battery charging

You could hook the transistor's emitter to ground, so driving the base with the timer, through a suitable resistor, would be easy. Then connect its collector to the the negative battery terminal, with the battery's positive terminal on the plus 15.

-- john

Yess, closing the loop the other way thanks

ken

Better still, use a power mosfet.

--

Cheers ......... Rheilly P

Where theres a will, I want to be in it.

Hi, Ken. You're not spamming -- you've got good basic questions, and you're in the right group to ask them.

All you need for basic ON/OFF control of your series NPN transistor with a 6V logic signal from a 555 is another NPN transistor and a few resistors, like this (view in fixed font or M$ Notepad): | |15Vo-----------o--------- -------->

| | Q1 \\ ^ To Battery | | --- | | ___ | | '--|___|---o | +6V | | + | | | | | .----o----. | | | | | | | | | | | | ___ |/ | | 3o-|___|- -| Q2 | | 555 | | |>

| | | .-. | | | | | | | | | | | | | | '----o----' '-' | | | | | | | | === === | GND GND (created by AACircuit v1.28.6 beta 04/19/05

When the output of the 555 goes high, it turns on Q2. That brings the base of Q1 down to about 0.2V, turning it completely off. You didn't describe your current requirements, but with appropriate choices of transistors and resistors, you can easily control amps of current with the 555.

I hope this is of help.

Good luck Chris

Yes, this is very intersting, basically its on all the time, when the 555 timer turns on, the charging stops. Just dont like the idea that the 15v supply is always discharging. If I forget it there, then I'm draining all this power from the grid for nothing. But I like the concept. It looks easy enough, and I feel like saying, why didn't I think of that :)

thank you

ken

Hi,

I got this circuit working earlier on. but my transformer adapter blew up (I think the coil inside, I checked it and no output right after the secondary coil) so I had to do one from scratch. it is working now (the transformer). I hook up the circuit again the same way. Does not work anymore. I had my timer on a 6 volt battery, when I decided to ground that battery with the rest of the circuit, the resistor at the output of the 555 (hook up to the base of the transistor) burns up . Aven after that the timer work good. That was a 50Ohm resistor. Is it ok if I leave the 6v battery by itself, or better to ground it to the system ?

k

The transistor is getting very hot too. I think I need to adjust the current coming from the supply. I 'll check it, tomorrow and post something about it.

k

It was bugging me way too much. I checked the output of the bridge, The capacitors are now showing me 180v.... (blown capacitor or a new step up transformer ??)

k

Surely you mean 18 volts, not 180 volts ?

Post a schematic. And tell us why you are using a 555 to shut off the charger. Do you think that you can always apply a charge for the same amount of time to the battery and get proper charging? That's not a good approach.

You've burned out some parts, so it's apparent there is something incorrect. If you can post an accurate schematic, we can tell you what's wrong.

Ed

Hi

I have been looking at schematics for battery charger. All the circuit I have seen so far seem to stop the charging to the battery from the source. most of them uses a pnp transistor to bypass the charge battery , therefore creating a link from the source + to ground.

Anyhow, the battery voltage will eventually decrease, and the charger will go again , and again .... How would i go about it so that the charger don't start again.

thanks

ken

use an SCR in series with the output? using a current pulse sensor when you put the dead battery on line should be used to auto switch the SCR on. or use a m-pushbutton switch.

Scr's will hold in the on state until the current being past drops below its holding spec. thus if you put the + on the anode side and use the cathode as the output and switch the SCR via the gate when you want the charger to start you will be all set. i've seen this type of charging switch used in many cases where you don't want the charger to come back on.

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

You could do this with a relay. Wire it such that the "start" switch pulls in the relay, which provides power to the charger. Also, pick off that power and supply the relay coil in parallel with the switch (maybe with isolation diodes). When the charger finishes its cycle, use that signal to open the lead to the relay, which drops out and removes power until you press the start switch again.

Good Luck! Rich

The circuit shown on that page will never shut off current to the battery completely. There is a path from the 18 volt supply through R1 (500 ohms) and R7 (.2 ohms) to the battery, regardless of anything else that happens.

I guess the designer's idea was this: The ~8 mA through that path, once the battery is fully charged, should make up for any self discharge, keeping the battery at full charge.

Ed

Yes , this is why I am looking for a method the the charger will not come back on once the battery is charged.

ken