Sorry, I was thinking to contruct the zener diode in this manner. I tried simulating without the zener diode but I couldnt get a constant output, so I was thinking to add on the zener diode.

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Thanks Sorry for my nonsense again. By the way, I'll try to come out the entire circuit connection by .... as soon as possible. Hopefully you don't mind helping me to correct it if there is something wrong with it.

Thanks in advance

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Need help again. Sorry.

:?: Would like to ask for advice on how should I supply the 555 timer or the PWM IC (at this stage, still undecided which to use for the boost DC/DC converter). Any advice on how should I operate this device? From the solar panel? If its from the solar panel, won't I get a varying operating value? Issit okay to operate it under this condition?

Need advice, thanks in advance.

:?: Apart from that, any suggestion on what op-amp can I use for my current to voltage converter? Will 741 opamp do? I've not read up more about it. Real sorry, was thinking that you don't mind giving me some exact hint. Too much to read, have not finish understanding the PIC. :cry:

Thanks in advance.

:?: Would like to ask regarding MOSFET. Mind to briefly explain the purpose of the diode found in the MOSFET? ops:

Thanks again.

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This isn't a good idea! - the whole point of the switchmode supply is to make the most of the limited available power, this zener on the output is going to waste most of the power that the panel provides!. To regulate a switchmode supply you apply feedback to the switching circuitry, this then regulates in an efficient manner.

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Thanks for "saving" me. Thanks a lot. But I tried simulating the boost DC/DC converter without the zener diode and I couldnt obtain a constant or steady output. Is this simply because of my wrong selection of capacitor and inductor? Mind to give some hints on how should I determine the capacitor as well as the inductor value?

Thanks a lot

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Did you simulate the circuit as shown above?, you don't have any control electronics - so there's no feedback. I'm also VERY dubious about the value of simulations, they rarely seem to work as the real world does.

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I'm afraid my posts are very messy. Sorry if it is, here I would like to rearrange a few of the latest post.

Thanks, I will contruct the circuit in practical and do some measurements and observations on the waveforms through the oscilloscope as soon as possible.

:?: By the way, do you mind giving me a hint on how do I determine the proper capacitance value and inductance value to use? Thanks.

:?: By the way, do you mind briefly explain on the purpose of the existing diode in the MOSFET? Real sorry to trouble you. Thanks a lot ops:

:?: Is the 741 Op-Amp suitable for me to use to implement in the Current-to-Voltage converter? I will post my circuit as soon as possible for advice as well. Thank you very much.

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1. You show a bipolar in the pic. A MOSFET is a much better idea for the high efficiency you require. Look for one listed as "logic level".
2. The Zener is unnecessary. It is not a good mechanism to prevent overcharging, and in any case these currents are far too low to damage the battery through overcharging. Frankly, it will be a miracle if you manage to charge the battery in the first place.
3. The capacitor is probably unnecessary. The battery will charge about the same if it's 30 mA pulsed at 50% or 15mA filtered into a constant DC current. I doubt it will do anything helpful, and if it's got a poor leakage resistance, will drain a small amount of current (under 1mA, but it's there) all the time.

The inductor size is important. If it's too low, the solar cell will be loaded with ripple current. This is not damaging, but the efficiency suffers since the solar cell is only optimally loaded at one voltage/current point and a ripple by definition means the current will vary over the period of the PWM.

 

Sorry, the Figure has not been updated. Real sorry. I'm now trying to use the BSH102 MOSFET, but I couldnt find this part here. Looking for a replacement, any suggestions?

Thanks for that advice, I will now remove the zener diode. But would you mind to suggest a method for me to prevent overcharging? The small current output from my panel might not overcharge the battery but I would like to get some info about methods to prevent overcharging. Mind to give some advice?

ops: Blur here. I thought the purpose of the capacitor is to perform some boost function during the charge-discharge process? :? Sorry, this seem to be a real nonsense from me. Mind to explain further?

Thanks a lot. I've tried simulating using 100mH and it seems that it works well, I don't get much ripple. But I will try again I practical.

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About the PIC that I will be using for my project, 16F819 recommended.

Nigel? The 16F819, I couldn't find this unit after trying to search for it in a few places in my country. Do you mind to recommend other PIC microcontroller? Please? Help needed.

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You don't have your location filled in!, so we don't have any idea where you might be?.

Search for PIC's you can get that have A2D built-in, the 16F876(A) is an 'older' one, but is 28 pin rather than 18 pin - but it should be available anywhere.

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Just to complicate your life even further :lol:

If you look on the MicroChip website there is a programmer called the 'PICKIT1', this is a USB powered programmer for FLASH devices - using the 16C745 USB PIC.

The full circuit diagram and software source code is provided by MicroChip, as a USB application demonstration.

The reason I'm mentioning this is that they use the PWM module in the 16C745 to create a boost converter to generate the 13V required for switching PIC's to programming mode. The output of the converter is fed back to one of the A2D inputs which regulates the width of the PWM to keep the output stable. It does all this while at the same time receiving the USB data and programming the chip.

I'm not suggesting you use the 16C745 (as it's OTP) but the 16F876 has similar PWM modules and A2D inputs - so it opens up the possibility of doing the PSU and monitoring all in a single chip!.

Just a thought!.

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1. Too many to mention. Just find an NMOS with a low threshold voltage.
2. Overcharge protection depends on battery type. For SLA, they use a constant "float" voltage. It is acceptable to charge at a higher voltage but once a full charge is detected- generally by the current going down with a fixed voltage, or if the voltage rises when you're using constant current.
3. The cap does nothing special. It charges up during the part of the cycle when the diode is conducting current to the load, and it discharges when it's not conduction. Otherwise the output is a string of current pulses. But a string of current pulses is probably fine for you.
4. 100mH may be physically large. Inductors are more complicated in the real world than capacitors and optimum selection is tough! Getting 100mH in a physically small pkg means a lot of turns of thin wire, making a large DC resistance. It could be 10-100 ohms. The voltage drop burns up power on both the charging and discharging phases. Also, an inductor will only carry so much current before it saturates and stops acting like an inductor and is just a DC resistance. But that's not likely with a few mA, like this in even the small ones.
Your simulation will give you a good idea how much inductance you need. The feature to design for is how smooth the current is off the solar cell. I'd look for under 5% ripple as a rough guess, preferrably half of that.

 

Thanks a lot for that advice. I will read up the PIC 16F876 as soon as possible, I'm sure a slow learner like me, I will have lots of questions later on.

By the way, would like to ask for advice regarding powering the PIC microcontroller. Should I have an additional supply, say an additional battery being included in my Charging & Monitoring Unit to power up the PIC microcontroller or it is advisable to tap the voltage from my 12V battery and regulate it to the operating voltage level of the PIC?

Will "one" say that my Charging & Monitoring Unit is "no good" simply because of that additional battery to power up the PIC? :? Your advice or opinion is very much needed

Oh, by the way, I'm from Malaysia...sorry for not posting that earlier.

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:arrow: About the MOSFET, thanks. I will try searching them.

:arrow: Yup, I'm using a SLA battery (12V, 1.3AH). I still don't understand on how can I prevent an overcharge. Sorry.

:arrow: Got it! Thanks. Can we put it in this way ops: : By having the capacitor, my charging process will be a little faster as it is constantly charging My phrases sounds a little funny.

:arrow: Regarding the inductor, does it mean that you suggest me to implement a 50mH unit?

Thank you very much.

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