes shaded and current falls below 400mA for thirty minutes the Roomba-500 will issue an error and halt charging!Using just one panel with a full day of collecting sun probably should be enough, but I would at best get 0.5 amp. Would that current allow to charge the battery even if it took the entire day?
Generally speaking that goal is usually met, although slight overcharging is a normal part of charge termination detection -- that is why post-charge terminal voltage is higher that one might expect. Even the subsequent trickle, or maintenance charging period can overcharge cells if their self-discharge rate is less than the assigned trickle-current value.I was thought that the roomba charging system would prevent over charging...
Except as just noted. Roomba manages the charging two ways. When charging mode is activated and the high-rate charging period begins, Roomba has switched ON its charging FETs in continuous mode, and from that point until charge termination occurs, Roomba expects charging current to be limited by a current roll off limiter within the switching mode PSU. You are not aware of that deign feature. A depleted battery will draw high current when connected to a voltage source that is even a few volts higher than the battery's no-load terminal voltage. Roomba's PSU ensures that charging current remains below, say, 1.4A by reducing its output voltage. As charging progresses, battery voltage rises, and there is a corresponding rise in PSU voltage. When charging current is relaxed to the 1.25A design point, PSU voltage is restored to the +22.5V regulation level.When you leave the roomba charging over night it manages the charge, preventing over charging.
Low current (I < 400mA, for 30 mins) would stop the charging. You should quit wishful thinking and do some engineering of your project. I have the impression that you have not been searching the net for useful information about solar energy conversion.I was thinking in plugging the panel to the romba itself and not having the hassle of unscrewing the roomba every time it needs the battery to be charged. I'm only afraid that the low voltage and low amperage would cause some malfunction... but I really think it would work!
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