Current regulator

---------------------------

Assuming the load is a battery, that is, something whose internal chemistry you have no control over, you can control the voltage, or the current, but not both. (I think the guy's name was Georg Ohm)

-- Roberto Waltman

[ Please reply to the group, return address is invalid ]

You would need to use the CMOS version of the 555 timer to operate at that low of voltage.

Using a buck boost switch you can generate higher voltages at lower currents, great for charging I guess.

Unless I miss understood your posting, I assume you're using a single cell as your DC source ? Or do you mean you want to charge a single cell from some other DC source?

Jamie

How many of these AA cells were you planing on using? Depending on the chemistry, lets say a basic carbon type is ~ 900 mAH, that is, you can expect 900 m-amps to be supplied up to an hour. AFter that, it's all down hill until dead! ALso, the batter voltage is going to drop so you most likely will lose it before that as your loaded device will fail, due to lack of proper operating voltage. SO you can scale that back according to the voltage drop, too.

So looking at your figures above, I can't see how you plan on getting

7 hours at 1 amp for example?

Jamie

--
With just a single 1.5V AA cell as your source, you're unlikely to
meet all of your goals.

What's your application?

"nescafe"

** Better use two ( in series) - cos using just one is never gonna work.

The voltage of a 1.5V cell drops steadily during discharge.

... Phil

One homemade cell can be charged up to 1A (max) and standard voltage is around 0.75 But to get to this 1A i have to charge the cell on the way i described before.

---------------------------------- Maybe there is one other solution to make this. I can connect 15 cells in series and charge it with 12/7Ah battery or car battery. I think that this is far better option.

----------------------------------- OK. How to make this charge process with some 12/7ah or stronger battery ? Any link to some schematics ?

555 is too fast. try CD4060 you won't get 7 hours at 1A from an AA

--
?? 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net

--- You could use a buck regulator.

View using a fixed-pitch font:

. +-------------+ . | +---------+ | .+12--+-[Rs]-+-|IpK SWC|-+ S1 A . | | SWE|-------+-[L]-+->>-[+AA]--+------+-------------+-----+-----+--------------------------+

S1 is a single pole 5 throw break-before-make switch used to switch between the various charging currents you want, and if 5% tolerances in charging currents are acceptable, then the values of the resistors will be: LABEL CURRENT RESISTANCE Ma OHMS

----------------------------- R1 50 4.7 R2 100 2.4 R3 200 1.2 R4 500 0.47 R5 1000 0.24

-- JF

+---------------+-----++ | 2N3904 | | 12 Volt in | ___ |/ | +-+-------+-+|___|--+--+| | + | |> + - 4.7K | + |/ 2N3055 --- | +--+-| | | |> 0.25 Ohm +--------++ | ___ Cell Load GND | | +---+--+-|___|-+-------+ + | | | | V | | .-. | - + U1 | | |

Where is the voltage limiting control? That is needed since he is only looking for charge around 0.75 volts, unless he made some mistake or I did?

I don't know exactly what he is doing , but as cell charge comes up the current usually drops back, in this circuit here, the voltage is just going to raise and raise.

The one I showed only goes up to ~ 1.0 Volt.

Did I missed something ?

Jamie

--
You did, since you assumed that the terminal voltage of the load was
relevant.

The OP stated that his goal was to push a fixed current through a load
for a specific amount of time, which makes the terminal voltage of the
load unimportant except in the context of the compliance of the
source.

--
Thank you guys !.
This is exactly what i need.

Regards !

that's fine, I'll stick with limiting the voltage.

As a cell increases with voltage, the current drops back. if you are attempting to maintain current, the voltage will just keep raising until at some point, the cell could get damaged. A little over is fine, which is needed, but really, using 12 volt source to charge a .75 volt cell?

Oh, so much for that. I hope you don't get into the charging business.

Jamie

Good luck. Wouldn't of been my choice.

Jamie

--
You seem to have missed the point that the voltage into the load will
be automatically limited to that voltage required to drive the
required current through the load and the low side current sensing
resistor.

--
Sour grapes?

Nope, absolutely not. I wouldn't use your circuit for a charger of such nature.. I was only trying to be nice to the originator asking for a sensible circuit that would fit properly and safely, for their needs.

I think you flatter yourself a little too much, you really should think of others and instead of passing on what you would like to ignore.

We have charging stations at work and none and I mean none of the chargers are allowed to exceed 10% of the battery voltage, regardless of condition. You on the other hand, would think it's ok to boil the battery off, even after its has reached the peak voltage.

Personally, I don't care what you do with your own cells, you can do what ever and take a chance of generating undesirable effects if you wish. It's your choice, but to give others advise with out taking that into consideration, thinking that maybe they don't care any more than you do is pure foolishness.

BTW, that circuit you posted can be modified very simply to add limiting voltage function, but since you're so self centered I'll allow you the honor or making a mess out of it.

Jamie

Jamie is too brainless to understand what you designed. His specialty is boot-licking. ...Jim Thompson

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