Could someone help me?

[liqi0003]

Hello, everyone, this is my first time to visit this forum. I am a Mechanical Engeering student, now, I have some problems about a circuit.

I am doing a class assignment, actually it is a project. There is one part need me to design a circuit that change the unstable AC input to be stable DC output.

In fact, I am using a batteryless bicycle light system as the dynamo, (**broken link removed**) when the dynamo friction with the tyre, it will generator some power, my generator is 12V(max), 6W(max). I want to use this power to charge batteries. But the output depend on the speed of the bicycle, so it is unstable. That is why I want to design a circuit to convert it to a stable voltage.

About the dynamo, you can get some basic knowing in this website (**broken link removed**)

I think the most confusing part about my question is the range of the voltage. After I have done some testing, I found most of the time , the output of the dynamo is about 5V to 9V.Can I change the circuit input range to 5V-9V. Because speed is the dominant factor affecting the output. I cannot stablize it. Could someone give me some idea about how to limit the output voltage,i.e. if my output of the dynamo is 5V to 9V, using what circuit can change the output to be 5V(no matter AC or DC)


I hope someone here can help me to design the whole circuit or give me some advise.

Thank you very much!

 

[ericgibbs]

hi liqi.
If I understand you corrrectly.
That is, you have frequency of 0 to 10kHz that represents 0 to +9volts, you require what is known as as 'frequency to voltage' convertor.
You can purchase such a semiconductor device from most electronic
component suppliers.

Do a search on google for ' frequency to voltage integrated circuits'.
download a data sheet, it will most likely have some application diagrams.

Regards
EricG

 

[liqi0003]

Hi, EricG:

Thank you very much, I will go to search it.

 

[stevez]

As I read his question it looks like he has an unstable (his words) AC source of 0 to 9 VAC/0-10 kHz as a source and that the AC voltage and frequency vary together, possibly proportionally. He says he wants a stable 6 VDC output. That's another way to read it.

If the output desired is a steady 6 VDC you will need a switching power supply and a battery - or a linear power supply and a battery but if and only if there is enough time/power present to charge the battery for the expected load.

At 0 VAC, there is nothing to make power from so it would need to come from a battery. With a switching supply you can get to the 6 VDC from some minimum - with the linear the arrangement would be different. You could charge some 1.5 VDC cells in a switching arrangement.

It might be helpful to restate the question and conditions- keeping in mind that 0 VDC is nothing - you can't do anything with it.

 

[liqi0003]

Hi, stevez:

Thank you for your explanation about my question. Actually, I want to use this circuit to charge some rechargeable batteries, I would like it work as a charger.
I have read some articles, I think we cannot use unstable voltage charge batteries, that's harmful for the cells.That's why I want to design a circuit to stablize the voltage.

 

[eng1]

You may filter or pre-regulate the voltage, but the batteries are usually charged with constant current. Which kind of batteries do you have? What current can be sourced from the input?

 

[Nigel Goodwin]

You've still not really given enough information for any sensible answer (and have now moved away completely from what your original question asked).

What is the source that you're talking about!.

 

[Hero999]

This sounds like a trick question to me.

You can't get 6VDC from 0VAC, that would involve an efficiency greater than 100%, energy from nowhere.

6VDC from 9V AC is perfectly realistic though.

 

[Nigel Goodwin]

This sounds like a trick question to me.

That because it doesn't explain what it's about - I'm presuming the idea is to charge a battery from some kind of generator? - but all we get is dribs and drabs that tell us nothing!.

However, I'm somewhat baffled thinking of a generator that puts out 10KHz?.

 

[Sig239]

Instead of being sneaky, he came right out and directly asked others to do his schoolwork, which is really no better.

 

[liqi0003]

Instead of being sneaky, he came right out and directly asked others to do his schoolwork, which is really no better.

hey, i am sorry I didn't explain well. Acutally, i am a Mechanical Engineering student, I am not good at electrical, so I want to get help from other.

 

[liqi0003]

That because it doesn't explain what it's about - I'm presuming the idea is to charge a battery from some kind of generator? - but all we get is dribs and drabs that tell us nothing!.

However, I'm somewhat baffled thinking of a generator that puts out 10KHz?.

Thank you very much for your concerning about my question.
In fact, I am using a batteryless bicycle light system as the dynamo, (**broken link removed**) when the dynamo friction with the tyre, it will generator some power, my generator is 12V(max), 6W(max). I want to use this power to charge batteries. But the output depend on the speed of the bicycle, so it is unstable. That is why I want to design a circuit to convert it to a stable voltage.

About the dynamo, you can get some basic knowing in this website (**broken link removed**) **broken link removed**

I think the most confusing part about my question is the range of the voltage. After I have done some testing, I found most of the time , the output of the dynamo is about 5V to 9V.Can I change the circuit input range to 5V-9V. Because speed is the dominant factor affecting the output. I cannot stablize it. Could someone give me some idea about how to limit the output voltage,i.e. if my output of the dynamo is 5V to 9V, using what circuit can change the output to be 5V(no matter AC or DC)

Is that more clear about my question?
By the way, thanks to all of you who has replied me

 

[liqi0003]

You may filter or pre-regulate the voltage, but the batteries are usually charged with constant current. Which kind of batteries do you have? What current can be sourced from the input?

Hello,
I think we only need a constant voltage.

Could you explain more criteria about the battery charger? Thanks

 

[Nigel Goodwin]

Is that more clear about my question?

Yes, you are worrying about nothing - all you need is a simple halfwave recifier (if the generator is DC) or a fullwave rectifier (if it's AC) directly to the battery. When you're going fast enough the battery will get charged, and when you're going too slow it won't - and it won't have enough power to overcharge anyway.

So no worries, simple answer - you just need to ask the right question!.

 

[liqi0003]

Yes, you are worrying about nothing - all you need is a simple halfwave recifier (if the generator is DC) or a fullwave rectifier (if it's AC) directly to the battery. When you're going fast enough the battery will get charged, and when you're going too slow it won't - and it won't have enough power to overcharge anyway.

So no worries, simple answer - you just need to ask the right question!.

Thank you very much

But I am not quite sure that, is it possible to charge batteries directly?
I mean, based on my situation, if I pass it through a full-wave recifier, it becomes DC output, but I still get a unstable voltage and unstable current related to the speed. I don't think it can be used to charge batteries, that will damage the cells. Is that true?

I think I have already know how to convert it. May I use a zener diode to stablize the output voltage?

 

[Nigel Goodwin]

Thank you very much

But I am not quite sure that, is it possible to charge batteries directly?
I mean, based on my situation, if I pass it through a full-wave recifier, it becomes DC output, but I still get a unstable voltage and unstable current related to the speed. I don't think it can be used to charge batteries, that will damage the cells. Is that true?

I think I have already know how to convert it. May I use a zener diode to stablize the output voltage?

Like I said, all you need is a simple rectifier, your generator doesn't produce enough power to damage the batteries!.

 

[liqi0003]

Hi, Nigel:
Firstly, let me introduce my dynamo.
It can produce maximum 12V and 6W work. I have check some normal charger, the output side, connect to the batteries are about 4-8V and 80-500mA. If we use the equation P = VI, I think the normal charger will work less than 6W. So, could you tell me whether I can consider the question like that, and could I still connect the dynamo directly?

Thank you.

 

[Nigel Goodwin]

Hi, Nigel:
Firstly, let me introduce my dynamo.
It can produce maximum 12V and 6W work. I have check some normal charger, the output side, connect to the batteries are about 4-8V and 80-500mA. If we use the equation P = VI, I think the normal charger will work less than 6W. So, could you tell me whether I can consider the question like that, and could I still connect the dynamo directly?

Trust me!!!! - it's NOT going to be a problem! - add a series resistor to limit the current if you wish, but it's not likely to be needed.

Turn the bike upside down (so you can turn the pedals by hand), connect the dynamo via a diode, and a ammeter (multi-meter on 2A range should be fine) to the battery. Then pedal away, and see what readings you get - bear in mind the highest reading you get will be just that, the MAXIMUM - most of the time it will be less than that. And if the lights are being used, most of the power will be going to the lights, and NOT the battery.

 

[liqi0003]

Okie, haha, thank you very much.
I trust you!

 

[eng1]

You have to go for a long ride to recharge your batteries Or are you going to use the dynamo with some machines?? Maybe adding an LM317 won't increase the cost so much?