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# How to use LM317T? Answered

I have a robot on wheels that uses 7.2v battery. The battery runs it for good amount of time it is a 2000mah nimh vex battery. I want to supplement and charge it during peak hours. I bought 4 solar panel that can produce 2 V near my window and 3 volts outside. They produce 200mah at full sun. I want to series the solar panel up and have voltage regulator that can regulate it. I was told that the current also needs to be constant and so I ordered a LM317T.

Here is the datesheet of lm317t

How does the lm317t react when my solar panel hit shade and current goes under 200mah. What voltage should I put on my voltage regulator that I will connect to LM317T. Should I make it 10 V or 9 V?

I really am new to this and want to use solar energy to charge my battery while it is connected to my robot in parallel. What current should be held constant to charge 7.2v 2000mah nimh?

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## 3 Replies

rickharris (author)2017-06-28

The data sheet tells you how to use it.

https://www.rapidonline.com/pdf/47-3318.pdf

an easier to read version here.

The 317 doesn't generate any current so if the solar pnls are in shade the output will fall (That's why you still need a battery)

MANY solar battery chargers ccts here. Study them.

1. Your solar pnls only give you 2 volts you say - is that each or all together?

2. You don't say what voltage or type of battery your using.

3. 200Ma isn't going to charge you battery very quickly. Find out what average current your robot uses and then you will have some ised of how fast you need to replace it.

4. Take the Robotics class here at Instructables. It will help you.

Downunder35m (author)2017-06-28

Despite the problem of sun or no sun, which Steveastrouk solved for you, there is also the general charging problem.
If you want to charge during use you not only need a suitable way for your type of battery but also a way to make sure it works.
Not all electronics agrre with the interference than can be produced during charging and LiPo batteries require a properly regulated charge control.
I would also advise to use a 12 solar panel as it will be much easier to handle in terms of losses.

What you need for starters is what I would call a "battery monitor" with two stages.
One input is your battery the other the voltage from the solar panel (after voltage regulator and load control).
If the panel voltage is sufficient the battery will be charged otherwise disconnected from the charging circuit.
Solar garden lights do this together with a simple joule thief to provide enough voltage for charging the tiny battery and also to get the 1,2V to whatever the LED needs.
For usinf the solar charge while the robot is active you shoul add a filter between battery and your robot's electronic if you notice any strange behaviour.

steveastrouk (author)2017-06-28

Set the 317 as a current regulator, not a voltage regulator like the attached picture. Put a blocking diode so that the 317 is protected when the light fails.

This example is adjustable with the pot. If you change the 0R5 to a 6R1, and connect the ADJ pin directly to the right, load end of the 6R1.