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Charging and Discharging a battery at the same time? Answered

I've been researching how to make a solar powered boombox and have a few questions about protecting the battery.

from solar panel to the battery: i understand that a charge controller is necessary to regulate power to the battery, as well as prevent overcharging it.

from the battery to boombox: most projects use an inverter directly from the battery.  I'd like to avoid this step and pull dc from the battery directly to the battery box in the stereo(the ac input of the stereo converts it back to dc again anyway i think).  From what i've read, inverters have a protective circuit that prevent the battery from becoming dangerously undercharged as well as regulate power from the battery.  Could i just build one of these discharge controllers and be done?  Is a discharge controller necessary?

cliff notes: what dangers are there in charging and discharging a battery at the same time, and how can i prevent them?

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framistan (author)2010-07-09

If your boombox requires 12volts... and your battery is 12 volts... then you can connect it direct. Most boomboxes use something like six batteries of 1.5 volts each. thats 9 volts not 12. so you need to connect a voltage regulator circuit to bring the volts down to 9v. If you overdischarge the battery, it can shorten its life (you will get fewer charge-discharge cycles out of it.. Deep discharge batteries can take this better than standard car batteries.

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rickharris (author)2010-07-09

A car charges and discharges it's batter as you drive. Essentially the electronics runs off the alternator and the battery is just another load.

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Re-design (author)2010-07-09

The only danger I see is if you are running a 12 v. (for example) appliance (boombox) it is expecting to see 12volts. If you are charging a 12 volt battery it is expecting to see 14 volts approx.

Some appliances are built to expect a little more or less voltage and can handle the +2 volts.  Lots can't and won't work.

You could build a regulator to regulate the charger voltage down to the voltage that the appliance needs.

I don't see any problem in over discharging the battery unless you never turn off the appliance.

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