I'm jealous.Okies I have a bunch (2000+) of never used but dropped down to 0V LiFePO4's
You've forgotten to take the forward voltage drop of the LED into account. The base voltage will have to be more like 2.7V.when the battery being charged rises in voltage to 3.31V the input into the base of Q2 rises to .7V
Even with the correct resistor values, I can't imagine the LED flashing, it would just come on and stay on; there is no positive feedback. The current to the cell would be reduced though when the set point was reached.charged rises in voltage to 3.31V the input into the base of Q2 rises to .7V at that time the base of Q1 get's starved until the voltage in the li-FePO4 cell drops below 3.3V then q2 turns back off and the charging will continue again untill the cell rises past 3.31V again so the LED will flash when the cell is precharged to 3.3V and the LED will keep flashing and the cell won't be able to charge past this point, which means it's protected as well.
Not as is.Will this circuit work am I missing something did I get something wrong?
Why not just use a 3.3V power supply and a single resistor to each LiPO cell? It's definitely cheaper, and won't charge your cell past 3.3V.so cheap and dirty is the goal here.
...Mike, I'm a little miffed that you never commented on the solar cell solution I offered.
I'm jealous.
You've forgotten to take the forward voltage drop of the LED into account. The base voltage will have to be more like 2.7V.
Even with the correct resistor values, I can't imagine the LED flashing, it would just come on and stay on; there is no positive feedback. The current to the cell would be reduced though when the set point was reached.
Not as is.
Why not just use a 3.3V power supply and a single resistor to each LiPO cell? It's definitely cheaper, and won't charge your cell past 3.3V.
... I thought I was using the transistors as switches, I saw his graph and it seems like the current stops rising but still continues flowing once the led goes onthis is not what I wanted to accomplish I wanted to short the base to ground through the led so Q1 would effectively turn off.
I figured once the current to the battery stops the voltage of the battery would drop (which is natural behavior for liFePO4 cells). Then the q2 would turn off and q1 would resume to conduct current and this would cycle until the voltage drop in the cell was so minute as not to immediatly turn off the led. So somewhere I went wrong here anyone got a hint or two? ...
...Is there a problem with saturation of q1 that is causing the current to decrease? I thought that when transistor is on there is virtually no voltage drop. Maybe I'm still thinking to close to a relay model and maybe another factor is the voltage drop over the resistor ? So what is causing the current to drop ? ...
You apparently have never looked at the schematic of a linear circuit such as an amplifier.I thought a transistor only has two states on or off?
You apparently have never looked at the schematic of a linear circuit such as an amplifier.
Or if you have, did you think all those transistors were switching on and off?
It's not clear to me what you actually want the circuit to do. Try to explain, and we can probably design something that will work.
I hate to say I told you so, but you should use a pot.oops got a problem the thing seems to terminate at 3.05V and I actually went out and bought 180Ohm resistors @ r1 being 150 ohms it was like 2.9 something could it be that this transistor MPSA 06 has a lower trigger voltage than 0.7V so the calculations are off?
I tried to read the data sheet but I can't make heads or tails of the thing (help)
terramir
The cutoff voltage is effected by four things: the forward drop across the LED, the Vbe of the lower transistor, and the voltage divider.
yeah the only pots I got laying around are 1k trimmers one turn so they would be a pain to adjust, and I need them for my chargers, someone is etching me a board to make 6 (on one 6 1/4 x 4") and then I'm gonna get 3 (so 18 more) more later in the month.I hate to say I told you so, but you should use a pot.
Do you want a true constant current "precharger", with an adjustable cutoff voltage and a little hysteresis? If so, tell us the charging current, the cutoff voltage adjustment range, and the hysteresis.Okies I got 10 circuits running but it's not as clean as I would like it to be. the voltage cut-off point is to fluid for my taste. Someone on another forum suggested using the lm339 which is a voltage comparitor. This would probably be optimal if I know how to work it. But honestly I dun have a clue.
Any ideas where the circuit would do the same thing but with a very distinct cutoff point set by let's say one lm317 for all 20 charging slots, let's say 5 of those lm339's for the 20 battery slots and well I can reuse those mpsa06 for the switching operations.
terramir
What's hysteresis? cutoff voltage range is 3.2V - 3.4V constant current is 100mA but a selectable range of 50mA to 200mA would be great for experimenting, on what does the 0V cells better in terms of revival rates.Do you want a true constant current "precharger", with an adjustable cutoff voltage and a little hysteresis? If so, tell us the charging current, the cutoff voltage adjustment range, and the hysteresis.
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