samcheetah

devonsc this might be of some help to you

http://www1.electusdistribution.com....d/slabatts.pdf

devonsc

Thanks, does this mean that I can use a zener diode to maintain a float voltage for the battery? Is this the easiest way but power consumption method? Need advice...

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Nigel Goodwin

It all depends on the charging power you have available, if you have enough power to overcharge the battery you would need a zener diode large enough to absorb the extra power - a large zener, mounted on a large heatsink. This used to be done on Triumph motor bikes, with the zener and heatsink mounted between the forks in the airflow.

If you're still talking about solar panels it's not needed at all, you don't have enough power to cause a problem.

Try telling us EXACTLY what you are trying to do, with what voltages and currents, and why - it's been so long, and so many different threads, I'm losing count :lol:

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devonsc

Sorry, hope you're not mad. As shown is what I intend to do.

(Dotted lines indicate detachable while the box shows the Charging and Monitoring Unit)

All this while, we have been talking about Battery Charging Circuit 1, which is the Boost DC/DC Converter. Was thinking to develop this circuit in such away where one can use different types of solar panels. Meaning, as long as the panels are needed to be boost to a certain level, it can be used. Thus, I was thinking to develop a circuit that takes into the consideration of preventing overcharging as well. I thought there are certain panels that are capable in doing overcharging this 12V 1.3AH battery? Thanks.

And just to reconfirm about the circuit posted on page 7, entitled Boost Converter. Can I implement that, with the changes such as a MOSFET, a zener diode and the PWM from PIC?

Attached Images

block_diagram_2_679.jpg (34.2 KB, 562 views)

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Nigel Goodwin

I would suggest that's not a good idea, trying to design your solar panel charging to accomodate any panel size is going to require comprimises - the worst point of which is that you are going to waste much more power than you can afford with the small panels.

MicroChip do in their PICKIT1 programmer, have a look at it - it even generates 13V which is pretty close to what you want!.

You could prevent over charging with the PIC as well, monitor the battery voltage and if it gets too high then reduce the charging rate via the PWM.

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Oznog

See what it takes to get a low input ripple current in your simulation. It would be good it have it under 5%, since any power you don't use isn't "saved" for later. And start looking for what inductors you can actually get ahold of and physically fit into your project.

The zener is not accurate enough to stop an overcharge. With a current of only mA, the voltage difference between charging and overcharging is small, less than the tolerance of the zener. Worry about overcharge if your current is going to be more than the 20-hr charge rate for weeks on end. Problem is, you're going to need a voltage divider (inaccurate and consumes current off the battery) and a more accurate voltage ref.

It's a incidental feature of the way they're manufactured. It can usually carry a lot of current and some designs forward bias it on purpose.

But the current is basically the same over time. Pulses of 30mA of current 1/3th the time (when the transistor is off) or a smoothed out 10mA 100% of the time does the same job. Actually, there are obscure, minor efficiency issues here, some for the cap, some against. It won't hurt to leave it in but it probably won't improve things.

Excellent question. The PIC needs at least 3v for the lowest of freq, and may not drive the MOSFET well. 5v is standard, 5.5v will cause it to latch up. Check your spec sheet for what your part needs. A 5.1v zener can keep the supply where it should be. Also diodes can be used in series to drop the voltage. And of course a reg may work, but it consumes quiescent current and may have minimum dropout issues.

Also, a solar cell is going to drop down to a voltage which won't cause it to turn off but it won't run properly either. When the sun comes back and voltage is restored, it may not have a valid state and won't run. There are several mechanisms to enable that will compensate for this, look up "brown out detection".

Did you ever decide what your panel voltage and current were going to be? I missed that.

devonsc

Sorry for my late reply. Thanks for that advice. I will now stick to one panel, at this moment, most probably the one with output voltage 7.5V.

Thanks a lot! I will read up the PICKIT1 programmer.

Hope you wont mind, I'll learn up the PIC for the PWM as well as the ADC first at this moment? ops: Slow learner here. Need help...

Thanks for everything.

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devonsc

Thousand apologies as I don't quite understand this portion. Do you mind explaining? Please?

Does it mean that it is buit in such a way to assure that the MOSFET does not damage when one applies a high current at the Source? Where at this point, it performs as a normal diode? But if yes, what is the purpose of having such construction? ops: Sorry, just asking...ignore this question if my question is meaningless. Real sorry.

Thanks for the detail explanation.

Does it mean that you advice me to tap the voltage supply from the 12V battery and regulate it to a 5V level instead of using additional batteries?

Thanks! I was about to ask the meaning of this term, "Brownout Detection" as I found it in the datasheet. But I've yet to understand. Will read up further, thanks again.

At this point, it would be an output voltage of 7.5V with the load current of 40mA. Thanks.

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Oznog

Say you want to use the average, optimum 40mA from the panel. If you have a 20mA peak-to-peak ripple due to a small inductance, the current will vary from 50 mA to 30mA. Look at the i/v curve for the cell. The voltage will drop to next to nothing if you try to draw 50mA, the power output is low. At 30mA you're not using the capacity of the cell. Now an input capacitor will help this to some degree, but it's not a magic bullet since the ripple voltage is much less than the current ripple due to the i/v curve of a solar cell. Caps are not as effective in this scenario.

As far as I know, it's unavoidable the way the silicon is layered.

This is inefficient. If the PIC needs 10mA, it would take 10mA of the input current if source off of the 7V solar cell, but due to the boost ratio this would consume 20 mA of the solar cell's current if it pulled it off the 13.6v battery output. No, source the power off the 7v solar cell. Don't use additional batteries, this is indeed "cheating".

By the way, don't use a normal silicon diode for the diode, that takes 0.7v. Use a Schottkey, it's around 0.3v forward drop. More efficient.

devonsc

Erm...I ops: tried reading it again and again but nothing goes in my brain. Sorry. I dare not ask for further explanation ops: I will try to search for more info to understand.

Thanks for such direct guides.

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gurgalesci

Solar power cars are NOT efficient in harnessing power. That is why I would use a 12D (jumbo size) battery with 14 inch modulators for that extra juice and power. Of course, you are going to have to find out a way to connect these large heavy duty batteries to the little solar car. Also, you should get 5 inch quadrum wheels to give it a lighter touch so that it can run more smoothly without friction. That should help your solar car run better. PLUS! GET LOTS OF LIGHT! :wink: You are going to need that.
__________________________________________________ ___________

THE WORLD ENDS AT EXACTLY 5:12:34 PM on December the 17th.

We die a little more each day, but on December the 17th, we all die.

Oznog

Which time zone? Or is each time zone destroyed independently as they hit 5:12PM?

devonsc

Hi there,

After all the guidance and teachings from you guys...As attached is the present circuit which will be used for the Charging Circuit 1.

In the meantime, I hope that this would be a great news as we are now given a better solar panel for this project. The solar panel will reach our hands by next week and I run a test on it to plot the IV Characteristic of it. However, according to the datasheet of the solar panel, its output voltage is 7.5V whereas the current at load is 150mA.

(The one earlier was: output voltage = 7.5V, current at load = 40mA)

:arrow: With reference to the attached circuit, the value of the inductor and capacitor is still under consideration. Is it true that proper selection of the inductance and capacitance value can only be done through testing to see the ripple? Or calculations can be done? ops: Nway, I'm working on it to get it done as soon as possible, thanks.

:arrow: I'm still searching for the appropriate NMOS transistor for the MOSFET.

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charging_circuit_1.jpg (17.5 KB, 440 views)

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gurgalesci

Gather 'round and listen to the tale of the End of the World. It all began at the Pumonkey Convention of 1854. A well known scientist and astrologist, Herbert Fabio van Stooben, had made a world braking discovery. This amazing discovery was the date of the End of the World. And this is how he found it:

By measuring the circumference of the moon each night, he found that it was approximately shrinking by .0000000000001 mm each night. 'Twas the beginning of a new era, the Era of Beginning. This was the start of the quest for knowledge and discovery...the discovery of the End of the World.

As van Stooben continued to study he also found that the world was heating up by .00000001 degree Celcius each day. After making calculations, he found that at December 17th, it would all be too much. The moon too far would fling the Earth out of place and the heat would burn us all. We will fling to the Sun, and without an ozone layer, we will burn.


Thus, ends my tale of Herbert Fabio van Stooben. And it is independently. Each time zone that hits the time will die. :twisted:

Oznog

So it's the end of the world as we know it? Funny, I feel fine.