Solar panel question.


Old 08-16-15, 02:29 AM
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Solar panel question.

Hy. I have a 100W solar panel rated at 5A, i did a simple charger using a simple LM388 ( 5A linear regulator for testing, i know a mppt would be better but the cost of it dosent realy make sense for me for that price i buy one more 100W panel and with loses and everything still i will get more that the mppt can get out from the singel 100w panel).

Everything was fine i got a 12V lead-acid battery so i put it to charge it was drawing 4.2amps yesterday tuday it draws only 0.8A so it prity much charged so i linked the inverter to the battery ( to drive a 50w water pump) the inverter needs about 3.8amp to drive the pump so i was hoping that the inverter will pull 3.6 +/- amps from the solar panel and if it requires more he can get it from the battery but it dose the reverse. When i start the inverter the panel give 1.2amps instead of 0.8 but thats all so the inverter pulls the 3.6amps from the battery wasting the power of the panel....

Is this normal because i used a linear regulator ? would a buck-converter (PWM step-down) solve this problem ?

THX for any help.
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Old 08-16-15, 10:37 AM
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Welcome to the forums.

Maybe you used an LM338 (TO-3 K version?). The LM388 is an audio amplifier chip.

You can't really connect high load devices directly to a solar panel. The solar panel puts out varying amounts of power based on the amount of sunlight it's receiving. It may only put out 100 watts of power with the glass completely clean as well as maximum sun.

You should keep the solar panel connected to the battery when using the inverter. The solar panel will contribute to the inverter operation as well as recharge the battery.
Old 08-16-15, 11:12 AM
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LM338 sorry i wrote it wrong.

Yes thats what i did but when the battery is almost charged it draws only 0.8A , the inverter pulls 4A , but when i start the inverter the solar panel gives only 1.2A ( about 0.4A more ) so the other 3.6A the inverter needs it's from the battery. I was thinking why the inverter dosent pull from the solar panel 2.8A and the 1.2A left from the battery i think it's not possible . I mean this way until the battery dosent discharge to a level where he will pull how much he can the power will be wasted from the PV bk instead of 3.8A it will provide only 1A while the inverter pulls out 4A from the battery
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