Capacitor Question : Different Charge and Discharge rates.

[0mega]

Dear All,

I am building a "scalable" capacitor array. I want to be able to use a dual dac (MAX519) to set the array charge and discharge rates. I was thinking of using both NPN and PNP darlington transistors to allow for different rates of charge. Can anyone point me in the right direction ?? I can't seem to get such a thing working.

CheerZ,
JB

 

[Nigel Goodwin]

Re: Capacitor Question : Different Charge and Discharge rate

Dear All,

I am building a "scalable" capacitor array. I want to be able to use a dual dac (MAX519) to set the array charge and discharge rates. I was thinking of using both NPN and PNP darlington transistors to allow for different rates of charge. Can anyone point me in the right direction ?? I can't seem to get such a thing working.

CheerZ,
JB

I haven't got a clue what you are trying to do, or how you are trying to do it! - or why?.

Could you explain further?, and give a circuit diagram of what you've done so far that doesn't work.

 

[0mega]

Ok. This is what i want to do. It is for a storage array in a solar car.

You can vary the charge and discharge rates like thus (i think) (see attachment).

What i want to do is make it compatible wif a microprocessor so you can vary the rates of charge and discharge using a dac.

CheerZ
JB

 

[Nigel Goodwin]

Ok. This is what i want to do. It is for a storage array in a solar car.

You can vary the charge and discharge rates like thus (i think) (see attachment).

What i want to do is make it compatible wif a microprocessor so you can vary the rates of charge and discharge using a dac.

I fail to see why you would want to do this in a solar car? - I thought the idea was to move the car, not just charge and discharge a capacitor?.

Certainly limiting the charging seems a bizarre idea, you want as much from the available light as you can - once it's fully charged you may wish to stop further charging, but not limit it.

The usual way of running solar panels is quite complicated, their output voltage (as well as current) varies with the incoming light. So you use a fairly complicated switchmode circuit, which increases the voltage when it's too low, and decreases the voltage when it's too high. Obviously this decreases, and increases, the current respectively - but gives some energy over a far greater light range.

I suggest you try searching for solar panel chargers.

 

[0mega]

Hey Nigel,

I'm trying to build a "smart" array ... 8) Secret ! If i get it working, i'll post the code....

The usual way of running solar panels is quite complicated, their output voltage (as well as current) varies with the incoming light. So you use a fairly complicated switchmode circuit, which increases the voltage when it's too low, and decreases the voltage when it's too high. Obviously this decreases, and increases, the current respectively - but gives some energy over a far greater light range.

Yes, we are using a buck/boost switchmode circuit attached to a maximum power point tracker.

JB

 

[0mega]

... bump ... :wink:

 

[Roff]

What are your current levels?

 

[0mega]

Hi,

The current draw is ~ 4A at maximum torque.

Cheerz,
JB

 

[Russlk]

I don't think you understand what you are trying to do, I certainly don't.

 

[pike]

pfft 4 amps from a solar array!! might be slow dont you think? Seriously you'll need a pretty big cap' bank for this that'll take a long time to charge.

You might want to take into account the stall current.

 

[Crofty]

I think I know what Omega's trying to do? I assume when he mentions a Cap-array, he's referring to Super or Ultra Caps?? the nice big many Farads type? I too am messing in this area at the moment.

I rigged up a cheap conventional solar garden lamp (Led type) using a 5.5V 1F cap instead of the 2xAA Nicads, purely to check an idea for another product, (not garden solar). Yes it works, it charged quite fast, even with the tiny solar cell (50x50mm) obviously it only runs for a few minutes, but the theory is sound. With bigger values, this would be much extended, albeit with longer charge times, also heavier initial current demands.

I'm not sure about your discharge rate scaling bit? are you talking about limiting the available current to the motor? capped @ 4Amps?

If your trying to power your car by cap storage instead of lead acid/Nicads, this will have a huge power to weight advantage

Am I on the right track Omega?

Steve