lm317 solar battery charger

[chuck]

I'd like some comments on the item below. Any comments are welcome and appreciated.

I built a very simple battery charger using an lm317, resister and diode. The input is a solar panel that typically is outputting about 15+/- volts and 100 to 200 ma. The battery charger is connected to 4 nimh AA battiers. The feed current into the battiers is about 54 ma.

Question 1: Is this circuit a legitimate way to keep or put a charge on the battiers?
Question 2: If I want to charge 6 AA's, will the 54 ma do it, but just take more time??
Question 3 Voltage level from the solar panel important?

The goal for all of this, at this point, is to use both battiers and/or solar to power my little 2 watt stereo amp that is connected to my mp3 music player. I use it outdoors while doing yard work. Right now the amplifier is powered by the solar panel using a 9 volt regulator similar to the lm317. The mp3 player has a separate, independent battery that I want to solar charge eventually.

Battiers appear to be almost mysterious when it come to charging them, but I want to use solar and I need to keep it real simple or my brain may strip a gear. I really don't know doodley about electronics but enjoy fooling around with it like this. Thank You.

 

[Hero999]

The voltage from the solar panel needs to be between 3.2V to 4.2V greater than the charged battery voltage.

I don't see the need for a current regulator, as long as you don't leave the batteries connected for too long 200mA won't damage them.

When I built a lead acid trickle charger I connected the LM317 as a voltage regulator, not a current regulator.

 

[audioguru]

For a single-ended amplifier to provide 2W into 8 ohms then it needs a power supply voltage of at least 14v.
A 4 ohm load on a 2W amplifier needs a power supply voltage of 12V.

If the amplifier is bridged then 2W into 8 ohms needs a power supply voltage of 9V and a 4 ohm load needs a supply of 7V.

 

[chuck]

"The voltage from the solar panel needs to be between 3.2V to 4.2V greater than the charged battery voltage."

I use a LM317 set @13.8 volts into a 12 volt sla. If the sky is cloudy and voltage low, does the lm317 drain the battery? I have a diode at the solar panel.

Regarding my questions above, I need the battery power for cloudy days (drats). I want to use solar as much as possible, but cannot avoid the need for batteries. I have been experimenting using any salvage battery I can find, but I bought some new 2500 ma Ni-mh batteries and want to do a respectable job of caring and feeding them. If overcharging defined as pumping in more amps than needed or using too high a voltage or both? Wish I knew this subject better, but I am listening, reading and trying. Thank you for your time.

 

[chuck]

The 2 watt amplifier is a kit fro Carl's. I did not use the jumpers for a gain of 20 to 200(26 to 46 db). I don't really have a clue, but I didn't need the jumpers for a good sould. It is a kii5, and uses 2 LM386N. I am using 2 small, salvage speaker from a broken cd player. I used the 9 volt regulator to protect the amplifier from too high a voltage from the solar panel. It plays great. I am about to try to power the amp using 6 of the Ni-mh batteries charged with a good, commercial charger I have. If the amp works and the play time is long enough(2-4 hours, at least) I will concentrate of how to charge the batteriers correctly using solar.

 

[Hero999]

"The voltage from the solar panel needs to be between 3.2V to 4.2V greater than the charged battery voltage."

I use a LM317 set @13.8 volts into a 12 volt sla. If the sky is cloudy and voltage low, does the lm317 drain the battery? I have a diode at the solar panel.

I forgot to say there are two 12V 14Ah SLAs connected in series with two 12V panels in series.

When it's dark, it does drain the battery but only very slightly. I chose a high value for R1 in the LM317 regulator circuit, 2k4 from memory, R2 is 47k which gives a voltage of just under 28V.

The discharge current is just 567µA so it would take 24,700 hours of darkness to discharge the batteries.

The solar panels have built in diodes which protect them and the LM317 from the battery discharging when it's dark.

The 12V panels have an open circuit voltage of 21V and the datasheet says the output voltage is 18V at maximum power.

Regarding my questions above, I need the battery power for cloudy days (drats). I want to use solar as much as possible, but cannot avoid the need for batteries. I have been experimenting using any salvage battery I can find, but I bought some new 2500 ma Ni-mh batteries and want to do a respectable job of caring and feeding them. If overcharging defined as pumping in more amps than needed or using too high a voltage or both? Wish I knew this subject better, but I am listening, reading and trying. Thank you for your time.

As your batteries are just 2500mAh a diode is required to prevent discharge.

How long are they going to be left on charge for?

As I said before 200mA shouldn't be a problem for a fully discharged battery as long as it's not left connected for days on end.

If you want to trickle charge then the current should be C/20 which is 125mA maximum.

 

[audioguru]

Carl's has a stereo amplifier kit K115 that has one LM386 amplifier IC per channel.
With a 6V supply its output per channel into an 8 ohms speaker is only 0.2W at clipping.
With a 9V supply its output per channel into an 8 ohms speaker is only 0.45W at clipping.
With a 12V supply its output per channel into an 8 ohms speaker is only 0.53W at clipping.
Its total output is only 0.9W with your 9V supply, not 2W.

Like a cheap clock radio.
I bought two name-brand clock radios on sale for only $1.75 each. Their sound is awful.

 

[chuck]

I apologize for my incorrect statements, but I ask questions to learn a little. The little amp I built does a great job even if I don't have a clue about the correct power output. Besides a great deal of enjoyment listening to music, I am learning a little something about how to use solar to charge the batteries.

I am now using 6 Ni mh, 2500 mah batteries. I have accumulated about 7 hours of play time and all is well so far on the first use of the batteries.

Question: The C/input charge = 10 (2500 ma/250 ma): is it generally safe to apply the 250 ma or less (for this example) without doing damage to batterys? I assume it will take 10 hours plus an extra amount of time at 250 ma to fully charge a fully discharged battery. How much charge can be applied to the 6 batteries -- is it 6 time 250 ma?

Thank you for your time and response. I really appreciate your effort to help.

 

[Hero999]

You're right, 250mA won't do any harm as long at the batteries aren't charged continuously which won't happen because it's a solar charger and the batteries will get a break overnight.

It will take over 10 hours to charge the batteries but the solar panels won't output 250mA continuously so it'll take a couple of days to completely charge the batteries.