devonsc said:
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.
devonsc said: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?
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.
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.
devonsc said: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.
1. Too many to mention. Just find an NMOS with a low threshold voltage.devonsc said: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".
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?
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.
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?
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.
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?
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.
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.
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.
samcheetah said:devonsc this might be of some help to you
https://www.electro-tech-online.com/custompdfs/2004/11/slabatts-1.pdf
devonsc said: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...
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
devonsc said: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?
Regarding the inductor, does it mean that you suggest me to implement a 50mH unit?
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.Would like to ask regarding MOSFET. Mind to briefly explain the purpose of the diode found in the MOSFET?
By having the capacitor, my charging process will be a little faster as it is constantly charging
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?
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
It would be good it have it under 5%, since any power you don't use isn't "saved" for later.
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.
But if yes, what is the purpose of having such construction?Sorry, just asking...ignore this question if my question is meaningless. Real sorry.
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?
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.
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.
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